An efficient procedure is developed for the hydrodynamic analysis of dam–reservoir systems. The governing equations of hydrodynamic pressure in the frequency as well as time domain are derived in the framework of the scaled boundary finite element method. The water compressibility and absorption of reservoir sediments can be conveniently taken into consideration. By extending the reservoir to infinity with uniform cross-section, only the dam–reservoir interface needs to be discretized to model the fluid domain, and the hydrodynamic pressure in the stream direction is solved analytically. Several numerical examples including a gravity dam with an inclined upstream face and an arch dam with a reservoir of arbitrary cross-section are provided to demonstrate the computational efficiency and accuracy of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.

Best estimate seismic analysis are generally based on time-domain simulations of structural responses. The seismic load is then modeled by a stochastic process representing ground motion. For this purpose, the analyst can use recorded accelerograms or work with synthetically generated ones. The number of ground motion time-histories available for a given scenario and site condition is limited and generally not sufficient for carrying out more advanced probabilistic structural response analysis. It is then necessary to have at our disposal methods that allow for generating synthetic accelerograms that realistically characterize earthquake ground motions. However, most of the methods proposed in literature for generating synthetic accelerograms do not accurately reproduce the natural variability of ground motion parameters (such as PGA, cumulative absolute velocity, and Arias intensity) observed for recorded time histories. In this paper, we introduce a new method for generating synthetic ground motion, based on Karhunen-Loève decomposition and a non-Gaussian stochastic model. The proposed method enables the structural analyst to simulate ground motion time histories featuring the properties mentioned above. To demonstrate its capability, we study the influence of the simulation method on different ground motion parameters and on soil response spectra. We finally compute fragility curves to illustrate the practical application of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.

Near-source pulse-like records resulting from rupture's directivity have been found to depart from so-called ordinary ground motions in terms of both elastic and inelastic structural seismic demands. In fact, response spectra may be strong if compared with what is expected from common ground motion prediction equations. Moreover, because not all spectral ordinates are affected uniformly, a peculiar spectral shape, with an especially amplified region depending on the pulse period, may follow. Consequently, inelastic seismic demand may show trends different to records not identified as pulse-like (i.e., ordinary). This latter aspect is addressed in the study reported in this short communication, where a relatively large dataset of identified impulsive near-source records is used to derive an analytical-form relationship for the inelastic displacement ratio. It is found that, similar to what was proposed in literature for soft soil sites, a double-opposite-bumps form is required to match the empirical data as a function of the structural period over the pulse period ratio. The relationship builds consistently on previous studies on the topic, yet displays different shape with respect to the most common equations for static structural assessment procedures. Copyright © 2012 John Wiley & Sons, Ltd.

For effective hazard mitigation planning and prompt-but-prudent post-disaster responses, it is essential to evaluate the reliability of infrastructure networks accurately and efficiently. A nonsimulation-based algorithm, termed as a recursive decomposition algorithm (RDA), was recently proposed to identify disjoint cut sets and link sets and to compute the network reliability. This paper introduces a ‘selective’ RDA, which preferentially identifies critical disjoint cut sets and link sets to calculate the probabilities of network disconnection events with a significantly reduced number of identified sets. To this end, the original RDA is improved by replacing the shortest path algorithm with an algorithm that identifies the most reliable path, and by using a graph decomposition scheme based on the probabilities associated with the subgraphs. The critical sets identified by the algorithm are also used to compute conditional probability-based importance measures that quantify the relative importance of network components by their contributions to network disconnection events. This paper also introduces a risk assessment framework for lifeline networks based on the use of the selective RDA, which can consider both interevent and intraevent uncertainties of spatially correlated ground motions. The risk assessment framework and the selective RDA are demonstrated by a hypothetical network example, and the gas and water transmission networks of Shelby County in Tennessee, USA. The examples show that the proposed framework and the selective RDA greatly improve efficiency of risk assessment of complex lifeline networks, which are characterized by a large number of components, complex network topology, and statistical dependence between component failures. Copyright © 2012 John Wiley & Sons, Ltd.

This paper focuses on the frequency property analysis of near-fault ground motions with and without distinct pulses, separately from the Chi-Chi and Northridge earthquakes. Ten scalar period parameters of ground motions, especially several nonlocal period parameters, are considered. Two new nonlocal parameters, namely the mean period of Hilbert marginal spectrum (T_mh) and the improved characteristic period (T_gi), are suggested. Moreover, comprehensive comparison and analysis indicate that T_mh, T_gi and T_avg (average spectral period) can distinguish the low-frequency components of near-fault ground motions; T_m (mean period of Fourier amplitude spectrum) and T_o (smoothed spectral predominant period) represent the moderate- and high-frequency components, respectively. The variance coefficient of predominant instantaneous frequency of Hilbert spectrum (H_cov) can be regarded as an alternative index to measure the non-stationary degree of near-fault ground motions. Finally, the velocity pulses and earthquake magnitude remarkably affect the frequency parameters of near-fault ground motions. Copyright © 2012 John Wiley & Sons, Ltd.

The effects of Rayleigh damping model on the engineering demand parameters of two steel moment-resisting frame buildings were evaluated. Two-dimensional models of the buildings were created and response history analysis were conducted for three different hazard levels. The response history analysis results indicate that mass-proportional damping leads to high damping forces compared with restoring forces and may lead to overestimation of floor acceleration demands for both buildings. Stiffness-proportional damping, on the other hand, is observed to suppress the higher-mode effects in the nine-story building resulting in lower story drift demands in the upper floors compared with other damping models. Rayleigh damping models, which combine mass-proportional and stiffness-proportional components, that are anchored at reduced modal frequencies lead to reasonable damping forces and floor acceleration demands for both buildings and does not suppress higher-mode effects in the nine-story building. Copyright © 2012 John Wiley & Sons, Ltd.

Horizontal bidirectional loading tests are conducted for real-sized high-damping rubber (HDR) bearings with diameters of 700 mm (HDR700) and 1300 mm (HDR1300). The hysteresis loops of these bearings under bidirectional horizontal loadings are compared with those under unidirectional loadings. The results show that the bearing force measurement in the primary direction of loading increases when there is displacement in the orthogonal direction. Unusually, the maximum restoring force in the orthogonal direction to the primary loading direction occurs near zero displacement. On the basis of the observations of the restoring forces, a rate-independent model is proposed. This model simulates well the test results under both bidirectional loading and unidirectional loading. It can reproduce the irregular restoring forces characteristics around zero displacement as described above. Bidirectional loading induced twist deformation in the HDR bearings that increased local shear strains. This phenomenon results in an early failure as observed in HDR700. The additional shear strain is estimated based on the twist deformation measured by video image analysis. The comparison of the nominal total shear stress demonstrates that the increase of shear stress because of bidirectional loading occurs when the average shear strain is larger than about 200%. The larger the shear strain, the greater the bidirectional effect. It is shown that the nominal total shear stress of average strain of 350% under bidirectional circular loading pattern is approximately the same as the average shear strain of 400% under unidirectional loading. This means that the average shear strain of 350% under a bidirectional circular loading corresponds to a local shear strain of 400%. Copyright © 2012 John Wiley & Sons, Ltd.

This paper investigates the seismic response control of a 20-story nonlinear benchmark building with a new recentering variable friction device (RVFD). The RVFD combines energy dissipation capabilities of a variable friction damper (VFD) with the recentering ability of shape memory alloy (SMA) wires. The VFD that is the first subcomponent of the hybrid device consists of a friction generation unit and piezoelectric actuators. The clamping force of the VFD can be adjusted according to the current level of ground motion by adjusting the voltage level of piezoelectric actuators. SMA wires that exhibit a unique hysteretic behavior and full shape recovery after experiencing large strains is the second subcomponent of the hybrid device. Numerical simulations of a seismically excited 20-story benchmark building are conducted to evaluate the performance of the hybrid device. A continuous hysteretic model is used to capture frictional behavior of the VFD and a neuro-fuzzy model is employed to describe highly nonlinear behavior of the SMA components of the hybrid device. A fuzzy logic controller is developed to adjust the voltage level of VFDs for favorable performance in an RVFD hybrid application. Results show that the RVFD modulated with a fuzzy logic control strategy can effectively reduce interstory drifts and permanent deformations without increasing acceleration response of the benchmark building for most cases. Copyright © 2012 John Wiley & Sons, Ltd.

The effects of seismic pounding on the structural performance of a base-isolated reinforced concrete (RC) building are investigated, with a view to evaluate the influence of adjacent structures and separation between structures on the pounding response. In particular, seismic pounding of a typical four-story base-isolated RC building with retaining walls at the base and with a four-story fixed-base RC building is studied. Three-dimensional finite element analyses are carried out considering material and geometric nonlinearities. The structural performance of the base-isolated building is evaluated considering various earthquake excitations. It is found that the performance of the base-isolated building is substantially influenced by the pounding. The investigated base-isolated building shows good resistance against shear failure and the predominant mode of failure due to pounding is flexural. Copyright © 2012 John Wiley & Sons, Ltd.

This paper presents results from a comprehensive experimental program on medium-size and large-size fluid dampers in an effort to extract their force output during cyclic loading by simply measuring the strain on the damper housing and the end-spacer of the damper. The paper first discusses the stress path within the damper and, subsequently via the use of linear elasticity, shows that the experimental data obtained with commercially available strain gauges yield a force output of the damper that is in good agreement with the readings from the load cell. This comparison is achieved via the use of a position and velocity transducer, which combines good accuracy together with robust performance in a marine environment. The paper then examines the performance of a portable data acquisition system that can be used to collect and transmit data from a damper installed on a bridge to a nearby location (order of a km) where data are collected via either a wired or a wireless Local Area Network (LAN). Alternatively, the data may be transmitted to any remote location via mobile telecommunication networks; however, this requires leased telephone lines. The data show that the proposed arrangement is promising for monitoring in situ the force output of fluid dampers and detecting possible loss of their energy dissipation capability. Copyright © 2012 John Wiley & Sons, Ltd.

The concept of equivalent linearization, in which the actual nonlinear structure is replaced by an equivalent linear single-degree-of-freedom (SDOF) system, is extended for soil-structure systems in order to consider the simultaneous effects of soil-structure interaction (SSI) and inelastic behavior of the structure on equivalent linear parameters (ELP). This is carried out by searching over a two-dimensional equivalent period–equivalent damping space for the best pair, which can predict the earthquake response of the inelastic soil-structure system with sufficient accuracy. The super-structure is modeled as an elasto-plastic SDOF system whereas the soil beneath the structure is considered as a homogeneous half-space and is replaced by a discrete model. An extensive parametric study is carried out for a wide range of soil-structure systems subjected to a suite of 59 ground motions. The effect of SSI on ELP is studied through introducing a set of non-dimensional key parameters, which define the soil-structure system. It is shown that ELP of soil-structure systems result from a trade-off between SSI effect and nonlinear behavior of the structure. The contribution of each of these two factors depends on the characteristics of the soil-structure system which, in turn, are defined by the introduced non-dimensional key parameters. Moreover, the reliability of the predicted response of soil-structure systems and its sensitivity to deviation from optimal ELP is studied in detail, which sheds light on the consequences of using improper pairs of ELP for interacting systems in the framework of performance-based design of structures. Copyright © 2012 John Wiley & Sons, Ltd.

Nonlinear static methods are reliable in the evaluation of the seismic response of planar structural schemes, but they are not very effective in the assessment of three-dimensional building structures. The authors of this paper have recently proposed a nonlinear static approach for asymmetric structures, which is an improvement on that stipulated by seismic codes. This method is based on the observation that the distribution of the maximum dynamic displacements of the deck can be enveloped by two pushover analyses performed by applying the lateral force with two eccentricities with respect to the center of mass of the deck. These eccentricities, named “corrective eccentricities”, are defined so that the two corresponding pushover analyses provide displacements that are equal to those evaluated by nonlinear dynamic analysis at the two sides of the deck. In this paper, the corrective eccentricities are determined for a wide set of single-story systems. The equations for their analytical evaluation are determined and their reliability is demonstrated. Finally, the analysis of a multi-story structure is conducted to show how the method can be applied to real buildings. Copyright © 2012 John Wiley & Sons, Ltd.

This study presents a ground-motion selection and scaling methodology that preserves the basic seismological features of the scaled records with reduced scatter in the nonlinear structural response. The methodology modifies each strong-motion recording with known fundamental seismological parameters using the estimations of ground-motion prediction equations for a given target hazard level. It provides robust estimations on target building response through scaled ground motions and calculates the dispersion about this target. This alternative procedure is not only useful for record scaling and selection but, upon its further refinement, can also be advantageous for the probabilistic methods that assess the engineering demand parameters for a given target hazard level. Case studies that compare the performance of the proposed procedure with some other record selection and scaling methods suggest its usefulness for building performance assessment and loss models. Copyright © 2012 John Wiley & Sons, Ltd.

Floor diaphragm in-plane stiffness affects building response to horizontal ground accelerations. This paper describes a series of elastic and inelastic time history analyses of symmetric structures with different deformation types, configurations and heights to quantify these effects. It is shown that displacements of single storey elastically responding structures tend to be most significantly affected by diaphragm flexibility. Analyses of these structures were cross-verified by a closed-form mechanics-based formulation developed to describe the response. Simple relationships were proposed to allow designers to conservatively estimate the increase in peak in-plane displacement resulting from diaphragm flexibility. Copyright © 2012 John Wiley & Sons, Ltd.

Forward directivity may cause large velocity pulses in ground motion time histories that are damaging to buildings at sites close to faults, potentially increasing seismic collapse risk. This study quantifies the effects of forward directivity on collapse risk through incremental dynamic analysis of building simulation models that are capable of capturing the key aspects of strength and stiffness degradation associated with structural collapse. The paper also describes a method for incorporating the effects of near-fault directivity in probabilistic assessment of seismic collapse risk. The analysis is based on a suite of RC frame models that represent both past and present building code provisions, subjected to a database of near-fault, pulse-like ground motions with varying pulse periods. Results show that the predicted collapse capacity is strongly influenced by variations in pulse period and building ductility; pulse periods that are longer than the first-mode elastic building period tend to be the most damaging. A detailed assessment of seismic collapse risk shows that the predicted probability of collapse in 50 years for modern concrete buildings at a representative near-fault site is approximately 6%, which is significantly higher than the 1% probability in the far-field region targeted by current seismic design maps in the US. Copyright © 2012 John Wiley & Sons, Ltd.

This paper rigorously assesses the efficiency of viscous dampers connecting two walls to result in “viscously coupled shear walls”. This assessment also holds for viscous dampers in wall structures as they are mounted on frames parallel to the walls leading to “wall-viscous frame” systems. A continuum approach is adopted to model the structure so as to enable non-dimensional formulation of the governing equations. Those equations reveal that, under the approximations considered, the system damping ratio (defined here by 0.5 sqrt(c^2/(m*EI))) is a convenient compact single parameter controlling the response reduction w.r.t. the response of the corresponding undamped system. In contrast to coupled shear walls, this controlling parameter does not depend on the height of the building; therefore, the viscously damped system is efficient for low-rise buildings as well. The continuum approach also allows a semi-analytical solution of the eigenproblem in the complex domain followed by a complex modal spectral analysis. Those solutions reveal the efficiency of the added damping in reducing not only the displacements, inter-story drifts, and wall moments but also the absolute accelerations, wall shear, total shear, and total overturning moments. The results of the analyses and the non-dimensional tables and graphs developed for important response parameters lead to a simple method that could easily be implemented in practice for the purpose of initial design. Copyright © 2012 John Wiley & Sons, Ltd.

The aim of this paper is to study the effects of soil–structure interaction on the seismic response of coupled wall-frame structures on pile foundations designed according to modern seismic provisions. The analysis methodology based on the substructure method is recalled focusing on the modelling of pile group foundations. The nonlinear inertial interaction analysis is performed in the time domain by using a finite element model of the superstructure. Suitable lumped parameter models are implemented to reproduce the frequency-dependent compliance of the soil-foundation systems. The effects of soil–structure interaction are evaluated by considering a realistic case study consisting of a 6-storey 4-bay wall-frame structure founded on piles. Different two-layered soil deposits are investigated by varying the layer thicknesses and properties. Artificial earthquakes are employed to simulate the earthquake input. Comparisons of the results obtained considering compliant base and fixed base models are presented by addressing the effects of soil–structure interaction on displacements, base shears, and ductility demand. The evolution of dissipative mechanisms and the relevant redistribution of shear between the wall and the frame are investigated by considering earthquakes with increasing intensity. Effects on the foundations are also shown by pointing out the importance of both kinematic and inertial interaction. Finally, the response of the structure to some real near-fault records is studied. Copyright © 2012 John Wiley & Sons, Ltd.

Three main topics including the floor motion action mechanism, the test frame design, and the target spectrum simulation presented in the paper are discussed specifically. Floor motion action mechanism is critical in understanding the seismic performance of architectural nonstructural components. Seismic sensitiveness and earthquake response properties of the nonstructural components should be considered in the design of the test frame for the shaking table test. Target spectrum simulation is also a challenging job in the shaking table test, in which dynamic characteristics of the specimen, performance of the shaking table facilities, and the control techniques should be all considered. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents the variations of vibration under different traffic conditions on the Fatih Sultan Mehmet suspension bridge in Istanbul, Turkey.The main intention is to determine the vibration amplifications under heavy-traffic as opposed to no-traffic conditions. This is the first study in this particular area that has been performed on this bridge, over which an average of 200,000 cars pass daily. Two full-scale ambient vibration surveys were carried out on two different days to determine the response of the bridge to diverse traffic conditions. Initial measurements were taken as the bridge experienced heavy stress conditions caused by rush-hour traffic. Secondary measurements were recorded after closing the bridge to traffic. The data were analyzed to gauge the vibration effects of heavy-traffic conditions on the bridge and to determine the effects of different traffic conditions on the free vibration characteristics of the bridge. The analyses were performed utilizing different amplification methods. Results show that there are important differences in the amplifications of the vibration amplitudes. Especially heavy-traffic on the bridge causes the vibration response of the bridge to be intensified in comparison to no-traffic conditions. Additionally, predominant frequencies are shifted as a direct result of traffic load acting on the bridge. Even more importantly and is probably analogous for all long-span bridges, is the fact that any movement causing vibration on the bridge is carried and amplified along its length. These significant amplifications indicate the important effect of varying traffic loads and how the bridge responds to the diverse movements it experiences. Copyright © 2011 John Wiley & Sons, Ltd.

Herein, an attempt is made to apply the method developed and verified in the companion paper (Part I) to physical data. To this end, stiffness parameters of the IASC-ASCE test structure are identified using data from the experimental phase of the benchmark studies. The physical specimen is a quarter-scale, four-story, braced-frame, steel structure. Ambient vibration and free vibration data induced by hammer strikes from various configurations of the structure are used to identify stiffness parameters of individual stories. These configurations had been created by removing various members from the test structure in an effort to mimic damage. Results indicate that the proposed method is successful in identifying even the minor changes (damage) introduced to the structure. An additional study on the method's sensitivity to structure's assumed mass distribution reveals that it is fairly robust to mass uncertainties. Copyright © 2011 John Wiley & Sons, Ltd.

A new parameter estimation algorithm is described for identifying the stiffness properties of torsionally coupled shear buildings from their linear response due to ambient excitations or during low-amplitude forced-vibration tests. The algorithm is based on the time-domain equations of motion, and yields estimates of the stiffness properties using a measure of the equilibrium of forces acting on each floor over a time interval. The banded structure of the stiffness matrix — a property intrinsic to torsion-shear buildings — is exploited to decompose the initial inverse problem into several problems of reduced size. This decomposition allows the identification of lateral and torsional stiffnesses of individual stories, independent of the others. The algorithm utilizes vibration data where input excitation is known/measured, which is typical for forced-vibration tests and earthquakes. If the ambient vibrations of the structure are adequately uncorrelated to the (unknown) external forces that induce such vibrations, then the algorithm can also be modified for output-only system identification. The proposed algorithm is verified — and its various attributes are investigated — using simulation data from the ‘Analytical Phase I’ of the IASC (International Association for Structural Control)-ASCE (American Society of Civil Engineers) benchmark studies. The companion article is devoted to the algorithm's application to experimental data, using data from the ‘Experimental Phase’ of the same benchmark studies. Copyright © 2011 John Wiley & Sons, Ltd.

This paper analyzes the dynamic behaviour of continuous bridges with transverse abutment restraint. These are a particular class of multi-span bridges whose transverse motion is restrained at the abutments.

The transverse dynamic behaviour of these partially-restrained bridges is described by a model consisting of a two-dimensional simply-supported beam with intermediate visco-elastic restraints. A minimal set of characteristic problem parameters that completely describe the dynamic response is initially identified and an analytical solution is developed for particular configurations. The influence of these characteristic parameters on the properties of the dynamic systems are analyzed by considering the undamped and the damped free vibrations separately.

Successively, in order to cover more general and complex configurations of realistic bridges, an extension of the definition of the characteristic parameters is proposed. The results obtained considering selected case studies are finally presented. Copyright © 2011 John Wiley & Sons, Ltd.

The cyclic behaviour of plastic hinges is an essential component in tracking the behaviour of RC frames to failure, not only for monotonically increasing force/pressure loads such as under extreme wind loads but also for dynamic displacement-driven loads such as under earthquake ground motions. To describe member deformations at ultimate loading, traditional moment–curvature techniques have required the use of an empirical hinge length to predict rotations, and despite much research a definitive generic expression for this empirical hinge length is yet to be defined. To overcome this problem, a discrete rotation approach, which directly quantifies the rotation between crack faces using mechanics, has been developed for beams and been shown to be accurate under monotonic loading. In this paper, the discrete rotation approach for monotonic loads is extended to cope with cyclic loads for dynamic analyses, and this has led to the development of a new partial interaction numerical simulation capable of allowing for reversals of slip of the reinforcing bars. This numerical tool should be very useful for the nonlinear analysis of reinforced concrete beams and reinforced concrete columns with small axial loads under severe dynamic loads. Copyright © 2011 John Wiley & Sons, Ltd.

Coupled steel plate shear wall (C-SPSW) consists of two or more steel plate shear walls interconnected by coupling beams at the floor levels. In this study, a six-story C-SPSW prototype building was designed. A 40% scale C-SPSW specimen, which is representative of the bottom two-and-half-story substructure of the prototype, was cyclically tested using Multi-Axial Testing System at the National Center for Research on Earthquake Engineering in 2009. In addition to a constant vertical force representing the gravity load effects, cyclic increasing displacements and the corresponding overturning moments transmitted from the upper stories were computed online and simultaneously applied on the substructural specimen. This paper firstly introduces the designs of the prototype C-SPSW and the test specimen. Then, the test results and the numerical simulation are discussed in detail. Test results confirm the effectiveness of the proposed column capacity design method, which aims at limiting the plastic hinge formation within the bottom quarter height of the bottom column. Test and analytical results suggest that the coupling beam rotational demands can be estimated as the design story drifts when the formation of desirable plastic mechanism of the C-SPSW is expected. Copyright © 2011 John Wiley & Sons, Ltd.

Real-time pseudodynamic (PSD) and hybrid PSD testing methods are displacement controlled experimental techniques that are used to investigate the dynamic behaviour of complex and load rate-dependent structures. Because the imposed command displacements are not predefined but generated during the test based on measured feedback, these methods are inherently prone to error propagation, which can affect the accuracy and even the stability of the entire experiment. As a result, to have these experimental methods as reliable tools, the accuracy of the test results needs to be assessed by carefully monitoring, and if possible, quantifying the errors involved. In this paper, phase and amplitude error indices (PAEI) are introduced to identify the experimental errors through uncoupled closed-form equations. Unlike the indicators that have been previously introduced in the literature for error identification purposes, PAEI do not use test setup specific parameters in their formulation, and can quantify the errors independent of the amplitude of the command displacements. As such, PAEI can be used as standard tools for assessing the quality of the experiments performed in different laboratories or under different conditions. Additionally, because they can quantify the error, when implemented online, PAEI have the potential to be incorporated in the control law and thereby improve the actuator control during the tests. The formulation and implementation of PAEI are provided in this paper. The enhanced performance of the proposed indices is demonstrated by processing several different measured and command signals using PAEI and comparing the results with those revealed by the previous indicators. Copyright © 2011 John Wiley & Sons, Ltd.

This paper investigates the seismic response of tall cantilever wall buildings subjected to pulse type ground motion, with special focus on the relation between the characteristics of ground motion and the higher-modes of response. Buildings 10, 20, and 40 stories high were designed such that inelastic deformation was concentrated at a single flexural plastic hinge at their base. Using nonlinear response history analysis, the buildings were subjected to near-fault seismic ground motions and simple closed-form pulses, which represented distinct pulses within the ground motions. Euler–Bernoulli beam models with lumped mass and lumped plasticity were used to model the buildings. The response of the buildings to the closed-form pulses fairly matched that of the near-fault records. Subsequently, a parametric study was conducted for the buildings subjected to three types of closed-form pulses with a broad range of periods and amplitudes. The results of the parametric study demonstrate the importance of the ratio of the fundamental period of the structure to the period of the pulse to the excitation of higher modes. The study shows that if the modal response spectrum analysis approach is used — considering the first four modes with a uniform yield reduction factor for all modes, and with the square root of sum of squares modal combination rule — it significantly underestimates bending moment and shear force responses. A response spectrum analysis method that uses different yield reduction factors for the first and the higher modes is presented. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents a new, improved, post-earthquake damage assessment method that takes into account residual deformations attained by the damaged structure during the earthquake. Local and global residual deformations and visual damage indicators are considered to estimate the maximum deformations experienced by the structure. As a particular development, the method allows measured displacements and rotations to be considered jointly. Uncertainties associated with both the excitation and the damaged structure are explicitly accounted for. The resulting maximum displacement estimates allow a more accurate evaluation of the extent of structural damage when judging the usability/reparability of the investigated structure. A trial application of the method to a real structure tested on a shaking table is presented. The results confirm the capability of the method to estimate the maximum displacement and the residual stiffness of the damaged structure. Copyright © 2011 John Wiley & Sons, Ltd.

This paper explores the effectiveness of a new approach to foundation seismic design. Instead of the present practice of over-design, the foundations are intentionally under-dimensioned so as to uplift and mobilize the strength of the supporting (stiff) soil, in the hope that they will thus act as a rocking–isolation mechanism, limiting the inertia transmitted to the superstructure, and guiding plastic ‘hinging’ into soil and the foundation–soil interface. An idealized simple but realistic one-bay two-story reinforced concrete moment resisting frame serves as an example to compare the two alternatives. The problem is analyzed employing the finite element method, taking account of material (soil and superstructure) and geometric (uplifting and P–Δ effects) nonlinearities. The response is first investigated through static pushover analysis. It is shown that the axial forces N acting on the footings and the moment to shear (M/Q) ratio fluctuate substantially during shaking, leading to significant changes in footing moment-rotation response. The seismic performance is explored through dynamic time history analyses, using a wide range of unscaled seismic records as excitation. It is shown that although the performance of both alternatives is acceptable for moderate seismic shaking, for very strong seismic shaking exceeding the design, the performance of the rocking-isolated system is advantageous: it survives with no damage to the columns, sustaining non-negligible but repairable damage to its beams and non-structural elements (infill walls, etc.). Copyright © 2011 John Wiley & Sons, Ltd.

This paper investigates circumstances behind the occurrence of negative ε (the normalized difference between the spectral acceleration of a recorded ground motion and the median response predicted by a ground motion prediction equation) in probabilistic seismic hazard deaggregation. Negative ε values are of engineering interest because of their impact on the conditional mean spectrum (CMS), which is a proposed alternative to the uniform hazard spectrum (UHS) as a target spectrum for ground motion selection. In the case where target ε values from deaggregation are positive, the CMS calculation produces relatively lower response spectra than the UHS. Positive target ε values occur almost universally in active seismic regions at long return periods of engineering interest, but the possibility of negative target ε values is important because in the case of negative target ε, some relationships between the CMS and UHS would reverse. This paper describes the calculation of target ε, performs parametric studies to determine when negative ε values occur in deaggregation, and investigates the potential impact on target spectrum calculation and ground motion selection. The case studies indicate that special seismicity models and certain ground motion prediction equations have the most significant effect on ε values and a combination of these characteristics in Eastern North America creates the most likely situation for negative target ε to occur. CMS results are nonintuitive when the target ε is negative, but it is not clear that this is a common practical concern because negative target ε occurs only in well-constrained areas. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents new results of centrifuge model tests exploring the behavior of rocking shallow foundations embedded in dry sand, which provides a variety of factors of safety for vertical bearing. The results of slow (quasi-static) cyclic tests of rocking shear walls and dynamic shaking tests of single-column rocking bridge models are presented. The moment–rotation and settlement–rotation relationships of rocking footings are investigated. Concrete pads were placed in the ground soil to support some models with the objective of reducing the settlement induced by rocking. The behavior of rocking foundation was shown to be sensitive to the geometric factor of safety with respect to bearing failure, L_f/L_c, where L_f was the footing length, and the L_c was the critical soil-footing contact length that would be required to support pure axial loading. Settlements were shown to be small if L_f/L_c was reasonably large. Placement of concrete pads under the edges of the footing was shown to be a promising approach to reduce settlements resulting from rocking, if settlements were deemed to be excessive and also had impacts on the energy dissipation and rocking moment capacity. A general discussion of the tradeoffs between energy dissipation and re-centering of rocking foundations and other devices is included. Copyright © 2011 John Wiley & Sons, Ltd.

A nonlinear finite element model for earthquake response analysis of arch dam–water–foundation rock systems is proposed in this paper. The model includes dynamic dam–water and dam–foundation rock interactions, the opening of contraction joints, the radiation damping of semi-unbounded foundation rock, the compressibility of impounded water, and the upstream energy propagating along the semi-unbounded reservoir. Meanwhile, a new equivalent force scheme is suggested to achieve free-field input in the model. The effects of the earthquake input mechanism, joint opening, water compressibility, and radiation damping on the earthquake response of the Ertan arch dam (240 m high) in China are investigated using the proposed model. The results show that these factors significantly affect the earthquake response of the Ertan arch dam. Such factors should therefore be considered in the earthquake response analysis and earthquake safety evaluation of high arch dams. Copyright © 2011 John Wiley & Sons, Ltd.

A full-scale shake table test on a six-story reinforced concrete wall frame structure was carried out at E-Defense, the world's largest three-dimensional earthquake simulation facility, in January 2006. Story collapse induced from shear failure of shear critical members (e.g., short columns and shear walls) was successfully produced in the test. Insights gained into the seismic behavior of a full-scale specimen subjected to severe earthquake loads are presented in this paper. To reproduce the collapse process of the specimen and evaluate the ability of analytical tools to predict post-peak behavior, numerical simulation was also conducted, modeling the seismic behavior of each member with different kinds of models, which differ primarily in their ability to simulate strength decay. Simulated results showed good agreement with the strength-degrading features observed in post-peak regions where shear failure of members and concentrated deformation occurred in the first story. The simulated results tended to underestimate observed values such as maximum base shear and maximum displacement. The effects of member model characteristics, torsional response, and earthquake load dimensions (i.e., three-dimensional effects) on the collapse process of the specimen were also investigated through comprehensive dynamic analyses, which highlighted the following seismic characteristics of the full-scale specimen: (i) a model that is incapable of simulating a specimen's strength deterioration is inadequate to simulate the post-peak behavior of the specimen; (ii) the torsional response generated from uniaxial eccentricity in the longitudinal direction was more significant in the elastic range than in the inelastic range; and (iii) three-dimensional earthquake loads (X–Y–Z axes) generated larger maximum displacement than any other loading cases such as two-dimensional (X–Y or Y–Z axes) or one-dimensional (Y axis only) excitation. Copyright © 2011 John Wiley & Sons, Ltd.

The design of a three-story buckling-restrained braced frame (BRBF) with a single-diagonal sandwiched BRB and corner gusset was evaluated in cyclic tests of a one-story, one-bay BRBF subassembly and dynamic analyses of the frame subjected to earthquakes. The test focused on evaluating (1) the seismic performance of a sandwiched BRB installed in a frame, (2) the effects of free-edge stiffeners and dual gusset configurations on the corner gusset behavior, (3) the frame and brace action forces in the corner gusset, and (4) the failure mode of the BRBF under the maximum considerable earthquake level. The subassembly frame performed well up to a drift of 2.5% with a maximum axial strain of 1.7% in the BRB. Without free-edge stiffeners, the single corner gusset plate buckled at a significantly lower strength than that predicted by the specificationof American Institute of Steel Construction (2005). The buckling could be eliminated by using dual corner gusset plates similar in size to the single gusset plate. At low drifts, the frame action force on the corner gusset was of the same magnitude as the brace force. At high drifts, however, the frame action force significantly increased and caused weld fractures at column-to-gusset edges. Nonlinear time history analyses were performed on the three-story BRBF to obtain seismic demands under both design and maximum considerable levels of earthquake loading. The analytical results confirmed that the BRB and corner gusset plate achieved peak drift under cyclic loading test. Copyright © 2011 John Wiley & Sons, Ltd.

Passive high force-to-volume (HF2V) dampers offer significant displacement reduction and energy dissipation, but cannot customise overall response. Semi-active resettable devices offer adaptive, custom hysteresis loops that reduce displacement and base shear, but have limited dissipation. This paper presents a new, combined concept to maximise displacement reduction without increasing base shear – a net-zero base-shear concept.

HF2V devices, up to a maximum of 10% structural weight, are combined with fixed stiffness resettable devices. Spectral analyses are run for the three SAC ground motion suites that iteratively size the HF2V device at each structural period to achieve maximum displacement reductions without increasing median base shear. HF2V velocity dependence and the need to scale HF2V capacity to spectral velocity are examined in terms of their impact on the results of these analyses.

The net-zero approach reduces base shear by up to 50% and displacements by 30–70% over all ground motions, exceeding reductions obtained by either device separately by 30–50% (relative). The net-zero condition is not reached within the device limits defined, except at relatively long periods (>3.5 s) because of a virtuous circle of reduced displacement from the resettable and HF2V devices outweighing the increased base shear from the HF2V devices alone. These results are independent of HF2V device scaling, design and velocity dependence. The overall net-zero concept offers a significant advantage in a combination that cannot be achieved by passive or semi-active solutions alone. Copyright © 2011 John Wiley & Sons, Ltd.

This paper reports on a semi-analytical/numerical method to model sloshing water in an arbitrarily shaped aqueduct. The water motion is assumed to be inviscid, compressible, and linear (small displacement). The transverse sloshing fluid in an aqueduct is equivalently simplified as a fixed rigid mass M₀ and a mass–spring system (M₁, K₁). According to a rule that the actual fluid (computed with finite element model) and its equivalent mechanical model have the same first sloshing frequency and acting effects on the aqueduct, the analytical solutions of the fixed (impulsive) mass M₀, sloshing (convective) massM₁, spring stiffness K₁, and their locations in the aqueduct body are acquired by the least squares (curve fitting) algorithm. Applying this equivalent principle, the equivalent mechanical models are respectively obtained for the sloshing water in rectangular, semicircular, U-shaped, and trapezoid aqueducts. The equivalent principle and fluid models are validated through comparison investigations involving rectangular and U-shaped aqueducts. The dynamic properties and seismic responses of the original and equivalent systems are simulated, compared, and discussed for a U-shaped aqueduct bridge. The main purpose of this paper is to provide a simplified model of sloshing fluid for the seismic/wind-resistant computation of the support structures of the aqueduct bridge. Copyright © 2011 John Wiley & Sons, Ltd.

Real-time hybrid simulation is a viable experiment technique to evaluate the performance of structures equipped with rate-dependent seismic devices when subject to dynamic loading. The integration algorithm used to solve the equations of motion has to be stable and accurate to achieve a successful real-time hybrid simulation. The implicit HHT α-algorithm is a popular integration algorithm for conducting structural dynamic time history analysis because of its desirable properties of unconditional stability for linear elastic structures and controllable numerical damping for high frequencies. The implicit form of the algorithm, however, requires iterations for nonlinear structures, which is undesirable for real-time hybrid simulation. Consequently, the HHT α-algorithm has been implemented for real-time hybrid simulation using a fixed number of substep iterations. The resulting HHT α-algorithm with a fixed number of substep iterations is believed to be unconditionally stable for linear elastic structures, but research on its stability and accuracy for nonlinear structures is quite limited. In this paper, a discrete transfer function approach is utilized to analyze the HHT α-algorithm with a fixed number of substep iterations. The algorithm is shown to be unconditionally stable for linear elastic structures, but only conditionally stable for nonlinear softening or hardening structures. The equivalent damping of the algorithm is shown to be almost the same as that of the original HHT α-algorithm, while the period elongation varies depending on the structural nonlinearity and the size of the integration time-step. A modified form of the algorithm is proposed to improve its stability for use in nonlinear structures. The stability of the modified algorithm is demonstrated to be enhanced and have an accuracy that is comparable to that of the existing HHT α-algorithm with a fixed number of substep iterations. Both numerical and real-time hybrid simulations are conducted to verify the modified algorithm. The experimental results demonstrate the effectiveness of the modified algorithm for real-time testing. Copyright © 2011 John Wiley & Sons, Ltd.

In this work, we present a new method in designing static output-feedback H_∞ controllers suitable for vibrational control of buildings under seismic excitation. The method produces a Linear Matrix Inequality (LMI) formulation that allows obtaining static output-feedback controllers with different information structure constraints by imposing a convenient zero–nonzero structure on the LMI variables. The application of the proposed methodology is illustrated by designing centralized and decentralized velocity-feedback H_∞ controllers to mitigate the seismic response of a five-story building. Copyright © 2011 John Wiley & Sons, Ltd.

This paper deals with the assessment of the seismic response of a portal frame pier belonging to an old reinforced concrete viaduct. A series of tests, consisting of cyclically imposed displacements, were carried out on three 1:4 scale mock-ups. The objective of the experimental campaign is twofold: (1) identification and evaluation of the local failure mechanisms and (2) calibration of a numerical model including all observed nonlinear phenomena. The experimental results show that the shear strength of the transverse beam and of the beam–column joints characterizes the post-elastic behavior of the piers. Other phenomena, like bond-slip and buckling of the longitudinal bars of the columns, typical of old reinforced concrete structures have also been observed. Finally, a numerical model, built in OpenSEES, was calibrated to reproduce in a satisfactory way the experimental results and to provide a reliable tool for the evaluation of the seismic response of the pier. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents the shake-table tests of a 2/3-scale, three-story, two-bay, reinforced concrete frame infilled with unreinforced masonry walls. The specimen is representative of the construction practice in California in the 1920s. The reinforced concrete frame had nonductile reinforcement details and it was infilled with solid masonry walls in one bay and infill walls with window openings in the other bay. The structure was subjected to a sequence of dynamic tests including white-noise base excitations and 14 scaled historical earthquake ground motion records of increasing intensity. The performance of the structure was satisfactory considering the seismic loads it was subjected to. The paper summarizes the design of the specimen and the major findings from the shake-table tests, including the dynamic response, the load resistance, the evolution of damage, and the final failure mechanism. Copyright © 2011 John Wiley & Sons, Ltd.

A series of hybrid and cyclic loading tests were conducted on a three-story single-bay full-scale buckling-restrained braced frame (BRBF) at the Taiwan National Center for Research on Earthquake Engineering in 2010. Six buckling-restrained braces (BRBs) including two thin BRBs and four end-slotted BRBs, all using welded end connection details, were installed in the frame specimen. The BRBF was designed to sustain a design basis earthquake in Los Angeles. In the first hybrid test, the maximum inter-story drift reached nearly 0.030 rad in the second story and one of the thin BRBs in the first story locally bulged and fractured subsequently before the test ended. After replacing the BRBs in the first story with a new pair, a second hybrid test with the same but reversed direction ground motion was applied. The maximum inter-story drifts reached more than 0.030 rad and some cracks were found on the gusset welds in the second story. The frame responses were satisfactorily predicted by both OpenSees and PISA3D analytical models. The cyclic loading test with triangular lateral force distribution was conducted right after the second hybrid test. The maximum inter-story drift reached 0.032, 0.031, and 0.008 rad for the first to the third story, respectively. This paper then presents the findings on the local bulging failure of the steel casing by using cyclic test results of two thin BRB specimens. It is found that the steel casing bulging resistance can be computed from an equivalent beam model constructed from the steel core plate width and restraining concrete thickness. This paper concludes with the recommendations on the seismic design of thin BRB steel casings against local bulging failure. Copyright © 2011 John Wiley & Sons, Ltd.

Damage has to be quantified in civil structures to assess their seismic performance and risk and loss on a regional scale. Fragility curves have proved to be suitable for coping with randomness inherent in such an issue. Recently, the cognitive source of uncertainty has been stressed. Because the seismic limit states are defined descriptively more than analytically, fuzziness is inherent as well. In this study, a model to include fuzziness in the seismic fragility curve is implemented and appraised. First, several methods to compute seismic fragility are briefly reviewed. Consistent with the first-order second-moment reliability method, a simple extension is proposed and the explicit formulation of the probability measure is derived. Conclusions about the effect of fuzziness are drawn based on this analytical formulation. Above all, fragility increases at lower seismic intensity, whereas it decreases at higher intensity. Steepness of the fragility curve, that is, sensitivity to the ground motion, decreases with increase of fuzziness. This effect is shown to be similar to the effect of randomness. However, the greater the randomness, the smaller is the importance of fuzziness. Fuzziness aside, deterministic capacity may give excessive overestimation of fragility. A numerical example is presented. The fuzzy random fragility curves of a masonry infilled reinforced concrete frame are compared with the curves with fuzziness neglected and with different degrees of randomness. All results by the proposed model are reasonable. Copyright © 2011 John Wiley & Sons, Ltd.

The evaluation of the out-of-plane behaviour of unreinforced walls is one of the most debated topics in the seismic assessment of existing masonry buildings. The discontinuous nature of masonry and its interaction with the remainder of the building make the dynamic modelling of out-of-plane response troublesome. In this paper, the results of a shaking table laboratory campaign on a tuff masonry, natural scale, U-shaped assemblage (façade adjacent to transverse walls) are presented. The tests, excited by scaled natural accelerograms, replicate the behaviour of external walls in existing masonry buildings, from the beginning of rocking motion to overturning. Two approaches have been developed for modelling the out-of-plane seismic behaviour: the discrete element method and an SDOF analytic model. Both approaches are shown to be capable of reproducing the experimental behaviour in terms of maximum rotation and time history dynamic response. Finally, test results and numerical time history simulations have been compared with the Italian seismic code assessment procedures. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents the results of an experimental and analytical/computational study of the performance of multi-unit particle dampers with an MDOF system. A series of shaking table tests of a three-storey steel frame with the particle damper system were carried out to evaluate the performance of the system and to verify the analysis method. An analytical solution based on the discrete element method is also presented. A comparison between the experimental and computational results shows that reasonably accurate estimates of the response of a primary system under earthquake excitations can be obtained. These results also indicate that the excitation characterization influences the performance of the particle damper system, for example, particle dampers have good performance in reducing the seismic response of structures and particle movements of plug flow pattern can yield good vibration attenuation effects. It is shown that by using properly designed multi-unit particle dampers, a lightly damped primary system can achieve a reasonable reduction in its response, with a small weight penalty. Copyright © 2011 John Wiley & Sons, Ltd.

Soil rotations around horizontal axes, during an earthquake, are studied through records collected by closely spaced arrays of strong motion accelerometers. The cross power spectrum of accelerations at nearby stations has been generally utilized to describe the spatial distribution of the motion. A number of cross spectra have been obtained during the training of these arrays. To take profit of these elaborations, a mathematical relation is established between the cross power spectrum and the power spectrum of the rotation.

Rotation data presented by Liu et al, concerning 52 earthquake records collected at a single station in Taiwan, are compared with rotation data computed according to our procedure. The two series of data are suitably normalized to the peak horizontal acceleration. The data are shown in function of the distance from epicentre. The same ratio, computed according to our procedure, is in good agreement with the average value of these data.

Direct measurements and the present approach have lead to evaluations of rotation higher than those predicted by mathematical investigations on the basis of the wave propagation theory, for comparable circumstances.

The relevance of this input motion for relatively tall structures is examined, with reference to the structural effects that the horizontal motion concurrently provides. Meaningful will be ranked those effects of the order of magnitude of 20% or higher than those implied by the horizontal excitation.

For understanding the relevance on building structures, the procedure has two areas of concern: 1) the coherence implicit in the cross power spectra, which depends on the interpolation process of the original records, collected in the arrays of instruments, and 2) the relative importance of the vertical to the horizontal input motion.

As to the second item, the relevance of the rotation component on structures largely depends on the relative importance of the vertical to the horizontal input motion. When the records in an area a few km from the epicenter are considered, the response spectrum of vertical motion is comparable and in some records even higher, than that of horizontal motion, over the entire range of frequencies. This has been observed as well for the 2009 earthquake event of L'Aquila, Italy, and that at the Christchurch (New Zealand) 2011. When the response spectrum of vertical motion is comparable to that of horizontal motion, the effects of rotational motions on most engineering structures can be meaningful. Copyright © 2011 John Wiley & Sons, Ltd.

The complementary sections of the studies carried out on the damped cable system, whose experimental and numerical characterization and assessment analyses are described in the companion paper, are presented herein. The first section includes a criterion for a preliminary evaluation of the section area of cables, the second branch stiffness of spring-dampers and the mutual installation preload, and suggestions for a simplified nonlinear dynamic computation of the damping coefficient of dissipaters. A second section follows, aimed at evaluating the influence of cable layout on damped cable system performance. A numerical enquiry is developed on a four-story and an eight-story RC plane frame, to assess their seismic response for several shapes of cables, and determine what geometrical configurations are the best performing ones. In the third section, a demonstrative application of the protective system, represented by the seismic retrofit of a hospital building with RC structure, is offered. The characteristics of the system designed for this case study, including locations, dimensions, layouts, and technical installation details of cables and spring-dampers, are illustrated, and the improvement of seismic performance as compared with the original conditions, is finally assessed. Copyright © 2011 John Wiley & Sons, Ltd.

Research studies on the damped cable system (DCS) for seismic protection of frame structures are presented in this paper and the accompanying one. This technology includes prestressed steel cables linked to pressurized fluid viscous spring-dampers fixed to the foundation at their lower ends, and to the top floor, or one of the upper floors, at their upper ends. The cables have sliding contacts with the floor slabs, to which they are joined by steel deviators. The general characteristics of the system, as well as of the constituting spring-dampers and cables, are initially discussed. The results of a laboratory testing campaign developed on a DCS prototype are examined, and transferred into the formulation of the finite element model of the system, conceived to be easily generated by commercial structural analysis programs. A second dynamic experimental investigation follows, concerning a pilot installation of the system on a full-scale mock-up building. The benefits of the protective technology are evaluated in terms of maximum displacements and accelerations, as well as of equivalent viscous damping coefficient and MDOF transmissibility ratio. Further sections of the study, including a preliminary sizing criterion of DCS, additional numerical enquiries aimed at optimizing its geometrical layout, and the application to a real case study building, are offered in the companion paper. Copyright © 2011 John Wiley & Sons, Ltd.

This study focuses on the use of strong motion data recorded during earthquakes and aftershocks to provide a preliminary assessment of the structural integrity and possible damage in bridges. A system identification technique is used to determine dynamical characteristics and high-fidelity first-order linear models of a bridge from low level earthquake excitations. A finite element model is developed and updated using a genetic algorithm optimization scheme to match the frequencies identified and to simulate data from a damaging earthquake for the bridge. Here, two criteria are used to determine the state of the structure. The first criteria uses the error between the data recorded or simulated by the calibrated nonlinear finite element model and the data predicted by the linear model. The second criteria compares relative displacements of the structure with displacement thresholds identified using a pushover analysis. The use of this technique can provide an almost immediate, yet reliable, assessment of the structural health of an instrumented bridge after a seismic event. Copyright © 2011 John Wiley & Sons, Ltd.

Building pounding damages observed in the February 2011 Christchurch earthquake are described in this paper. The extent and severity of pounding damage is presented based on a street survey of Christchurch's central business district. Six damage severity levels and two confidence levels are defined to classify the observed damage. Generally, pounding was observed to be a secondary effect. However, over 6% of the total surveyed buildings were observed to have significant or greater pounding damage. Examples of typical and exceptional pounding damage are identified and discussed. Extensive pounding damage was observed in low-rise unreinforced masonry buildings that were constructed with no building separation. Modern buildings were also endangered by pounding when building separations were infilled with solid architectural flashings. The damage caused by these flashings was readily preventable. The observed pounding damage is compared to that observed in the September 2010 Darfield earthquake to explore if the damage could have been predicted. It is found that pounding prone buildings can be identified with reasonable accuracy by comparing configurations to characteristics previously noted by researchers. However, detailed pounding damage patterns cannot currently be precisely predicted by these methods. Copyright © 2011 John Wiley & Sons, Ltd.

The seismic structural response is affected by temporal and spatial variations in strong ground motion. It can be evaluated through the fault-structure system: the fault mechanism, wave propagation through the crust, amplification near the surface, and soil-structure interaction. To analyze this system at high resolution and accuracy, we previously proposed a new multiscale analysis method and numerically verified its validity. However, the problem of the extremely large computation cost of constructing a three-dimensional numerical model and solving the discretized governing equations still remains. Here, we introduce a new method to resolve these difficulties. By combining this new method with our multiscale analysis, we developed a tool for fault-structure system analysis. The accuracy of this tool is verified by comparing it to a Green's function solution. Finally, we demonstrate the potential utility of the method by estimating the seismic response of a large and complex underground highway junction in a given earthquake scenario. Copyright © 2011 John Wiley & Sons, Ltd.

A tuned mass damper (TMD) system consists of an added mass with properly functioning spring and damping elements for providing frequency-dependent damping in a primary structure. The advantage of a friction-type TMD, that is, a nonlinear TMD, is its energy dissipation via a friction mechanism. In contrast, the disadvantages of a passive friction TMD (PF-TMD) are its fixed and predetermined slip load and loss of tuning and energy dissipation capabilities when it is in a stick state. A semi-active friction TMD (SAF-TMD) is used to overcome these disadvantages. The SAF-TMD can adjust its slip force in response to structure motion. To verify its feasibility, a prototype SAF-TMD was fabricated and tested dynamically using a shaking table test. A nonsticking friction control law was used to keep the SAF-TMD activated and in a slip state in earthquakes at varying intensities. The shaking table test results demonstrated that: (i) the experimental results are consistent with the theoretical results; (ii) the SAF-TMD is more effective than the PF-TMD given a similar peak TMD stroke; and (iii) the SAF-TMD can also prevent a residual TMD stroke in a PF-TMD system. Copyright © 2011 John Wiley & Sons, Ltd.

The present paper investigates the seismic reliability of the application of buckling restrained braces (BRBs) for seismic retrofitting of steel moment resisting framed buildings through fragility analysis. Samples of regular three-storey and eight-storey steel moment resisting frames were designed with lateral stiffness insufficient to comply with the code drift limitations imposed for steel moment resisting frame systems in earthquake-prone regions. The frames were then retrofitted with concentrically chevron conventional braces and BRBs. To obtain robust estimators of the seismic reliability, a database including a wide range of natural earthquake ground motion records with markedly different characteristics was used in the fragility analysis. Nonlinear time history analyses were utilized to analyze the structures subjected to these earthquake records. The improvement of seismic reliability achieved through the use of conventional braces and BRBs was evaluated by comparing the fragility curves of the three-storey and eight-storey model frames before and after retrofits, considering the probabilities of four distinct damage states. Moreover, the feasibility of mitigating the seismic response of moment resisting steel structures by using conventional braces and BRBs was determined through seismic risk analysis. The results obtained indicate that both conventional braces and especially BRBs improve significantly the seismic behavior of the original building by increasing the median values of the structural fragility curves and reducing the probabilities of exceedance of each damage state. Copyright © 2011 John Wiley & Sons, Ltd.

Loss ratio, which is the ratio of the repair cost to the total replacement cost, is an effective parameter for representing structural and nonstructural damage caused by earthquakes. A probabilistic loss estimation framework is first presented that directly relates hazard to response and hence to losses. A key feature of the loss estimation approach is the determination of losses without need for customary fragility curves. Relationships between intensity measures and engineering demand parameters are used to define the demand model. An empirically calibrated loss model in the form of a power curve with upper and lower cut-offs is used in conjunction with the demand model to estimate loss ratios. Loss ratios for each of the damage states take into account epistemic uncertainty and an effect on price surge following a major hazardous event. The loss model is calibrated and validated for bridges designed based on the prevailing Caltrans, Japan, and New Zealand standards. The loss model is then transformed to provide a composite seismic hazard–loss relationship that is used to estimate the expected annual loss for structures. The closed-form four-step stochastic loss estimation model is applied to the bridges designed for ductility. Results of these ductile designs are compared to a bridge detailed to an emerging damage avoidance design philosophy. Copyright © 2011 John Wiley & Sons, Ltd.

The collapse capacity of earthquake-excited inelastic nondeteriorating SDOF systems, which are vulnerable to the destabilizing effect of gravity loads (P-delta effect), is evaluated. In this paper, the collapse capacity of the system subjected to a ground motion is defined as spectral acceleration at its initial structural period, at which the structure becomes unstable. Characteristic structural parameters, which affect the collapse capacity, are identified. Ground motion records of the ATC 63 far-field set characterize severe earthquake excitation. In extensive incremental dynamic analyses studies, the impact of these parameters and of aleatory uncertainties on the collapse capacity is assessed and quantified. Median and percentile collapse capacities are plotted against the initial structural period leading to collapse capacity spectra. Nonlinear regression analyses are applied to derive analytical expressions of the design collapse capacity spectra and collapse fragility curves. The ultimate objective is to provide collapse capacity spectra for easy application and yet sufficient accurate assessment of the dynamic stability of flexible multistory buildings. Copyright © 2011 John Wiley & Sons, Ltd.

The concept of the hybrid passive control system is studied analytically by investigating the seismic response of steel frame structures. Hybrid control systems consist of two different passive elements combined into a single device or system. The hybrid systems investigated in this research consist of a rate-dependent damping device paired with a rate-independent energy dissipation element. The innovative configurations exploit individual element strengths and offset their weaknesses through multiphased behavior. A nine-story, five-bay steel moment-frame was used for the analysis. Six different seismic resisting systems were analyzed and compared. The conventional systems included a special moment-resisting frame (SMRF) and a dual SMRF–buckling-restrained brace (BRB) system. The final four configurations are hybrid passive systems. The different hybrid configurations utilize a BRB and either a high-damping rubber damper or viscous fluid damper. The analyses were run in the form of an incremental dynamic analysis. Several damage measures were calculated, including maximum roof drift, base shear, and total roof acceleration. The results demonstrate the capability of hybrid passive control systems to improve structural response compared with conventional lateral systems and to be effective for performance-based seismic design. Each hybrid configuration improved some aspect of structural response with some providing benefits for multiple damage measures. The multiphased nature provides improved response for frequent and severe seismic events. Copyright © 2011 John Wiley & Sons, Ltd.

Fragility functions are commonly used in performance-based earthquake engineering for predicting the damage state of a structure subjected to an earthquake. This process often involves estimating the structural damage as a function of structural response, such as the story drift ratio and the peak floor absolute acceleration. In this paper, a new framework is proposed to develop fragility functions to be used as a damage classification/prediction method for steel structures based on a wavelet-based damage sensitive feature (DSF). DSFs are often used in structural health monitoring as an indicator of the damage state of the structure, and they are easily estimated from recorded structural responses. The proposed framework for damage classification of steel structures subjected to earthquakes is demonstrated and validated with a set of numerically simulated data for a four-story steel moment-resisting frame designed based on current seismic provisions. It is shown that the damage state of the frame is predicted with less variance using the fragility functions derived from the wavelet-based DSF than it is with fragility functions derived from an alternate acceleration-based measure, the spectral acceleration at the first mode period of the structure. Therefore, the fragility functions derived from the wavelet-based DSF can be used as a probabilistic damage classification model in the field of structural health monitoring and an alternative damage prediction model in the field of performance-based earthquake engineering. Copyright © 2011 John Wiley & Sons, Ltd.

This paper deals with the estimation of peak inelastic displacements of SDOF systems, representative of typical steel structures, under constant relative strength scenarios. Mean inelastic deformation demands on bilinear systems (simulating moment resisting frames) are considered as the basis for comparative purposes. Additional SDOF models representing partially-restrained and concentrically-braced (CB) frames are introduced and employed to assess the influence of different force-displacement relationships on peak inelastic displacement ratios. The studies presented in this paper illustrate that the ratio between the overall yield strength and the strength during pinching intervals is the main factor governing the inelastic deformations of partially-restrained models and leading to significant differences when compared with predictions based on bilinear structures, especially in the short-period range. It is also shown that the response of CB systems can differ significantly from other pinching models when subjected to low or moderate levels of seismic demand, highlighting the necessity of employing dedicated models for studying the response of CB structures. Particular attention is also given to the influence of a number of scalar parameters that characterise the frequency content of the ground motion on the estimated peak displacement ratios. The relative merits of using the average spectral period T_aver, mean period T_m, predominant period T_g, characteristic period T_c and smoothed spectral predominant period T_o of the earthquake ground motion, are assessed. This paper demonstrates that the predominant period, defined as the period at which the input energy is maximum throughout the period range, is the most suitable frequency content scalar parameter for reducing the variability in displacement estimations. Finally, noniterative equivalent linearisation expressions based on the secant period and equivalent damping ratios are presented and verified for the prediction of peak deformation demands in steel structures. Copyright © 2011 John Wiley & Sons, Ltd.

Real-time hybrid simulation provides a viable method to experimentally evaluate the performance of structural systems subjected to earthquakes. The structural system is divided into substructures, where part of the system is modeled by experimental substructures, whereas the remaining part is modeled analytically. The displacements in a real-time hybrid simulation are imposed by servo-hydraulic actuators to the experimental substructures. Actuator delay compensation has been shown by numerous researchers to vitally achieve reliable real-time hybrid simulation results. Several studies have been performed on servo-hydraulic actuator delay compensation involving single experimental substructure with single actuator. Research on real-time hybrid simulation involving multiple experimental substructures, however, is limited. The effect of actuator delay during a real-time hybrid simulation with multiple experimental substructures presents challenges. The restoring forces from experimental substructures may be coupled to two or more degrees of freedom (DOF) of the structural system, and the delay in each actuator must be adequately compensated. This paper first presents a stability analysis of actuator delay for real-time hybrid simulation of a multiple-DOF linear elastic structure to illustrate the effect of coupled DOFs on the stability of the simulation. An adaptive compensation method then proposed for the stable and accurate control of multiple actuators for a real-time hybrid simulation. Real-time hybrid simulation of a two-story four-bay steel moment-resisting frame with large-scale magneto-rheological dampers in passive-on mode subjected to the design basis earthquake is used to experimentally demonstrate the effectiveness of the compensation method in minimizing actuator delay in multiple experimental substructures. Copyright © 2011 John Wiley & Sons, Ltd.

A method is presented for simulating arrays of spatially varying ground motions, incorporating the effects of incoherence, wave passage, and differential site response. Non-stationarity is accounted for by considering the motions as consisting of stationary segments. Two approaches are developed. In the first, simulated motions are consistent with the power spectral densities of a segmented recorded motion and are characterized by uniform variability at all locations. Uniform variability in the array of ground motions is essential when synthetic motions are used for statistical analysis of the response of multiply-supported structures. In the second approach, simulated motions are conditioned on the segmented record itself and exhibit increasing variance with distance from the site of the observation. For both approaches, example simulated motions are presented for an existing bridge model employing two alternatives for modeling the local soil response: i) idealizing each soil-column as a single-degree-of-freedom oscillator, and ii) employing the theory of vertical wave propagation in a single soil layer over bedrock. The selection of parameters in the simulation procedure and their effects on the characteristics of the generated motions are discussed. The method is validated by comparing statistical characteristics of the synthetic motions with target theoretical models. Response spectra of the simulated motions at each support are also examined. Copyright © 2011 John Wiley & Sons, Ltd.

The seismic capacity of beam-to-column connections in steel high-rise frames is a matter of concern, particularly when they are subjected to long-period ground motions. A previous full-scale shaking table test conducted at the E-Defense National Research Institute for Earth Science and Disaster Prevention in Japan disclosed cracks and fractures in such beam-to-column connections. This paper examines the effects of three types of beam-to-column connection retrofit: supplemental welds, wing plates, and a haunch. Quasi-static member tests and a series of shaking table tests applied to a full-scale specimen are conducted to quantify the respective performances of the retrofit schemes. The performance of a total of 28 connections tested by the member and shaking table tests is evaluated together with that of an additional 12 unretrofitted connections tested in the previous test. When the supplemental welds are applied only to the shear tab to the web, the connection fractures at the same instant as the connection without retrofit. The corresponding cumulative plastic rotation is not improved. When the supplement welds are further applied to the web-to-column connection, strain concentration at the bottom flange, primarily promoted by the presence of the RC floor slab, is significantly reduced, and the cumulative plastic rotation capacity is increased to eight times that of the connection without retrofit. For the wing plate connection and haunch connection, the critical section is moved from the beam end to the beam cross-section corresponding to the tip of the wing plates or haunch, resulting in an improvement of ductility by eight times that of the unretrofitted connection. Copyright © 2011 John Wiley & Sons, Ltd.

Lumped parameter models with a so called “gyro-mass” element (GLPMs) have been proposed recently in response to a strong demand for efficiently and accurately representing frequency-dependent impedance functions of soil–foundation systems. Although GLPMs are considered to be powerful tools for practical applications in earthquake engineering, some problems remain. For instance, although GLPMs show fairly close agreement with the target impedance functions, the accuracy of the transfer functions and the time-histories of dynamic responses in structural systems comprising GLPMs have never been verified. Furthermore, no assessment has been performed on how much difference appears in the accuracy of dynamic responses obtained from GLPMs and those from conventional Kelvin–Voigt models comprising a spring and a dashpot arranged in parallel with various frequency-independent constants. Therefore, in this paper, these problems are examined using an example of 2×4 pile groups embedded in a layered soil medium, supporting a single-degree-of-freedom system subjected to ground motions. The results suggest that GLPMs are a new option for highly accurate computations in evaluating the dynamic response of structural systems comprising typical pile groups, rather than conventional Kelvin–Voigt models. Copyright © 2011 John Wiley & Sons, Ltd.

In order to enhance the durability of high-performance buckling-restrained braces (BRBs) used in bridge engineering, which are expected to withstand severe earthquakes three times without being replaced, aluminum alloys were employed to manufacture BRBs. A series of low-cycle fatigue tests, including 18 specimens, were conducted to address the low-cycle fatigue strength of the aluminum alloy BRB. Test results of all specimens show that stable hysteretic curves were obtained without overall buckling occurrence. Failure mode of the welded aluminum alloy BRB is obviously affected by the ribs' welding under the variable or constant strain amplitude condition. Therefore, another type of aluminum alloy BRB, the bolt-assembled BRB with or without spot-welded stoppers, is proposed and tested. Results showed that the low-cycle fatigue performance of bolt-assembled BRBs with stoppers improved four to five times compared with welded BRBs. However, the stoppers' spot welding has an adverse effect on the failure mode because the crack, which induced the specimen's failure, initiated from the spot weld toes of the stoppers. Both bolt-assembled BRBs with and without stoppers can meet the cumulative inelastic deformation requirement proposed for high-performance BRBs under the constant strain amplitude, not larger than 2%. In addition, under the variable strain amplitude condition, only the bolt-assembled BRB without stoppers has an excellent cumulative inelastic deformation capacity and sustains two cycles of 2.5% strain amplitude. Finally, recommended Manson–Coffin equations and preliminary cumulative damage formulae for welded and bolt-assembled BRBs are given as the references of the strain-based damage evaluation. Copyright © 2011 John Wiley & Sons, Ltd.

Structural identification based on analysis of vibration signals is usually formulated as an optimization problem. Nevertheless, identifying a structural system as a whole often involves a great number of unknowns and degrees of freedom, resulting in considerable convergence difficulty and expensive evaluation of objective function. To handle these issues, this paper aims to propose a frequency domain substructural identification method applicable to arbitrary excitations. This is done by introducing the exponential window method in the formulation so that the effect caused by initial condition is alleviated without using zero padding. The proposed identification method is verified through both numerical and experimental studies. It is shown that significant reduction in computer time can be achieved in addition to remarkable identification accuracy. The experimental study also indicates that the proposed strategy is effective in identifying small structural changes. Copyright © 2011 John Wiley & Sons, Ltd.

Design guidelines have traditionally oversimplified the vertical ground motion effects by defining a constant vertical-to-horizontal response spectral ratio (V/H). With the recognition that such practice is not always conservative, recent studies have proposed improvements to the representation of vertical seismic effects in design codes, based on empirical ground motion relations.

Conventional empirical modeling requires selecting the functional form of the predictive model. Because of the complicated nature of ground motions, identification of the underlying function is a challenge. A related drawback to this approach is its high susceptibility to overfitting, especially with today's highly complex models.

To address these issues, this paper proposes a nonparametric approach to characterize the vertical seismic effects. Using support vector machines, the V/H ratio is determined without an assumed functional form. The accuracy of the model is measured by adopting an epsilon-insensitive residual function with a regularization term added to prevent overfitting.

An example application using ground motion records from strike-slip and normal faulting earthquakes is presented, and the results are compared with a current empirical model, for different magnitude, distance, and local soil conditions. The median V/H estimates from the two models are shown to be in good general agreement. The standard deviation estimates from the proposed model are consistently larger than the estimates from the empirical model.

The results from this study show that the proposed method is a viable alternative and offers the opportunity to characterize vertical seismic effects without an assumed functional form. Copyright © 2011 John Wiley & Sons, Ltd.

This study presents a seismic fragility analysis of low-rise masonry in-filled (MI) reinforced concrete (RC) buildings using a proposed coefficient-based spectral acceleration method. The coefficient-based method, without requiring any complicated finite element analysis, is a simplified procedure for assessing the spectral acceleration demand (or capacity) of buildings subjected to earthquakes. This paper begins with a calibration of the proposed coefficient-based method for low-rise MI RC buildings using published experimental results obtained from shaking table tests. Spectral acceleration-based fragility curves for low-rise MI RC buildings under various inter-story drift limits are then constructed using the calibrated coefficient-based method. A comparison of the experimental and estimated results indicates that the simplified coefficient-based method can provide good approximations of the spectral accelerations at peak loads of low-rise MI RC buildings, if a proper set of drift-related factors and initial fundamental periods of structures are used. Moreover, the fragility curves constructed using the coefficient-based method can provide a satisfactory vulnerability evaluation for low-rise MI RC buildings under a given performance level. Copyright © 2011 John Wiley & Sons, Ltd.

In the presented practice-oriented probabilistic approach for the seismic performance assessment of building structures, the SAC-FEMA method, which is a part of the broader PEER probabilistic framework and permits probability assessment in closed form, is combined with the pushover-based N2 method. The most demanding part of the PEER probabilistic framework, that is incremental dynamic analysis, is replaced by the much simpler N2 method, which requires considerably less input data and much less computational time, but which can, nevertheless, often provide: acceptable estimates for the mean values of the structural response. Using some additional simplifying assumptions that are consistent with seismic code procedures, an explicit equation for a quick estimation of the annual probability of “failure” (i.e. the probability of exceeding the near collapse limit state) of a structure can be derived, which is appropriate for practical applications, provided that predetermined default values for the dispersion measures are available. In the paper, this simplified approach is summarized and applied to the estimation of the “failure” probability of reinforced concrete frame buildings representing both old structures, not designed for earthquake resistance, and new structures designed according to Eurocode 8. The results of the analyses indicate a high probability of the “failure” of buildings, which have not been designed for seismic loads. For a building designed according to a modern code, the conservatively determined probability of “failure” is about 30 times less but still significant (about 1% over the lifetime of the structure). Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, different formulations of a macro-element model for non-linear dynamic soil-structure interaction analyses of structures lying on shallow foundations are first reviewed, and secondly, a novel formulation is introduced, which combines some of the characteristics of previous approaches with several additional features. This macro-element allows one to model soil-footing geometric (uplift) and material (soil plasticity) non-linearities that are coupled through a stiffness degradation model. Footing uplift is introduced by a simple non-linear elastic model based on the concept of effective foundation width, whereas soil plasticity is treated by means of a bounding surface approach in which a vertical load mapping rule is implemented. This mapping is particularly suited for the seismic loading case for which the proposed model has been conceived. The new macro-element is subsequently validated using cyclic and dynamic large-scale laboratory tests of shallow foundations on dense sand, namely: the TRISEE cyclic tests, the Public Works Research Institute and CAMUS IV shaking table tests. Based on this comprehensive validation process against a set of independent experimental results, a unique set of macro-element parameters for shallow foundations on dense sand is proposed, which can be used to perform predictive analyses by means of the present model. Copyright © 2011 John Wiley & Sons, Ltd.

Nine large-scale beam specimens were constructed. Of which, one was used as the control, whereas the other eight ones were divided into four sets. Each set had two specimens and was subjected to accelerated corrosion using an imposed current for the same time interval. Following the corrosion, a specimen in each set was tested using cyclic loading to examine the seismic performance, whereas the other one was demolished to examine the extent of corrosion. Cyclic loading results indicated that with an increasing corrosion level, the ultimate drift, ductility, plastic rotation capacity, and energy dissipation of the beams initially increased and later decreased. The failure mode switched from flexural failure, largely owing to buckling of the longitudinal reinforcement to flexural-shear failure, which is mainly caused by fracturing of the transverse reinforcement. Corrosion increased shear deformation and the spread of plasticity of the plastic hinge region. The residual flexural strength, as estimated by an empirical equation based on the maximum pit depth in the longitudinal reinforcement, closely corresponds to experimental values. Furthermore, the residual shear strength estimated based on the minimum reduced cross-sectional area of transverse reinforcement correlates better with the experimental observations than that based on the weight loss. Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, a practical method is developed for performance-based design of RC structures subjected to seismic excitations. More efficient design is obtained by redistributing material from strong to weak parts of a structure until a state of uniform deformation or damage prevails. By applying the design algorithm on 5, 10 and 15-storey RC frames, the efficiency of the proposed method is initially demonstrated for specific synthetic and real seismic excitations. The results indicate that, for similar structural weight, designed structures experience up to 30% less global damage compared with code-based design frames. The method is then developed to consider multiple performance objectives and deal with seismic design of RC structures for a design spectrum. The results show that the proposed method is very efficient at controlling performance parameters and improving structural behaviour of RC frames. Copyright © 2011 John Wiley & Sons, Ltd.

This paper evaluates the hysteretic behavior of an innovative compressed elastomer structural damper and its applicability to seismic-resistant design of steel moment-resisting frames (MRFs). The damper is constructed by precompressing a high-damping elastomeric material into steel tubes. This innovative construction results in viscous-like damping under small strains and friction-like damping under large strains. A rate-dependent hysteretic model for the compressed elastomer damper, formed from a parallel combination of a modified Bouc–Wen model and a non-linear dashpot is presented. The model is calibrated using test data obtained under sinusoidal loading at different amplitudes and frequencies. This model is incorporated in the OpenSees [17] computer program for use in seismic response analyses of steel MRF buildings with compressed elastomer dampers. A simplified design procedure was used to design seven different systems of steel MRFs combined with compressed elastomer dampers in which the properties of the MRFs and dampers were varied. The combined systems are designed to achieve performance, which is similar to or better than the performance of conventional steel MRFs designed according to current seismic codes. Based on the results of nonlinear seismic response analyses, under both the design basis earthquake and the maximum considered earthquake, target properties for a new generation of compressed elastomer dampers are defined. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents a non-linear, kinematic model for triple friction pendulum isolation bearings. The model, which incorporates coupled plasticity and circular restraining surfaces for all sliding surfaces, is capable of capturing bi-directional behavior and is able to explicitly track the movement of each internal component. The model is general so that no conditions regarding bearing properties, which effect the sequence of sliding stages, are required for the validity of the model. Controlled-displacement and seismic-input experiments were conducted using the shake table at the University of California, Berkeley to assess the fidelity of the proposed model under bi-directional motion. Comparison of the experimental data with the corresponding results of the kinematic model shows good agreement. Additionally, experiments showed that the performance of TFP bearings is reliable over many motions, and the behavior is repeatable even when initial slider offsets are present. Copyright © 2011 John Wiley & Sons, Ltd.

A mechanism of horizontal floor response spectra amplification in the vicinity of higher modes' frequencies is investigated. It is demonstrated, by means of a simple two-degrees-of-freedom model, that in the case of unsymmetrical superstructure, such amplification may occur because of the coupling between vertical excitation and horizontal response of the non-isolated modes. This phenomenon is further illustrated by the results of analyses of a model of a nuclear plant. Copyright © 2011 John Wiley & Sons, Ltd.

In this study, we propose a new seismic control device, tuned viscous mass damper (TVMD), for building systems. We give a detailed description of an apparent mass amplifier using a ball-screw mechanism, which is one of the most important components for realizing the new device. We also derive a closed-form solution of an optimum seismic control design for a single-degree-of-freedom structure subjected to harmonic excitation. The performance of the new device is compared with those of the conventional viscous damper and viscous mass damper systems. The vibration control system using the TVMD is shown to be the most effective for linear structural systems with dampers having the same additional damping coefficient. The effectiveness of the TVMD for seismic excitation is verified by analyses and shake table tests with a small-scale TVMD. Copyright © 2011 John Wiley & Sons, Ltd.

The essence of real time hybrid simulation (RTHS) is the reliance on a physical test (virtual finite element) in support of a numerical simulation, which is unable to properly simulate it numerically. Hence, the computational support for a hybrid simulation is of paramount importance, and one with anything less than a state of the art computational support may defeat the purpose of such an endeavor. A critical, yet often ignored, component of RTHS is precisely the computational engine, which unfortunately has been a bottleneck for realistic studies. Most researches have focused on either the control or on the communication (mostly in distributed, non-real time hybrid simulation) leaving the third leg of RTHS (computation) ignored and limited to the simulation of simple models (small number of degrees of freedom and limited nonlinearities). This paper details the development of a specialized software written explicitly to perform, single site, hybrid simulation ranging from pseudo-dynamic to hard real time ones. Solution strategy, implementation details, and actual applications are reported. Copyright © 2011 John Wiley & Sons, Ltd.

Arias intensity, I_a, has been identified as an efficient intensity measure for the estimation of earthquake-induced losses. In this paper, a new model for the prediction of Arias intensity, which incorporates nonlinear site response through the use of the average shear-wave velocity and a heteroskedastic variance structure, is proposed. In order to estimate the effects of ground motions on spatially-distributed systems, it is important to take into account the spatial correlation of the intensity measure. However, existing loss-estimation models, which use I_a as an input, do not take this aspect of the ground motion into account. Therefore, the potential to model the spatial correlation of Arias intensity is also investigated. The empirical predictive model is developed using recordings from the Pacific Earthquake Engineering Research Center Next Generation of Attenuation database whereas the model for spatial correlation makes use of the well-recorded events from this database, that is the Northridge and Chi-Chi earthquakes. Copyright © 2011 John Wiley & Sons, Ltd.

Probabilistic seismic analysis of structures involves the construction of seismic demand models, often stated as probabilistic models of structural response conditioned on a seismic intensity measure. The uncertainty introduced by the model is often a result of the chosen intensity measure. This paper introduces the concept of using fractional order intensity measures (IMs) in probabilistic seismic demand analysis and uses a single frame integral concrete box-girder bridge class and a seismically designed multispan continuous steel girder bridge class as case studies. The fractional order IMs considered include peak ground response and spectral accelerations at 0.2 and 1.0 s considering a single degree of freedom system with fractional damping, , as well as a linear single degree of freedom system with fractional response, . The study reveals the advantage of fractional order IMs relative to conventional IMs such as peak ground acceleration, peak ground velocity, or spectral acceleration at 0.2 and 1.0 s. Metrics such as efficiency, sufficiency, practicality, and proficiency are measured to assess the optimal nature of fractional order IMs. The results indicate that the proposed fractional order IMs produce significant improvements in efficiency and proficiency, whereas maintaining practicality and sufficiency, and thus providing superior demand models that can be used in probabilistic seismic demand analysis. Copyright © 2011 John Wiley & Sons, Ltd.

The influence of vertical ground motions on the seismic response of highway bridges is not very well understood. Recent studies suggest that vertical ground motions can substantially increase force and moment demands on bridge columns and girders and cannot be overlooked in seismic design of bridge structures. For an evaluation of vertical ground motion effects on the response of single-bent two-span highway bridges, a systematic study combining the critical engineering demand parameters (EDPs) and ground motion intensity measures (IMs) is required. Results of a parametric study examining a range of highway bridge configurations subjected to selected sets of horizontal and vertical ground motions are used to determine the structural parameters that are significantly amplified by the vertical excitations. The amplification in these parameters is modeled using simple equations that are functions of horizontal and vertical spectral accelerations at the corresponding horizontal and vertical fundamental periods of the bridge. This paper describes the derivation of seismic demand models developed for typical highway overcrossings by incorporating critical EDPs and combined effects of horizontal and vertical ground motion IMs depending on the type of the parameter and the period of the structure. These models may be used individually as risk-based design tools to determine the probability of exceeding the critical levels of EDP for pre-determined levels of ground shaking or may be included explicitly in probabilistic seismic risk assessments. Copyright © 2011 John Wiley & Sons, Ltd.

This paper examines the rocking response and stability of rigid blocks standing free on an isolated base supported: (a) on linear viscoelastic bearings, (b) on single concave and (c) on double concave spherical sliding bearings. The investigation concludes that seismic isolation is beneficial to improve the stability only of small blocks. This happens because while seismic isolation increase the ‘static’ value of the minimum overturning acceleration, this value remains nearly constant as we move to larger blocks or higher frequency pulses; therefore, seismic isolation removes appreciably from the dynamics of rocking blocks the beneficial property of increasing stability as their size increases or as the excitation pulse period decreases. This remarkable result suggests that free- standing ancient classical columns exhibit superior stability as they are built (standing free on a rigid foundation) rather than if they were seismically isolated even with isolation system with long isolation periods. The study further confirms this finding by examining the seismic response of the columns from the peristyle of two ancient Greek temples when subjected to historic records. Copyright © 2011 John Wiley & Sons, Ltd.

A simple structure under earthquake excitation is modeled as a single-degree-of-freedom system with nonlinear stiffness subject to modulated Kanai–Tajimi excitation. The nonstationary responses including the nonstationary probability densities of the system responses and the statistical moments are obtained in semi-analytical form. By applying the stochastic averaging method based on the generalized harmonic functions, the averaged Fokker–Planck–Kolmogorov(FPK) equation governing the nonstationary probability density of the amplitude is derived. Then, the solution of the FPK equation is approximately expressed by a series expansion in terms of a set of properly selected basis functions with time-dependent coefficients. According to the Galerkin method, the time-dependent coefficients are solved from a set of linear first-order differential equations. Thus, the nonstationary probability densities of the amplitude and the state responses as well as the statistic moments of the amplitude are obtained. Finally, two types of the modulating functions, i.e. constant function and exponential function, are considered to give some semi-analytical formulae. The proposed procedures are checked against the Monte Carlo simulation. The effects of the structure natural frequency and the intensity of the excitation as well as the ground stiffness on the system responses are discussed. It should be pointed out that the proposed method is good for broadband excitation and light damping. Copyright © 2011 John Wiley & Sons, Ltd.

Near-fault ground motions are characterized by long-period horizontal pulses and high values of the ratio between the peak value of the vertical acceleration, PGA_V, and the analogous value of the horizontal acceleration, PGA_H, which can become critical for base-isolated (BI) structures. The objective of the present work is to check the effectiveness of the base isolation of framed buildings when using High-Damping-Rubber Bearings (HDRBs), taking into consideration the combined effects of the horizontal and vertical components of near-fault ground motions. To this end, a numerical investigation is carried out with reference to BI reinforced concrete buildings designed according to the European seismic code (Eurocode 8). The design of the test structures is carried out in a high-risk region considering (besides the gravity loads) the horizontal seismic loads acting alone or in combination with the vertical ones and assuming different values of the ratio between the vertical and horizontal stiffnesses of the HDRBs. The nonlinear seismic analysis is performed using a step-by-step procedure based on a two-parameter implicit integration scheme and an initial-stress-like iterative procedure. At each step of the analysis, plastic conditions are checked at the potential critical sections of the girders (i.e. end sections of the sub-elements in which a girder is discretized) and columns (i.e. end sections), where a bilinear moment–curvature law is adopted; the effect of the axial load on the ultimate bending moment (M-N interaction) of the columns is also taken into account. The response of an HDRB is simulated by a model with variable stiffness properties in the horizontal and vertical directions, depending on the axial force and lateral deformation, and linear viscous damping. Copyright © 2011 John Wiley & Sons, Ltd.

A shaking table testing program was undertaken with the main objective of providing basic information for the calibration of analytical models, and procedures for determining seismic response of typical stone masonry temples of the 16–18th centuries stone masonry construction in Mexico. A typical colonial temple was chosen as a prototype. A model at a 1:8 geometric scale was built with the same materials and techniques as the prototype, and was subjected to horizontal and vertical motions of increasing intensities. The maximum applied intensity corresponded to a base shear force of about 58 of the total building weight. Vertical component of the base motion significantly affected the response and increased the damage of the model. Damage patterns were similar to those observed in actual temples. Damping coefficients of the response ranged from 7 for undamaged state, reached about 14 for severe damage.

The main features of the measured response were compared with those computed using a nonlinear, finite element model; for the latter, a constitutive law developed for plain concrete was adopted for reproducing cracking and crushing of the irregular stone masonry. Observed damage patterns as well as measured response could be reproduced with reasonable accuracy by the analytical simulation, except for some local vibrations, as those at the top of the bell towers. It can be concluded that the simple constitutive law adopted for the simulation was able to reproduce the experimental response with reasonable level of accuracy. Copyright © 2011 John Wiley & Sons, Ltd.

An analytical model, which aims at reproducing the response of a large-scale dynamic testing facility, that is a system composed of the specimen/shaking table/reaction-mass/airbags/dampers/soil is developed. The Lagrangian of the system is derived, under the assumption of large displacements and rotations. A set of four nonlinear differential equations is obtained and solved with numerical methods. Preliminary verifications of the derived model are carried out by reproducing both well-known results in the literature as well as those of a lumped model employed in the design of an existing dynamic testing facility. The case-study for validating the nonlinear equations of motion is the shaking table of the EUCENTRE Laboratory. Copyright © 2011 John Wiley & Sons, Ltd.

By means of a simplified three degrees of freedom model, seismic behavior of reinforced concrete bridge piers and foundations were evaluated based on pseudo-dynamic (PsD) tests for cases where pier strengthening and foundation strengthening are implemented. In addition, analysis based on PsD test results was conducted to investigate the influence of pier strengthening on seismic damage to the foundation. The PsD tests and the analysis show that the foundation suffers increased hysteretic response when pier strengthening is applied. The results also show that the foundation strengthening can prevent foundation damage. Copyright © 2011 John Wiley & Sons, Ltd.

A hybrid numerical and experimental simulation to collapse was conducted on a one-half scale moment-resisting frame building with two experimental substructures at different locations. An extensible hybrid test framework was used that adopts a generalized interface to encapsulate each numerical or tested substructure, through which only boundary displacements and forces are exchanged. Equilibrium and compatibility between substructures are enforced by an iterative quasi-Newton procedure, while adopting a predictor-and-corrector method to avoid loading reversals on physically tested substructures. To overcome difficulties in controlling stiff axial and rotational deformations at the boundaries, the flexible test scheme employs either open-loop or closed-loop control at the boundaries: enforcing either compatibility or equilibrium, or both requirements at critical boundaries. The effectiveness of the extensible framework and its capability to simulate structural behavior through collapse is demonstrated by a geographically distributed test that reproduced the collapse behavior of a four-story, two-bay, steel moment frame previously tested on an earthquake simulator. A comparison of both experiments highlights the viability of the hybrid test as an effective tool for the performance evaluation of structural systems from the onset of damage through collapse. Copyright © 2011 John Wiley & Sons, Ltd.

The results of experimental tests carried out on reinforced concrete (RC) full-scale 2-storey 2-bays framed buildings are presented. The unretrofitted frame was designed for gravity loads only and without seismic details; such frame was assumed as a benchmark system in this study. A similar RC frame was retrofitted with buckling-restrained braces (BRBs). The earthquake structural performance of both prototypes was investigated experimentally using displacement-controlled pushover static and cyclic lateral loads. Modal response properties of the prototypes were also determined before and after the occurrence of structural damage. The results of the dynamic response analyses were utilized to assess the existing design rules for the estimation of the elastic and inelastic period of vibrations. Similarly, the values of equivalent damping were compared with code-base relationships. It was found that the existing formulations need major revisions when they are used to predict the structural response of as-built RC framed buildings. The equivalent damping ratio ξ_eq was augmented by more than 50% when the BRBs was employed as bracing system. For the retrofitted frame, the overstrength Ω and the ductility µ are 1.6 and 4.1, respectively; the estimated R-factor is 6.5. The use of BRBs is thus a viable means to enhance efficiently the lateral stiffness and strength, the energy absorption and dissipation capacity of the existing RC substandard frame buildings. The foundation systems and the existing members of the superstructure are generally not overstressed as the seismic demand imposed on them can be controlled by the axial stiffness and the yielding force of the BRBs. Copyright © 2011 John Wiley & Sons, Ltd.

A method for generating an ensemble of orthogonal horizontal ground motion components with correlated parameters for specified earthquake and site characteristics is presented. The method employs a parameterized stochastic model that is based on a time-modulated filtered white-noise process with the filter having time-varying characteristics. Whereas the input white-noise excitation describes the stochastic nature of the ground motion, the forms of the modulating function and the filter and their parameters characterize the evolutionary intensity and nonstationary frequency content of the ground motion. The stochastic model is fitted to a database of recorded horizontal ground motion component pairs that are rotated into their principal axes, a set of orthogonal axes along which the components are statistically uncorrelated. Model parameters are identified for each ground motion component in the database. Using these data, predictive equations are developed for the model parameters in terms of earthquake and site characteristics and correlation coefficients between parameters of the two components are estimated. Given a design scenario specified in terms of earthquake and site characteristics, the results of this study allow one to generate realizations of correlated model parameters and use them along with simulated white-noise processes to generate synthetic pairs of horizontal ground motion components along the principal axes. The proposed simulation method does not require any seed recorded ground motion and is ideal for use in performance-based earthquake engineering. Copyright © 2011 John Wiley & Sons, Ltd.