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This paper presents a systematic evaluation approach that allows the design professional to estimate the performance of damaged buildings subjected to sets of ground motions representing different hazard levels. The performance of damaged buildings for a future seismic event prior to repair and/or rehabilitation was evaluated using an elastic model and stiffness of the structure. The linear static model using the damaged state of brittle fractured connections in steel moment resisting frame buildings provides a reasonable estimation of the interstory drift of the damaged buildings when compared to nonlinear time history analysis. Then, this result was incorporated in a reliability-based procedure that provides a degree of confidence that a building before and after the damage will exceed the given performance levels. Finally, examples of confidence level calculations are presented. The results showed that the linear static model and the performance evaluation procedure are very useful and allow the design professional to determine the level of safety of damaged buildings. [ABSTRACT FROM AUTHOR]

Shaking table testing is a common experimental method in earthquake engineering for performance assessment of structures subjected to dynamic excitations. As most shaking tables are driven by servo hydraulic actuators to meet the potentially significant force stroke demand, the review is restricted to hydraulic shaking tables. The purpose of the control systems of hydraulic shaking tables is to reproduce reference signals with low distortion. Accurate control of actuators is vital to the effectiveness of such apparatus. However, the system dynamics of a shaking table and the specimens to be tested on the shaking table are usually very complex and nonlinear. Achieving the control goal can prove to be challenging. A variety of closed- and open-loop control algorithms has been developed to solve different control problems. With the focus placed on the control schemes for hydraulic shaking tables, the paper reviews algorithms that are currently used in the testing industry, as well as those which are the subject of academic and industrial research. It is by no means a complete survey but provides key reference for further development. [ABSTRACT FROM AUTHOR]

In a medium-to-large earthquake, there are often reports of people being trapped or injured in elevators. This study investigates using an earthquake early warning (EEW) system, which provides seconds to tens of seconds warning before seismic waves arrive at a site, to help people escape from the elevators before a strong shaking arrives. However, such an application remains as a major engineering challenge due to the uncertainty of the EEW information and the short lead time available. A recent study presented an earthquake probability- based automated decision-making (ePAD) framework to address these issues. This paper focuses on studying the influence of two commonly ignored factors, uncertainty of warning and lead time, on the decision of stopping the elevators and opening the doors when an EEW message is received. Application of the ePAD framework requires using the performance-based earthquake engineering methodology for elevator damage prediction, making decision based on a cost-benefit model and reducing computational time with a surrogate model. The authors' results show that ePAD can provide rational decisions for elevator control based on EEW information under different amounts of lead time and uncertainty level of the warning. [ABSTRACT FROM AUTHOR]

Performance-based design in earthquake engineering is a structural optimization problem that has, as the objective, the determination of design parameters for the minimization of total costs, while at the same time satisfying minimum reliability levels for the specified performance criteria. Total costs include those for construction and structural damage repairs, those associated with non-structural components and the social costs of economic losses, injuries and fatalities. This paper presents a general framework to approach this problem, using a numerical optimization strategy and incorporating the use of neural networks for the evaluation of dynamic responses and the reliability levels achieved for a given set of design parameters. The strategy is applied to an example of a three-story office building. The results show the importance of considering the social costs, and the optimum failure probabilities when minimum reliability constraints are not taken into account. [ABSTRACT FROM AUTHOR]

The performance assessment and optimal design of fluid viscous dampers through life-cycle cost criteria is discussed in this paper. A probabilistic, simulation-based framework is described for estimating the life-cycle cost and a stochastic search approach is developed to support an efficient optimization under different design scenarios (corresponding to different seismicity characteristics). Earthquake losses are estimated using an assembly-based vulnerability approach utilizing the nonlinear dynamic response of the structure whereas a point source stochastic ground motion model, extended here to address near-fault pulse effects, is adopted to describe the seismic hazard. Stochastic simulation is utilized for estimation of all the necessary probabilistic quantities, and for reducing the computational burden a surrogate modeling methodology is integrated within the framework. Two simplified design approaches are also examined, the first considering the optimization of the stationary response, utilizing statistical linearization to address nonlinear damper characteristics, and the second adopting an equivalent lateral force procedure that defines a targeted damping ratio for the structure. These designs are compared against the optimal life-cycle cost one, whereas a compatible comparison is facilitated by establishing an appropriate connection between the seismic input required for the simplified designs and the probabilistic earthquake hazard model. As an illustrative example, the retrofitting of a three-story reinforced concrete office building with nonlinear dampers is considered. [ABSTRACT FROM AUTHOR]

A large-scale, two-span bridge model constructed by assembling precast elements was tested under a series of bi-axial ground motions simulated on a shake table at the Earthquake Engineering Laboratory at the University of Nevada, Reno. The response of the bridge was estimated before the tests using a three-dimensional computational model developed in OpenSees software. After the tests, key measured seismic responses were compared to those predicted by the computational model to assess the modeling assumptions. Relatively large errors for the displacements, base shears, and hysteretic response of the bridge were observed. The influence of the earthquake loading, materials, connectivity of the precast elements, and boundary conditions in the computational model on the errors are discussed in this paper. Future modeling directions are proposed to reduce these errors. [ABSTRACT FROM AUTHOR]

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SUMMARY Substructure hybrid simulation has been the subject of numerous investigations in recent years. The simulation method allows for the assessment of the seismic performance of structures by representing critical components with physical specimens and the rest of the structure with numerical models. In this study the system level performance of a six-storey structure with telescoping self-centering energy dissipative (T-SCED) braces is validated through pseudo-dynamic (PsD) hybrid simulation. Fragility curves are derived for the T-SCED system. This paper presents the configuration of the hybrid simulation, the newly developed control software for PsD hybrid simulation, which can integrate generic hydraulic actuators into PsD hybrid simulation, and the seismic performance of a structure equipped with T-SCED braces. The experimental results show that the six-storey structure with T-SCED braces satisfies performance limits specified in ASCE 41. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Next generation performance-based earthquake engineering involves the use of a probability framework, which incorporates the inherent uncertainty and variability in seismic hazard, structural and non-structural responses, damage states and economic and casualty losses. One key issue in seismic performance assessment is the scaling of ground motions for nonlinear response-history analysis. In this paper, the impact of ground-motion scaling procedures, including 1) geometric-mean scaling of pairs of ground motions, 2) spectrum-matching of ground-motions, 3) first-mode-based scaling to a target spectral acceleration and 4) maximum-minimum orientation scaling, on the distributions of floor acceleration, story drift and floor spectral acceleration of a sample high-rise building is investigated using a series of nonlinear response-history analyses of a 34-story moment-resisting frame building. The advantages and disadvantages of each ground-motion scaling method are discussed for seismic performance assessment of a 34-story building. [ABSTRACT FROM AUTHOR]

Abstract: Structural reinforcement is an economical and ecological method of preventing damage caused by seismic loading. Indeed, it is estimated that two out of three buildings will become unsafe over the next 40years if no policy of treatment for existing constructions is adopted. FRP strengthening appears to be an advantageous method of structural strengthening due to the mechanical properties of the composite and the ease of application in the damage area. Various reinforcement systems have been presented in the literature, characterized by several parameters (FRP materials, configuration, reinforcement ratio, anchored bars etc.). This paper proposes the use of a performance index, based on a damage index, to assess the efficiency of external FRP reinforcement retrofitting using three experimental investigations. The influence of (i) axial compressive loading, (ii) the shape of the reinforced short column, (iii) the presence of FRP bars and (iv) FRP reinforcement on the performance index of the columns is determined. A parameter ξ is also defined to evaluate the performance of the columns according to the geometrical configuration and mechanical properties of the FRP reinforcement. [Copyright &y& Elsevier]

Abstract: Significant investments are undergoing internationally to develop earthquake early warning (EEW) systems. So far, reasonably, the most of the research in this field was lead by seismologists as the issues to determine essential feasibility of EEW were mainly related to the earthquake source. Many of them have been brilliantly solved, and the principles of this discipline are collected in the so-called real-time seismology. On the other hand, operating EEW systems rely on general-purpose intensity measures as proxies for the impending ground motion potential and are suitable for population alert. In fact, to date, comparatively little attention was given to EEW by earthquake engineering, and design approaches for structure-specific EEW are mostly lacking. Applications to site-specific systems have not been extensively investigated and EEW convenience is not yet proven except a few pioneering cases, although the topic is certainly worthwhile. For example, in structure-specific EEW the determination of appropriate alarm thresholds is important when the false alarm may induce significant losses; similarly, economic appeal with respect to other risk mitigation strategies as seismic upgrade should be assessed. In the paper the least issues to be faced in the design of engineering applications of EEW are reviewed and some work done in this direction is discussed. The review presented intends to summarize the work of the author and co-workers in this field illustrating a possible performance-based approach for the design of structure-specific applications of EEW. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the seismic performance of reinforced concrete exterior wide beam–column connections with shallow spandrel beams lightly reinforced for torsion and moderate levels of gravity loads was investigated experimentally. The study focuses on existing frames designed and detailed according to construction practices used over ten years ago in the moderate-seismicity Mediterranean area. The results can be useful for assessing the seismic vulnerability of older structures and orienting seismic retrofit alternatives. Two 3/5 scale test models representative of exterior sub-assemblages in a prototype six-story building were subjected to gravity-load levels typical of those acting during an earthquake, and quasi-static cyclic lateral loads until failure. The performance was studied in terms of strength, displacement, ductility and energy dissipation capacity. The data are analyzed in conjunction with the results of previous tests. The specimens exhibited a “strong column–weak beam” type of flexural yielding mechanism. The average drift ratios at first yielding of the wide beam longitudinal reinforcement, , and at failure, , were 2.2% and 4.5% respectively; the displacement ductility ratio was approximately 2.2. Comparison to similar connections without added gravity loads showed that moderate levels of gravity loading increased by about 40%, and decreased by a similar percentage the value of and the energy dissipated in each half cycle of displacement expressed in terms of an equivalent viscous damping ratio. Finally, two approaches for estimating the wide-beam flexural capacity are examined. [Copyright &y& Elsevier]

Abstract: Several studies have shown that the lateral response of concentrically-braced frames is dominated by the inelastic behavior of the bracing members. However, the overall performance of the entire frame depends on the frame configuration including its connections. In this study, the hysteretic characteristics of modular steel-braced frames under reversed cyclic loading are evaluated. The design and construction of the test specimen accounted for the unique detailing requirements of these frames. A regular concentrically-braced frame with similar physical characteristics was also tested for comparison. Both test specimens consisted of a one-storey X-braced system with tubular brace cross-section. This paper describes the behavior characteristics and provides a detailed comparison of the two systems to assess the strength, stiffness, inelastic force and deformation, and energy dissipation characteristics of the modular system. An analytical model capable of capturing the effect of the system’s unique detailing requirements is proposed and validated using the test results. [Copyright &y& Elsevier]

Numerous devices exist for reducing or eliminating seismic damage to structures. These include passive dampers, semi-active dampers, and active control devices. The performance of structural systems with these devices has often been evaluated using numerical simulations. Experiments on structural systems with these devices, particularly at large-scale, are lacking. This paper describes a real-time hybrid testing facility that has been developed at the Lehigh University NEES Equipment Site. The facility enables real-time large-scale experiments to be performed on structural systems with rate-dependent devices, thereby permitting a more complete evaluation of the seismic performance of the devices and their effectiveness in seismic hazard reduction. The hardware and integrated control architecture for hybrid testing developed at the facility are presented. An application involving the use of passive elastomeric dampers in a three story moment resisting frame subjected to earthquake ground motions is presented. The experiment focused on a test structure consisting of the damper and diagonal bracing, which was coupled to a nonlinear analytical model of the remaining part of the structure (i.e., the moment resisting frame). A tracking indictor is used to track the actuator's ability to achieve the command displacement during a test, enabling the quality of the test results to be assessed. An extension of the testbed to the real-time hybrid testing of smart structures with semi-active dampers is described. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tubular columns have been studied extensively worldwide. Such columns provide stable energy dissipation, which is ideal for earthquake engineering application. However, most applications use rectangular steel tubular sections. In the location of wall intersections, these sections often create sharp corners, which are architecturally displeasing. In some facilities such as schools and correctional facilities, sharp corners are even prohibited due to their potential hazard to occupants. To resolve the issue, concrete-filled crisscross steel tubular columns (CCSTCs) have been proposed. Three half-scaled specimens were constructed and tested under cyclic displacement loading history. The experimental results were used to calibrate numerical models of the components and further used to examine the seismic behavior of a three-story prototype office building located in Los Angeles. The results showed the proposed CCSTC has excellent energy dissipation and postearthquake performance, and hence it can be used as an alternative lateral force resisting system for seismic applications. [ABSTRACT FROM AUTHOR]

An innovative variable stiffness device is proposed and investigated based on numerical simulations. The device, called a folding variable stiffness spring (FVSS), can be widely used, especially in tuned mass dampers (TMDs) with adaptive stiffness. An important characteristic of FVSS is its capability to change the stiffness between lower and upper bounds through a small change of distance between its supports. This special feature results in lower time-lag errors and readjustment in shorter time intervals. The governing equations of the device are derived and simplified for a symmetrical FVSS with similar elements. This device is then used to control a single-degree-of-freedom (SDOF) structure as well as a multi-degree-of-freedom (MDOF) structure via a semi-active TMD. Numerical simulations are conducted to compare several control cases for these structures. To make it more realistic, a real direct current motor with its own limitations is simulated in addition to an ideal control case with no limitations and both the results are compared. It is shown that the proposed device can be effectively used to suppress undesirable vibrations of a structure and considerably improves the performance of the controller compared to a passive device. [ABSTRACT FROM AUTHOR]

The equivalent linearization method approximates the maximum displacement response of nonlinear structures through the corresponding equivalent linear system. By using the particle swarm optimization technique, a new statistical approach is developed to determine the key parameters of such an equivalent linear system over a 2D space of period and damping ratio. The new optimization criterion realizes the consideration of the structural safety margin in the equivalent linearization method when applied to the performance-based seismic design/evaluation of engineering structures. As an application, equations for equivalent system parameters of both bilinear hysteretic and stiffness degrading single-degree-offreedom systems are deduced with the assumption of a constant ductility ratio. Error analyses are also performed to validate the proposed approach. [ABSTRACT FROM AUTHOR]

The article discusses a study comparing self-centering system with conventional reinforced concrete (RC) system to assess the possible benefits of reduced residual displacements on bridge structures using performance-based earthquake engineering (PBEE) framework. The design of the bridge utilized in the study was executed by the Californian Department of Transportation (Caltrans) engineers, which was modeled through open-source structural analysis software. It mentions that the PBEE analysis developed by the Pacific Earthquake Engineering Research Center (PEER) involves four main steps including hard analysis, structural analysis, and damage analysis. It reveals that self-centering column system sustains lower residual displacements under large earthquakes compared to conventional system.

The results of a parametric study are presented, concerned with the evaluation of the structural overstrength, the global ductility and the available behaviour factor of existing reinforced concrete (RC) buildings designed and constructed according to past generations of earthquake resistant design codes in Greece. For the estimation of these parameters, various failure criteria are incorporated in a methodology established to predict the failure mode of such buildings under planar response, as described in detail in a companion publication. A collection of 85 typical building forms is considered. The influence of various parameters is examined, such as the geometry of the structure (number of storeys, bay width etc.), the vertical irregularity, the contribution of the perimeter frame masonry infill walls, the period of construction, the design code and the seismic zone coefficient. The results from inelastic pushover analyses indicate that existing RC buildings exhibit higher overstrength than their contemporary counterparts, but with much reduced ductility capacity. The presence of perimeter infill walls increases considerably their stiffness and lateral resistance, while further reducing their ductility. Fully infilled frames exhibit generally good behaviour, while structures with an open floor exhibit the worst performance by creating a soft storey. Shear failure becomes critical in the buildings with partial height infills. It is also critical for buildings with isolated shear wall cores at the elevator shaft. Out of five different forms of irregularity considered in this study, buildings with column discontinuities in the ground storey exhibit the worst performance. Furthermore, buildings located in the higher seismicity zone are more vulnerable, since the increase of their lateral resistance and ductility capacity is disproportional to the increase in seismic demand. [ABSTRACT FROM AUTHOR]

A reliable estimate of the actual capacity and deformability of existing reinforced concrete buildings in earthquake prone areas is essential in pre- or post-earthquake interventions. This study is concerned with the evaluation of the structural overstrength, the global ductility and available behaviour factor of existing reinforced concrete buildings, designed and constructed according to past generations of earthquake resistant design codes. For the estimation of these global performance characteristics different failure criteria are incorporated in a methodology established to predict the failure mode of the buildings. As an application, a typical five-storey building of the 1960s, designed according to the prevailing design codes, is selected and analysed in the inelastic range. Both bare and infilled structural forms of this building are studied. For this structure, the plastic hinge rotation capacity is the critical failure criterion. The same structure, designed according to current design codes, is re-evaluated using the same methodology, in order to calibrate the procedure and to compare the static and dynamic inelastic performances of the two frames. The results indicate that existing buildings exhibit higher overstrength than their contemporary counterparts, but with much reduced ductility capacity. Perimeter infill walls correct for their lack of ductility by augmenting their stiffness and their overall lateral resistance. The methodology is subsequently applied to a larger inventory of typical existing buildings, as described in a companion publication. [ABSTRACT FROM AUTHOR]