Seismic assessment of existing unreinforced masonry buildings represents a current challenge in structural engineering. Many historical masonry buildings in earthquake regions were not designed to withstand seismic loading; thus, these structures often do not meet the basic safety requirements recommended by current seismic codes and need to be strengthened considering the results from realistic structural analysis. This paper presents an efficient modelling strategy for representing the nonlinear response of unreinforced masonry components under in-plane cyclic loading, which can be used for practical and accurate seismic assessment of masonry buildings. According to the proposed strategy, generic masonry perforated walls are modelled using an equivalent frame approach, where each masonry component is described utilising multi-spring nonlinear elements connected by rigid links. When modelling piers and spandrels, nonlinear springs are placed at the two ends of the masonry element for describing the flexural behaviour and in the middle for representing the response in shear. Specific hysteretic rules allowing for degradation of stiffness and strength are then used for modelling the member response under cyclic loading. The accuracy and the significant potential of the proposed modelling approach are shown in several numerical examples, including comparisons against experimental results and the nonlinear dynamic analysis of a building structure. Copyright © 2016 John Wiley & Sons, Ltd.

Integral abutment bridges (IABs) are jointless structures without bearings or expansion joints which require minimum or zero maintenance. The barrier to the application of long-span integral abutment bridges is the interaction of the abutment with the backfill soil during the thermal expansion and contraction of the bridge deck, that is, serviceability, or when the bridge is subjected to dynamic loads, such as earthquakes. The interaction of the bridge with the backfill leads to settlements and ratcheting of the soil behind the abutment and, as a result, the soil pressures acting on the abutment build up in the long term. This paper provides a solution for the aforementioned challenges by introducing a novel isolator that is a compressible inclusion of reused tyre-derived aggregates placed between the bridge abutment and the backfill. The compressibility of typical tyre-derived aggregates was measured by laboratory tests, and the compressible inclusion was designed accordingly. The compressible inclusion was then applied to a typical integral frame abutment model, which was subjected to static and dynamic loads representing in-service and seismic loads correspondingly. The response of both the conventional and the isolated abutment was assessed based on the settlements of the backfill, the soil pressures and the actions of the abutment. The study of the isolated abutment showed that the achieved decoupling of the abutment from the backfill soil results in significant reductions of the settlements of the backfill and of the pressures acting on the abutment. Hence, the proposed research enables extending the length limits of integral frame bridges subjected to earthquake excitations.

Several factors influence the behaviour of infilled frames, which have been a subject of research in the past with moderate success. The new generation of European design standards imposes the need to prevent brittle collapse of the infills and makes the structural engineer accountable for this requirement, yet it fails to provide sufficient information for masonry infills design. Therefore, the present work aims at understanding the seismic behaviour of masonry infill walls within reinforced concrete frames, using both unreinforced and reinforced solutions (bed joint reinforcement and reinforced plaster). For this purpose, three reinforced concrete buildings with different infill solutions were constructed at a scale of 1:1.5, all with the same geometry, and were tested on the shaking table of the National Laboratory for Civil Engineering, Portugal. All solutions performed adequately for the design earthquake, with no visible damage. Still, the experimental tests show that the double-leaf-unreinforced infill walls underperformed during a large earthquake, collapsing out of plane by rotating as rigid bodies with multiple configurations. Also the reinforced concrete buildings collapsed, because of the adverse interaction with the infill walls. The infill walls with bed joint reinforcement and reinforced plaster did not collapse out of plane, because of their connection to the concrete frame, which is an essential requirement. Copyright © 2016 John Wiley & Sons, Ltd.

This discussion deals with recommendations in the paper on appropriate damping formulations for use in nonlinear response history analysis of buildings. Concern over potentially excessive damping forces and moments should extend beyond the damping moments produced by the stiffness proportional part of Rayleigh damping that corresponds to rotational springs used to explicitly model plastic hinges. The key to an appropriate damping formulation for nonlinear analysis is a realistic mechanism that allows all damping forces and moments to be meaningfully assessed. Then features can be added to keep these forces and moments within reasonable bounds. Copyright © 2016 John Wiley & Sons, Ltd.

Reinforced concrete shear wall buildings have shown, in statistical terms, an adequate performance in past seismic events. However, a specific damage pattern was observed in 2010 Chile earthquake in some shear walls located in the lower building stories, usually associated with high axial stresses, lack of transverse reinforcement, and vertical irregularity. Results show that the nature of this failure led to a sudden degradation in strength and stiffness of walls and resulted in very limited ductility. This research aims to study analytically this damage pattern of shear wall buildings during the 2010 earthquake. By starting with two-dimensional inelastic pushover finite element models using diana, two walls that were severely damaged during the earthquake were studied in detail using different load patterns and stress–strain constitutive relationships for concrete in compression. These models were validated with experimental data of four reinforced concrete walls available in the literature. It can be shown that the geometry of the damage in the building walls cannot be correctly represented by conventional pushover load patterns that ignore the lateral and axial interaction. Indeed, the failure mechanism of walls shows strong coupling between lateral and vertical deformations within the plane of the wall. Results shown for a three-dimensional inelastic analysis of the building are consistent with these two-dimensional results, and predict a brittle failure of the structure. However, these models predict a large increase in axial load in the walls, which needs to be validated further with more experimental and analytical studies. Copyright © 2016 John Wiley & Sons, Ltd.

In many applications of seismic isolation, such as in high-rise construction, lightweight construction, and structures with large height-to-width aspect ratios, significant tension forces can develop in bearings, raising concerns about the possible rupture of elastomeric bearings and the uplift of sliding bearings. In this paper, a novel tension-resistant lead plug rubber bearing (TLRB) with improved tension-resisting capabilities is developed and experimentally and numerically assessed. This TLRB consists of a common lead plug rubber bearing (LRB) and several helical springs. After describing the theory underlying the behavior of the TLRB, the mechanical properties of reduced-scale prototype bearings are investigated through extensive horizontal and vertical loading tests. The test results indicate that TLRBs can improve the shear stiffness and tension resistance capacity even under significant tensile loads. A series of shaking table tests on scaled models of high-rise buildings with different aspect ratios were conducted to investigate the dynamic performance of the TLRB and the seismic responses of base-isolated high-rise buildings. Three different cases were considered in the shaking table tests: a fixed base condition and the use of TLRB and LRB isolation systems. The results of the shaking table test show that (a) base-isolated systems are effective in reducing the structural responses of high-rise buildings; (b) an isolated structure's aspect ratio is an important factor influencing its dynamic response; (c) TLRBs can endure large tensile stresses and avoid rupture on rubber bearings under strong earthquakes; and (d) the experimental and numerical results of the responses of the models show good agreement.

Recent improvements in performance-based earthquake engineering require realistic description of seismic demands and accurate estimation of supplied capacities in terms of both forces and deformations. Energy based approaches have a significant advantage in performance assessment because excitation and response durations, accordingly energy absorption and dissipation characteristics, are directly considered whereas force and displacement-based procedures are based only on the maximum response parameters. Energy-based procedures mainly consist of the prediction of earthquake input energy imposed on a structural system during an earthquake and energy dissipation performance of the structure.

The presented study focuses on the prediction of earthquake input energy. A large number of strong-ground motions have been collected from the Next Generation Attenuation (NGA) project database, and parametric studies have been conducted for considering the effects of soil type, epicentral distance, moment magnitude, and the fault type on input energy. Then prediction equations for input energy spectra, which are expressed in terms of the equivalent velocity (*V _{eq}*) spectra, are derived in terms of these parameters. Moreover, a scaling operation has been developed based on consistent relations between pseudo velocity (

This study proposes an improved energy-based approach for quantitative classification of velocity-pulse-like ground motions. The pulse amplitude is determined, in its value and in time location, by the amplitude of the half-cycle pulse having the largest seismic energy. After conducting statistical analyses, a newly-determined threshold level for selecting pulse-like ground motions is derived; and then what followed is a comparison analysis of three pulse-detecting schemes, one using the wavelet analysis, the other two using the energy concept. It is believed that other than providing a useful way of classifying pulse-like ground motions for structural demand analysis, knowledge of this work could also benefit the development of the ground motion prediction equations accounting for pulse effects, and further to aid the probabilistic seismic hazard analysis in a near-fault environment.

In this paper, vertical peak floor acceleration (*P**F**A*_{v}) demands on elastic multistory buildings are statistically evaluated using recorded ground motions. These demands are applicable to the assessment of nonstructural components that are rigid in the vertical direction and located at column lines or next to columns. Hence, *P**F**A*_{v} demands of the floor system away from column lines and their effects on nonstructural components are not addressed. This study is motivated by the questionable general assumption that typical buildings are considered to be relatively flexible in the horizontal (lateral) direction but relatively rigid in the vertical (longitudinal) direction. Consequently, only few papers address the evaluation of vertical component acceleration demands throughout a building, and there is no consensus on the relevance of vertical accelerations in buildings. The results presented in this study show that the vertical ground acceleration demands are amplified throughout the column line of a steel frame structure. This amplification is in many cases significant, depending on the vertical stiffness of the load-bearing system, damping ratio, and the location of the nonstructural component in the building. From these outcomes it can be concluded that the perception of a rigid-body response of the column lines in the vertical direction is highly questionable, and further research on this topic is required. Copyright © 2016 John Wiley & Sons, Ltd.

The paper presents the results of an investigation into the dispersion values, expressed in terms of limit-state spectral accelerations, which could be used for the pushover-based risk assessment of low-height to mid-height reinforced concrete frames and cantilever walls. The results of an extensive parametric study of a portfolio of test structures indicated that the dispersion values due to record-to-record variability and modelling uncertainty (*β*_{LS,RU}) are within the range from 0.3 to 0.55 for the near collapse limit state, and between 0.35 and 0.60 for the collapse limit state. The dispersions *β*_{LS,RU} proposed for the code-conforming and the majority of old (non code-conforming) frames are in between these values. On the other hand, the dispersions proposed for the old frames with a soft storey and an invariant plastic mechanism, and for the code-conforming cantilever walls, are at the lower and upper bounds of the presented values, respectively. The structural parameters that influence these dispersions were identified, and the influence of different ground motion sets, and of the models used for the calculation of the rotation capacities of the columns, on the calculated fragility parameters was examined and quantified. The proposed dispersion values were employed in a practice-oriented pushover-based method for the estimation of failure probability for eight selected examples. The pushover-based risk assessment method, although extremely simple and economical when compared with more rigorous probabilistic methods, was able to predict seismic risk with reasonable accuracy, thus showing it to be a practical tool for engineers.

Inter-story drift displacement data can provide useful information for story damage assessment. The authors' research group has developed photonic-based sensors for the direct measurement of inter-story drift displacements. This paper proposes a scheme for evaluating the degree of damage in a building structure based on drift displacement sensing. The scheme requires only measured inter-story drift displacements without any additional finite element analysis. A method for estimating yield drift deformation is proposed, and then, the degree of beam end damage is evaluated based on the plastic deformation ratios derived with the yield drift deformation values estimated by the proposed method. The validity and effectiveness of the presented scheme are demonstrated via experimental data from a large-scale shaking table test of a one-third-scale model of an 18-story steel building structure conducted at E-Defense.

This study proposes a new design method for an active mass damper (AMD) that is based on auto-regressive exogenous models of a building structure. The proposed method uses the results of system identification in the field of active structural control. The uncontrolled structure is identified as auto-regressive exogenous models via measurements under earthquake excitation and forced vibration. These models are linked with an equation of motion for the AMD to introduce a state equation and output equation for the AMD–structure interaction system in the discrete-time space; the equations apply modern control theories to the AMD design. In the numerical applications of a 10-degree-of-freedom building structure, linear quadratic regulator control is used to understand the fundamental characteristics of the proposed design procedure. The feedback control law requires the AMD's acceleration, velocity and stroke; the structure's acceleration; and the ground acceleration as vibration measurements. The numerical examples confirm the high applicability and control effectiveness of the proposed method. One remarkable advantage of the proposed method is that an equation of motion for the structure becomes unnecessary for designing controllers.

This study aims to develop a joint probability function of peak ground acceleration (PGA) and cumulative absolute velocity (CAV) for the strong ground motion data from Taiwan. First, a total of 40,385 earthquake time histories are collected from the Taiwan Strong Motion Instrumentation Program. Then, the copula approach is introduced and applied to model the joint probability distribution of PGA and CAV. Finally, the correlation results using the PGA-CAV empirical data and the normalized residuals are compared. The results indicate that there exists a strong positive correlation between PGA and CAV. For both the PGA and CAV empirical data and the normalized residuals, the multivariate lognormal distribution composed of two lognormal marginal distributions and the Gaussian copula provides adequate characterization of the PGA-CAV joint distribution observed in Taiwan. This finding demonstrates the validity of the conventional two-step approach for developing empirical ground motion prediction equations (GMPEs) of multiple ground motion parameters from the copula viewpoint.

This paper presents three-dimensional nonlinear dynamic analyses of a full-scale four-story steel building tested to collapse in 2007 at the E-Defense shake-table facility in Japan, using strong ground motion. Local buckling and consequent strength deterioration of all six columns at the first-story level were observed as the main reason for the building collapse. Fiber hinge element that consists of fibers discretizing the column cross section is used model each end of the column. It has zero length but considers finite yield-zone length for the fiber to simulate elastoplastic behavior and local buckling. Other parts of the building are modeled by standard column, beam, truss, and spring elements. Despite the unavoidable limitation of the parameters defining the fiber hinge element's properties that are empirically determined from the behavior of the cantilever column tested using an identical steel member, the analysis using the element appears to simulate well the column behavior because of the axial load and biaxial bending moment whose relative magnitudes differ considerably because of the locations. The analysis results indicate different deterioration patterns of the columns and effects of complex loading such as compression and tensile axial load applied alternately, additional high frequency axial load caused by vertical accelerations, and shifting of the principal directions of the bending moments cycle by cycle. Responses such as story drift, accelerations, base shear, and energy dissipation are also simulated well, and progress of local deterioration in the first-story columns and global soft-story mechanism is clarified by the analysis.

This paper presents applications of the modified 3D-SAM approach, a three-dimensional seismic assessment methodology for buildings directly based on *in situ* experimental modal tests to calculate global seismic demands and the dynamic amplification portion of natural torsion. Considering that the building modal properties change from weak to strong motion levels, appropriate modification factors are proposed to extend the application of the method to stronger earthquakes. The proposed approach is consistent with the performance-based seismic assessment approach, which entails the prediction of seismic displacements and drift ratios that are related to the damage condition and therefore the functionality of the building. The modified 3D-SAM is especially practical for structures that are expected to experience slight to moderate damage levels and in particular for post-disaster buildings that are expected to remain functional after an earthquake. In the last section of this paper, 16 low to mid-rise irregular buildings located in Montreal, Canada, and that have been tested under ambient vibrations are analyzed with the method, and the dynamic amplification portion of natural torsion of the dataset is reported and discussed. The proposed methodology is appropriate for large-scale assessments of existing buildings and is applicable to any seismic region of the world.

This paper presents a new analytical model for describing the large rocking response of an elastic multi-mass structure resting on ideally rigid ground. Using the experimental results from a rocking steel column, the ability of the proposed analytical model to estimate the rocking and translational acceleration response under free vibration, pulse and earthquake excitations is evaluated. It is observed that the classical treatment of impact may result in an unrealistically large transfer of energy to vibrations. Therefore a new Dirac-delta type impact model that spreads the effects of impact over time and space is proposed. The use of a Dirac-delta model and accurate restitution factors play a pivotal role in prediction of rocking and acceleration responses. In order to characterize the nonlinear response better, a modal analysis of the linearized system is proposed. With this approach, the vibration mode frequencies and shapes during rocking action were determined. A comparison of analytical and experimental modal estimations suggests good agreement. The results emphasize that the vibration characteristics of several vibration modes are affected by rocking action, and these modes may be excited at impact. Copyright © 2016 John Wiley & Sons, Ltd.

In this study, a constitutive model of high damping rubber bearings (HDRBs) is developed that allows the accurate representation of the force–displacement relationship including rate-dependence for shear deformation. The proposed constitutive model consists of two hyperelastic springs and a nonlinear dashpot element and expresses the finite deformation viscoelasticity laws based on the classical Zener model. The Fletcher–Gent effect, manifested as high horizontal stiffness at small strains and caused by the carbon fillers in HDRBs, is accurately expressed through an additional stiffness correction factor *α* in the novel strain energy function. Several material parameters are used to simulate the responses of high damping rubber at various strain levels, and a nonlinear viscosity coefficient *η* is introduced to characterize the rate-dependent property. A parameter identification scheme is applied to the results of the multi-step relaxation tests and the cyclic shear tests, and a three-dimensional function of the nonlinear viscosity coefficient *η* with respect to the strain, and strain rate is thus obtained. Finally, to investigate the accuracy and feasibility of the proposed model for application to the seismic response assessment of bridges equipped with HDRBs, an improved real-time hybrid simulation (RTHS) test system based on the velocity loading method is developed. A single-column bridge was used as a test bed and HDRBs was physically tested. Comparing the numerical and RTHS results, advantage of the proposed model in the accuracy of the predicted seismic response over comparable hysteretic models is demonstrated.

This paper deals with the use, for seismic applications, of a Maxwell element in parallel with a low damping isolator. The study of the properties of the frequency response function shows that this isolator is capable to reduce the base displacement of isolated structures with no considerable amplification of the non-isolated modes. This is, also, confirmed by the floor response spectra under earthquake excitations. Hence, the previously mentioned isolator does not present the drawbacks met when base displacement is reduced by increasing damping. Moreover, it seems that its performance is comparable with that of more elaborated and expensive techniques combining passive and semi-active devices.

Automatic seismic shutoff devices are used to reduce the risk to gas and liquid distribution systems from earthquakes. In the USA, the gas shutoff devices are tested and certified according to the American Society of Civil Engineers' Standard ASCE 25. During tests, devices are shaken by simple harmonic (sinusoidal) motions of different frequencies and checked for actuation. Because earthquake motions are not sinusoidal, the amplitude of earthquake motions that will actuate these devices is not clearly understood. This paper determines the probability of actuating devices by earthquake motions of different amplitudes. The probability of actuation increases with increase in the resultant peak horizontal ground acceleration (PGA). The probability of actuation is 50% for PGA = 0.23*g* and 90% for PGA = 0.31*g*, where *g* = 9.81 m/s^{2} = acceleration due to gravity. On a ‘stiff soil’ site in San Francisco, CA, the mean recurrence interval of actuation is 51 years. On a similar site in Boston, MA, the mean recurrence interval of actuation is 3000 years. ASCE 25 compliant devices are actuated by high frequencies in ground motions. There is greater uncertainty in the actuation of these devices by ground motions that are damaging to very flexible systems.

Current models describing the behavior for the triple friction pendulum (TFP) bearing are based on the assumption that the resultant force of the contact pressure acts at the center of each sliding surface. Accordingly, these models only rely on equilibrium in the horizontal direction to arrive at the equations describing its behavior. This is sufficient for most practical applications where certain constraints on the friction coefficient values apply as a direct consequence of equilibrium.

This paper presents a revised model of behavior of the TFP bearing in which no assumptions are made on the location of the resultant forces at each sliding surface and no constraints on the values of the coefficient of friction are required, provided that all sliding surfaces are in full contact. To accomplish this, the number of degrees of freedom describing the behavior of the bearing is increased to include the location of the resultant force at each sliding surface and equations of moment equilibrium are introduced to relate these degrees of freedom to forces. Moreover, the inertia effects of each of the moving parts of the bearing are accounted for in the derivation of the equations describing its behavior.

The model explicitly calculates the motion of each of the components of friction pendulum bearings so that any dependence of the coefficient of friction on the sliding velocity and temperature can be explicitly accounted for and calculations of heat flux and temperature increase at each sliding surface can be made. This paper presents (a) the development of the revised TFP bearing model, (b) the analytic solution for the force–displacement relations of two configurations of the TFP bearing, (c) a model that incorporates inertia effects of the TFP bearing components and other effects that are useful in advanced response history analysis, and (d) examples of implementation of the features of the presented model. Copyright © 2016 John Wiley & Sons, Ltd.

A series of seismic tests were conducted on a 1½-bay by 1½-story special steel moment-resisting frame subassembly from the onset of damage through incipient collapse. These tests were conducted using hybrid simulation with substructuring as a mean to demonstrate efficient testing methods for system-level collapse assessment of large-scale structural subassemblies. The ½-scale specimen was designed to capture the behavior and interactions of beams, columns, panel zones, and composite floor slab. The experimental test setup permitted the application of lateral as well as varying vertical forces on the test specimen while maintaining realistic boundary conditions on the subassembly. With the overarching objective to advance knowledge on the collapse assessment of frame structures under earthquake loading, this paper focuses on the seismic performance of a steel moment-resisting frame through collapse. The failure mechanisms of the test frame are described and compared with numerical simulations based on state-of-the-art modeling approaches.

Reinforced concrete structures that lack proper seismic detailing commonly have increased vulnerability to collapse during strong earthquake shaking. A major contributor to building collapse vulnerability is the prevalence of columns with widely spaced and poorly configured transverse reinforcement. Such columns are susceptible to shear failures, which can lead to axial failures and local or global building collapse. This study presents a laboratory test program that was designed to gain insight into the effects of column detailing on the dynamic response including collapse of concrete frames. Twelve concrete frames were tested on a shaking table and were subjected to two types of ground motions: one relatively short-duration motion with strong velocity pulse and one relatively long-duration motion with multiple cycles. The study also evaluates the effectiveness of modern analytical methods to simulate the nonlinear dynamic response of concrete structures. Two lumped plasticity models employing nonlinear rotational and shear springs at the column ends were used to simulate the collapse response of the tested specimens.

The study demonstrates that modern analytical techniques can simulate reliably the nonlinear dynamic response of concrete structures in the post-yielding stage and can identify the onset of shear failure and collapse of concrete frames. However, in the majority of cases, the analytical models overestimated the effects of damage accumulation, especially for long-duration motions. Response predictions were improved by adjusting the damage modeling parameters.

In this paper, the effectiveness of different design solutions for tuned mass dampers (TMD) applied to high-rise cross-laminated (X-Lam) timber buildings as a means to reduce the seismic accelerations was investigated. A seven-storey full-scale structure previously tested on shaking table was used as a reference. The optimal design parameters of the TMDs, i.e. damping and frequency ratios, were determined by using a genetic algorithm on a simplified model of the reference structure, composed by seven masses each representing one storey. The optimal solutions for the TMDs were then applied to a detailed finite element model of the seven-storey building, where the timber panels were modelled with shell elements and the steel connectors with linear spring. By comparing the numerical results of the building with and without multiple TMDs, the improvement in seismic response was assessed. Dynamic time-history analyses were carried out for a set of seven natural records, selected in accordance with Eurocode 8, on the simplified model, and for Kobe earthquake ground motion on the detailed model. Results in terms of acceleration reduction for different TMD configurations show that the behaviour of the seven-storey timber building can be significantly improved, especially at the upper storeys. Copyright © 2016 John Wiley & Sons, Ltd.

Steel-concrete composite moment frames have been shown to be an effective alternative for use as the primary seismic force-resisting system of building structures. However, little data are available to justify the structural system performance factors (i.e., *R*, *C _{d}*, and Ω

Robust estimation of collapse risk should consider the uncertainty in modeling of structures as well as variability in earthquake ground motions. In this paper, we illustrate incorporation of the uncertainty in structural model parameters in nonlinear dynamic analyses to probabilistically assess story drifts and collapse risk of buildings. Monte Carlo simulations with Latin hypercube sampling are performed on ductile and non-ductile reinforced concrete building archetypes to quantify the influence of modeling uncertainties and how it is affected by the ductility and collapse modes of the structures. Inclusion of modeling uncertainty is shown to increase the mean annual frequency of collapse by approximately 1.8 times, as compared with analyses neglecting modeling uncertainty, for a high-seismic site. Modeling uncertainty has a smaller effect on drift demands at levels usually considered in building codes; for the same buildings, modeling uncertainty increases the mean annual frequency of exceeding story drift ratios of 0.03 by 1.2 times. A novel method is introduced to relate drift demands at maximum considered earthquake intensities to collapse safety through a joint distribution of deformation demand and capacity. This framework enables linking seismic performance goals specified in building codes to drift limits and other acceptance criteria. The distributions of drift demand at maximum considered earthquake and capacity of selected archetype structures enable comparisons with the proposed seismic criteria for the next edition (2016) of ASCE 7. Subject to the scope of our study, the proposed drift limits are found to be unconservative, relative to the target collapse safety in ASCE 7. Copyright © 2016 John Wiley & Sons, Ltd.

This paper examines various parameters that provide a measure of spectral shape and studies how they relate to the potential of ground motion records to cause the collapse of a given structure. It is shown that when measuring the ground motion intensity by the spectral acceleration at the first-mode period of the structure, *Sa*(*T _{1}*), records causing collapse at low ground motion intensities typically have significantly different spectral shapes than those that do not cause collapse until much higher ground motion intensities. A spectral shape typical of damaging records is identified, and a metric for quantifying the spectral shape of a record called

The seismic performance of three- and six-story buildings with fluidic self-centering system is probabilistically assessed. The fluidic self-centering systems consist of devices that are based on the technology of fluid viscous dampers but built in a way that pressurization of the devices results in preload that is explored to reduce or eliminate residual drift. The design of these buildings followed a procedure that parallels the design for structures with damping systems in ASCE 7 but modified to include the preload effect. Reference conventional buildings were also designed per ASCE 7 for comparison. These buildings were then analyzed to examine and compare their seismic collapse resistance and residual drift, where the residual drift limits of 0.2, 0.5, 1.0 and 2.0% of story height were selected as important thresholds. The study further calculated the mean annual frequency of collapse and corresponding exceedance probability over 50 years, and the mean annual frequency of exceeding the threshold residual story drift limits and the corresponding exceedance probability over 50 years. Variations in the design procedures by considering increased displacement capacity or damping or preload of the devices, different types of damping, increased ultimate strength of the self-centering device–brace systems and increased frame strength were considered. It was found that increasing either the ultimate force capacity of the self-centering device–brace system or the frame strength results in important improvements in the collapse resistance and in minimizing residual drift, whereas the variation of other design parameters has minor effects. Copyright © 2016 John Wiley & Sons, Ltd.

State-of-the-art methods for the assessment of building fragility consider the structural capacity and seismic demand variability in the estimation of the probability of exceeding different damage states. However, questions remain regarding the appropriate treatment of such sources of uncertainty from a statistical significance perspective. In this study, material, geometrical and mechanical properties of a number of building classes are simulated by means of a Monte Carlo sampling process in which the statistical distribution of the aforementioned parameters is taken into consideration. Record selection is performed in accordance with hazard-consistent distributions of a comprehensive set of intensity measures, and issues related with *sufficiency*, *efficiency*, *predictability* and *scaling robustness* are addressed. Based on the appraised minimum number of ground motion records required to achieve statistically meaningful estimates of response variability conditioned on different levels of seismic intensity, the concept of *conditional fragility functions* is presented. These functions translate the probability of exceeding a set of damage states as a function of a secondary *sufficient* intensity measure, when records are selected and scaled for a particular level of primary seismic intensity parameter. It is demonstrated that this process allows a hazard-consistent and statistically meaningful representation of uncertainty and correlation in the estimation of intensity-dependent damage exceedance probabilities. Copyright © 2016 John Wiley & Sons, Ltd.

Viscoelastic–plastic (VEP) dampers are hybrid passive damping devices that combine the advantages of viscoelastic and hysteretic damping. This paper first formulates a semi-analytical procedure for predicting the peak response of nonlinear SDOF systems equipped with VEP dampers, which forms the basis for the generation of Performance Spectra that can then be used for direct performance assessment and optimization of VEP damped structures. This procedure is first verified against extensive nonlinear time-history analyses based on a Kelvin viscoelastic model of the dampers, and then against a more advanced evolutionary model that is calibrated to characterization tests of VEP damper specimens built from commercially available viscoelastic damping devices, and an adjustable friction device. The results show that the proposed procedure is sufficiently accurate for predicting the response of VEP systems without iterative dynamic analysis for preliminary design purposes. A design method based on the Performance Spectra framework is then proposed for systems equipped with passive VEP dampers and is applied to enhance the seismic response of a six-storey steel moment frame. The numerical simulation results on the damped structure confirm the use of the Performance Spectra as a convenient and accurate platform for the optimization of VEP systems, particularly during the initial design stage. Copyright © 2016 John Wiley & Sons, Ltd.

One of the key limit states of buckling-restrained braces (BRBs) is global flexural buckling including the effects of the connections. The authors have previously proposed a unified explicit equation set for controlling the out-of-plane stability of BRBs based on bending-moment transfer capacity at the restrainer ends. The proposed equation set is capable of estimating BRB stability for various connection stiffnesses, including initial out-of-plane drift effects. However, it is only valid for symmetrical end conditions, limiting application to the single diagonal configuration. In the chevron configuration, the out-of-plane stiffness in the two ends differs because of the rotation of the attached beam. In this study, the equation set is extended to BRBs with asymmetric end conditions, such as the chevron configuration. Cyclic loading tests of the chevron configuration with initial out-of-plane drifts are conducted, and the results are compared with the proposed equation set, which is formulated as a function of the normalized stiffness of the attached beam. © 2016 The Authors. Earthquake Engineering & Structural Dynamics published by John Wiley & Sons Ltd.

Reinforced concrete shear walls are used because they provide high lateral stiffness and resistance to extreme seismic loads. However, with the increase in building height, these walls have become slenderer and hence responsible of carrying larger axial and shear loads. Because 2D/3D finite element inelastic models for walls are still complex and computationally demanding, simplified but accurate and efficient fiber element models are necessary to quickly assess the expected seismic performance of these buildings. A classic fiber element model is modified herein to produce objective results under particular loading conditions of the walls, that is, high axial loads, low axial loads, and nearly constant bending moment. To make it more widely applicable, a shear model based on the modified compression field theory was added to this fiber element. Consequently, this paper shows the formulation of the proposed element and its validation with different experimental results of cyclic tests reported in the literature. It was found that in order to get objective responses in the element, the regularization techniques based on fracture energy had to be modified, and nonlinearities because of buckling and fracture of steel bars, concrete crushing, and strain penetration effects were needed to replicate the experimental cyclic behavior. Thus, even under the assumption of plane sections, which makes the element simple and computationally efficient, the proposed element was able to reproduce the experimental data, and therefore, it can be used to estimate the seismic performance of walls in reinforced concrete buildings. Copyright © 2016 John Wiley & Sons, Ltd.

Nonlinear static procedures, which relate the seismic demand of a structure to that of an equivalent single-degree-of-freedom oscillator, are well-established tools in the performance-based earthquake engineering paradigm. Initially, such procedures made recourse to inelastic spectra derived for simple elastic–plastic bilinear oscillators, but the request for demand estimates that delve deeper into the inelastic range, motivated investigating the seismic demand of oscillators with more complex backbone curves. Meanwhile, near-source (NS) pulse-like ground motions have been receiving increased attention, because they can induce a distinctive type of inelastic demand. Pulse-like NS ground motions are usually the result of rupture directivity, where seismic waves generated at different points along the rupture front arrive at a site at the same time, leading to a double-sided velocity pulse, which delivers most of the seismic energy. Recent research has led to a methodology for incorporating this NS effect in the implementation of nonlinear static procedures. Both of the previously mentioned lines of research motivate the present study on the ductility demands imposed by pulse-like NS ground motions on oscillators that feature pinching hysteretic behaviour with trilinear backbone curves. Incremental dynamic analysis is used considering 130 pulse-like-identified ground motions. Median, 16% and 84% fractile incremental dynamic analysis curves are calculated and fitted by an analytical model. Least-squares estimates are obtained for the model parameters, which importantly include pulse period T_{p}. The resulting equations effectively constitute an R − μ − T − T_{p} relation for pulse-like NS motions. Potential applications of this result towards estimation of NS seismic demand are also briefly discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Beam–column sub-assemblages are the one of the most vulnerable structural elements to the seismic loading and may lead to devastating consequences. In order to improve the performance of the poorly/under-designed building structures to the critical loading scenarios, introduction of steel bracing at the RC beam–column joint is found to be one of the modern and implementable techniques. In the present work, a diagonal metallic single haunch/bracing system is introduced at the beam–column joints to provide an alternate load path and to protect the joint zone from extensive damage because of brittle shear failure. In this paper, an investigation is reported on the evaluation of tae influence of different parameters, such as angle of inclination, location of bracing and axial stiffness of the single steel bracing on improving the performance through altering the force transfer mechanism. Numerical investigations on the performance of the beam–column sub-assemblages have been carried out under cyclic loading using non-linear finite element analysis. Experimentally validated numerical models (both GLD and upgraded specimen) have been further used for evaluating the performance of various upgrade schemes. Cyclic behaviour of reinforcement, concrete modelling based on fracture energy, bond-slip relations between concrete and steel reinforcement have been incorporated. The study also includes the numerical investigation of crack and failure patterns, ultimate load carrying capacity, load displacement hysteresis, energy dissipation and ductility. The findings of the present study would be helpful to the engineers to develop suitable, feasible and efficient upgrade schemes for poorly designed structures under seismic loading. Copyright © 2016 John Wiley & Sons, Ltd.

There has been a significant increase in the size of building structures in recent years. Huge structures such as high-rise buildings and large-domed stadiums require high-performance structural control, including the use of high-capacity dampers, especially in an earthquake-prone country like Japan. The objective of the present study was the enhancement of both human and structural safety in such structures through the development of a rate-dependent type of damper with a high damping capacity. Among the various available types of rate-dependent dampers, the authors focused on the oil damper owing to its stable performance against long-duration vibrations. The target maximum damping force was 6000 kN, which is higher than that of any existing oil damper utilized in building structures. The authors developed a novel concept for achieving this high capacity while maintaining the size of the damper within acceptable dimensions from an architectural point of view. The concept involves the use of multiple damper units that produce mechanically parallel damping forces spatially arranged in series. As a prototype, a 1500-kN oil damper was fabricated by combining three 500-kN dampers. The 1500-kN prototype damper was conceived as a full-scale prototype of a damper that is more slender than comparable commercially available dampers in Japan, and as a scaled model of the proposed 6000-kN damper.

Sinusoidal loading tests were conducted on the prototype damper using a frequency range of 0.1–1.5 Hz and a velocity range of 0.4–300 mm/s. The results confirmed that the damper produced the design damping forces. The results of earthquake loading tests also revealed that the damper exerted a stable damping force against a large earthquake and maintained its performance after the earthquake. The damper is particularly effective against earthquakes with long-period components that could increase the temperature of a damper. This is afforded by its high heat capacity compared to conventional dampers.

Considering that the proposed 6000-kN damper will generate a damping force that is about 2–3 times that of the strongest conventional oil damper, existing manufacturer test machines would be inadequate for evaluating its full performance characteristics. To address this issue, the authors also propose a test method for evaluating the overall damping force. The method is premised on the fact that the characteristic feature of the proposed damper is its combination of multiple damper units. The overall performance is thus evaluated using the test results for the individual damper units while the other dampers are bypassed. This method was verified by the results of the abovementioned sinusoidal loading tests, with the error for the 1500-kN prototype damper found to be less than 5%. Copyright © 2016 John Wiley & Sons, Ltd.

Yield frequency spectra (YFS) are introduced to enable the direct design of a structure subject to a set of seismic performance objectives. YFS offer a unique view of the entire solution space for structural performance. This is portrayed in terms of the mean annual frequency (MAF) of exceeding arbitrary ductility (or displacement) thresholds, versus the base shear strength of a structural system having specified yield displacement and capacity curve shape. YFS can be computed nearly instantaneously using publicly available software or closed-form solutions, for any system whose response can be satisfactorily approximated by an equivalent nonlinear single-degree-of-freedom oscillator. Because the yield displacement typically is a more stable parameter for performance-based seismic design compared with the period, the YFS format is especially useful for design. Performance objectives stated in terms of the MAF of exceeding specified ductility (or displacement) thresholds are used to determine the lateral strength that governs the design of the structure. Both aleatory and epistemic uncertainties are considered, the latter at user-selected confidence levels that can inject the desired conservatism in protecting against different failure modes. Near-optimal values of design parameters can be determined in many cases in a single step. Copyright © 2016 John Wiley & Sons, Ltd.

The reinforced concrete frame-core tube structure is a common form of high-rise building; however, certain vertical components of these structures are prone to be damaged by earthquakes, debris flow, or other accidents, leaving no time for repair or retrofit. This study is motivated by a practical problem—that is, the seismic vulnerability and collapse resistant capability under future earthquakes when a vertical member has failed. A reduced scale model (1:15 scale) of a typical reinforced concrete frame-core tube with a corner column removed from the first floor is designed, fabricated, and tested. The corner column is replaced by a jack, and the failure behavior is simulated by manually unloading the jack. The model is then excited by a variety of seismic ground motions on the shaking table. Experimental results concerning the seismic responses and actual process of collapse are presented herein. Finally, the earthquake-induced collapse process is simulated numerically using the software program ANSYS/LS-DYNA. Validation and calibration of the model are carried out by comparison with the experimental results. Furthermore, based on both experimental investigations and numerical simulations, the collapse mechanism is discussed, and some suggestions on collapse design are put forward. Copyright © 2016 John Wiley & Sons, Ltd.

Earthquake-induced pounding of adjacent structures can cause severe structural damage, and advanced probabilistic approaches are needed to obtain a reliable estimate of the risk of impact. This study aims to develop an efficient and accurate probabilistic seismic demand model (PSDM) for pounding risk assessment between adjacent buildings, which is suitable for use within modern performance-based engineering frameworks. In developing a PSDM, different choices can be made regarding the intensity measures (*IM*s) to be used, the record selection, the analysis technique applied for estimating the system response at increasing *IM* levels, and the model to be employed for describing the response statistics given the *IM*. In the present paper, some of these choices are analyzed and evaluated first by performing an extensive parametric study for the adjacent buildings modeled as linear single-degree-of-freedom systems, and successively by considering more complex nonlinear multi-degree-of-freedom building models. An efficient and accurate PSDM is defined using advanced intensity measures and a bilinear regression model for the response samples obtained by cloud analysis. The results of the study demonstrate that the proposed PSDM allows accurate estimates of the risk of pounding to be obtained while limiting the number of simulations required. Copyright © 2016 John Wiley & Sons, Ltd.

A refined substructure technique in the frequency domain is developed, which permits consideration of the interaction effects among adjacent containers through the supporting deformable soil medium. The tank-liquid systems are represented by means of mechanical models, whereas discrete springs and dashpots stand for the soil beneath the foundations. The proposed model is employed to assess the responses of adjacent circular, cylindrical tanks for harmonic and seismic excitations over wide range of tank proportions and soil conditions. The influence of the number, spatial arrangement of the containers and their distance on the overall system's behavior is addressed. The results indicate that the cross-interaction effects can substantially alter the impulsive components of response of each individual element in a tank farm. The degree of this impact is primarily controlled by the tank proportions and the proximity of the predominant natural frequencies of the shell-liquid-soil systems and the input seismic motion. The group effects should be not a priori disregarded, unless the tanks are founded on shallow soil deposit overlying very stiff material or bedrock. Copyright © 2016 John Wiley & Sons, Ltd.

A three-dimensional beam–truss model (BTM) for reinforced concrete (RC) walls that explicitly models flexure–shear interaction and accurately captures diagonal shear failures was presented in the first part of this two-paper series. This paper extends the BTM to simulate RC slabs and coupled RC walls through slabs and beams. The inclination angle of the diagonal elements for coupled RC walls is determined, accounting for the geometry of the walls and the level of coupling. Two case studies validate the model: (1) a two-bay slab–column specimen experimentally tested using cyclic static loading and (2) a five-story coupled T-wall–beam–slab specimen subjected to biaxial shake table excitation. The numerically computed lateral force–lateral displacement and strain contours are compared with the experimentally measured response and observed damage. The five-story specimen is characterized by diagonal shear failure at the bottom story of the walls, which is captured by the BTM. The BTM of the five-story specimen is used to study the effects of coupling on shear demand for lightly reinforced RC coupled walls. The effect of mesh refinement and bar fracture of non-ductile transverse reinforcement is studied.

A three-dimensional beam-truss model for reinforced concrete (RC) walls developed by the first two authors in a previous study is modified to better represent the flexure–shear interaction and more accurately capture diagonal shear failures under static cyclic or dynamic loading. The modifications pertain to the element formulations and the determination of the inclination angle of the diagonal elements. The modified beam-truss model is validated using the experimental test data of eight RC walls subjected to static cyclic loading, including two non-planar RC walls under multiaxial cyclic loading. Five of the walls considered experienced diagonal shear failure after reaching their flexural strength, while the other three walls had a flexure-dominated response. The numerically computed lateral force–lateral displacement and strain contours are compared with the experimentally recorded response and damage patterns for the walls. The effects of different model parameters on the computed results are examined by means of parametric analyses. Extension of the model to simulate RC slabs and coupled RC walls is presented in a companion paper. Copyright © 2016 John Wiley & Sons, Ltd.

This paper presents the development of a deformable connection that is used to connect each floor system of the flexible gravity load resisting system (GLRS) with the stiff lateral force resisting system (LFRS) of an earthquake-resistant building. It is shown that the deformable connection acts as a seismic response modification device, which limits the lateral forces transferred from each floor to the LFRS and allows relative motion between the GLRS and LFRS. In addition, the floor accelerations and the LFRS story shears related to the higher-mode responses are reduced. The dispersion of peak responses is also significantly reduced. Numerical simulations of the earthquake response of a 12-story reinforced concrete shear wall example building with deformable connections are used to define an approximate feasible design space for the deformable connection. The responses of the example building model with deformable connections and the example building model with rigid-elastic connections are compared. Two configurations of the deformable connection are studied. In one configuration, a buckling restrained brace is used as the limited-strength load-carrying hysteretic component of the deformable connection, and in the other configuration, a friction device is used. Low damping laminated rubber bearings are used in both configurations to ensure the out-of-plane stability of the LFRS and to provide post-elastic stiffness to the deformable connection. Important experimental results from full-scale tests of the deformable connections are presented and used to calibrate numerical models of the connections. Copyright © 2016 John Wiley & Sons, Ltd.

In this paper the effect of causal parameter bounds (e.g. magnitude, source-to-site distance, and site condition) on ground motion selection, based on probabilistic seismic hazard analysis (PSHA) results, is investigated. Despite the prevalent application of causal parameter bounds in ground motion selection, present literature on the topic is cast in the context of a scenario earthquake of interest, and thus specific bounds for use in ground motion selection based on PSHA, and the implications of such bounds, is yet to be examined. Thirty-six PSHA cases, which cover a wide range of causal rupture deaggregation distributions and site conditions, are considered to empirically investigate the effects of various causal parameter bounds on the characteristics of selected ground motions based on the generalized conditional intensity measure (GCIM) approach. It is demonstrated that the application of relatively ‘wide’ bounds on causal parameters effectively removes ground motions with drastically different characteristics with respect to the target seismic hazard and results in an improved representation of the target causal parameters. In contrast, the use of excessively ‘narrow’ bounds can lead to ground motion ensembles with a poor representation of the target intensity measure distributions, typically as a result of an insufficient number of prospective ground motions. Quantitative criteria for specifying bounds for general PSHA cases are provided, which are expected to be sufficient in the majority of problems encountered in ground motion selection for seismic demand analyses. Copyright © 2016 John Wiley & Sons, Ltd.

The potential of post-tensioned self-centering moment-resisting frames (SC-MRFs) and viscous dampers to reduce the economic seismic losses in steel buildings is evaluated. The evaluation is based on a prototype steel building designed using four different seismic-resistant frames: (i) conventional moment resisting frames (MRFs); (ii) MRFs with viscous dampers; (iii) SC-MRFs; or (iv) SC-MRFs with viscous dampers. All frames are designed according to Eurocode 8 and have the same column/beam cross sections and similar periods of vibration. Viscous dampers are designed to reduce the peak story drift under the design basis earthquake (DBE) from 1.8% to 1.2%. Losses are estimated by developing vulnerability functions according to the FEMA P-58 methodology, which considers uncertainties in earthquake ground motion, structural response, and repair costs. Both the probability of collapse and the probability of demolition because of excessive residual story drifts are taken into account. Incremental dynamic analyses are conducted using models capable to simulate all limit states up to collapse. A parametric study on the effect of the residual story drift threshold beyond which is less expensive to rebuild a structure than to repair is also conducted. It is shown that viscous dampers are more effective than post-tensioning for seismic intensities equal or lower than the maximum considered earthquake (MCE). Post-tensioning is effective in reducing repair costs only for seismic intensities higher than the DBE. The paper also highlights the effectiveness of combining post-tensioning and supplemental viscous damping by showing that the SC-MRF with viscous dampers achieves significant repair cost reductions compared to the conventional MRF. Copyright © 2016 John Wiley & Sons, Ltd.

Risk-based seismic design, as introduced in this paper, involves the use of different types of analysis in order to satisfy a risk-based performance objective with a reasonable utilization rate and sufficient reliability. Differentiation of the reliability of design can be achieved by defining different design algorithms depending on the importance of a structure. In general, the proposed design is iterative, where the adjustment of a structure during iterations is the most challenging task. Rather than using automated design algorithms, an attempt has been made to introduce three simple guidelines for adjusting reinforced concrete frames in order to increase their strength and deformation capacity. It is shown that an engineer can design a reinforced concrete frame in a few iterations, for example, by adjusting the structure on the basis of pushover analysis and checking the final design by means of nonlinear dynamic analysis. A possible variant of the risk-based design algorithm for the collapse safety of reinforced concrete frame buildings is proposed, and its application is demonstrated by means of an example of an eight-storey reinforced concrete building. Four iterations were required in order to achieve the risk-based performance objective with a reasonable utilization rate. Copyright © 2016 John Wiley & Sons, Ltd.

Residual displacements of single-degree-of-freedom systems due to ground motions with velocity pulses or fling step displacements are presented as a function of period *T* and of its ratio to the pulse period *T*_{p}. Four hysteretic behaviors are considered: bilinear elastoplastic, stiffness-degrading with cycling, stiffness-cum-strength degrading, with or without pinching. When expressed in terms of *T*/*T*_{p}, peak inelastic and residual displacements due to motions with a pulse or fling appear similar to those due to far-fault motions, if the response to far-field records are expressed in terms of the ratio of *T* to the record's characteristic period. However, as the latter is usually much shorter than the pulse period of motions with fling, the range of periods of interest for common structures becomes a short-period range under fling motions and exhibits very large amplification of residual and peak inelastic displacements. Similar, but less acute, are the effects of motions with a velocity pulse. Wavelets of different complexity are studied as approximations to near-fault records. Simple two-parameter wavelets for fling motions overestimate peak inelastic displacements; those for pulse-type motions overestimate residual displacements. A more complex four-parameter wavelet for motions with a velocity pulse predicts overall well residual and peak displacements due to either pulse- or fling-type motions; a hard-to-identify parameter of the wavelet impacts little computed residual displacements; another significantly affects them and should be carefully estimated from the record. Even this most successful of wavelets overpredicts residual displacements for the periods of engineering interest. Copyright © 2016 John Wiley & Sons, Ltd.

This paper describes the results of an experimental and numerical study that focused on multi-directional behavior of unreinforced masonry walls and established the requisite of the related proposed design equations. The tests were conducted following several sets of multi-directional loading combinations imposed on the top plane of the wall along with considering monotonic and cyclic quasi-static loading protocols. Various boundary conditions, representing possible wall–roof connections, were also considered for different walls to investigate the influence of rotation of the top plane of the wall on the failure modes. The results of the tests were recorded with a host of high precision data acquisition systems, showing three-dimensional displacements of a grid on the surface of the wall. Finite element models of the walls are developed using the commercial software package ABAQUS/Explicit compiled with a FORTRAN subroutine (VUMAT) written by the authors. The experimental results were then used to validate the finite element models and the developed user-defined material models. With the utility of validated models, a parametric study was performed on a set of parameters with dominant influence on the behavior of the wall system under in-plane and out-of-plane loading combinations. The experimental and numerical results are finally used to investigate the adequacy of ASCE 41 empirical equations, and some insights and recommendations are made. Copyright © 2016 John Wiley & Sons, Ltd.

Real-time hybrid simulation (RTHS) is a powerful cyber-physical technique that is a relatively cost-effective method to perform global/local system evaluation of structural systems. A major factor that determines the ability of an RTHS to represent true system-level behavior is the fidelity of the numerical substructure. While the use of higher-order models increases fidelity of the simulation, it also increases the demand for computational resources. Because RTHS is executed at real-time, in a conventional RTHS configuration, this increase in computational resources may limit the achievable sampling frequencies and/or introduce delays that can degrade its stability and performance. In this study, the Adaptive Multi-rate Interface rate-transitioning and compensation technique is developed to enable the use of more complex numerical models. Such a multi-rate RTHS is strictly executed at real-time, although it employs different time steps in the numerical and the physical substructures while including rate-transitioning to link the components appropriately. Typically, a higher-order numerical substructure model is solved at larger time intervals, and is coupled with a physical substructure that is driven at smaller time intervals for actuator control purposes. Through a series of simulations, the performance of the AMRI and several existing approaches for multi-rate RTHS is compared. It is noted that compared with existing methods, AMRI leads to a smaller error, especially at higher ratios of sampling frequency between the numerical and physical substructures and for input signals with high-frequency content. Further, it does not induce signal chattering at the coupling frequency. The effectiveness of AMRI is also verified experimentally. Copyright © 2016 John Wiley & Sons, Ltd.

No abstract is available for this article.

]]>The vulnerability of infilled frames represents a critical issue in many regions with high seismicity around the world where infills are typically made of heavy masonry as they are used for thermal control of the buildings because of their thermal inertia. In this context, the use of earthen masonry infills can give a superior performance because of their ability to regulate thermal-hygrometric performance of the building and sustainability of its life-cycle.

This paper presents a numerical study on the seismic behaviour of infill walls made of earthen masonry and partitioned with horizontal wooden planks that allow the relative sliding of the partitions. The combination of the deformability of earthen masonry and the sliding mechanism occurring along the wooden planks gives a high ductility capacity to the in-plane response of the infill and, at the same time, significantly reduces its stiffness and strength, as compared with traditional solid infills made of fired clay units. As a result, the detrimental interaction with the frame and the damage in the infill when subjected to in-plane loading can be minimized.

The numerical model is validated with results from an experimental study and is used to perform a parametric analysis to examine the influence of variations in the geometry and mechanical properties of the infill walls, as well as the configuration of the sliding joints. Based on the findings of this study, design guidelines for practical applications are provided, together with simple formulation for evaluating their performance. Copyright © 2016 John Wiley & Sons, Ltd.

Hybrid simulations of a full-scale soft-story woodframe building specimen with various retrofits were carried out as part of the Network for Earthquake Engineering Simulation Research project – NEES-Soft: seismic risk reduction for soft-story woodframe buildings. The test structure in the hybrid simulation was a three-story woodframe building that was divided into a numerical substructure of the first story with various retrofits and a full-scale physical substructure of the upper two stories. Four long-stroke actuators, two at the second floor and two at the roof diaphragm, were attached to the physical substructure to impose the simulated seismic responses including both translation and in-plane rotation. Challenges associated with this first implementation of a full-scale hybrid simulation on a woodframe building were identified. This paper presents the development and validation of a scalable and robust hybrid simulation controller for efficient test site deployment. The development consisted of three incremental validation phases ranging from small-scale, mid-scale, to full-scale tests conducted at three laboratories. Experimental setup, procedure, and results of each phase of the controller development are discussed, demonstrating the effectiveness and efficiency of the incremental controller development approach for large-scale hybrid simulation programs with complex test setup. Copyright © 2016 John Wiley & Sons, Ltd.

Hybrid simulations that combine numerical computations and physical experiment represent an effective method of evaluating the dynamic response of structures. However, it is sometimes impossible to take all the uncertain or nonlinear parts of the structure as the physical substructure. Thus, the modeling errors of the numerical part can raise concerns. One method of solving this problem is to update the numerical model by estimating its parameters from experimental data online. In this paper, an online model updating method for the hybrid simulation of frame structures is proposed to reduce the errors of nonlinear modeling of numerical substructures. To obtain acceptable accuracy with acceptable extra computation efforts as a result of model parameter estimation, the sectional constitutive model is adopted, therein considering axial-force and bending-moment coupling; moreover, the unscented Kalman filter is used for parameter estimation of the sectional model. The effectiveness of the sectional model updating with the unscented Kalman filter is validated via numerical analyses and actual hybrid tests on a full-scale steel frame structure, with one column as the experimental substructure loaded by three actuators to guarantee the consistency of the boundary conditions. Copyright © 2016 John Wiley & Sons, Ltd.

Earthquake ground motion records are nonstationary in both amplitude and frequency content. However, the latter nonstationarity is typically neglected mainly for the sake of mathematical simplicity. To study the stochastic effects of the time-varying frequency content of earthquake ground motions on the seismic response of structural systems, a pair of closely related stochastic ground motion models is adopted here. The first model (referred to as ground motion model I) corresponds to a fully nonstationary stochastic earthquake ground motion model previously developed by the authors. The second model (referred to as ground motion model II) is nonstationary in amplitude only and is derived from the first model. Ground motion models I and II have the same mean-square function and global frequency content but different features of time variation in the frequency content, in that no time variation of the frequency content exists in ground motion model II. New explicit closed-form solutions are derived for the response of linear elastic SDOF and MDOF systems subjected to stochastic ground motion model II. New analytical solutions for the evolutionary cross-correlation and cross-PSD functions between the ground motion input and the structural response are also derived for linear systems subjected to ground motion model I. Comparative analytical results are presented to quantify the effects of the time-varying frequency content of earthquake ground motions on the structural response of linear elastic systems. It is found that the time-varying frequency content in the seismic input can have significant effects on the stochastic properties of system response. Copyright © 2016 John Wiley & Sons, Ltd.

The design of floor isolation systems (FISs) for the protection of acceleration sensitive contents is examined considering multiple objectives, all quantified in terms of the probabilistic system performance. The competing objectives considered correspond to (i) maximization of the level of protection offered to the sensitive content (acceleration reduction) and (ii) minimization of the demand for the isolator displacement capacity and, more importantly, for the appropriate clearance to avoid collisions with surrounding objects (floor displacement reduction). Both of these objectives are probabilistically characterized utilizing a versatile, simulation-based framework for quantifying seismic risk, addressing all important uncertainties related to the seismic hazard and the structural model. FIS performance is assessed through time-history analysis, allowing for all important sources of nonlinearity to be directly addressed in the design framework. The seismic hazard is described through a stochastic ground motion model. For efficiently performing the multi-objective optimization, an augmented surrogate modeling methodology is established, considering development of a single metamodel with respect to both the uncertain model parameters and the design variables for the FIS system. This surrogate model is then utilized to simultaneously support the probabilistic risk assessment and the design optimization to provide the Pareto front of dominant designs. Each of these designs establishes a different compromise between the considered risk-related objectives offering a variety of potential options to the designer. Within the illustrative example, the efficiency of the established framework is exploited to compare three different FIS implementations, whereas the impact of structural uncertainties on the optimal design is also evaluated. Copyright © 2016 John Wiley & Sons, Ltd.

Recent earthquakes have confirmed the role played by infills in the seismic response of reinforced concrete buildings. The control and limitation of damage to such nonstructural elements is a key issue in performance-based earthquake engineering. The present work is focused on modeling and analysis of damage to infill panels, and, in particular, it is aimed towards linear analysis procedures for assessing the damage limitation limit state of infilled reinforced concrete frames.

First, code provisions on infill modeling and acceptance criteria at the damage limitation limit state are reviewed. Literature contributions on damage to unreinforced masonry infill panels and corresponding displacement capacity are reported and discussed.

Two procedures are then proposed aiming at a twofold goal: (i) the determination of ‘equivalent’ interstory drift ratio limits for a bare frame model and (ii) the estimation of the stiffness of equivalent struts representing infill walls in a linear model. These two quantities are determined such that a linear model ensures a reliable estimation of seismic capacity at the damage limitation limit state, providing the same intensity level as that obtained from nonlinear analyses carried out on structural models with infills.

Finally, the proposed procedures are applied to four-story and eight-story case study-infilled frames, designed for seismic loads according to current technical codes. The results of these application examples are presented and discussed. Copyright © 2016 John Wiley & Sons, Ltd.

In modern unreinforced masonry buildings with stiff RC slabs, walls of the top floor are most susceptible to out-of-plane failure. The out-of-plane response depends not only on the acceleration demand and wall geometry but also on the static and kinematic boundary conditions of the walls. This paper discusses the influence of these boundary conditions on the out-of-plane response through evaluation of shake table test results and numerical modelling. As a novum, it shows that the in-plane response of flanking elements, which are orthogonal to the wall whose out-of-plane response is studied, has a significant influence on the vertical restraint at the top of the walls. The most critical configuration exists if the flanking elements are unreinforced masonry walls that rock. In this case, the floor slabs can uplift, and the out-of-plane load-bearing walls loose the vertical restraint at the top. Numerical modelling confirms this experimentally observed behaviour and shows that slab uplift and the difference in base and top excitation have a strong influence on the out-of-plane response of the walls analysed. Copyright © 2016 John Wiley & Sons, Ltd.

This study evaluates the effect of considering ground motion duration when selecting hazard-consistent ground motions for structural collapse risk assessment. A procedure to compute source-specific probability distributions of the durations of ground motions anticipated at a site, based on the generalized conditional intensity measure framework, is developed. Targets are computed for three sites in Western USA, located in distinct tectonic settings: Seattle, Eugene, and San Francisco. The effect of considering duration when estimating the collapse risk of a ductile reinforced concrete moment frame building, designed for a site in Seattle, is quantified by conducting multiple stripe analyses using groups of ground motions selected using different procedures. The mean annual frequency of collapse (*λ*_{collapse}) in Seattle is found to be underestimated by 29% when using typical-duration ground motions from the PEER NGA-West2 database. The effect of duration is even more important in sites like Eugene (*λ*_{collapse} underestimated by 59%), where the seismic hazard is dominated by large magnitude interface earthquakes, and less important in sites like San Francisco (*λ*_{collapse} underestimated by 7%), where the seismic hazard is dominated by crustal earthquakes. Ground motion selection procedures that employ causal parameters like magnitude, distance, and *V**s*_{30} as surrogates for ground motion duration are also evaluated. These procedures are found to produce poor fits to the duration and response spectrum targets because of the limited number of records that satisfy typical constraints imposed on the ranges of the causal parameters. As a consequence, ground motions selected based on causal parameters are found to overestimate *λ*_{collapse} by 53%. Copyright © 2016 John Wiley & Sons, Ltd.

The purpose of this study is to propose an accurate and efficient method for selecting and scaling ground motions matching target response spectrum mean and variance, which does not require excessive computation and simulation. In the proposed method, a desired number of ground motions are sequentially scaled and selected from a ground motion library without iterations. Copyright © 2016 John Wiley & Sons, Ltd.