This paper attempts to re-analyze the piled raft foundation in the Shanghai Center Tower as a fully compensated foundation using a hybrid method of superstructure–foundation interaction and other methods. Some cases were used to the applicability of the methods. The deformation analysis is divided into four parts: (a) Part 1: heave due to the weight of the excavated soil, (b) Part 2 : recompression due to the dead load of the structure, (c) Part 3 : recompression due to the live load of the structure and (d) Part 4 : settlement due to the constant load. Load acting on the top of the pile group and load sharing between the raft and the piles are also considered. The results are also compared in detail with the measured ones. In addition, research based on earth pressure theory was conducted to determine how to reduce or control the overturning moment caused by wind. Finally, this paper suggests that the Shanghai Center Tower, which is currently under construction, can have more than 121 stories by improving the design, which will also result in great investment savings. Copyright © 2013 John Wiley & Sons, Ltd.

This paper presents the motivation and the mathematics required for the introduction of Bayesian structural reliability theory into the process of evaluating and strengthening any tall building located in the Los Angeles region. Copyright © 2013 John Wiley & Sons, Ltd.

Steel moment-resisting frames (SMRFs) are the most common type of structural systems used in steel structures. The first step of structural design for SMRFs starts with the selection of the structural sections on the basis of story drift limitation. ASCE 7 (2010) requires that the inelastic story drifts be obtained by multiplying the deflections determined by elastic analysis under design earthquake forces with a deflection amplification factor (C_d). For special moment-resisting frames, C_d is given as 5.5 in ASCE 7 (2010). Lower C_d values will increase the overall inelastic response of the structure. On the other hand, the inelastic response of the structure is expected to be less severe when designed for higher C_d values. The performance objective is that the structure should sustain the inelastic deformation demand imposed due to design earthquake ground motions. This study aims at investigating the inelastic seismic response that low-rise, medium-rise and high-rise SMRFs can experience under design earthquake ground motions and maximum considered earthquake (MCE) level ground motions and evaluating the deflection amplification factors (C_d) for SMRFs in a rational way. For this purpose, nonlinear dynamic time history and pushover analyses will be carried out on SMRFs with 4, 9 and 20 stories. The results indicate that the current practice for computing the inelastic story drifts for SMRFs is rational and the frames designed complying with the current code requirements can sustain the inelastic deformations imposed during design earthquake ground motions when seismically designed and detailed. Copyright © 2013 John Wiley & Sons, Ltd.

The devastating effects observed in the recent earthquakes, in terms of loss of lives as well as immediate and long-term economic losses, have prompted the need to provide documents concerning the assessment and improvement of the structural performance of existing buildings at the time of an earthquake. In this regard, performance engineering is defined as performance-based seismic design and rehabilitation. There are many reasons for rehabilitation of existing buildings. Changing the building's usage is one of the most common reasons. In the present study, the residential steel buildings were subject to performance-based rehabilitation, converting to educational use. Several steel frames with dual lateral-resistant systems (MRF–EBF) and different numbers of stories were initially designed as residential buildings. The frames were rehabilitated according to the current seismic rehabilitation codes and regulations. Cover plates were used to strengthen structural elements. Variations in structural responses were evaluated before and after retrofitting by the use of nonlinear analysis. Moreover, the performance of rehabilitated structures was evaluated, considering the gross features observed in near-field records. Copyright © 2013 John Wiley & Sons, Ltd.

As an effective factor for force-controlled components, in special moment frames, the main advantage of using box column is high biaxial bending strength. Most research studies have been concentrated on the box column performance subjected to unidirectional loading. On the other hand, seismic provisions given so far in codes are limited to beam to wide flange column connections with planar webs. In the research work presented, the bidirectional loading configurations are adopted to better simulate the actual response of the box column subjected to a ground motion excitation. The connection used in the article is welded unreinforced flange–welded web, being the direct connection that was introduced in the American Institute of Steel Construction as one of the prequalified connection. Analytical results from finite element method indicate that when the structure is subjected to bidirectional loading, the level of shear and flexural strength capacity of the box column reduces. Because of the yielding of the panel zone and the inner diaphragm, the distribution of stress and strain in the finite element models reveals that the design criteria presented in most seismic codes seem not to place the plastic hinge out of the panel zone region and therefore need to be modified. Copyright © 2013 John Wiley & Sons, Ltd.

Post-earthquake fire (PEF) presents a high risk to buildings that have been partially damaged in a prior earthquake, particularly in urban areas. As most standards and criteria ignore the possibility of fire after earthquake, buildings are not adequately designed for that possibility, and thus, PEF is a high-risk load needed to be scrutinized further, codified and become part of a routine design. An investigation based on sequential analysis inspired by FEMA356 is performed here on two RC frames, of three and five stories, at the Life Safety performance level and designed to the ACI 318-08 code, after they have been subjected to a spectral peak ground acceleration of 0.35 g. A fire analysis of the weakened structures follows, from which the time it takes for the damaged structures to collapse is determined. As a point of reference, the fire resistance is also determined for undamaged structures and before the occurrence of earthquake. The results show that structures previously damaged by the earthquake and exposed to PEF are considerably more vulnerable than those that have not been damaged previously. A method using carbon fiber-reinforced polymer as a means of relocation of plastic hinges away from the column faces towards the beams is introduced as a function of the time required for fire extinguishment or evacuation. This is carried out to increase the structural load-carrying capacity, thus reducing the potential damage for the anticipated earthquake and thereby improve the PEF resistance. The results show a considerable improvement in the PEF resistance of the frames. While the investigation and the proposition relate to a certain class of structures (ordinary buildings, intermediate RC structures, three and five stories) and the results can therefore be applied only to the cases investigated, it is hoped that this study paves the way for further research into this very important phenomenon and leads to an eventual revision of codes. Copyright © 2013 John Wiley & Sons, Ltd.

Demand for efficient and economical hyperbolic cooling towers has driven engineers toward designing tall and lightweight towers, specially, in regions with high-seismic ground motions. An effective way to achieve this goal is using steel cooling towers. Also, by using tubular diagonal grid (Diagrid) system as the structural system, the weight of cooling tower will reduce, significantly. Therefore, in this investigation, a steel hyperbolic cooling tower is modeled with Diagrid system. A linear analysis, under dead and wind load, is performed on several systems with different angles of Diagrids to reach the optimal angle of grids. Furthermore, the effect of stiffening rings on the cooling tower is examined, and it is observed that the use of stiffening rings makes the tower lighter. And, by performing nonlinear time history and stability analyses, the behavior of the cooling tower is investigated under strong earthquakes, and it is represented that the system shows very good performance during strong earthquakes. Copyright © 2013 John Wiley & Sons, Ltd.

In this study, the effects of in-cycle strength degradation of steel moment connections are investigated on global behavior of multiple degree-of-freedom structures. Two types of degrading connection models are defined and compared with a bilinear non-degrading model. Due to dispersion of the experimental test results on connections performance, two models are considered for each type. A probability assessment is carried out by implementation of incremental dynamic analysis to find the capacity of the structures for various performance levels. A sensitivity study is conducted on hysteresis parameters of connection models to investigate the effect of these parameters on global behavior of the structures. Due to increased dispersion of displacement demands observed in degrading cases, a reliability analysis is carried out to consider the effect of uncertainty on confidence level of the structures. Results show that in-cycle strength degradation can lead to abrupt dynamic instability and as a consequence decrease in reliability of the system against collapse. Copyright © 2013 John Wiley & Sons, Ltd.

This study focuses on the seismic vulnerability assessment of process towers. A 96-m process tower, located at the Shazand Refinery, is considered for a case study sample. The vulnerability of this structure is expressed with the development of fragility curves, which provide the probability of exceeding a prescribed level of damage for a wide range of ground motion intensities. The methodology of developing fragility curves for process towers is shown. The developed fragility curves can be very useful for emergency management agencies and insurance companies wishing to estimate the overall loss after an earthquake. The vulnerability of nonstructural equipments of tower is also assessed in subsequent step. To model the process tower with its base details, a nonlinear finite element model is generated. It was found that the fragility curves should be developed for external pressure condition because it is more critical state of loading. The results show that the damage to the process tower occurs in the shell; and the other types of damages, i.e. yielding of anchor bolts, structural damage to foundation and overturning of tower, do not occur. Copyright © 2013 John Wiley & Sons, Ltd.

In this study, an efficient analytical model for the dynamic analysis of tall buildings with a shear wall–frame structural system has been proposed. A shear wall–frame structural system usually consists of a core wall showing flexural behavior and a frame presenting shear behavior. Therefore, the deformed shape of the shear wall–frame structural system is shown by the combination of flexural mode and shear mode. To consider this characteristic in developing an efficient analytical model, the effect of shear wall and frame on the dynamic behavior of a tall building with a dual system has been separately investigated. In order to consider the effect of the shear wall in the frame model without shear wall, a rigid body was used instead of the shear wall. Each equivalent model for the separated shear wall part and frame part has been independently developed, and two equivalent models were then combined to create an efficient analytical model for tall buildings with a shear wall–frame structural system. In order to verify the efficiency and accuracy of the proposed method, time history analyses of tall buildings with a shear wall–frame system were performed. With analytical results, it has been confirmed that the proposed method can provide accurate results with significantly reduced computational time and memory. Copyright © 2013 John Wiley & Sons, Ltd.

The time-dependent behavior is a major consideration in the design and construction of tall buildings, especially in concrete and composite structural systems. To make an analysis of long-term effect of steel-reinforced concrete structures, the method of using master–slave constraint to deduce substructure element model of composite members was introduced, and the problem of co-work between steel and concrete was solved. The creep calculation method of combined Age-adjusted Effective Modulus Method (AEMM) and finite element method was adopted. Steel Reinforced Concrete Construction Modeling (SRCCM), a calculation program based on Visual C++ and ObjectARX, was developed for simulating the construction process of high-rise composite structures. The use of the method is illustrated through one computation example of Shanghai Center Tower, which is a super high-rise steel-reinforced concrete structures. The method provides valuable information about time effects that may be used in designing new structures or in diagnosis existing structures. The results also indicate that the vertical shortening of Shanghai Center Tower between column and core-tube is significant. Such differential length changes should be compensated during the construction process of high-rise composite structures. Copyright © 2013 John Wiley & Sons, Ltd.

The peculiar building style and special structural system of the National Hall of China Pavilion for Expo 2010 Shanghai is a long-span and large cantilevered steel–concrete hybrid structure with a shape of an inverted trapezoid in elevation and local discontinuity of floor slabs in plan for esthetic and functional considerations. Because of these characteristics, the building is classified as an irregular and complex structure. To investigate the seismic behavior of the structure, a refined finite element model was established by using NosaCAD. To simulate the nonlinear behavior of the members, the fiber section model was chosen for compression-flexure frame members, and nonlinear flat shell element was chosen for tube wall. Nonlinear analysis was carried out to study the seismic behavior of the structure under the minor and major earthquakes at the level of intensity 7. With the analysis, the deformations, internal forces and damage states of the structure were investigated. Analysis results show that there is no damage on structure under minor earthquake, the structural system has sufficient capacity and ductility to resist major earthquake, and seismic performance objective of no damage under minor earthquake and no collapse under major earthquake can be reached. The deformation of the structure is less than the limit of the Chinese code. The order and distribution of damages on components of the tubes are reasonable, which can dissipate some dynamic energy. Finally, weak points were identified, and some corresponding suggestions were put forward to improve the overall seismic performance of this structure. Copyright © 2013 John Wiley & Sons, Ltd.

This paper presents behaviors of semi-precast beams made of recycled aggregate concrete (RAC) including flexural and shear performance. Specially, cracking patterns, deflections and bearing capacities of U-typed and C-typed beams are intensively examined, analyzed and discussed. In the study of flexural behavior, a main parameter is reinforcement ratio, whereas the shear span-to-depth ratio and types of precast section are parameters in the investigation of shear behavior. First, the flexural tests show that the bearing capacity and stiffness of RAC beams are increased with the increase of reinforcement ratio, whereas the ductility is decreased with the reinforcement ratio; the plane section assumption that applies to semi-precast beam with RAC is possible. Second, the shear tests show that the shear capacity of RAC semi-precast beam increases with the decrease of the shear span-to-depth ratio. The types of semi-precast section have no significant influence on performances of semi-precast beam. However, the testing phenomenon of the interface between the precast and cast-in situ parts is presented in this study and needs further study. Finally, both flexural and shear test results reveal that the formulas in the current Chinese technical code for RAC are feasible for design. Copyright © 2013 John Wiley & Sons, Ltd.

The yield point spectra and modal pushover procedures have already been used in seismic design of new buildings and vulnerability evaluation of existing structures. This paper initially identifies the similarities and differences of the two procedures. Then, the modal characteristics of damaged structure are used to modify their methodologies. The applications of the procedures in estimating displacement, interstory drift index and plastic hinge rotation responses of asymmetric buildings are investigated for three 5-story reinforced concrete moment-resisting frame-building models. The results show considerable improvement in estimating the responses of those asymmetric buildings. Copyright © 2013 John Wiley & Sons, Ltd.

The most common device for control of tall buildings under wind loads is the tuned mass damper (TMD). However, during their lifetimes, high-rise and slender buildings may experience natural frequency changes under wind speed, ambient temperatures and relative humidity variations, among other factors, which make the TMD design challenging. In this paper, a proposed approach for the design of robust TMDs is presented and investigated. The approach accounts for structural uncertainties, optimization objectives and input excitation (wind or earthquake). For the use of TMDs in buildings, practical design parameters can be different from the optimum ones. Nevertheless, predetermined optimal parameters for a primary structure with uncertainties are useful to attain design robustness. To illustrate the applicability of the proposed approach, an example of a very slender building with uncertain natural frequencies is presented. The building represents a case study of an engineered design that is instructive. Basically, due to its geometry, the building behaves differently in one lateral direction (cantilever building) than the other (shear building). The proposed approach shows its robustness and effectiveness in reducing the response of tall buildings under multidirectional wind loads. In addition, linear-quadratic Gaussian and fuzzy logic controllers enhanced the performance of the TMD. Copyright © 2012 John Wiley & Sons, Ltd.

Performance-based design method, particularly direct displacement-based design (DDBD) method, has been widely used for seismic design of structures. Estimation of equivalent viscous damping factor used to characterize the substitute structure for different structural systems is a dominant parameter in this design methodology. In this paper, results of experimental and numerical investigations performed for estimating the equivalent viscous damping in DDBD procedure of two lateral resistance systems, moment frames and braced moment frames, are presented. For these investigations, cyclic loading tests are conducted on scaled moment resisting frames with and without bracing. The experimental results are also used to calibrate full-scale numerical models. A numerical investigation is then conducted on a set of analytical moment resisting frames with and without bracing. The equivalent viscous damping and ductility of each analytical model are calculated from hysteretic responses. On the basis of analytical results, new equations are proposed for equivalent viscous damping as a function of ductility for reinforced concrete and steel braced reinforced concrete frames. As a result, the new equation is used in direct displacement-based design of a steel braced reinforced concrete frame. Copyright © 2012 John Wiley & Sons, Ltd.

With the nonstationary wind-induced acceleration data from full-scale measurements, an approach for estimation of the wind-induced overturning bending moments for super-tall buildings was proposed in this paper. The empirical mode decomposition was employed to decompose the measured acceleration data into a set of intrinsic mode functions and a residual component. To remove the baseline offset, the residual component and the intrinsic mode function components with long-period were eliminated before their integrations into velocity and displacement components. Then, the intrinsic mode function components, which have the same dominant periods as the natural periods of the studied tall buildings, were extracted from the original signals, and the natural frequency and damping ratio for the first vibration mode of the building were identified. Finally, the wind-induced overturning bending moments of the building were obtained from the generalized wind loads for the first vibration mode, which could be obtained from the time history analysis of dynamic equation. The Hilbert spectrum of wind-induced overturning bending moments was utilized to observe its characteristics in both time and frequency domains, and the Strouhal number was thus identified. The proposed scheme and some selected results may be helpful for further understanding of wind effects on super-tall buildings. Copyright © 2012 John Wiley & Sons, Ltd.

A buckling-restrained brace (BRB) is a system with excellent earthquake-proof performance, but it does not dissipate energies caused by the load from weak earthquakes or winds. A hybrid BRB (H-BRB), which improved the performance of the BRB, is a type of composite damper system consisting of a BRB and a viscoelastic damper. To explain the wind-induced vibration control performance of H-BRB, a 40-story steel building was designed and used as an analysis model in this study, on the basis of the damping ratio from a structural performance test, using normal steel braces, BRB and H-BRB. In addition, to evaluate the optimal location of H-BRB, a time-history analysis of four models was conducted in the study. For such time-history analysis, wind-load data in a 10-year recurrence interval, which were calculated from the wind tunnel test, were used. The result of the time-history analysis showed that H-BRB is effective in improving both the lateral stiffness and serviceability of a building using the existing BRB. It also confirmed that it is most effective to position H-BRBs mainly on the lower stories. Copyright © 2012 John Wiley & Sons, Ltd.

A practical application of ‘beam on nonlinear Winkler foundation’ approach has been utilized in this paper for a case study on seismic performance of concrete shear wall frames to assess the soil–foundation–structure interaction effects. A set of 3-, 6-, 10- and 15-story concrete shear wall frames located on hypothetically soft, medium and hard soils were designed and modeled using the OpenSees platform. The numerical model of each frame was constructed employing the distributed and lumped plasticity elements as well as the flexure–shear interaction displacement-based beam–column elements incorporating the soil–footing interface. Pushover analysis was performed, and the results were studied through two code-based viewpoints: (a) force-based design and (b) performance-based design. A comparison was made afterwards between the frame behaviors in the fixed-/flexible-base conditions. The results indicate some degree of inaccuracy in the fixed-base assumption, which is regularly applied in analysis and design practice. The study emphasizes on how the fixed-base assumption overestimates the design of the wall element and underestimates the design of the connected moment frame. Copyright © 2012 John Wiley & Sons, Ltd.

The study concentrated on investigating the relationship of the continuous cumulative damage, macroscopic deformation development and failure process of mid-rise shear walls. Nonlinear fiber element model considering the effect of cumulative damage is proposed for evaluating the seismic performance of shear wall. Numerical analyses of shear wall specimens are carried out according to the proposed model to obtain the evolution of damage index of the shear wall. Experiments of six L-shaped shear wall specimens subjected to reversed cyclic loading are carried out to verify the proposed model. Correlation of damage index and performance level is established, which provides good reference for the safety assessment of the structure under seismic type of loading. The model is efficient to evaluate the seismic performance of shear wall proved by the satisfactory agreement between analytical and experimental results. Copyright © 2012 John Wiley & Sons, Ltd.

This paper investigates the potential of double-layer space structures to be applied vertically as a new structural system in super-tall buildings. The investigation using case studies covers four stages: structural designs of 100-storey buildings in order to obtain internal force distributions and determine appropriate structural member sizes, analyses of the impacts of wind and seismic loads on the structures, sensitivity of structural weight ratios and lateral deflection constraints to changing structural geometry, and comparison of the lateral deflected shapes and structural weights per unit area with those of other current tall structural systems. The results show that changing the angles of diagonal members to make them span two storeys rather than one storey reduces structural weight and has little impact on lateral deflection. Compared with other current tall structures, vertical double-layer space structures are relatively efficient structurally. The study concludes that double-layer space structures can be applied vertically as a structural system of super-tall buildings. Copyright © 2012 John Wiley & Sons, Ltd.

Current effective flexural rigidities proposed for use in design and analyses of reinforced concrete structures have been examined. The level of accuracy in the estimation of section rigidity plays a very important role in determining realistic values for the structural stiffness and hence the seismic forces imposed. The most significant parameters influencing the effective rigidity, which reflects the effect of cracking as well as the theoretical yielding of reinforced concrete sections, have been determined through comprehensive moment–curvature analyses of various reinforced concrete sections. The geometry, axial load level, concrete strength and the amount of compression and tension reinforcements have been identified as the most important factors affecting the effective rigidity. New relationships that are believed to represent the effective stiffness of reinforced concrete members have been adequately developed. Efficiency of the code-specified and proposed values has been investigated through experimental data and parametric studies. It has been observed that the relationships developed herein have provided the most accurate results in prediction of the effective rigidity of older-type structural elements with low-strength and longitudinal reinforcement ratio. They can be used for assessment of ordinary buildings. Copyright © 2012 John Wiley & Sons, Ltd.

Industrialized building system (IBS) is a construction process that uses techniques, products, components or building systems that involve prefabricated components and on-site installation. The structural behaviour of a prefabricated frame structure is widely affected by the specifications of the beam-to-column connection. The understanding on the real behaviour of a connection can be assessed by conducting full-scale experimental tests. In this study, a new IBS hybrid steel–concrete connection in a full-scale H-subframe under monotonic loading is investigated. This innovative connection system, consists of precast concrete beam-and-column elements with embedded steel end connectors, is patented as Smart IBS. This paper reports the testing procedures and results of this semi-rigid IBS beam-to-column connection to obtain the important attributes of the connection as well as its comparison with monolithic cast-in-place reinforced concrete model. The height of both H-subframes is 3.3 m while the free length of the beam is 3.2 m. The incremental loads were applied as two point loads in one-third and two-third of the beam length. The characteristic relationships of the connection such as load to mid-span deflection, strength, stiffness, ductility, failure modes and crack patterns are studied and compared between both structural systems. Copyright © 2012 John Wiley & Sons, Ltd.

The term progressive collapse is typically used to refer to the spread of an initial local failure within a structure. This paper proposes a new and simple method to calculate of the dynamic load amplification factor due to sudden column loss within a progressive collapse event in a structure. The conceptual basis of this method is the ability of the remaining structure after column loss to transfer the kinetic energy. Five principal stages are used in this research to achieve its purpose: (1) achieving the nonlinear static response of the remained structure to load using finite element method, (2) using the conceptual ductility at the maximum level of dynamic deformation to calculate the amplification factor, (3) designing a flowchart to determine the dynamic load amplification factor versus a ratio load, (4) achieving a series equation based on the statistical analyses to calculate dynamic load amplification factor and (5) designing a simplified graph using the results achieved from the previous stages. Copyright © 2012 John Wiley & Sons, Ltd.

In this study, to determine the elastic and inelastic structural responses of mid-rise building frames under the influence of soil–structure interaction, three types of mid-rise moment-resisting building frames, including 5-storey, 10-storey and 15-storey buildings are selected. In addition, three soil types with the shear wave velocities less than 600 m/s, representing soil classes C_e, D_e and E_e according to AS 1170.4–2007 (Earthquake action in Australia, Australian Standards), having three bedrock depths of 10 m, 20 m and 30 m are adopted. The structural sections are designed after conducting nonlinear time history analysis, on the basis of both elastic method and inelastic procedure considering elastic-perfectly plastic behaviour of structural elements. The frame sections are modelled and analysed, employing finite difference method adopting FLAC2D software under two different boundary conditions: (a) fixed base (no soil–structure interaction) and (b) considering soil–structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted, and the results in terms of the maximum lateral displacements and base shears for the above mentioned boundary conditions for both elastic and inelastic behaviours of the structural models are obtained, compared and discussed. With the results, a comprehensive empirical relationship is proposed to determine the lateral displacements of the mid-rise moment-resisting building frames under earthquake and the influence of soil–structure interaction. Copyright © 2012 John Wiley & Sons, Ltd.

The active control of engineering structures is one of the best methods to reduce structural responses under seismic excitation for the best performance of structures. This study presents an effective approach for the optimal control of structures under strong ground motion using the colonial competitive algorithm. The colonial competitive algorithm was developed over the last few years in an attempt to overcome the inherent limitations of traditional optimize method. The colonial competitive algorithm has been applied due to its ideal performance in optimal control problem. The effectiveness and performance of the proposed method have been investigated through two numerical examples for the response control of earthquake-excited structures. The obtained results have been compared with the Linear Quadratic Regulator (LQR) control algorithm, and the performance of the proposed control approach has been found to be better than the LQR controller. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, considering horizontal components of seismic excitation, an algorithm for the nonlinear multi-component analysis of building structures by the Endurance Time (ET) method is proposed, and results of the ET method for various steel moment frames with one to seven stories are verified by comparing with the results from Nonlinear Time History Analysis with use of two different sets of ground motions. In addition, several parameters such as eccentricities and irregularities in structure, rotational and lateral stiffness, effect of hysteresis type and ductility have been considered for sensitivity analysis on results, obtained by ET method. Results show that on the basis of recommendations of structural codes for bidirectional time history analysis, which requires applying horizontal components of earthquakes simultaneously, the ET method can be used to predict the seismic response of structures with reasonable approximation and reduced computational effort. Copyright © 2012 John Wiley & Sons, Ltd.

The usage of special materials with unique properties in seismic resistant structures has increased since the 1994 Northridge earthquake to overcome limited energy dissipation and ductility. Among them, shape memory alloy (SMA) is a unique metallic alloy that has the ability to undergo large deformations and revert back to its original un-deformed shape. Thus, a simple and practical hybrid damping device equipped with SMA that provides both energy-dissipating and re-centering (strain-recovering) capabilities is developed and evaluated in the present paper. Quasi-static loading tests on Nitinol bars are conducted to obtain their mechanical properties in tension and compression. The optimum proportion of SMA and steel in the device is achieved through analyzing various models. Placing the proposed device in semi-rigid bracing members of special structures will localize the energy-dissipating and ductility while providing the brace with strain-recovering capability. Copyright © 2012 John Wiley & Sons, Ltd.

Concrete-filled-steel-tube (CFST) columns have been widely adopted for column construction of tall buildings due to its superior strength and ductility performance contributed by the composite action. However, this beneficial composite action cannot be fully developed at early elastic stage as steel dilates more than concrete and thereby causing imperfect interface bonding. Hence, it reduces the elastic strength and stiffness of the CFST columns. To resolve the problem, external confinement in the form of steel rings is proposed in this study to restrict the lateral dilation of concrete and steel at initial elastic stage. In this paper, CFST columns of various dimensions cast with normal-strength or high-strength concrete and installed with external steel rings were tested under uni-axial compression. From the results, it was evident that (a) the external steel rings could restrict the lateral dilation of CFST columns and improve the interface bonding condition and (b) externally confined CFST columns had uni-axial strength and stiffness larger than those of unconfined CFST columns. With the experimental results, an analytical model taking into account the confining effects of steel tube and rings has been developed to predict the uni-axial strength of ring-confined CFST columns. Copyright © 2012 John Wiley & Sons, Ltd.

Irregular buildings behave differently as compared with regular buildings. Seismic design codes have quantified the irregularities in terms of magnitude only ignoring the effect of irregularity location. In the present study, a single parameter to quantify mass, stiffness and strength irregularity in terms of both magnitude and location is proposed on the basis of the dynamic characteristics of the building. Furthermore, building models with different types of irregularity with variation in magnitude and location of irregularity are analyzed by subjecting them to an ensemble of 27 ground motions to create a seismic response databank. In the analysis, the torsional effects generated due to irregularities in the building systems (as per EC 8:2004 provisions) are included. On the basis of regression analysis conducted on this seismic response databank, equations to estimate seismic response parameters such as fundamental period, maximum roof displacement and maximum inter-story drift ratio etc. are proposed for the irregular buildings in terms of the proposed irregularity index. Finally, applicability of the proposed equations is discussed in brief, and these equations are validated for 2D and 3D building models. Copyright © 2012 John Wiley & Sons, Ltd.

The 11 March 2011 M 9.0 Great East Japan earthquake generated significant long-duration shaking that propagated hundreds of kilometers from the epicenter and affected urban areas throughout much of Honshu. Recorded responses of a tall building at 770 km from the epicenter of the mainshock and other related or unrelated events show how structures sensitive to long-period motions can be affected by distant sources. Even when the largest peak input motions to the building is about 3% g, the strong-shaking duration was about 140 s. The 300- to 1000-s prolonged responses of the building are primarily due to a combination of site resonance (e.g. structural fundamental frequency ~0.15 Hz and site frequency ~0.13–0.17 Hz) and low damping (~1–2%) of the structure. Response modification technologies can improve the response of the building during future earthquakes. The need-to-consider risks to such built environments from distant sources are emphasized. Copyright © 2012 John Wiley & Sons, Ltd.

The Firefly Algorithm (FA) as a recent new meta-heuristic optimization algorithm is developed for determining optimum design of tower shaped structures. The FA mimics the social behavior of fireflies, which communicate, search for pray and find mates using bioluminescence with varied flashing patterns. In this paper, an adaptive FA is presented that utilizes the feasible-based method to handle constraints. This method is effective in improving the convergence and also suitable for expensive optimization tasks such as large-scale structures. Three tower structures are selected to evaluate the performance of the algorithm. The results are better than the other results proposed in the literature and confirm the validity of the proposed algorithm. Copyright © 2012 John Wiley & Sons, Ltd.

Optimal design of tall buildings, as large-scale structures, is a rather difficult task. To efficiently achieve this task, the computational performance of the employed standard meta-heuristic algorithms needs to be improved. One of the most popular meta-heuristics is particle swarm optimization (PSO) algorithm. The main aim of the present study is to propose a modified PSO (MPSO) algorithm for optimization of tall steel buildings. In order to achieve this purpose, PSO is sequentially utilized in a multi-stage scheme where in each stage an initial swarm is generated on the basis of the information derived from the results of previous stages. Two large-scale examples are presented to investigate the efficiency of the proposed MPSO. The numerical results demonstrate the computational advantages of the MPSO algorithm. Copyright © 2012 John Wiley & Sons, Ltd.

Many steel–concrete hybrid buildings have been built in China. The seismic performance of such hybrid system is much more complicated than that of steel structure or reinforced concrete (RC) structure. A steel–concrete hybrid frame-tube super-tall building structure with new type of shear walls to be built in a district of seismic intensity 8 in China was studied for its structural complexity and irregularity. Both model test and numerical simulation were applied to obtain the detailed knowledge of seismic performance for this structure. First, a 1/30 scaled model structure was tested on the shaking table under different levels of earthquakes. The failure process and mechanism of the model structure are presented here. Nonlinear time-history analysis of the prototype structure was then conducted by using the software PERFORM-3D. The dynamic characteristics, inter-story drift ratios and energy dissipation conditions are introduced. On the basis of the comparison between the deformation demand and capacity of main structural components at individual performance level under different earthquake level, the seismic performance at the member level was also evaluated. Despite the structural complexity and code-exceeding height, both experimental and analytical results indicate that the overall seismic performance of the structure meet the requirements of the Chinese design code. Copyright © 2012 John Wiley & Sons, Ltd.

One of the most popular damage indexes for reinforced concrete (RC) members is Park–Ang damage index model. This model has been established on the basis of experimental results of RC beams and columns with different modes of damage. It has considerable uncertainty on the basis of its authors' remarks. In this study, precision of Park–Ang model for RC columns is improved by using some experimental results from Pacific Earthquake Engineering Research information bank. In proposed model, it focused on RC columns with specific sections and collapse modes. Finally, in order to define damage index more exactly in concrete columns under seismic loadings, capability of IDARC-2D computer program has been improved by this proposed model. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, on the basis of the D'Alembert's principle, approximate formulas for dynamic response of tubular tall building structures are presented. Using D'Alembert's principle and applying the compatibility conditions on deformation of the tubes, the governing dynamic equation of the tubular structure's motion is derived. Then, natural boundary conditions of the parallel cantilevered flexural–shear beams are derived, and by using Rayleigh–Ritz method, value problem is solved, and trivial and nontrivial solutions are derived, which can be used for calculating natural frequencies and mode shapes of tubular structures. By solving numerically the frequency equation, a design chart and graph are given for the first five nondimensional natural frequencies of tubular tall buildings. The proposed mathematical model gives dynamic characteristics and provides a simple, efficient and reasonably accurate algorithm for free vibration studies that are needed to be quick at the preliminary design stages of tall buildings with tubular systems. Copyright © 2012 John Wiley & Sons, Ltd.

Due to its simplicity, lumped plasticity approach is usually used for nonlinear characterization of reinforced concrete (RC) members in pushover analysis. In this approach, the inelastic force deformation of hinges could be defined as either the nonlinear properties suggested in FEMA-356 and ATC-40 or defined hinges quantified on the basis of the properties of RC members. However, the nonlinear response of RC structures relies heavily on the inelastic properties of the structural members concentrated in the plastic hinges. To provide a comparative study, this paper attempts to show the results of pushover analyses of RC structures modeled on the basis of the FEMA nonlinear hinges and defined hinges. Following the validation of the adopted models, the force–deformation curves of the defined hinges are determined in a rigorous approach considering the material inelastic behavior, reinforcement details and dimensions of the members. For the case studies, two four-story and one eight-story frames are considered in order to represent low-rise and mid-rise buildings with different ductility. Nonlinear responses of both models are elaborated in terms of the inter-story drift, hinging pattern, failure mechanism and the pushover curve. It is confirmed that FEMA hinges underestimate the strength and more importantly the displacement capacity, especially for the frame possessing low ductility. Copyright © 2012 John Wiley & Sons, Ltd.

Employing twisted forms for tall buildings is a recent architectural phenomenon. This paper studies various structural system design options for twisted tall buildings and their performances based on lateral stiffness. Twisted tall buildings of various heights and rates of twist are designed with different types of contemporary tall building structural systems, such as diagrids, braced tubes and outrigger systems. The heights of the studied buildings range from 60 to 100 stories, and the rates of twist range from 0° to 3° per floor. As the rate of twist increases, the lateral stiffness of the tower decreases. The stiffness reduction rate caused by twisting is very much dependent upon the structural systems employed for twisted tall buildings. While an emphasis is placed on the structural performance of twisted tall buildings, other aspects, such as architectural and constructional issues, are also discussed holistically. Copyright © 2012 John Wiley & Sons, Ltd.

Large-span reinforced concrete (RC) shells collapses that occurred in the last decade caused many death toll as well as significant losses to national economies. The most famous cases were the collapse of the aqua park cover in Moscow on February 2004 and the 2E terminal roof destruction at Charles de Gaulle Airport near Paris on May 2004. Following the publications of the appropriate commissions that have studied the reasons of these events, the influence of concrete creep and changes in the shell geometry on buckling of RC thin-walled shells was not properly considered in the design. This study is focused on buckling of such shells, taking into account geometrical and physical nonlinear behaviour of compressed concrete. Other important reasons of concrete shells collapse are also analysed. The study is based on available experimental and theoretical investigations of ferro-cement shells' models previously performed by the first author. The results of these investigations, obtained for small-scale ferro-cement models of thin-walled shallow RC shells, are discussed. Behaviour of the tested models is compared with that of the above-mentioned real shells and similar structures, which also collapsed. The critical buckling loads for the shells are obtained. It is shown that these loads are lower than the actual ones; thus, the shells buckling was unavoidable. To prevent brittle shell failure, they should be designed using other dominant failure modes that appear before the buckling. Possible failure schemes of real RC shells can be predicted using dominant failure modes obtained by laboratory testing of scaled models. Copyright © 2012 John Wiley & Sons, Ltd.

The well-known Hilbert–Huang transform (HHT) consists of empirical mode decomposition to extract intrinsic mode functions (IMFs) and Hilbert spectral analysis to obtain time–frequency characteristics of IMFs through the Hilbert transform. There are two mathematical requirements that limit application of the Hilbert transform. Moreover, noise effects caused by the empirical mode decomposition procedure add a scatter to derivative-based instantaneous frequency determined by the Hilbert transform. In this paper, a new enhanced HHT is proposed in which by avoiding mathematical limitations of the Hilbert spectral analysis, an additional parameter is employed to reduce the noise effects on the instantaneous frequencies of IMFs. To demonstrate the efficacy of the proposed method, two case studies associated with structural modal identification are selected. In the first case, through identification of a typical 3-DOF structural model subjected to a random excitation, accuracy of the enhanced method is verified. In the second case, ambient response data recorded from a real 15-story building are analyzed, and nine modal frequencies of the building are identified. The case studies indicate that the enhanced HHT provides more accurate and physically meaningful results than HHT and is capable to be an efficient tool in structural engineering applications. Copyright © 2012 John Wiley & Sons, Ltd.

Semi-rigid connections are widely used in different countries. These connections are usually used in semi-rigid frames with bracing system. Considering the frequent use of these connections, studying their behavior as an individual connection or as a frame with a semi-rigid connection is of great importance. In this paper, moment–rotation behavior of bolted angle connection as a usual semi-rigid connection is studied, and the affecting factors on there are investigated. Finite element connection models are developed. These models are verified by comparing the results of finite element analyses with the results of experimental test, and the verified models are used to investigate the behavior of the connections. The behavior of semi-rigid frame with bolted angle connection is then studied conducting time-history analyses. The results show that the increase in shear stiffness of angle bolted connections significantly decreases the lateral drift and increase the frame stability against lateral loading. Copyright © 2012 John Wiley & Sons, Ltd.

The originality of form is one of the new trends that can be identified in the current design of tall buildings. In this design trend, the so-called diagrid structures, which represent the latest mutation of tubular structures, play a major role due to their inherent esthetic quality, structural efficiency and geometrical versatility. In this paper, an overview on application of such typology to high-rise buildings is carried out; in particular, in the first part of the paper, the peculiarities of diagrid systems are described: starting from the analysis of the internal forces arising in the single diagrid module due to vertical and horizontal loads, the resisting mechanism of diagrid buildings under gravity and wind loads is described, and recent researches and studies dealing with the effect of geometry on the structural behavior are discussed. In the second part of the paper, a comparative analysis of the structural performance of some recent diagrid tall buildings, characterized by different number of stories and different geometries, namely the Swiss Re building in London, the Hearst Headquarters in New York and the West Tower in Guangzhou, is carried out, and some general design remarks are derived. Copyright © 2012 John Wiley & Sons, Ltd.

It is expected that application of torsion provisions in typical seismic codes shows different levels of efficiency for torsionally stiff and flexible buildings. This paper studies difference in performances of a range of code designed torsionally stiff and flexible five-story building models. The models are classified in eight configurations to cover common range of buildings designed with the seismic provisions of Iranian Standard 2800 as a typical seismic design code. Seismic nonlinear dynamic time history behavior of eight building models subjected to seven horizontal bi-directional design spectra compatible ground motions is investigated. These models cover a wide band of very torsionally stiff to very flexible buildings. Response parameters are element ductility demand and building story drift ratio. These criteria are appropriate indices for structural and nonstructural damages, respectively. The results indicate that the present linear static procedure of building codes such as the Iranian Standard 2800 is not generally adequate for structures with very low torsional stiffness. Copyright © 2012 John Wiley & Sons, Ltd.

A new metaheuristic optimization algorithm is developed to solve truss optimization problems. The new algorithm, called cuckoo search (CS), is examined by solving five truss design optimization problems with increasing numbers of design variables and complexity in constraints. The performance of the CS algorithm is further compared with various classical and advanced algorithms, selected from a wide range of the state-of-the-art algorithms in the area. The results identify that the final solutions obtained by the CS are superior compared with the best solutions obtained by the other algorithms. Finally, the unique search features used in the CS and the implications for future researches are discussed in detail. Copyright © 2012 John Wiley & Sons, Ltd.

A displacement-based design scheme can be applied to the seismic designs of special reinforce concrete (RC) shear walls. However, the displacement-based design in the current seismic design codes does not consider the contribution of yield deformation of RC shear walls. In this study, the evaluation method of the deformation capacity for seismic designs of RC shear walls was analyzed and applied to a parametric study for the lateral deformations of RC shear walls. From the results of analyses with various design conditions, the contribution of yield deformation to the deformation capacity of an RC shear wall was analyzed. It was demonstrated that, for RC shear walls in tall buildings, the yield deformation increased as the ratio of wall height to length increased and reached more than 50% of total deformation. Therefore, for the reasonable design of special RC shear walls in tall buildings, the design equation including the yield deformation in the displacement-based design process is proposed. Copyright © 2012 John Wiley & Sons, Ltd.

This study investigates a direct displacement-based design procedure for dual system structures composed of reinforced concrete frames and steel bracings. In this procedure, in order to establish the design displacement profile before any analysis, strength proportions between bracings and frames are assigned. By using the displacement profile and damping characteristics of the structural components, the structure can be represented as an equivalent single-degree-of-freedom system. The effective period and secant stiffness of the structure are then calculated, and finally, after the base shear was computed, the design process can be implemented. Structures with 4, 8 and 12 stories have been designed using this methodology, and in order to validate it, seven accelerograms have been used for nonlinear time-history analysis of the above structures. The results demonstrate the efficiency of this procedure. Copyright © 2012 John Wiley & Sons, Ltd.

The Shanghai World Financial Center Tower is the tallest landmark building in mainland China, with a height of 492 m. In order to mitigate wind-induced vibration, a set of two identical damping devices was installed at the 90th floor. The damping devices are active tuned mass dampers: under wind loading, the active control feature is enabled, while the active control feature becomes disabled under earthquake conditions, and the damping devices function as passive tuned mass dampers. The dynamic parameters of the damping devices, structural analysis results and field measurement results under different vibration scenarios are presented in this paper. The analysis and field measurement results show that the damping devices performed well and had the following characteristics: they increased the damping ratio up to eight times in field measurements and reduced the wind acceleration response up to 60% when wind speed is below the designed value in the analysis. Copyright © 2012 John Wiley & Sons, Ltd.

At present, corrugated plates have numerous applications such as web of plate girders and aerospace applications. Higher out-of-plane stiffness and initial elastic strength of the corrugated plates compared with flat plates are reasons for consideration. This study investigates the behavior of trapezoidally corrugated steel plate shear walls (TCSPSWs) under monotonic and cyclic loadings. Finite element analyses that include both material and geometric nonlinearities are employed for the examination. The results from finite element analysis are verified through tested specimen findings. Moreover, the behavior of the steel shear walls with the flat infill panels and the corrugated plate infill panels is compared. The results show that explicit dynamic analysis is the most suitable analysis for the TCSPSWs under quasi-static loading. Furthermore, although strength of the TCSPSWs obtained from the finite element analysis and the test are fully coincident in elastic region, nonetheless, they are fairly coincident in elastic–plastic and plastic region. Copyright © 2012 John Wiley & Sons, Ltd.

Performance assessment of high-rise buildings has attracted peculiar attention among engineers. Care should be taken once higher-mode effects are to be incorporated into analyses and designs. Recently, performance-based evaluations have been widely used by designers to meet the required target capacities of engineering projects. A common tool to perform such studies is incremental dynamic analysis (IDA), which has been utilized for first-mode-dominant ordinary structures, whereas taller buildings demand other considerations to be made so that a thorough assessment of the structural response can be achieved.

In this paper, performance-based studies have been carried out for a sample 30-story tall building, which takes advantage of tubular frame as lateral-load-resisting system. IDA is performed subsequently to quantify the structural response against a wide-range of seismic loadings. Advanced intensity measures (IMs) are applied to optimize the capacity assessments resulting from multitude of non-linear time-history analyses. Finally, performance-based evaluations have been carried out to provide a thorough assessment of target capacities that are normally advised by widely accepted codes. Results are also compared with regular short buildings where higher-mode effects do not contribute significantly to structural response. Copyright © 2012 John Wiley & Sons, Ltd.

Dynamic analysis of structures deals with scaling of ground motions, which is vital for estimation of seismic responses. A major source of variability in seismic responses of structures arises from scaling of ground motions. In this paper, the accuracy of six conventional scaling methods on estimation of engineering demand parameters of soil–structure interacting systems is investigated. Two-dimensional structural models of 5, 10, and 20 stories shear buildings are studied by using stick models, whereas the underlying soil is modeled using the cone model concept. This research attempts to elucidate the accuracy of considered methods for the evaluation of responses. The results show that a suitable scaling method for a response may differ from one to another in terms of accuracy and efficiency. Copyright © 2012 John Wiley & Sons, Ltd.

In most of the seismic design provision, the concept of strength reduction factor has been developed to account for inelastic behavior of structures under seismic excitations. Most recent studies considered soil–structure interaction (SSI) in inelastic response analysis are mainly based on idealized structural models of single degree-of-freedom (SDOF) systems. However, an SDOF system might not be able to well capture the SSI and structural response characteristics of real multiple degrees-of-freedom (MDOF) systems. In this paper, through a comprehensive parametric study of 21600 MDOF and its equivalent SDOF (E-SDOF) systems subjected to an ensemble of 30 earthquake ground motions recorded on alluvium and soft soils, effects of SSI on strength reduction factor of MDOF systems have been intensively investigated. It is concluded that generally, SSI reduces the strength reduction factor of both MDOF and more intensively SDOF systems. However, depending on the number of stories, soil flexibility, aspect ratio and inelastic range of vibration, the strength reduction factor of MDOF systems could be significantly different from that of E-SDOF systems. A new simplified equation, which is a function of fixed-base fundamental period, ductility ratio, the number of stories, structure slenderness ratio and dimensionless frequency, is proposed to estimate strength reduction factors for MDOF soil–structure systems. Copyright © 2012 John Wiley & Sons, Ltd.

There are special guidelines to design the structures resistant to earthquake forces; parameters such as conditions of the site, seismicity of the site, importance of the structure and the type of the structure are the main effective factors. Consideration of these parameters in calculation and distribution of the earthquake forces are significantly different in various design codes. In most of these design codes, the computation and distribution of earthquake forces are based upon the elastic structural analysis. In this approach, the real behavior of structure is not considered and it may consequently sustain big displacements and irretrievable damages. Therefore, a new design method has been utilized in this paper by which the base shear and its distribution in the height of the structure are calculated according to the plastic behavior of structure and takes advantage of energy balance. The latter is known as performance-based plastic design method. The study of the behavior of eccentrically braced frames with vertical links while undertaking earthquake loads using performance-based plastic design method is the main purpose of this study. It is also worthy of notion that the frames are designed using a capacity design method. In addition, the results are compared with those of the International Building Code 2009 method; the results demonstrate that the plastic hinges, the interstory drifts and plastic rotation of links are distributed more uniformly in the height of frames designed by the suggested method compared to International Building Code 2009. Copyright © 2012 John Wiley & Sons, Ltd.

Damage levels of building structures under a design earthquake are closely related to the assigned values of strength reduction factors. This paper is to investigate the strength reduction factor demands of building structures that were designed considering various earthquake ground intensity levels, soil ground types, and strength reduction factors. In the investigation, a huge number of rigorous nonlinear inelastic dynamic response analyses of various analytical models of five-story and nine-story frame structures were conducted under various generated ground motions with variations in phrase angles but identical response spectral acceleration amplitudes. Various scaled earthquake records were also considered for evidence of the investigation. The obtained results showed that when the same values of the strength reduction factors were used for determination of the design lateral seismic forces, the damage and reliability level demands of the structures designed for moderate seismic areas were much less than those for severe seismic ones. As a result, it is proposed that the strength reduction factor demands given in design codes can additionally be expressed in a linear relation of the maximum ground acceleration. Copyright © 2012 John Wiley & Sons, Ltd.

Traditional shear wall structure has small space, is not flexible, causes waste of material and has bad economic efficiency. Through complete transformation of traditional shear wall, a new structure system has been created. The research and application of short-leg shear wall structure calculation theory are based on the national codes, from which the short-leg shear wall design principles are established. Traditional shear wall structure is discussed because of the world's first short-leg shear wall structure design formation and development research. According to short-leg shear wall force characteristics, horizontal displacement is divided into destructive storey drift and harmless storey drift; the formula for calculating the destructive storey drift is obtained, using destructive storey drift angle parameters and the change of main section height to control the deformation, to control structural rigidity and to ensure that the structural design attains excellence. Copyright © 2012 John Wiley & Sons, Ltd.

In this study, effects of applying higher order axial displacement distribution to solve a continuum model for static analysis of the combined system of framed tube, shear core and outrigger–belt truss system in high-rise buildings are investigated. Framed tube system is modeled using an orthotropic box beam analogy approach and the interaction between shear core and outrigger–belt truss system on framed tube is modeled with rotating spring placed at outrigger–belt truss location. The axial displacement distributions in web and flange panels along structure's height are proposed to be fifth-order and fourth-order polynomials, respectively. Analytic analyses are carried out on the basis of the principle of minimum potential energy. A detailed work is carried out through two numerical examples and the accuracy of proposed approximation functions is compared with previous work and finite element analysis. Results demonstrate that the proposed parametric stress distribution and displacement functions are more accurate than previously proposed functions in comparison with the finite element solution. Copyright © 2012 John Wiley & Sons, Ltd.

Pushover analysis is a simplified method to determine the lateral load capacity of buildings. However, recent studies have suggested that pushover analysis could underestimate the capacity by as much as 25%. Thus, this study uses dynamic collapse analysis to determine the overstrength of a 16-storey and a 25-storey building, which are typical in Singapore. The results are compared with previously performed pushover analyses to justify the adequacy of pushover analysis for determining the ultimate capacity of such buildings. It is found that the buildings in Singapore, which are not designed for earthquake loads, possess overstrength varying from 4 to 12 times the design strength depending on the type of building. Furthermore, the pushover analysis could underestimate the capacity of such buildings up to 14%. It is suggested that one may choose to adopt pushover analysis to evaluate the lateral load capacity of such high-rise buildings to err on the conservative side. Copyright © 2012 John Wiley & Sons, Ltd.

In this study, the progressive collapse resisting capacities of tilted buildings are evaluated on the basis of arbitrary column removal scenario. As analysis model structures both regular and tilted moment-resisting frames, structures with outrigger trusses, and tubular/diagrid structures are designed, their progressive collapse resisting capacities are evaluated by nonlinear static and dynamic analyses. It turns out that the tilting of the structures requires increased steel tonnage due to the increased p-delta effect. In addition in the tilted structures the plastic hinges are more widely distributed throughout the bays and stories when a column is removed from a side or a corner of the structures. With the analysis results, it is concluded that the tilted building structures, once they are properly designed to satisfy a given design code, may have at least an equivalent resisting capacity for progressive collapse caused by sudden loss of a column. Copyright © 2012 John Wiley & Sons, Ltd.

In most of tall buildings, the main contribution of lateral loads is carried by coupled shear walls. In some cases, the necessary stiffness to withstand the lateral load may not be afforded due to low depth of connecting beams. In order to increase the capacity of the coupled shear walls, beams with high stiffness are added to the system at particular levels. Hence, stiffened coupled shear walls (SCSW) will be produced. Such walls are under axial load resulting from their weight, and this axial load affects the behavior of walls because of their excessive height. In this paper, a new method considering the effect of axial force for geometrically nonlinear analysis of the SCSW has been presented. A computer program has been developed in matlab, and numerical examples have been solved to demonstrate the reliability of this method. The results of the examples show the agreement between the present method and the other methods given in the literature. The effects of the various positions and rigidities of the stiffening beam on the internal forces and the lateral deflection of the structure considering axial force effect have also been investigated. Copyright © 2012 John Wiley & Sons, Ltd.

In order to improve the efficiency of tube-type structures in tall buildings, a new structural system, called hexagrid, is introduced in this paper. In comparison with diagrid system, it consists of multiple hexagonal grids on the face of the building. In this research, a set of structures using diagrid system having four various diagonal angles and hexagrid system were designed on a strength and stiffness-based approach for buildings with 30, 50, 70 and 90 stories to withstand wind load. The impact of different geometric configurations of structural members on the maximum lateral displacement and architectural performance in both diagrid and hexagrid systems is compared. The stiffness sensitivity using a similar interior bracing system in both systems is also discussed. In this study, the seismic performance of a 30-story diagrid structure and a hexagrid structure was evaluated using nonlinear static and dynamic analyses. According to the results, the hexagrid system has a better architectural view and more ductility and stiffness sensitivity, which are about three times than that of the diagrid system. And finally, in comparison with the diagrid system, the hexagrid system has enough potential to push the height limit. The guidelines discussed here are for architectural and structural engineers to improve freehand design. Copyright © 2012 John Wiley & Sons, Ltd.

Currently, nonlinear base isolation systems are widely used in the construction of earthquake resistant structures. However, they are found to be vulnerable in near-fault regions as a result of long-period pulses that may exist in near-source ground motions. Various control strategies including passive, active and semi-active control systems have been studied in order to handle this issue. In this study, a semi-active control algorithm based on the different performance levels anticipated from an isolated building during different levels of ground shaking was developed. The proposed performance-based algorithm is based on a modified version of the well-known semi-active skyhook control algorithm. A series of analyses were performed on the base-isolated benchmark building, suggested by the American Society of Civil Engineers committee, subject to seven pairs of scaled ground-motion records. The results proved that the new control algorithm is successful in improving structural and nonstructural performance of isolated buildings under near-fault earthquakes. Copyright © 2012 John Wiley & Sons, Ltd.

In this study, the progressive collapse-resisting capacities of axi-symmetric or rotor-type diagrid structural system buildings were evaluated based on arbitrary column removal scenario. For analysis models, 33-story buildings with cylindrical, convex, concave and gourd shapes were designed, and their nonlinear static and dynamic analysis results were compared. The effect of design variables such as the number of total stories, slope of diagrids and the location of removed members was also investigated. According to the analysis results, the rotor-type diagrid structures showed sufficient progressive collapse-resisting capacity regardless of the differences in shapes when a couple of diagrids were removed from the first story. The design parameter such as building height and the slope of the diagrids did not affect the results significantly as long as they were designed to meet the current design code. Copyright © 2012 John Wiley & Sons, Ltd.

High statistics of damages in modern structures (buildings structured based on new codes) exposed to near-fault earthquake illustrates the necessity of more studies on this kind of earthquake effects on the structures. A specification of near-fault earthquakes is the directivity effects. Existing records of near-fault quakes containing directivity effects including records of Iran and abroad were modified and used for linear time history analysis of three steel moment frames (5, 8 and 12 story frames), and the results were compared with nonlinear time history analysis and pushover analysis of far-fault quakes in this paper. The results showed that these records (near fault) motivate high modes of the structure, and especially for the 12-story structure, high response was detected, but none of these results made the frames collapse. By comparing nonlinear dynamic analysis (time history) with nonlinear static analysis (pushover), it was concluded that various lateral load patterns in pushover cannot cover the time history result needs. Load distribution pattern based on the first vibration mode covers these demands in the lower floors, but in higher floors, this method is not applicable. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, the seismic performance of reinforced concrete (RC) staggered wall structures with middle corridor was evaluated. To this end, 6-, 12- and 18-storey structural models were designed and were analyzed to investigate the seismic load-resisting capacity. The response modification factors were computed based on the overstrength and the ductility capacities obtained from pushover curves. The effect of a few retrofit schemes on the enhancement of strength and ductility was also investigated. The pushover analysis results showed that the response modification factors ranged between about 4.0 and 6.0 with the average value around 5.0. When the bending rigidity of the link beams increased up to 100%, the overall overstrength increased by only about 25%. When the rebar ratio of the link beams was increased by 50%, the overstrength increased by about 40%. The replacement of the RC link beams with steel box beams resulted in superior performance of the structures with reduced beam depth. The displacement time histories of the model structures subjected to the earthquake ground motions scaled to the design seismic load showed that the maximum interstorey drifts were well below the limit state specified in the design code. Based on the analysis results, it was concluded that the staggered wall systems with a middle corridor had enough capacity to resist the design seismic load. Copyright © 2012 John Wiley & Sons, Ltd.

Super tall building projects commonly inherit a slow and lengthy decision making process due to financial uncertainties, in spite of large investments. However, current decision-making practices depend upon detailed cost estimating and scheduling during the design development phase and not rough cost estimating and scheduling during the schematic design phase. Discrepancies between a project budget and program with estimated construction cost and construction period often result in architect and consultants having to perform costly re-design work. To mitigate these issues, this study proposes a decision support system (DSS) model. An interim design development phase is introduced between the schematic design phase and the design development phase. Design alternative generation, database, cost and schedule estimation modules are developed. The design alternative generation module provides design alternatives that change proportionately in response to increases or decreases in the number of building stories. The database module is established for cost and schedule estimation modules. The cost and schedule estimation modules produce construction costs and construction period for design alternatives. Finally, the proposed DSS is validated through the case study of an ongoing real super tall building. Ultimately, the new DSS can assist project control groups in performing efficient and financially beneficial decision making in terms of construction cost and construction period. This research provides a fundamental step towards the development of the DSS for super tall building projects. Copyright © 2012 John Wiley & Sons, Ltd.

The collapse probability of ductile and non-ductile concentrically braced frames was investigated using nonlinear dynamic response analysis. Two buildings with three and nine stories located in Boston and Los Angeles, respectively, were designed and subjected to ground motions from the areas. In Boston area, three-story and nine-story buildings were designed as ordinary concentrically braced frame with response modification reduction factor R equal to 3 1/4 to be considered as non-ductile structural systems; comparatively, in Los Angeles area, three-story and nine-story buildings were designed as special concentrically braced frame with response modification reduction factor R equal to 6 to be considered as ductile structural systems. In order to evaluate the performance of ductile and non-ductile concentrically braced frames in moderate and severe seismic regions, ATC-63 would be used as reference to assess the seismic behaviors. Evaluation approach recommended by ATC-63 was adopted, and hundreds of nonlinear dynamic analyses were performed. Through alternating the scale factors of designated ground motions, median of structural collapse intensity was presented for each structure. By observing the results of statistical performance assessment, the seismic performance of the systems was evaluated, and some observations are made based on the study. Copyright © 2012 John Wiley & Sons, Ltd.

A methodology based on the progressive incremental dynamic analysis has been introduced in this paper to estimate the structural response and the corresponding annual probability of failure. The proposed methodology employs the genetic algorithm optimisation technique and an equivalent single-degree-of-freedom system corresponding to the first-mode period of a considered structure. The proposed methodology can significantly reduce the number of ground motion records needed for estimating the annual probability of failure. The numerical results indicate that the proposed method can effectively reduce the computational effort needed for computation of probability of failure for the first-mode dominated structures, which is advantageous as the structure becomes larger. A relatively huge set of single-degree-of-freedom systems as well as three multi-degree-of-freedom systems including 3, 8 and 12 storeyed reinforced concrete structures was taken into account to test the proposed methodology. It has been shown that the probability of failure can be estimated within ±15% error with 95% confidence. The proposed method can speed up the decision-making process in the probability-based seismic performance assessment of structures, and it also incorporates the randomness of strong ground motions explicitly. Copyright © 2012 John Wiley & Sons, Ltd.

In recent earthquakes, many buildings have been damaged due to the soft-storey mechanism failure. The seismic design codes for buildings do not contain enough criteria to predict the real displacement of such buildings. This paper focuses on evaluating the nonlinear displacement of buildings that fail in soft-storey mechanism form. Results show that the nonlinear static procedure with coefficient method, which is described in Chapter 3 of ASCE/SEI 41-06, does not have sufficient accuracy for estimation of structure displacement demand in such buildings. In this paper, the coefficient methodology is used for evaluating the target displacement for 5-storey, 8-storey and 15-storey special moment resisting steel frames. For this purpose, dynamic nonlinear time-history analysis has been applied for the mentioned structures having a soft-storey mechanism failure form. The numerical results of storey displacement and interstorey drift were compared with those values obtained from the coefficient method described in Chapter 3 of ASCE/SEI 41-06. Copyright © 2012 John Wiley & Sons, Ltd.

It is a common practice to model multi-storey tall buildings as frame structures where the loads for structural design are supported by beams and columns. Intrinsically, the structural strength provided by the walls and slabs are neglected. As the building height increases, the effect of lateral loads on multi-storey structures increases considerably. The consideration of walls and slabs in addition to the frame structure modelling shall theoretically lead to improved lateral stiffness. Thus, a more economic structural design of multi-storey buildings can be achieved. In this research, modelling and structural analysis of a 61-storey building have been performed to investigate the effect of considering the walls, slabs and wall openings in addition to frame structure modelling. Sophisticated finite element approach has been adopted to configure the models, and various analyses have been performed. Parameters, such as maximum roof displacement and natural frequencies, are chosen to evaluate the structural performance. It has been observed that the consideration of slabs alone with the frame modelling may have negligible improvement on structural performance. However, when the slabs are combined with walls in addition to frame modelling, significant improvement in structural performance can be achieved. Copyright © 2012 John Wiley & Sons, Ltd.

Sway analyses of reinforced concrete buildings generally are carried out with computer programs. However, as the number of iterative solutions increase, the process may become tedious. This paper proposes a simple analytical method to evaluate sway of dual buildings subject to various types of lateral loads. The proposed method is based on the continuum model. Story drift limited by building codes can be controlled by the proposed method. Likewise, design engineers can use the simple analytical expressions to calculate the stability index, which includes sway terms at each story level. Stability index equation without sway terms is obtained by using the developed analytical expressions. Use of the equation, which is free of sway terms, is quite simple. Additionally, by using the proposed method, shear wall–frame interaction can be modeled simply. Thus, moment at the base of shear walls can be determined by using this model. Copyright © 2012 John Wiley & Sons, Ltd.

In the present article, the seismic performance of frames with reduced beam section (RBS) connections is evaluated. A key purpose of this study is the inclusion of connections flexibility in the seismic performance of RBS frames. Almost in every research projects carried out on seismic performance and design of RBS frames, the beam-to-column connection is typically assumed as fully rigid. The results of nonlinear finite element analysis performed on investigating the local performance of RBS connection reveal that they are within the American Institute of Steel Construction-defined semirigid connections. Three building frames, including 4, 8 and 16 stories considering the semirigid connection as well as fully rigid connection, are considered. A numerical study of the overall seismic response of the building frames subjected to near as well as far field earthquake ground motions using nonlinear static and/or nonlinear dynamic analysis is presented. Results in terms of inter-story drifts, total drifts, story shears and shear deformation in panel zone indicate that overlooking the flexibility of beam-to-column connections may lead to erroneous conclusions and unsafe seismic behavior that subsequently become significant in some cases. Copyright © 2012 John Wiley & Sons, Ltd.

This paper numerically studies the behavior of castellated beams with two simply supported ends under moment gradient loading and investigates the effect of beam and braced lengths on rotational capacity of castellated beams. To assure the ability of numerical models in predicting the complex behavior (especially at the location of opening) as well as the failure modes, numerical models of two experimentally tested specimens are developed. Comparison of force–displacement curves and failure modes shows that neglecting the boundary condition of the specimens, the numerical method can properly predict the behavior of castellated beams. All geometrical properties of the beams are the same as the study parameters so that the finite element model of the corresponding plain-webbed beams can be easily created by filling the web openings in castellated beams. The accuracy of finite element models of plain-webbed beams is evaluated by comparing the moment–rotation behavior with that of numerical models developed by other researchers. Rotational capacity of castellated beams derived from numerical models is compared with that of the corresponding I-shaped plain-webbed steel beams, and it is observed that in the case of short beams, web openings reduce energy absorption and plastic moment capacity of the beams compared with that of long ones. Copyright © 2012 John Wiley & Sons, Ltd.

Many tests and numerical research for RCS frame consisted of reinforced concrete (RC) column and steel (S) beam have been conducted in the USA and Japan over the past decades; they showed that the performance of the RCS system is superior to traditional concrete frame and steel frame. Up to the present, no research reports on composite CCSHRCS frame structure consisted of high-strength concrete columns confined with continuous compound spiral stirrups (CCSHRC) and steel (S) beam. Herein, an accurate finite element model of composite CCSHRCS frame is developed; the finite element model is investigated in order to fully include important factors such as local buckling of steel beam and nonlinear behavior of confined concrete; the validity of the proposed models is examined by comparing with the results of cyclic loading experiments on the RCS frame in reference. With the proposed model, the effect of composite CCSHRCS frame is discussed in detail. Copyright © 2012 John Wiley & Sons, Ltd.

Seismic evaluation of power plants is an extremely vital task in Iran. Iran is a seismically active region, and experience of major earthquakes in recent years has created an environment that requires special attention to all major and important structures throughout the country. In this project, a 150-m reinforced concrete stack in a thermal power plant in the western province of Hamedan was investigated. This study of course included all different sections of the power plant; however, in this paper, only the seismic behavior of this tall stack will be presented. The main document used for the evaluation of this stack was ACI 307. According to the recommendation of this manual, bar elements and concentrated mass were utilized for the analysis. Also, to further investigate the true behavior and compare the results by the recommendations, a finite element analysis was performed. In finite element analysis, due to modeling capabilities, all of the openings were considered. In this study, by using both methods, periods, displacements, modal participation factors, base shear and overturning moments were studied and compared. This paper is to present the procedures used, comparisons made and results obtained. Copyright © 2012 John Wiley & Sons, Ltd.

This paper focuses on the development of peak factor formulas of non-Gaussian wind pressure processes after reviewing the current estimation methods of non-Gaussian peak factors. A skewness-dependent peak factor is proposed by accounting for the contribution of skewness and kurtosis parameters in some existing Hermite moment-based formulas. The possible correction on the upcrossing rate used in the translation process approach is also investigated. Wind tunnel pressure data on a practical 43-story building with unusual shape is used to validate the accuracy of the skewness-dependent peak factor by investigating various statistical properties of wind-induced fluctuating pressure field on the complex-shaped tall building example. Copyright © 2012 John Wiley & Sons, Ltd.

The behavior of bolted angle connections under the combination of shear and tensile forces is studied in this paper to simulate the force applied on a connection in a real fire. First, ansys is used to develop a 3D model of these connections. These models are analyzed in a similar condition to experimental tests, ignoring the tensile force, and the results are compared with those of the experimental tests. Having assured of the accuracy, we studied the connection models in several conditions under the combination of shear and tensile forces. The results show that the strength of connection is rapidly decreased when the temperature is increased, and the decrease pattern of connection strength is similar to decrease pattern of bolts used in the connection. Moreover, investigation of strength reduction value of these connections by the increase of temperature under shear and tensile forces obviously shows that it is possible that the failure of steel frames at elevated temperatures occurs at the connections, and thus utilization of catenary action to enhance the fire resistance of structural steel beams requires investigation of the capacity of steel connections to resist the tying forces generated at the ends of the beams. Copyright © 2012 John Wiley & Sons, Ltd.

The procedure to obtain the inelastic demand curves for the multi-degree-of-freedom system, composed of inter-story shear versus inter-story displacement curve is introduced. The demand curves are established by using mode spectrum method, and the dynamical characteristic of structure under different earthquake hazard levels is taken into account. The relation of structure performance object and displacement ductility is adopted to deduce the relation of structure performance object and inter-story demand curve. Therefore, the inter-story demand curves take into account the inelastic behavior of structure under earthquake action adequately. Then, considering the seismic responding characteristic and the capacity curve of the frame structure, a new method named Inter-Story Capacity Spectrum (ISCS) is put forward for the performance-based seismic design of vertically irregular frame structures. Examples are presented to demonstrate the applicability and the utility of the proposed method. It is concluded that the new method can control the inter-story drift, the order and position of hinges of vertically irregular structures under different earthquake hazard levels. Comparing with time-history analysis method, it leans to safe and is superior to direct displacement-based design method. Copyright © 2011 John Wiley & Sons, Ltd.

The numerical analysis of the seismic performance for tall chevron panel buckling-restrained braced steel frames (PBRBFs) under small and strong earthquake excitations has been carried out to investigate a capacity design procedure for chevron PBRBFs and to examine the effects of axial strength distribution of braces along the height of buildings, vertical supports of braces for the braced beams and the overstrength of braces on the seismic response of PBRBFs. It revealed that the chevron braces that remained elastic can actually provide the vertical supports for the braced beams. Under severe earthquake excitations, the vertical supports deteriorated greatly after braces yielding. The PBRBFs designed by omitting vertical supports of braces for the braced beams and considering the overstrength of braces exhibited superior performance with smaller plastic deformations for braced beams and reduction in ductility demands for panel buckling-restrained braces (PBRBs) as compared with the others. The distribution of yielding for PBRBs in 10-story buildings verified that the participation from the higher modes is not very remarkable and that the capacity design based on the first-mode response can be considered for multistory PBRBFs. Moreover, on the basis of the analysis results of the 30-story PBRBF, the participation of the higher modes should be taken into account for high-rise PBRBFs. Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, the seismic behavior of dual structural systems in forms of steel moment-resisting frames accompanied with reinforced concrete shear walls and steel moment-resisting frames accompanied with concentrically braced frames, have been studied. The nonlinear behavior of the mentioned structural systems has been evaluated as, in earthquakes, structures usually enter into an inelastic behavior stage and, hence, the applied energy to the structures will be dissipated. As a result, some parameters such as ductility factor of structure (μ), over-strength factor (R_s) and response modification factor (R) for the mentioned structures have been under assessment. To achieve these objectives, 30-story buildings containing such structural systems were used to perform the pushover analyses having different load patterns. Analytical results show that the steel moment-resisting frames accompanied with reinforced concrete shear walls system has higher ductility and response modification factor than the other one, and so, it is observed to achieve suitable seismic performance; using the first system can have more advantages than the second one. Copyright © 2011 John Wiley & Sons, Ltd.

The traditional trial-and-error design approach is inefficient to determine an economical design satisfying also the safety criteria. Structural design optimization, on the other hand, provides a numerical procedure that can replace the traditional design approach with an automated one. The objective of this work is to propose a performance-based seismic design procedure, formulated as a structural design optimization problem, for designing steel and steel–reinforced concrete composite buildings subject to interstorey drift limitations. For this purpose, eight test examples are considered, in particular four steel and four steel–reinforced concrete composite buildings are optimally designed with minimum initial cost. Life-cycle cost analysis (LCCA) is considered as a reliable tool for measuring the damage cost due to future earthquakes that will occur during the design life of a structure. In this study, LCCA is employed for assessing the optimum designs obtained for steel and steel–reinforced concrete composite design practices. Copyright © 2011 John Wiley & Sons, Ltd.

Numerous studies have shown that the interaction between adjacent buildings can result in changes in nonlinear dynamic response of structures, damage, and performance level, depending on the dynamic specifications of structures involved and the frequency content of the input motion.

To study these effects, finite element method is used for the analytical investigations, and total soil–foundation–structure system is modeled all together. For modeling purposes and in order to realize the effects of the adjacent buildings on the dynamic response, two buildings, namely, 15-story and 30-story tall buildings, which were separated by distances of 1/4 and 1/8 of the width of the foundation and were located on hard and soft soil profiles, were considered.

It was concluded that in the case where the soil and structure's periods were near to each other, the interaction of adjacent structures on increasing nonlinear responses (displacement and interstory drift) and structural damage indexes was noticeable and therefore was not negligible. Whereas in the case where periods are distant from each other, the interaction of adjacent buildings has a decreasing effect on damage indexes and nonlinear responses and therefore was negligible. Copyright © 2011 John Wiley & Sons, Ltd.

Concrete is generally fire resistant. A fire in a concrete structure rarely results in a serious damage as to require substantial demolition. But, loss of the utility of a building could result in serious financial consequences for the owner, which calls for immediate reinstatement. To work out proper and efficient repair strategy, however, would require a thorough investigation of the effect of fire on the structural properties of the concrete and steel; the significance which any permanent change in material characteristics may have on the future structural performance of the member; the feasibility of repairs to compensate of any unacceptable reduction in structural performance, durability, and so on; and the influence which fire exposure of individual member may have on the performance of the entire structure. These all said tasks are dependent on the complete analysis of the fire-damaged building. Without it, no repair works estimation, extent of repair and kind of repair can be carried out for the fire-damaged buildings. Therefore, the impeccable analysis and design is of utmost importance for repair of such buildings after preliminary investigation of the extent of fire damages to the concrete structural members. This forms the basis of this research study, which aims at detailed analysis and design of the actual existing high-rise fire-damaged buildings for fire retrofitting and assessment of fire damages by non-destructive techniques. Fire damages in buildings due to explosion, accidents or by some other reasons cause severe structural damages. The structural integrity of existing buildings is now a burning issue. Analytical, theoretical and design-cum-construction techniques are constantly being reviewed by government agencies and engineering consultants. Therefore, researchers are delving into this matter to find the best retrofitting techniques for fire-damaged buildings. This paper is an outcome of such detailed research studies. It covers the actual case study of existing buildings, review of existing knowledge for fire damages and their mitigation and protective design technologies, and analytical and computational techniques, which have limited research data. In this study, Extended 3D Analysis of Building Systems (ETABS) is used as software for fire retrofitting analysis, and UBC-97 is used as a code for the fire analysis and design. The ETABS building model is verified by manual calculations as well. Copyright © 2011 John Wiley & Sons, Ltd.

The synchronous multipoint scanning system technique in wind tunnel tests and random vibration theory method were used to analyze the wind-induced torsion vibration of some irregularly shaped super high-rise buildings in downtowns. The torsion vibration modes and the spectra of torsion wind load were studied, and the proportions of mean wind torsion, inertia torsion and the mass eccentricity torsion caused by horizontal inertia forces are discussed. The following conclusions can be drawn. First, the third and fourth modes have torsion vibration shapes, and their frequencies are in the high-energy area of the spectra of the torsion wind load; the third and fourth modes are included in the resonant component of the spectra of the top torsion angle of the building, and the third mode is dominant. Second, the torsion stiffness is weak in the high stories of the building, so the inertia torsion is dominant, whereas the torsion stiffness is strong in the low stories; the mean wind torsion is dominant. The proportion of the mass eccentricity torsion moment caused by horizontal inertia forces is small. Finally, the wind-induced torsion moment at a 90° wind angle is the largest, whereas the torsion eccentricity is 46% of the radius of gyration and is much greater than the mass eccentricity; thus, the wind-induced torsion should be considered. The wind-induced torsion vibration of the building is sensitive to wind directions. Copyright © 2011 John Wiley & Sons, Ltd.

Most structures with masonry infills that are continuous along their height, which are interrupted in the lowest storey, are damaged by earthquakes. These structures are anticipated to collapse due to the undesirable soft-storey mechanism formed by lateral stiffness of masonry infills in other storeys. The seismic design criteria of UBC97 code for special moment-resisting steel frame (SMRSF) are reviewed. In this paper, a new criterion for seismic design of such structures is presented. The proposed criteria are used to design three SMRSFs: 5, 8 and 15 storeys. Nonlinear time-history dynamic analyses are applied for the designed SMRSFs based on the proposed criteria. Displacements and storey drifts, which are obtained by the proposed method, are compared with nonlinear time-history dynamic analysis results, finally. Copyright © 2011 John Wiley & Sons, Ltd.

In the last two decades, many researchers have implemented various kinds of meta-heuristic algorithms in order to overcome the complex nature of the optimum design of structures. In this paper, the optimum design of two-dimensional steel frames for discrete variables based on the Cuckoo Search (CS) algorithm is developed. The CS is one of the recently developed population-based algorithms inspired by the behavior of some cuckoo species in combination with the Lévy flight behavior of some birds and insects. The design algorithm is supposed to obtain minimum weight frame through suitable selection of sections from a standard set of steel sections such as the American Institute of Steel Construction (AISC) wide-flange (W) shapes. Strength constraints of AISC load and resistance factor design specification and displacement constraints are imposed on frames. In order to demonstrate the effectiveness and robustness of the CS, low-weight design and performance comparisons are made between the CS and other algorithms for some benchmark frames. Copyright © 2011 John Wiley & Sons, Ltd.

Damping ratio is an important component in the dynamic analysis and plays a key role in design of supertall buildings. It is necessary to have reliable field measurement records for estimation of structural dynamic characteristics. The main objective of this paper is to estimate eigen mode damping ratio of TV towers as a kind of supertall buildings with the height of more than 250 m. In this regard, field measurements were performed on Milad TV tower, located in Tehran, which has a height of 435 m by ambient vibration monitoring. Damping ratio of this tower is determined using random decrement technique and compared with available data of a few other TV towers.

For proposing eigen mode damping ratio of TV towers, it is shown that Rayleigh damping coefficients could not be calibrated properly for tall slender TV towers. A damping estimation chart of TV tower that is a function of natural frequency and structural aspect ratio is proposed, and the chart validity has been checked with field measurement results of other TV towers. The chart shows that structural damping for wind analysis proposed in design codes and standards is overestimated for tall slender TV towers. Copyright © 2011 John Wiley & Sons, Ltd.

In a strong earthquake, a standard reinforced concrete (RC) column may develop plastic deformations in regions often termed as plastic hinge regions. A plastic hinge is basically an energy dampening device that dampens energy through the plastic rotation of a rigid column connection, which triggers redistribution of bending moments. The formation of a plastic hinge in an RC column in regions that experience inelastic actions depends on the characteristics of the earthquakes as well as the column details. Recordings from recent earthquakes have provided evidence that ground motions in the near field of a rupturing fault can contain a large energy or ‘directivity’ pulse. A directivity pulse occurs when the propagation of the fault proceeds at nearly the same rate as the shear wave velocity. This pulse is seen in the forward direction of the rupture and can cause considerable damage during an earthquake, especially to structures with natural periods that are close to those of the pulse. In the present paper, 1316 inelastic time-history analyses have been performed to predict the nonlinear behaviour of RC columns under both far-fault and near-fault ground motions. The effects of axial load, height over depth ratio and amount of longitudinal reinforcement, as well as different characteristics of earthquakes, were evaluated analytically by finite element methods and the results were compared with corresponding experimental data. Based on the results, simple expressions were proposed that can be used to estimate plastic hinge length of RC columns subjected to both far-fault and near-fault earthquakes that contain a forward-directivity effect. Copyright © 2011 John Wiley & Sons, Ltd.

This study considered the crack control design method of reinforced concrete wall subjected to uniaxial tension caused by drying shrinkage. From this study, a practical crack control design method of RC wall by controlling the restraint tensile strain caused by drying shrinkage was proposed. In addition, the validity of the proposed method was investigated by comparing with the experimental results (restraint ratio and restraint tensile strain) of small-scale RC wall specimens under the uniaxial restrained condition. In conclusion, there was good agreement between the values predicted by the proposed method and the experimental values. It is expected that the method proposed in this study enables quantitative crack control design through rational combinations between the materials and structural design. Copyright © 2011 John Wiley & Sons, Ltd.

Considering the deterioration of steel properties by temperature increase and the importance of the influence of connection behavior on the behavior of steel structures, we find that the exact understanding of the behavior of a specific steel connection in fire as well as the information about the effect of fire on the principal constitutive characteristics of the connection is necessary for safe design against fire. Thus, in this paper, the behavior of welded angle connections is studied at elevated temperatures using the abaqus finite element software. Steel members and connection components are considered to behave nonlinearly; the degradation of steel properties with increasing temperature is considered according to EC3, BS5950 recommendations. The results of finite element and experimental tests conducted on welded angle connections are compared, and the obtained failure modes and moment–rotation–temperature characteristics are in good agreement with those associated with the experimental tests. In the following, since the knowledge about moment–temperature–rotation behavior of a specific connection is needed for a fire-resistant design, these properties are accurately determined, and finally, the effect of some parameters such as the moment applied on beam, change of column axial force and change of beam shear force on the stiffness of these connections at elevated temperatures is determined. Copyright © 2011 John Wiley & Sons, Ltd.

Damage of expensive equipment installed in the raised floor system of high-tech fabs was often observed during past earthquakes in Taiwan. This resulted in a huge loss of manufacturing functions and properties for the high-tech industry. Therefore, there is an urgent need to understand the dynamic characteristics of the raised floor system for future seismic protection. This paper explores the seismic performance of a raised floor system under shake-table excitations. The raised floor used was a pedestal–stringer frame structure supporting the simulated equipment. This raised floor system was the typical system frequently used in semi-conductor fabs of Taiwan. The input motions for the shake-table tests were the waffle-slab floor accelerations of a typical semi-conductor fab to simulated ground motions. The ground motions were simulated according to the phase spectrum and the maximum potential earthquake of the site located at Hsin-Chu Science Park, Taiwan. The dynamic characteristics of the raised floor system were studied and discussed. This study also employed the finite element package to carry out numerical simulation on seismic responses of raised floor systems. Comparison with the experimental data showed that the proposed simulation model achieved excellent performance. Finally, the effectiveness of base isolation for reducing the acceleration of the system was also studied. Copyright © 2011 John Wiley & Sons, Ltd.

The composite structure of steel frame–reinforced concrete infill wall (CSRC) combines the advantages of steel frames and reinforced concrete shear walls. Reinforced concrete infill walls increase the lateral stiffness of steel frames and reduce seismic demands on steel frames thus providing opportunities to use partially restrained connections. In order to study seismic behavior and load transfer mechanism of CSRC, a two-story one-bay specimen was tested under cyclic loads. With that, the main characters such as, strength, stiffness, ductility, energy dissipation, load distribution, performance of steel frames, partially restrained connections and studs, are analyzed and evaluated. The experimental results show that the structure has adequate strength redundancy and sufficient lateral stiffness. The CSRC system has good ductility and energy dissipation capability. Partially restrained connections could enhance ductility and avoid abrupt decreases in strength and stiffness after the failure of infill walls. The composite interaction is ensured by headed studs, which have failed because of low-cycle fatigue. Steel frames bear 80%–100% of overturning moments, and the remainder is undertaken by infill walls; steel frames and infill walls resisted 10%–20% and 80%–90% of lateral loads, respectively. Furthermore, relevant design recommendations are presented. Copyright © 2011 John Wiley & Sons, Ltd.

Shear wall systems are the most commonly used lateral load resisting systems in high-rise buildings. Six 1:2 scale mid-rise T-shaped reinforced concrete shear wall specimens with aspect ratio of 1.75, 2.15 and 2.80 were respectively tested under reversed cyclic loading. The seismic behavior and displacement ductility were investigated. The effects of aspect ratio, axial load level and transverse steel ratio on the seismic behavior and displacement ductility were also analyzed. Test results were discussed and compared with T-shaped steel–concrete composite shear wall. Results mainly showed that the T-shaped shear wall specimens mainly presented bending–shear failure mode and were all destroyed because of the concrete crushing at the web (negative direction) and the longitudinal reinforcement of the web reaching the limited deformation (positive direction), showing that the web was the weakest part of T-shape shear wall. The ductility of the specimens was decreased, and the ultimate load-bearing capacity was increased by increasing the axial load. To specimens with smaller aspect ratio and higher axial load ratio, the special transverse steel ratio of the web should be increased to improve the crushing strain of the confined concrete of the web in order to satisfy the ductility of the walls. The seismic performance was obviously improved in the T-shaped steel–concrete shear wall compared with that of the T-shaped reinforced concrete shear wall. Copyright © 2011 John Wiley & Sons, Ltd.

Shanghai Center Tower, which is 632 m in height with 126 stories, will be the tallest building in China at the end of 2014. The extreme height of the building combined with the exterior shrink-constructed and torsion-constructed curtain wall imposes a great challenge on the seismic design of the curtain wall. This paper establishes a finite element (FE) model of the real-scale building by considering the combination of the curtain wall and the main structure. The lower order modes of the building's vibration have been predicted, and good agreement has been observed between the numerical and experimental data, which validates the FE model of the building. Seismic response of the curtain wall was then investigated under three earthquake levels, including frequent, moderate and severe earthquakes. The acceleration magnification factors, the inter-story drift ratios and the interior forces of the curtain wall met the requirements of the Chinese Design Code, which indicates that the structure is a good solution to withstand earthquakes. The present study provides an important database for the seismic design of curtain wall structure in Shanghai Center Tower, and it can be used as a seismic design reference for similar projects. Copyright © 2011 John Wiley & Sons, Ltd.

Irregular frame buildings with discontinuous columns in one or several stories have been vulnerable to collapses during strong earthquakes. This paper presents the investigation of the seismic response demands at irregular stories of such buildings in terms of story strength factor demand. In this study, a story strength factor was defined to represent the relative reserve strength against the formation of a story failure mechanism of the structure. In addition, a huge number of rigorous nonlinear inelastic dynamic time-history analyses of various analytical models of 7-story, 8-story and 15-story frame structures with discontinuous columns in one and two irregular stories were conducted under 29 strong earthquake records with various characteristics. The results show that the seismic response demands at irregular stories of the structures were well evaluated in terms of the story strength factor demand to avoid development of a story failure mechanism of the structures when subject to strong earthquakes. Copyright © 2011 John Wiley & Sons, Ltd.

Friction dampers, whose configuration is optimized on the basis of the probabilistic seismic loss associated with a building's damage due to ground motion, were utilized in this study to optimally retrofit a 15-story steel structure. In line with the concept of performance-based earthquake engineering (PBEE), a decision-making procedure based on the monetary seismic loss was incorporated for optimizing the dampers' configuration. A nonlinear numerical model was initially established for representing the structure. In this regard, a brace–damper system was modeled with the buckling of brace elements being addressed accurately and by representing the friction damper's load–displacement relationship on the basis of laboratory evidences. By monitoring the structural deformations in two different response levels, two patterns were established for the distribution of the dampers' strengths throughout the structure, and a number of retrofit alternatives were proposed subsequently. By using incremental dynamic analysis and following the PBEE methodology, the annualized loss (AL), which accounts for all potential damage states in the building and a broad range of seismic intensities, was calculated for each alternative frame. The AL is regarded as a decision variable upon which the best damper configuration is selected. Revealing conclusions were finally made regarding optimal configuration of the damper–brace system. Copyright © 2011 John Wiley & Sons, Ltd.

The differential length changes of vertical members in a high-rise building due to elastic, creep and shrinkage shortenings are of primary concern since the differential shortening of the vertical members causes unexpected damages on structural and nonstructural members. In contrast to researches on prediction methods for calculation of the amount of the shortenings, only few methods or algorithms of compensation of the differential column shortenings have been reported. In this paper, a practical compensation method using moving average correction is presented. The proposed method is applied to the compensation of the differential shortenings of the vertical members in a 70-story high-rise building. The performance of the moving average correction method is compared with the optimal compensation method based on simulated annealing algorithm. It is demonstrated that the magnitude of the differential shortening or the degree of the slab tilt due to the length changes in the vertical members can be controlled without using structural optimization techniques. Copyright © 2011 John Wiley & Sons, Ltd.

The use of high-performance materials (HPMs) such as high-strength concrete (HSC) and high-strength steel (HSS) is becoming more popular in the construction of beams and columns of tall buildings. These HPMs not only increase the stiffness and decrease the strength-to-weight ratio, but also provide a more sustainable construction method by minimising the construction materials needed. However, HSC and HSS are more brittle than normal-strength concrete and steel, respectively. Therefore, it will adversely affect the deformability of concrete beams. To evaluate the pros and cons of adopting HPM in beam design, the author will investigate the flexural strength and deformability of concrete beams made of HPMs. The deformability in this study is expressed in normalised rotation capacity and investigated by a parametric study using nonlinear moment–curvature analysis taking into account the degree of reinforcement, confining pressure, concrete and steel yield strength. From the results, it is evident that the deformability of concrete beams increases as the degree of reinforcement decreases or confining pressure increases. However, the effects of concrete and steel yield strength depend on other factors. For practical design purpose, charts and formulas are produced for designing high-performance concrete beams to meet with specified flexural strength and deformability requirement. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents the comparison of the earthquake behavior of reinforced concrete (RC) minarets using fiber-reinforced polymer (FRP) composite. A Turkish-style RC minaret with two balconies of a mosque located in Trabzon, Turkey, was selected as an application. A 3D finite element model of the minaret was created using ansys finite element program to determine the earthquake behavior. The earthquake behavior of the minaret was investigated using the 1992 Erzincan earthquake ground motion record. Also, the cylindrical body of the minaret (below the first balcony, between two balconies and above the second balcony) was wrapped by four layers of FRP, and earthquake behavior was determined. Total thickness of the FRP was selected as 6.0 mm. At the end of the study, earthquake responses of the RC minaret such as displacements and maximum–minimum principal stresses before and after using FRP composite were compared with each other. It was seen from the earthquake analyses that using FRP is very effective on the earthquake responses of the minaret. Copyright © 2011 John Wiley & Sons, Ltd.