In‐plane quasi‐static cyclic tests of nonstructural lightweight steel drywall partitions for seismic performance evaluation

An experimental program was performed for evaluating the seismic response and fragilities of nonstructural lightweight steel drywall partitions, also considering the interaction with structural elements and other nonstructural building components, ie, outdoor façade walls. Therefore, in‐plane quasi‐static reversed cyclic tests were carried out on 8 specimens of indoor partition walls infilled in a frame and on 4 specimens of indoor partition walls connected at its ends with transversal outdoor façade walls. Constructive parameters under investigation include type of connections used for connecting the indoor partition walls to the surrounding elements, stud spacing, type of sheathing panels, and type of jointing finishing. The effect of the constructive parameters on the lateral response in secant stiffness and strength is examined. Furthermore, the main damage phenomena observed during the tests are reported and associated to 3 damage limit states distinguished for the required repair level for the tested partition walls. Fragility curves are used for the experimental assessment of seismic fragility of the tested specimens, in accordance with the interstorey drift limits required by the European code. Finally, the quantitative estimation of the repair action costs starting from the damage observation is also developed. The obtained results could be considered a starting point for developing the in‐plane seismic design assisted by testing of lightweight steel drywall partition walls.     

Seismic performance evaluation of non‐structural components: drywall partitions

As the first part of non‐structural component test series, interior drywall partitions are selected for an experimental program. This test series will cover non‐structural components that are significant in the economic losses in buildings subjected to seismic loading, namely interior drywall partitions, exterior cladding and window glasses, and ceilings. Four full‐scale drywall partitions with light‐gage steel stud framing were tested to observe damage in cyclic loading conditions. Effects of a door and an intersecting wall on the behaviour of drywall partition are studied. Damage was concentrated to perimeter regions where gypsum boards made contacts with ceiling, floor, or columns. Dynamic loading did not amplify the damage on a drywall partition over the damage observed from the quasi‐static test. Damage–repair cost relationships show that the repair cost reaches almost the initial cost under 2% radian interstorey drift. Copyright © 2006 John Wiley & Sons, Ltd.     

Seismic performance evaluation of plasterboard partitions via shake table tests

The damage of nonstructural components represents the largest contribution to the economic loss caused by an earthquake. Since nonstructural components are not amenable to traditional structural analysis, full-scale experimental testing is crucial to understand their behaviour under earthquake. For this reason, shaking table tests are performed to investigate the seismic behaviour of plasterboard partitions. A steel test frame is properly designed in order to simulate the seismic effects at a generic building storey. The tests are performed shaking the table simultaneously in both horizontal directions. To investigate a wide range of interstorey drift demand and seismic damage, the shakes are performed scaling the accelerograms at eleven different intensity levels. The tested plasterboard partitions from Siniat exhibit a good seismic behaviour, both in their own plane and out of plane, showing limited damage up to 1.1 % interstorey drift ratio. The correlation between the dynamic characteristics of the test setup and the recorded damage is evidenced. Finally, an interesting comparison between the experimental results and the analytical model is also performed.     

Fragility functions for masonry infill walls with in‐plane loading

Recent seismic events have provided evidence that damage to masonry infills can lead not only to large economic losses but also to significant injuries and even fatalities. The estimation of damage of such elements and the corresponding consequences within the performance‐based earthquake engineering framework requires the construction of reliable fragility functions. In this paper, drift‐based fragility functions are developed for in‐plane loaded masonry infills, derived from a comprehensive experimental data set gathered from current literature, comprising 152 masonry infills with different geometries and built with different types of masonry blocks, when tested under lateral cyclic loading. Three damage states associated with the structural performance and reparability of masonry infill walls are defined. The effect of mortar compression strength, masonry prism compression strength, and presence of openings is evaluated and incorporated for damage states where their influence is found to be statistically significant. Uncertainty due to specimen‐to‐specimen variability and sample size is quantified and included in the proposed fragility functions. It is concluded that prism strength and mortar strength are better indicators of the fragility of masonry infills than the type of bricks/blocks used, whose influence, in general, is not statistically significant for all damage states. Finally, the presence of openings is also shown to have statistically relevant impact on the level of interstory drift ratio triggering the lower damage states.     

钢框架内填竖缝RC墙结构的性态指标

为研究钢框架内填竖缝RC墙结构（Steel frame with slit RC wall,简称"SRCW"）在不同地震水平下的性态指标,结合我国现行抗震规范,对已完成的8榀SRCW试验数据进行了统计分析,基于修正的Park-Ang模型及损伤指数与性态指标的对应关系,提出了以层间位移角表征的SRCW结构的性态指标矩阵。分析结果表明:SRCW结构在显著屈服和倒塌时的层间位移角均值分别为0.63%和2.36%。SRCW结构在正常使用、基本完好、轻微破坏、中等破坏、严重破坏和倒塌状态下的层间位移角限值分别为1/170、1/130、1/100、1/70、1/50和1/40,研究成果可为SRCW结构开展基于性态的抗震设计及地震易损性分析提供参考。     

Critical limit states in seismic buckling‐restrained brace and connection designs

A welded end‐slot buckling‐restrained brace (WES‐BRB) has been developed at the Taiwan National Center for Research on Earthquake Engineering (NCREE). A steel frame equipped with a WES‐BRB can offer a cost‐effective solution to meet interstory drift and earthquake‐resistant design requirements for seismic steel buildings. According to the WES‐BRB and connection design procedure proposed by NCREE, there are seven key elements of a buckling‐restrained braced frame (BRBF) design that require design checking. In order to assist an engineer with the design of the WES‐BRB members and connections, an innovative cloud service named Brace on Demand has been constructed at NCREE. In this study, using 581 BRBF design examples, the effectiveness of the proposed design procedures to meet all design checks is demonstrated. It is found that the most critical limit states for an initial design are joint region buckling, gusset plate buckling, and gusset‐to‐beam and gusset‐to‐column interface strength. Accordingly, the causes of improper designs and associated strategies for improving the initial designs are discussed in this paper. Recommendations on initial selections including the BRB joint size and gusset plate thickness are given. The paper provides the detailed road map for engineers to develop the spreadsheet for BRB and connection designs. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of earthquake ground‐motion duration on damage estimation: application to steel moment resisting frames

This paper presents an analytical study evaluating the influence of ground motion duration on structural damage of 3‐story, 9‐story, and 20‐story SAC steel moment resisting frame buildings designed for downtown Seattle, WA, USA, using pre‐Northridge codes. Two‐dimensional nonlinear finite element models of the buildings are used to estimate the damage induced by the ground motions. A set of 44 ground motions is used to study the combined effect of spectral acceleration and ground motion significant duration on drift and damage measures. In addition, 10 spectrally equivalent short‐duration shallow crustal ground motions and long‐duration subduction zone records are selected to isolate duration effect and assess its effect on the response. For each ground motion pair, incremental dynamic analyses are performed at at least 20 intensity levels and response measures such as peak interstory drift ratio and energy dissipated are tracked. These response measures are combined into two damage metrics that account for the ductility and energy dissipation. Results indicate that the duration of the ground motion influences, above all, the combined damage measures, although some effect on drift‐based response measures is also observed for larger levels of drift. These results indicate that because the current assessment methodologies do not capture the effects of ground motion duration, both performance‐based and code‐based assessment methodologies should be revised to consider damage measures that are sensitive to duration. Copyright © 2016 John Wiley & Sons, Ltd     

Shake table tests on standard and innovative temporary partition walls

Shake table tests are performed on temporary internal partitions for office buildings. Four different specimens are tested. A steel frame is designed to exhibit relative displacements which typically occur at a given story of ordinary buildings. Four different partition walls are tested simultaneously for each specimen typology. This allows investigating the influence of an innovative device on the seismic performance of the tested components. The innovative device avoids the unhooking of the panels from the supporting studs. Several shake table tests are performed subjecting the specimens to interstory drift ratios up to 1.57%. Both the hysteretic curves and the natural frequency trend highlight that the partitions do not contribute to the lateral stiffness of the test setup. The damping ratio increases after the partition walls are installed within the test frame, causing a beneficial effect in the dynamic response. Minor damage state occurs for interstory drift ratio (IDR) in the range 0.41–0.65% in standard specimens, whereas moderate and major damage states are attained for IDR in the range 0.51–0.95%. Significant increase of collapse IDR is recorded with the introduction of the innovative device, up to IDR larger than 1.45%. It can be therefore concluded that a simple innovative device is defined, which significantly improves the seismic performance of the tested specimen. Copyright © 2017 John Wiley & Sons, Ltd.     

Development of fragility functions as a damage classification/prediction method for steel moment‐resisting frames using a wavelet‐based damage sensitive feature

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.     

Generalized force vectors for multi‐mode pushover analysis of torsionally coupled systems

A generalized multi‐mode pushover analysis procedure was developed for estimating the maximum inelastic seismic response of symmetrical plan structures under earthquake ground excitations. Pushover analyses are conducted with story‐specific generalized force vectors in this procedure, with contributions from all effective modes. Generalized pushover analysis procedure is extended to three‐dimensional torsionally coupled systems in the presented study. Generalized force distributions are expressed as the combination of modal forces to simulate the instantaneous force distribution acting on the system when the interstory drift at a story reaches its maximum value during seismic response. Modal contributions to the generalized force vectors are calculated by a modal scaling rule, which is based on the complete quadratic combination. Generalized forces are applied to the mass centers of each story incrementally for producing nonlinear static response. Maximum response quantities are obtained when the individual frames attain their own target interstory drift values in each story. The developed procedure is tested on an eight‐story frame under 15 ground motions, and assessed by comparing the results obtained from nonlinear time history analysis. The method is successful in predicting the torsionally coupled inelastic response of frames responding to large interstory drift demands. Copyright © 2014 John Wiley & Sons, Ltd.     

Generalized force vectors for multi‐mode pushover analysis

A generalized pushover analysis (GPA) procedure is developed for estimating the inelastic seismic response of structures under earthquake ground excitations. The procedure comprises applying different generalized force vectors separately to the structure in an incremental form with increasing amplitude until a prescribed seismic demand is attained for each generalized force vector. A generalized force vector is expressed as a combination of modal forces, and simulates the instantaneous force distribution acting on the system when a given response parameter reaches its maximum value during dynamic response to a seismic excitation. While any response parameter can be selected arbitrarily, generalized force vectors in the presented study are derived for maximum interstory drift parameters. The maximum value of any other response parameter is then obtained from the envelope of GPAs results. Each nonlinear static analysis under a generalized force vector activates the entire multi‐degree of freedom effects simultaneously. Accordingly, inelastic actions develop in members with the contribution of all ‘instantaneous modes’ in the nonlinear response range. Target seismic demands for interstory drifts at the selected stories are calculated from the associated drift expressions. The implementation of the proposed GPA is simpler compared with nonlinear response history analysis, whereas it is less demanding in computational effort when compared with several multi‐mode adaptive nonlinear static procedures. Moreover, it does not suffer from the statistical combination of inelastic modal responses obtained separately. The results obtained from building frames have demonstrated that GPA is successful in estimating maximum member deformations and member forces with reference to the response history analysis. When the response is linear elastic, GPA and response spectrum analysis produce identical results. Copyright © 2010 John Wiley & Sons, Ltd.     

Dynamic characteristics and seismic behavior of prefabricated steel stairs in a full‐scale five‐story building shake table test program

This paper investigates the dynamic characteristics and seismic behavior of prefabricated steel stairs in a full‐scale five‐story building shake table test program. The test building was subjected to a suite of earthquake input motions and low‐amplitude white noise base excitations first, while the building was isolated at its base, and subsequently while it was fixed to the shake table platen. This paper presents the modal characteristics of the stairs identified using the data recorded from white noise base excitation tests as well as the physical and measured responses of the stairs from the earthquake tests. The observed damage to the stairs is categorized into three distinct damage states and is correlated with the interstory drift demands of the building. These shake table tests highlight the seismic vulnerability of modern designed stair systems and in particular identifies as a key research need the importance of improving the deformability of flight‐to‐building connections. Copyright © 2015 John Wiley & Sons, Ltd.     

Dynamic FE simulation of four‐story steel frame modeled by solid elements and its validation using results of full‐scale shake‐table test

Dynamic finite element analyses of a four‐story steel building frame modeled as a fine mesh of solid elements are performed using E‐Simulator, which is a parallel finite element analysis software package for precisely simulating collapse behaviors of civil and building structures. E‐Simulator is under development at the National Research Institute for Earth Science and Disaster Prevention (NIED), Japan. A full‐scale shake‐table test for a four‐story frame was conducted using E‐Defense at NIED, which is the largest shaking table in the world. A mesh of the entire structure of a four‐story frame with approximately 19 million degrees of freedom is constructed using solid elements. The density of the mesh is determined by referring to the results of elastic–plastic buckling analyses of a column of the frame using meshes of different densities. Therefore, the analysis model of the frame is well verified. Seismic response analyses under 60, 100, and 115% excitations of the JR Takatori record of the 1995 Hyogoken‐Nanbu earthquake are performed. Note that the simulation does not reproduce the collapse under the 100% excitation of the Takatori record in the E‐Defense test. Therefore, simulations for the 115% case are also performed. The results obtained by E‐Simulator are compared with those obtained by the E‐Defense full‐scale test in order to validate the results obtained by E‐Simulator. The shear forces and interstory drift angles of the first story obtained by the simulation and the test are in good agreement. Both the response of the entire frame and the local deformation as a result of elastic–plastic buckling are simulated simultaneously using E‐Simulator. Copyright © 2014 John Wiley & Sons, Ltd.     

Seismic performance of a 3D full‐scale high‐ductile steel–concrete composite moment‐resisting frame—Part II: Test results and analytical validation

This paper presents the results of a multi‐level pseudo‐dynamic seismic test program that was performed to assess the performance of a full‐scale three‐bay, two‐storey steel–concrete composite moment‐resisting frame built with partially encased composite columns and partial‐strength beam‐to‐column joints. The system was designed to develop a ductile response in the joint components of beam‐to‐column joints including flexural yielding of beam end plates and shear yielding of the column web panel zone. The ground motion producing the damageability limit state interstorey drift caused minor damage while the ultimate limit state ground motion level entailed column web panel yielding, connection yielding and plastic hinging at the column base connections. The earthquake level chosen to approach the collapse limit state induced more damage and was accompanied by further column web panel yielding, connection yielding and inelastic phenomena at column base connections without local buckling. During the final quasi‐static cyclic test with stepwise increasing displacement–amplitudes up to an interstorey drift angle of 4.6%, the behaviour was ductile although cracking of beam‐to‐end‐plate welds was observed. Correlations with numerical simulations taking into account the inelastic cyclic response of beam‐to‐column and column base joints are also presented in the paper together. Inelastic static pushover and time history analysis procedures are used to estimate the structural behaviour and overstrength factors of the structural system under study. Copyright © 2008 John Wiley & Sons, Ltd.     

Probabilistic evaluation of seismic performance of 3‐story 3D one‐ and two‐way steel moment‐frame structures

This paper presents the results of a probabilistic evaluation of the seismic performance of 3D steel moment‐frame structures. Two types of framing system are considered: one‐way frames typical of construction in the United States and two‐way frames typical of construction in Japan. For each framing system, four types of beam–column connections are considered: pre‐Northridge welded‐flange bolted‐web, post‐Northridge welded‐flange welded‐web, reduced‐beam‐section, and bolted‐flange‐plate connections. A suite of earthquake ground motions is used to compute the annual probability of exceedence (APE) for a series of drift demand levels and for member plastic‐rotation capacity. Results are compared for the different framing systems and connection details. It is found that the two‐way frames, which have a larger initial stiffness and strength than the one‐way frames for the same beam and column volumes, have a smaller APE for small drift demands for which members exhibit no or minimal yielding, but have a larger APE for large drift demands for which members exhibit large plastic rotations. However, the one‐way frames, which typically comprise a few seismic frames with large‐sized members that have relatively small rotation capacities, may have a larger APE for member failure. The probabilistic approach presented in this study may be used to determine the most appropriate frame configuration to meet an owner's performance objectives. Copyright © 2008 John Wiley & Sons, Ltd.     

Seismic reliability of steel moment resisting framed buildings retrofitted with buckling restrained braces

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.     

Seismic design procedure and seismic response of post‐tensioned self‐centering steel frames

Post‐tensioned (PT) self‐centering moment‐resisting frames (MRFs) have recently been developed as an alternative to welded moment frames. The first generation of these systems incorporated yielding energy dissipation mechanisms, whereas more recently, PT self‐centering friction damped (SCFR) moment‐resistant connections have been proposed and experimentally validated. Although all of these systems exhibited good stiffness, strength and ductility properties and stable dissipation of energy under cyclic loading, questions concerning their ultimate response still remained and a complete design methodology to allow engineers to conceive structures using these systems was also needed. In this paper, the mechanics of SCFR frames are first described and a comprehensive design procedure that accounts for the frame behavior and the nonlinear dynamics of self‐centering frames is then elaborated. A strategy for the response of these systems at ultimate deformation stages is then proposed and detailing requirements on the beams in order to achieve this response are outlined. The proposed procedure aims to achieve designs where the interstory drifts for SCFR frames are similar to those of special steel welded moment‐resisting frames (WMRFs). Furthermore, this procedure is adapted from current seismic design practices and can be extended to any other PT self‐centering steel frame system. A six‐story building incorporating WMRFs was designed and a similar building incorporating SCFR frames were re‐designed by the proposed seismic design procedure. Time‐history analyses showed that the maximum interstory drifts and maximum floor accelerations of the SCFR frame were similar to those of the WMRF but that almost zero residual drifts were observed for the SCFR frame. The results obtained from the analyses confirmed the validity of the proposed seismic design procedure, since the peak drift values were similar to those prescribed by the seismic design codes and the SCFR frames achieved the intended performance level under both design and maximum considerable levels of seismic loading. Copyright © 2008 John Wiley & Sons, Ltd.     

Fragility analysis of low‐rise masonry in‐filled reinforced concrete buildings by a coefficient‐based spectral acceleration method

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.     

Multiobjective optimization for performance‐based seismic design of steel moment frame structures

The performance‐based seismic design of steel special moment‐resisting frame (SMRF) structures is formulated as a multiobjective optimization problem, in which conflicting design criteria that respectively reflect the present capital investment and the future seismic risk are treated simultaneously as separate objectives other than stringent constraints. Specifically, the initial construction expenses are accounted for by the steel material weight as well as by the number of different standard steel section types, the latter roughly quantifying the degree of design complexity related additional construction cost; the seismic risk is considered in terms of maximum interstory drift demands at two hazard levels with exceedance probabilities being 50% and 2% in 50 years, respectively. The present formulation allows structural engineers to find an optimized design solution by explicitly striving for a desirable compromise between the initial investment and seismic performance. Member sizing for code‐compliant design of a planar five‐story four‐bay SMRF is presented as an application example using the proposed procedure that is automated by a multiobjective genetic algorithm. Copyright © 2004 John Wiley & Sons, Ltd.     

Seismic risk assessment of liquid storage tanks via a nonlinear surrogate model

A performance‐based earthquake engineering approach is developed for the seismic risk assessment of fixed‐roof atmospheric steel liquid storage tanks. The proposed method is based on a surrogate single‐mass model that consists of elastic beam‐column elements and nonlinear springs. Appropriate component and system‐level damage states are defined, following the identification of commonly observed modes of failure that may occur during an earthquake. Incremental dynamic analysis and simplified cloud are offered as potential approaches to derive the distribution of response parameters given the seismic intensity. A parametric investigation that engages the aforementioned analysis methods is conducted on 3 tanks of varying geometry, considering both anchored and unanchored support conditions. Special attention is paid to the elephant's foot buckling formation, by offering extensive information on its capacity and demand representation within the seismic risk assessment process. Seismic fragility curves are initially extracted for the component‐level damage states, to compare the effect of each analysis approach on the estimated performance. The subsequent generation of system‐level fragility curves reveals the issue of nonsequential damage states, whereby significant damage may abruptly appear without precursory lighter damage states.