Search

This paper quantified the seismic resilience (SR) of different bridge classes by performing three-dimensional advanced numerical simulations in Opensees. SR was calculated by performing the seismic resilience for recovery investments of bridge (SRRIB) methodology that is based on the quantification of the losses and the repair time. In particular, the probabilistic-based methodology developed by the Pacific Earthquake Engineering Research Center (PEER) was implemented to produce fragility curves by considering the longitudinal displacement of the deck as the reference parameter. The recovery process was modeled using a linear formulation due to the unavailability of information from past earthquakes. SR for the selected bridge classes was calculated in terms of the seismic intensities to be applied for decision-making procedures during pre- and postearthquake assessments. [ABSTRACT FROM AUTHOR]

Recent studies in earthquake engineering have outlined the difficulty of ground response analyses (GRAs) to replicate the observed ground motion and related variability at borehole array sites. Improvement of the seismic site response estimation requires accounting for and propagating the uncertainties in local soil conditions into surface ground motion. Uncertainties in site conditions arise from a number of factors, which include the uncertainties in the shear-wave velocity (VS) that are mainly caused by the natural spatial variability of soils and rocks. In this paper, a novel VS randomization approach is proposed to propagate the small-scale spatial VS heterogeneities into samples of VS profiles within a nonstationary probabilistic framework, to be further used in one-dimensional (1D) GRAs. The nonstationary approach is based on partitioning a borehole base-case VS profile into several locally stationary layers. The proposed approach was applied at three European sites exhibiting different subsurface soil conditions. Compared with both the classical stationary and an approach from the literature for VS randomization, the proposed approach provides a set of VS profiles fully consistent with the pseudoexperimental site signatures in terms of surface-wave dispersion curves, fundamental and higher-mode resonance frequencies, and site amplification. This paper also outlines the importance of the method used to measure VS profile in both the estimation of depth-dependent variability of VS at a given site and the prediction of site response variability. [ABSTRACT FROM AUTHOR]

Thick rubber bearings (TRBs) have been proven to be effective in mitigating horizontal shaking induced by earthquakes as well as railway-induced vertical vibration. During earthquake excitations, TRBs might be subjected to tension, which should be carefully assessed during design. This paper presents experimental and numerical studies on the behavior of TRBs under tensile loading. Four full-scale thick natural rubber bearing (TNRB) and lead thick rubber bearing (LTRB) specimens were designed and tested under tension, with and without lateral offset. The test results showed that increasing the applied lateral offset decreased the tensile stress and stiffness of the TNRBs, while the LTRBs did not exhibit any reduction. In addition, the test results were compared with design specifications in current codes for conventional rubber bearings. Finally, finite element (FE) models of TRBs were built and validated against the results of uniaxial and offset tensile experiments, and the cavitation of rubber was modeled via a two-phase model. To further estimate the damage due to previous tensile loading, damage variables under cyclic tensile loading were also taken into account. The experimental and numerical results showed that the lead core only slightly increased the initial tensile stiffness of the bearing under uniaxial testing, while it had a significant influence on the tensile properties of the LTRBs under offset displacement. [ABSTRACT FROM AUTHOR]

This paper is the second of two companion papers that seeks to compare homeowners' expectations of damage and engineering predictions of damage to timber-framed houses before and after undertaking seismic structural strengthening. Part I analyzed the seismic vulnerability of wooden-framed houses located on slopes in Wellington, New Zealand, investigating factors of plan shape relative to the slope, slope variations, and wall distribution, and how they influence the final seismic performance of houses. A structural survey provided data on the form and typical details for the subfloor bracing, and this was then used as the basis for a simple strengthening solution that is numerically investigated here. This companion paper analyzes the improvement of seismic performance after undertaking strengthening to the subfloor structure using a multiple stripe analysis. In the last phase of this work, engineering-based predictions of performance as determined using the numerical models were compared to homeowners' expectations of damage before and after undertaking strengthening. This comparison paper found that although strengthened timber-framed houses located on slopes satisfy the minimum requirement of New Zealand design codes, there is still a probability of damage occurring, which would not satisfy owners' expectations of performance in all scenarios. [ABSTRACT FROM AUTHOR]

Evaluation of the liquefaction susceptibility of soils is one of the most important subjects in geotechnical earthquake engineering. The energy-based liquefaction evaluation procedure, with a focus on seismic energy propagation and dissipation in soils, has attracted increasing attention in recent years. This paper presents a systematic analysis of cyclic triaxial test data of three series of silty sands through the energy-based approach. The stress-normalized accumulative dissipated strain energy per unit volume required for triggering liquefaction is used to evaluate the liquefaction potential of sands. It is a function of void ratio, fines content, and sand type. The pore pressure generation with the stress-normalized accumulative dissipated energy per unit volume can be simulated by a one-parameter pore pressure model, and the model parameter is affected by void ratio, fines content, and sand type. Unified characterizations of the stress-normalized accumulative dissipated energy per unit volume required for liquefaction and the fitting parameter of the pore pressure model are proposed in the framework of critical state soil mechanics. [ABSTRACT FROM AUTHOR]

This paper presents the analytical formulation and computational implementation of a conceptual probabilistic performance-based seismic design (PBSD) framework for ordinary standard bridge (OSB) structures. An updated probabilistic performance-based earthquake engineering (PBEE) assessment methodology is used for the parametric performance assessment of four distinct OSBs in California to investigate the effects of varying key structural design parameters over a primary design parameter space on risk-based structural performance measures. The dire need for a systematic PBSD framework for OSBs is illustrated given the significant variability in risk-based performance levels exhibited by these traditionally designed testbed OSBs. A PBSD methodology involving the design of the bridge piers is proposed wherein a risk-based feasible design domain in the primary design parameter space is identified which facilitates the risk-informed design/decision making process in the face of uncertainty. Sensitivities of risk-based feasible design domains compared with other (secondary) design variables and with the method employed for damage hazard assessment are investigated. [ABSTRACT FROM AUTHOR]

The existing machine learning (ML) models for vibration-based damage assessments often use highly compressed features or are restricted to preprocessed signals with fixed durations and sampling rates. Additionally, the learning capacities of ML models and computational resources are limited, which restricts using raw signals as direct input. This paper studied Mel filter banks (MFBs) for seismic signal processing, inspired by speech recognition technology. It is argued that the same filter designs in audio engineering may not be appropriate for seismic records, and therefore, a customized filter bank formulation was developed. Hybrid deep learning models for rapid assessments (HyDRA) were introduced as multibranch neural network architectures that enable end-to-end training for different types of processed vibration data structures. Moreover, the performance-based earthquake engineering (PBEE) equation was adjusted to integrate ML model uncertainties for probabilistic assessments. The proposed concepts were validated in a case study based on a data set of 32,400 nonlinear time-history analyses of a highway bridge in California. Insights and guidelines are provided for optimum filter design based on 5,184 experiments. Several HyDRA architectures were compared with benchmark models. The optimized MFB feature type outperformed features obtained from continuous wavelet transform and a stacked vector of conventional earthquake engineering indexes. A Bayesian variant of HyDRA was investigated to showcase its integration in the modified PBEE equation. Adopting custom filter banks with the HyDRA architecture enables effective feature extraction from raw vibration records by diversifying feature space and preserving information in the time and frequency domains. [ABSTRACT FROM AUTHOR]

This paper presents the development, testing, and characterization of an innovative low-cost fail-safe sustainable energydissipation device in which the material surrounding the moving piston and enclosed within the damper housing is pressurized sand. The proposed sand damper does not suffer from the challenge of viscous heating and failure of its end seals, and it can be implemented in harsh environments with either high or low temperatures. Its symmetric force output is velocity-independent, and it can be continuously monitored and adjusted at will with standard commercially available strain gauges installed along the post-tensioned rods that exert the pressure on the sand. Component testing at various levels of pressure, stroke amplitude, and cycling frequency show that the proposed pressurized sand damper exhibits stable hysteretic cyclic behavior with increasing pinching at larger strokes. The paper examines the fidelity of an eight-parameter Bouc-Wen hysteretic model capable to model pinching and concludes that the proposed hysteretic model is able to capture the pronounced pinching of the hysteretic behavior at larger stroke amplitudes. Four of the eight parameters of the proposed hysteretic model can be determined a priori from physical arguments; therefore, only the remaining four parameters need to be determined from nonlinear regression analysis. [ABSTRACT FROM AUTHOR]

Tennessee has been known as The Volunteer State since the War of 1812 when thousands of Tennesseans enlisted in response to Governor Blount's call for volunteers. Similarly, the state of Tennessee recently adopted the International Building Code, 2012 Edition, without amendments, expecting its exempt counties and cities to voluntarily follow suit. The seismic design sections in building codes have been one of the most controversial sections in code adoption and implementation with many voluntary adopters trying to amend seismic sections or eliminate them entirely. This is due to the lack of earthquake occurrences and the perceived cost of seismic design, an ongoing problem in the central and eastern United States for at least the last 50 years. However, although not a technical paper, this paper discusses the history of seismicity and seismic design/assessment, i.e., earthquakes and earthquake engineering in Tennessee, even before seismic design was accepted and implemented in Tennessee building codes. The paper discusses many issues that have arisen when (1) determining the seismic hazard, (2) developing the seismic designs of new structures, systems, and components (building design issues), and (3) conducting seismic assessments of existing structures, systems, and components. [ABSTRACT FROM AUTHOR]

The application of steel castings in earthquake engineering has increased significantly in recent years, and steel casting technology has been proven as a viable solution for the design and development of energy dissipative yielding elements. The first-generation of cast steel replaceable modular yielding links were recently proposed as an off-the-shelf energy dissipative product line for use in steel eccentrically braced frames (EBF). The performance of the links was validated through an extensive full-scale experimental program. These links featured a design approach in which the effective length of all links across the product line was identical. As a result of this design approach, a wide range was observed in the ductility capacity, with the smaller- to medium-capacity links achieving larger rotation capacities than the larger-capacity links. This paper presents the design and experimental validation of an alternative design of cast steel replaceable yielding links where, rather than ensuring equal length across the product line, a similar link ductility capacity is targeted for all link sizes. The new cast steel links with targeted ductility capacity are presented, and the performance of two link sizes is validated through large-scale experiments to confirm that the proposed design achieved the targeted design ductility. Each link size was tested twice: once as a standalone element and once as part of a one-story EBF system that imparted a large axial load to the link. Based on the results, the effect of axial load on the performance of EBF links is discussed. [ABSTRACT FROM AUTHOR]

Composite plate shear walls–concrete-filled (C-PSW/CF) are a new and innovative lateral force–resisting system intended for high-rise buildings. High-rise building applications of this system are particularly efficient in the coupled wall configuration, in which the walls are C-PSW/CF and the coupling beams are concrete filled steel box sections. This paper presents a capacity design principle for the seismic design of coupled composite plate shear wall–concrete filled (CC-PSW/CF) systems. The capacity design principle implements a strong wall–weak coupling beam approach, in which flexural yielding occurs in the coupling beams before flexural yielding at the base of walls. The coupling beams are sized to resist the calculated seismic lateral force level. The composite walls are sized to resist an amplified seismic lateral force corresponding to the overall plastic mechanism for the structure, while accounting for the capacity-limited forces from the coupling beams and the coupling action between the walls. The paper summarizes the recommendations and requirements for appropriate sizing of the composite coupling beams and walls. These recommendations were used along with the capacity design principle to design four example (8–22-story) structures and evaluate their seismic behavior. The structures were modeled using benchmarked finite-element models and fiber-based models that accounted for the various limit states, including steel yielding, local buckling, fracture, concrete crushing, confinement, and tension cracking. The numerical models were analyzed for monotonic pushover loading and scaled seismic ground motions. The structural responses from the nonlinear pushover analysis and the nonlinear time history analyses were in accordance with the capacity limited design philosophy, thus confirming its efficacy. [ABSTRACT FROM AUTHOR]

The capability of the wave method for structural health monitoring, based on fitting a layered Timoshenko beam by waveform inversion of impulse responses, to localize damage is investigated using shake table experiment data. The specimen is a full-scale slice of a seven-story reinforced concrete (RC) shear wall building, which was tested on the University of California San Diego–Network for Earthquake Engineering Simulation (UCSD-NEES) outdoor shake table under consecutive exposure to four earthquake motions with increasing intensity, which progressively damaged the structure. The damage is localized by partitioning the beam into horizontal layers, comprising a single floor in the parts with the most severe damage and a group of floors in the lightly damaged parts, and detecting changes in the wave velocities in each layer with respect to a reference state. Small amplitude, ambient vibration response data were used as input for the inversion. The paper describes a number of improvements in the methodology, which were necessary to improve the quality of the inversion, the success of the method to detect the existence and the intensity of the damage in different parts of the structure, and how it fared in comparison to other methods applied to the same test structure. Also, recommendations are proposed for future improvements of the method. [ABSTRACT FROM AUTHOR]

There are two goals in this paper: (1) the presentation of a comprehensive database of over 4,000 fundamental period and damping measurements from nearly 1,000 buildings; and (2) the derivation of predictive models for period and damping. The modeling approach presented in the companion paper, which accounts for the statistically nonconforming properties that characterize building data, is used herein to derive models which include two intrinsic sources of variability: that associated with multiple measurements from different excitations on the same building and variability between buildings that are nominally identical. The period models are in general agreement with those currently used, with model parameters that are in terms of height, material, and lateral force resisting system. The damping models show a decrease in damping as building height increases and, for steel and reinforced structures, a twofold increase in damping for earthquake excitations as opposed to other, lower amplitude excitations. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of rebars' corrosion monitoring systems on the vulnerability assessment and life-cycle cost analysis (LCCA) of reinforced concrete (RC) bridge piers subjected to repeated earthquake loading. A methodology is proposed to investigate the life-cycle economic savings gained with the use of a structural health monitoring (SHM) system made of corrosion sensors, exploiting the construction of damage-dependent fragility curves and using the pacific earthquake engineering research (PEER) equation to calculate the seismic probability of failure. The availability of corrosion sensors' data is accounted for in the degradation model for assessing the probability of failure by assuming that the recorded corrosion parameters are deterministic variables during the monitored period. Monitoring data are simulated by choosing values from the literature for the parameters representing the corrosion conditions. Seismic damage accumulation is considered through Monte Carlo (MC) simulations of long-term seismic scenarios considering the mean annual rate of earthquake occurrence obtained by the seismic hazard curves. The results of the methodology application to a case study highlight the importance of incorporating corrosion effects for the correct estimation of seismic life-cycle vulnerability. They are also used to discuss the advantage in terms of the safety and economy of including corrosion sensors for optimizing maintenance activities as opposed to purely inspection-based evaluations. [ABSTRACT FROM AUTHOR]

This paper presents full-scale experiments and computational analyses on exposed column–base plate connections with ductile anchors. The aim is to examine the seismic performance of these connections for their prospective use as weak bases, wherein steel moment frames are designed to concentrate inelastic rotations in the base connections rather than in the connected columns. The connections feature upset thread anchor rods in which the threads are milled to a smooth shank, providing a designated stretch length over which inelastic deformations may be concentrated. The shank is frictionally isolated from the footing using polyethylene tape. The four full-scale experiments investigate the effects of axial force, rod diameter, and rod material grade. The test specimens withstand (without anchor rod failure) the application of two Applied Technology Council–the Joint Venture partners of the Structural Engineers Association of California, the Applied Technology Council, and the Consortium of Universities for Research in Earthquake Engineering (ATC-SAC) protocols applied consecutively (each to drift amplitudes of 5%), followed by additional cycles to 6.5% drift amplitude. Complementary line element–based and continuum finite-element simulations are conducted to examine to what extent the experimentally observed response may be generalized to untested configurations. Implications for design are summarized, along with the limitations of the study. [ABSTRACT FROM AUTHOR]

Fluidic self-centering devices operate on principles similar to those of fluid viscous dampers, but with additional capabilities to provide recentering force (or preload) and stiffness. The functions of preload, stiffness, and damping are entirely controlled by the physical properties, volume, and initial pressure of fluid, and the shaping of the orifices. They are characterized by compactness in comparison to the output force and stroke. They are proposed as self-centering bracing systems for buildings. This paper presents: (1) a description of the behavior of these devices that is on the basis of principles of mechanics, (2) models of behavior of the devices, (3) results of testing of a number of these devices to demonstrate their behavior, and (4) validation of the analytical models. The test results include those of two devices tested over a period of 22 years that demonstrate the stability of the properties of the devices. [ABSTRACT FROM AUTHOR]

With the occurrence of devastating natural disasters worldwide, even though initially used interchangeably with green or environmental development, sustainability has evolved to possess social and economic implications as well. Therefore, a complete sustainability assessment of any civil infrastructure requires an evaluation of its three major components: cost, and environmental and social impacts. Because the construction industry is a pioneer in the sustainability movement, the civil engineering community at large needs an integrated methodology for conducting sustainability assessment of civil infrastructure. This paper focuses on the environmental impact assessment component of sustainability within a comprehensive framework for conducting a life-cycle assessment of structures subjected to natural hazards. Although environmental emissions and waste generation in the initial manufacturing and construction phases make significant contributions to the total environmental impact, long-term structural performance (including damage resulting from natural hazards) plays an important role in the sustainability of a structure. The damage experienced by a structure in future natural hazards might substantially increase the total environmental impact because of repair activities. In this paper, a life-cycle environmental impact assessment methodology is proposed with specific emphasis on RC buildings subjected to earthquakes. The methodology is applied to a RC building, and the results confirm the importance of the lifecycle environmental impact assessment as an essential component of sustainability in the presence of seismic threats. [ABSTRACT FROM AUTHOR]

This paper describes the cyberinfrastructure (CI) of the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) and examines the evidence that this infrastructure is facilitating earthquake engineering research. Among the key features of the CI are the NEES Project Warehouse (PW), which is a data repository for earthquake engineering, an environment that supports the use of tools for web-based data analysis and simulation, and tools that support research collaboration. The value that such CI offers to the user community is discussed. The CI also gathers a myriad of usage statistics, some of which are presented in this paper. Among them are the number of users, pageviews, recorded NEES projects, and other stored resources. This information demonstrates that the CI is used significantly and increasingly so. [ABSTRACT FROM AUTHOR]

Realistic time history simulation of drilled pier/pile-soil systems under dynamic and static loading is essential for the development of effective performance-based earthquake designs of deep foundations. This paper presents the results of the numerical simulation of a series of static and dynamic tests on drilled piers performed at the University of California, Berkeley. A nonlinear soil model was implemented based on multiaxial cyclic bounding-surface plasticity within a general finite-element framework, OpenSees. The model requires a small number of parameters that can be easily obtained through conventional site investigations. The results of the simulations show that the model can reasonably simulate nonlinear response of the soil and that it does a good job of capturing the actual load deformation curves obtained from in situ dynamic and static pier load tests. Although the model is suitable for a fully nonlinear total stress analysis of soil-pile systems under multidirectional shaking, further studies are needed to enhance the model capacity by incorporating the cyclic stiffness and strength degradation caused by full stress reversals. [ABSTRACT FROM AUTHOR]

In this paper the resulting equation for natural vibration of buildings with coupled shear walls is proved to be the forth-order Sturm–Liouville differential equation, and a hand method for determining the first two periods of natural vibration of the buildings is presented. The method is accurate and simple, compared with other calculating methods. Once the structural parameters αH and μ of coupled shear wall building are computed, the periods of the buildings can be readily obtained. The value of the method is that it will allow a more consistent and accurate use of code formulas for calculating the earthquake induced maximum base shear in a building. Use of the method is economical with respect to both computer time and equipment, e.g., a hand calculator would suffice to handle the calculations of periods of the buildings. This paper is thought to be useful for the practicing engineer. [ABSTRACT FROM AUTHOR]

This paper analyzes the economic impact of an earthquake on transportation network that contains more detail for the Midwest states. Two aspects of cost are considered in the paper: final demand loss and transport cost increase. The 1812 New Madrid earthquake is used to develop a scenario for the analysis. The modeling system includes a transportation network loss function, a final demand loss function, and an integrated commodity flow model. After running the earthquake scenario, the analysis identifies the most significant link on the network in an economic sense as well as the link with the greatest physical disruption. The results reveal that the links with greater physical disruption are not always the ones exhibiting the greater economic damage. The resulting outputs can provide information to perform a cost-benefit analysis as well as to support a decision-making process on the optimal retrofit priority of bridges and links on the transportation network. [ABSTRACT FROM AUTHOR]

This paper examines the feasibility of roll-threading superelastic Cu-Al-Mn shape memory allow (SMA) rods. The key idea behind this study was to perform roll-threading between quenching and aging, where cold workability of the material is relatively high. To obtain excellent superelasticity, single-crystal superelastic Cu-Al-Mn SMA rods were prepared with 16-mm diameter and 300-mm length. Threadability was studied by dimensional inspection and surface observations. Mechanical properties of the threaded rods were examined by cyclic tension tests. Comparisons between rolled and cut threads were made by cutting each single-crystal rod into halves to obtain two rod specimens having the same crystal orientation, thus ensuring fair comparison by excluding the influence of variations in orientations of the single-crystal rod. From the study, it was demonstrated that roll-threading of Cu-Al-Mn SMA rods was possible if roll-threading is performed between quenching and aging. Since additional heat treatment from the ordinary manufacturing process is unnecessary, roll-threading of Cu-Al-Mn SMA rods is as easy as that of steel rods. It was also demonstrated that the roll threads had significantly superior fatigue resistance compared with the cut threads of the same size. These results suggest that superelastic Cu-Al-Mn SMA rods with rolled threads are suitable for mass production to be used in structural and earthquake engineering applications. [ABSTRACT FROM AUTHOR]

Engineering practitioners have widely adopted probabilistic methods for estimating liquefaction triggering hazards. Unfortunately, incorrect application of these methods has become commonly accepted in the United States and throughout many parts of the world. In this paper, we describe two specific incorrect applications of probabilistic liquefaction triggering prediction models that are commonly used in engineering practice: (1) improper parametric uncertainty characterization when using the models, and (2) the application of a conservative factor of safety thresholds to deterministic cyclic resistance ratio boundaries. These two practices and their implications are discussed, and illustrative examples and figures are presented. We also discuss the apparent inconsistencies in what constitutes an acceptable risk for liquefaction hazards and other significant geotechnical hazards, such as slope stability. We demonstrate the need to collectively consider the likelihoods of all aspects of liquefaction hazard problems—susceptibility, initiation, and effects—when calculating and considering liquefaction risk. Finally, we point to the concept and framework of performance-based earthquake engineering as a logical and objective path forward for dealing with the challenges raised in this study. [ABSTRACT FROM AUTHOR]

Research was conducted to investigate the seismic performance of steel plate shear walls (SPSWs) having infill plates designed to resist different percentages of the applied lateral loads. The FEMA P695 methodology, which defines the performance in terms of collapse potential under maximum considered earthquake (MCE) ground motions, was used to compare the performance of the SPSWs under consideration. This paper describes the development of component strength deterioration models that are needed to perform the collapse assessment of SPSWs, focusing on stress-strain or force-deformation relationships for infill plates and boundary elements. The approach began with identifying the deterioration and failures modes of SPSW from 36 tested specimens. Cyclic deformation capacities of these SPSWs when reaching their ultimate strength, failure points, and rates of degradation were statistically quantified. Based on these statistical results, initial deterioration models for SPSW components were developed in a format compatible for use with the FEMA P695 procedures. The chosen deteriorated material models for infill plates and boundary elements were calibrated to four selected SPSW specimens varying from one to four stories. A companion paper presents the steps and results of the seismic performance assessments. [ABSTRACT FROM AUTHOR]

In performance-based earthquake engineering framework, seismic fragility functions play a fundamental role for quantifying the seismic resilience. There are three main approaches for performing the seismic fragility analysis: cloud analysis, incremental dynamic analysis (IDA), and multiple strip analysis (MSA). These approaches require different levels of computational efforts and yield different levels of accuracy on fragility curve estimates, leading to different predictions of seismic resilience. This paper presents an efficient method for converting fragility curves from the cloud to IDA and MSA and from IDA to MSA toward an efficient and high-fidelity resilience assessment. The proposed method requires two fragility points to obtain the fragility median and dispersion parameters that yield converted fragility curves agreeing with the target fragility curves. This method and associated resilience assessment are demonstrated through two case studies, one a typical two-span highway bridge in firm ground under longitudinal seismic excitations and the other an extended pile-shaft-supported bridge in liquefaction-induced laterally spreading ground under transverse seismic excitations. The results show that the converted fragility curves coincide very well with the target fragility curves. An efficient and high-fidelity resilience assessment can be achieved leveraging the proposed method. For easy implementation, codes of the proposed method are available online. [ABSTRACT FROM AUTHOR]

Superelastic shape memory alloys (SMAs) have attracted considerable interest in the field of earthquake engineering recently due to their excellent self-centering and moderate energy dissipating capabilities. This unique feature provides promising solutions that can be used in the passive control of structures under strong earthquakes. However, the hysteresis properties of the SMAs have a great influence on the response of the structures. A prominent problem of most previous SMA constitutive models is that they do not consider the strain-rate-dependent effect, especially the mechanical behavior in the typical frequency range of interest for seismic applications. Moreover, the variability effect of the SMA's hysteresis parameters on the performance in seismic applications is not addressed comprehensively. For this reason, it is important to explore the response sensitivity analysis of an improved SMA constitutive model and gain insight into the effects of various thermomechanical parameters. This paper presents an efficient and accurate sensitivity analysis method for the strain-rate-dependent model of SMAs based on the direct differentiation method (DDM). The constitutive model of SMAs involves three coupled quantities, i.e., stress, martensite fraction, and temperature. The model is expressed numerically using the first-order ordinary differential equations and is solved by the fourth-order Runge–Kutta method. Both the consistent tangent modulus and the stress sensitivity of the SMAs are derived and integrated into the DDM framework. The newly developed algorithms are implemented in a general nonlinear finite element analysis program, OpenSees, and are further verified by the time history analyses of a multi-story steel frame designed with SMA braces. The results demonstrate that the developed DDM-based sensitivity algorithm is accurate and efficient and can provide an excellent solution to the response sensitivity analysis of the thermomechanical strain-rate-dependent model of SMAs. [ABSTRACT FROM AUTHOR]

Liquefaction-induced lateral spread has caused substantial damage to buildings, bridges, embankments, buried utilities, and other critical components of infrastructure in numerous past earthquakes. Although many practitioners use analytical Newmark-based seismic slope displacement models to estimate liquefaction-induced lateral spread displacements, empirical regression models remain popular among most practicing professionals today. However, all lateral spread estimates have a significant level of uncertainty. This paper introduces a procedure to develop performance-based estimates of liquefaction-induced lateral spread displacement by incorporating a widely used empirical model into a probabilistic framework. Utilizing the same principles used in probabilistic seismic hazard analysis, the empirical lateral spread equation is modified and inserted into a performance-based framework modeled after the framework introduced by the Pacific Earthquake Engineering Research Center. Lateral spread hazard curves are developed for 10 sites located across the United States using a generic soil profile. The results of the performance-based lateral spread method are compared with those of conventional pseudoprobabilistic methods. Consistent application of the conventional methods is shown to produce inconsistent actual lateral spread displacement hazards in different seismic environments. Practical design implications for the proposed performance-based procedure are discussed, and a simple example application is presented. [ABSTRACT FROM AUTHOR]

With the increasing occurrence of extreme wind events (e.g., hurricanes) and growing interest in performance-based wind engineering, a better understanding of the structural response and collapse under extreme wind loads is needed. Studying the inelastic nonlinear response of buildings through collapse under wind hazards can lead to safer structures and inform future economic designs. The objective of this paper is to investigate the performance of a 20-story steel moment-resisting frame, from the SAC project, under wind loads at different wind speeds. SAC is a joint venture between the Structural Engineers Association of California (SEAOC; the S in SAC), the Applied Technology Council (ATC; the A in SAC), and California Universities for Research in Earthquake Engineering (CUREe; the C in SAC). The building design was first assessed for compliance based on the latest code requirements. Next, a nonlinear dynamic analysis under three different hazard levels was used to conduct a performance-based assessment. The analysis showed that the building conservatively meets the different performance targets. The building was deliberately underdesigned, which resulted in an 18% reduction in used materials, to conduct a comparative nonlinear response analysis and performance-based assessment. The nonlinear analysis for both building designs was extended under increased wind loads through collapse. Overall, the different parts of the study confirm that current code methods can lead to overly conservative structural designs and suggest that incorporating a performance-based approach along with a well-controlled nonlinear response under extreme wind events can lead to safer and more economical designs and is worthy of further investigations. [ABSTRACT FROM AUTHOR]

Ductile concrete materials with randomly oriented fibers have been studied to improve the strength, displacement capacity, and damage tolerance of reinforced concrete structural components in seismic applications. Performance-based earthquake engineering requires numerically efficient models that are capable of estimating the hysteretic behavior, including the strength, stiffness, cyclic degradation behavior, and failure criteria. This paper discusses the development of an experimental database and its use in the calibration of a phenomenological model to simulate the nonlinear behavior of reinforced ductile concrete components under cyclic loading. The modeling parameters are calibrated to predict the initial stiffness, lateral strength, deformation capacity, and cyclic and in-cycle degradation. Backbone parameters were selected using a mechanics-based approach combined with a calibration of hysteretic parameters to match an energy-based damage index. A large-scale experimental database with a variability in material properties, geometry, testing configurations, and fiber types was used for calibration purposes. A forward stepwise regression analysis was conducted to develop an empirical equation for a stiffness reduction factor and a cyclic strength degradation parameter as functions of material behavior and geometry. The modeling strategy is validated by comparing an experimental and simulated cyclic response across a range of metrics. The spring-hinge models are then applied to evaluate the collapse risk of the archetype frame structures using ductile concrete material in the potential plastic hinge region of the beams. The collapse performance is evaluated through an incremental dynamic analysis in which the results of reinforced concrete structures with and without ductile concrete material are compared in terms of the median collapse capacity, fragility curve, mean annual frequency, and sequence of hinge formation in the collapse mechanism. The outcome of this research provides much needed insight into how ductile concrete materials can influence structural system-level seismic performance. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study that was conducted to investigate the postfire seismic behavior of reinforced concrete columns. Five full-scale, flexure-critical code-complying (e.g., ACI 318-14) cast-in-place reinforced concrete columns were tested to failure under a constant axial load and reversed cyclic lateral displacements after being exposed to an ISO-834 standard fire for 30, 60, and 90 min. Other than the effects of the duration of the fire exposure, the effects of the thickness of the concrete cover (25 and 40 mm) on the structural performance was also investigated for the short fire exposure duration (30 min). The responses of the columns were analyzed in terms of lateral load-displacement relationships, ductility, stiffness, energy dissipation capacities, and residual displacements. The test results indicated that the fire exposure reduced the lateral load capacity of the columns, whereas the deformability capabilities were found to be satisfactory in terms of a structural response. It was also observed that the thickness of the concrete cover had only a slight influence on the postfire seismic behavior of the columns. Furthermore, a numerical study was conducted to predict the load-displacement response of the fire exposed columns. The comparison of the experimentally and numerically obtained load-displacement relationships indicated that the principles of structural mechanics usually applied to conventional columns are also valid for the columns exposed to fire. [ABSTRACT FROM AUTHOR]

This paper investigates the limit states of a circular masonry arch supported on rectangular buttresses when subjected to lateral inertial loading in addition to gravity loading by employing the principle of stationary potential energy. Depending on the slenderness of the arch compared to the slenderness of the buttresses, the study identifies two lower failure mechanisms: (1) a four-hinge mechanism within the arch alone; and (2) hinging of the arch in three locations together with a hinge at the base of the downstream buttress. In this analysis, radial ruptures are assumed for the arch, while the buttresses may rupture either horizontally or develop an oblique elongation failure along which the compression-free portion of the buttress separates. It is concluded that the hinging mechanism that triggers an oblique elongation failure of the downstream buttress is the most critical and initiates at a lower value of the seismic coefficient than the value associated with the mechanism that involves a horizontal fracture at the buttress. Finally, it is shown that the discrete-element method (DEM) captures the results of the proposed variational method with remarkable accuracy. [ABSTRACT FROM AUTHOR]

Ground-improvement techniques, such as jet-grout columns, may have positive effects on structures founded on soft soil when subjected to earthquake loading. The main objectives of this paper are first to evaluate the effects of soil-improvement width and depth on the ground response of a layered soil and, second, to define critical zones in which cemented columns might crack. A series of numerical calculations are performed by means of the finite-element method, considering a linear viscoelastic model for soil layers and rigid bedrock condition, and also by applying an advanced constitutive model for simulating the behavior of jet-grout columns. The soil profile consists of a 10-m loose sand layer overlain and underlain by a 5-m dense sand layer. The acceleration time recorded during the Loma Prieta earthquake in 1989 is used as the input motion. The results show that the seismic load is decreased or may increase as a result of ground improvement. In addition, it is shown that by applying an advanced model, possible crack zones in cemented columns can be identified. [ABSTRACT FROM AUTHOR]

Bridge design spectra in the current design specifications are geometric mean based. In other words, the underlying research on which ground motion data are based predicts the geometric mean spectral acceleration of two horizontal components. This is, perhaps, transparent to many engineers performing bridge design in regions subject to extreme seismic loading. For response spectrum analyses, this does prove problematic when estimating structural response to bidirectional ground motions. Prevailing combination rules rely on the assumption that, when one component produces the maximum structural response, the second component produces 30% of the corresponding maximum. The purpose of this paper is to assess the validity of this prevalent rule for sites characterized by large magnitude earthquakes (MW = 67.7) and Site Class D/E subsurface conditions. This study further provides estimates of maximum-to-geometric mean displacement ratios for various levels of ductility and provides estimates of dispersion for inelastic displacements. [ABSTRACT FROM AUTHOR]

In nonlinear structural dynamics, direct integration algorithms are used to solve the differential equations of motion after they are temporally discretized. Explicit algorithms do not require iterations and thus avoid numerical problems of convergence by making use of certain approximations. Thus, they are appealing for multi-degree-of-freedom (MDOF) nonlinear dynamic problems. In this paper, the study previously conducted by the authors for nonlinear single-degree-of-freedom systems is extended to MDOF ones to investigate the Lyapunov stability of explicit algorithms. For this purpose, a generic-explicit integration algorithm is formulated for generic MDOF nonlinear systems with softening or stiffening behavior governed by nonlinear functions of the restoring forces. This approach transforms the stability analysis of the formulated nonlinear system to investigating the strictly positive realness of its corresponding transfer function matrix. Furthermore, this is equivalent to a problem of convex optimization that can be solved numerically. Using this approach, a sufficient condition that the bounds where the explicit algorithm is stable in the sense of Lyapunov for the MDOF nonlinear system can be obtained. This approach is applied to two commonly used explicit integration algorithms for a bridge structure and also demonstrated by a generic nonlinear multistory shear building. [ABSTRACT FROM AUTHOR]

A previous study by the authors provides an overview of existing seismic risk assessment approaches and available seismic fragility information and highlights the lack of relevant information for nonengineered residential buildings. The current paper proposes a procedure for developing empirical seismic fragility curves for nonengineered residential buildings using the U.S. Geological Survey (USGS) seismic ground motion and shaking intensity maps presented in a geographic information system (GIS) format, to overcome the lack of ground motion recordings. The proposed procedure has been applied to a damage data set collected in Bantul Regency, Indonesia, in the aftermath of the May 2006 Yogyakarta earthquake. Fragility curves for nonengineered single-story unreinforced masonry (URM) residential buildings have been derived using the damage data set for the peak ground acceleration (PGA) and pseudospectral acceleration (PSA) as the ground motion intensity measures. The developed fragility curves indicate the high seismic vulnerability of nonengineered residential buildings. This study also demonstrates the potential of utilizing USGS seismic ground motion data to develop empirical fragility curves for nonengineered residential buildings in developing countries. In addition, a comparison of the results from other seismic risk assessment studies highlights the significant influence of the derivation method used on the fragility curve characteristics. [ABSTRACT FROM AUTHOR]

Design of bridges for seismic effects has changed significantly since it was originally included in the AASHTO Standard Specifications for Highway Bridges (the standard specifications) as Division IA in 1991. In addition to design changes, the seismic hazard in many areas of the United States has changed significantly in the AASHTO LRFD Bridge Design Specifications (the LRFD specifications) based on a change in the return period of the design earthquake and seismological research. A new option for seismic design, the AASHTO Guide Specifications for LRFD Seismic Bridge Design (the guide specifications), has been published providing an alternative, displacement-based design procedure. This paper provides a case study of three existing bridges in Alabama designed according to the standard specifications. The seismic resisting system of the existing bridges was redesigned based on the guide specifications and the LRFD specifications. The paper explores the effect of changes in design procedures and seismic hazard on detailing of bridges in a moderate seismic zone. The two specifications are compared for the worst-case hazard in Alabama; i.e., Seismic Design Category B. The results demonstrate that using the guide specifications results in larger spacing of lateral reinforcing in the plastic hinge regions of substructure components and drilled shafts resulting in more economical designs. [ABSTRACT FROM AUTHOR]

In catastrophe risk and probabilistic hazard evaluations, one overarching issue is how to account for uncertainties. One influential school of thought employs a sharp distinction between aleatory (pertaining to randomness) uncertainty and epistemic (pertaining to knowledge) uncertainty, and uses this distinction to derive total uncertainty in risk and probabilistic hazard evaluations. This paper first critiques two quantitative versions of this sharp distinction. The first version applies only to single models. The second version applies to a weighted combination of rival models. This paper shows that serious contradictions and biases arise for each version, as elaborated by its advocates. Given these contradictions and the need to address the overarching issue of uncertainties in risk evaluations, this paper goes on to sketch an alternative approach called robust simulation, which applies to catastrophe risk and probabilistic hazard results. Robust simulation first develops results from a single preferred model, and then proceeds to find and evaluate results from the most divergent yet credible rival models. In addition to producing many simulations from models, this approach also tests resulting distributions in terms of their stability. [ABSTRACT FROM AUTHOR]

It is known that the effectiveness of tuned mass dampers (TMDs) decreases as the input duration shortens. As a result, their use is commonly discouraged against short-duration, pulse-like ground motions, such as those occurring in near-field (NF) zones in the presence of forward directivity or fling-step effects. Yet a systematic assessment of such control impairment is still missing. In this paper, a recent analytical model of ground motion pulses is applied to the design and evaluation of TMDs against impulsive earthquakes. Based on this model, first, a new optimization method is introduced as an alternative to the classical approach. Then, the two strategies are tested on single- and multi- degrees-of-freedom linear structures subject both to analytical pulses and to a large set of NF records possessing pulse-like features. The resulting statistical evaluation, expressed by percentile response spectra, shows the pros and cons of a pulse-oriented TMD design and improves the general understanding of TMD performance under impulsive ground motions. [ABSTRACT FROM AUTHOR]

Parallel computing in civil engineering has been restricted to monotonic shock or blast loading with explicit algorithm which is characteristically feasible to be parallelized. In the present paper, efficient parallelization strategies for the highly demanded implicit nonlinear finite-element analysis (FEA) program for real scale reinforced concrete (RC) structures under cyclic loading are proposed. Quantitative comparison of state-of-the-art parallel strategies in terms of factorization were carried out, leading to the problem-optimized solver, which successfully embraces the penalty method and banded nature. Particularly, the penalty method employed imparts considerable smoothness to the global response, which yields practical superiority of the parallel triangular system solution over those of advanced solvers such as the parallel preconditioned conjugate gradient method. Other salient issues on parallelization are also addressed. By virtue of the parallelization, the analysis platform offers unprecedented access to physics-based mechanisms and probabilistic randomness at theentire system level and realistically reproduces global degradation and localized damage, as reflected from the application to a RC structure. Equipped with accuracy, stability and scalability, the parallel platform is believed to serve as a fertile ground for the introducing of further physical mechanisms into various research fields, as well as the earthquake engineering community. [ABSTRACT FROM AUTHOR]

In seismically active areas, waste-containment systems (WCS) can be damaged by earthquakes that generate significant ground acceleration. In such circumstances, contaminants can be released into the environment. Current state-of-the-art earthquake damage risk-assessment methodologies, Hazards U.S. Multi-Hazard (HAZUS-MH), need to incorporate contaminant-release models to enable more complete environmental impact assessments for existing and planned waste-containment systems. Contaminant-release and transport probabilities that determine the prospect of functional failure of waste-containment systems depend on a wider range of structural, geologic, hydrologic, and human factors than are covered by the structural failure probabilities of conventional structures such as buildings, roads, and bridges. The release of contaminants from WCS, and the cost of remediation depend on conditional probabilities that span the intensity and frequency of the initiating event, the structural damage of the WCS, and the fate and transport of the released contaminants in the subsurface. In this paper, the necessity and approach to linking HAZUS-MH to contaminant-release models are discussed along with relevant factors. The quantitative link that is advocated in this paper would expand the utility of HAZUS-MH in facilities design and environmental impact assessments. [ABSTRACT FROM AUTHOR]

This paper describes a displacement-based method of analysis for the performance-based seismic design of regular buildings with reinforced-concrete bearing walls acting as the lateral-force resisting system. The method considers two performance levels: immediate occupancy (IO) and life safety (LS), each anchored at a specific seismic hazard level. It explicitly accounts for the combined effects of inelastic first mode of response, kinematic system overstrength, and higher modes of response. Quantification of these effects is required to capacity-protect the structure and to ensure the intended performance. As an example, the method is applied to a full-scale 7-story reinforced-concrete building slice, built and tested on the George E. Brown Jr. Network for Earthquake Engineering Simulation Large Outdoor High-Performance Shake Table at the University of California-San Diego. The response of the test building largely verified the method discussed in this paper. [ABSTRACT FROM AUTHOR]

This paper develops a new framework for modeling design earthquake loads for inelastic structures. Limited information on strong ground motions is assumed to be available only at the given site. The design earthquake acceleration is expressed as a Fourier series, with unknown amplitude and phase angle, modulated by an envelope function. The design ground acceleration is estimated by solving an inverse dynamic problem, using nonlinear programming techniques, so that the structure performance is minimized. At the same time, the design earthquake is constrained to the available information on past recorded ground motions. New measures of the structure performance based on energy concepts and damage indexes are introduced in this paper. Specifically, the structural performance is quantified in terms of Park and Ang damage indexes. Damage indexes imply that the structure is damaged by a combination of repeated stress reversals and high-stress excursions. Furthermore, the use of damage indexes provides a measure on the structure damage level, and making a decision on necessary repair possible. The material stress-strain relationship is modeled as either bilinear or elastic-plastic. The formulation is demonstrated by deriving the design earthquake loads for inelastic frame structures at a firm soil site. The damage spectra for the site are also established, to provide upper bounds of damage under possible future earthquakes. [ABSTRACT FROM AUTHOR]

The energy dissipated per cycle and the characteristic strength of lead-rubber bearings reduce with increasing number of cycles as a result of heating of the lead core. The reduction is substantial depending on the geometric characteristics of the bearing and the speed of motion. This paper presents a theory that is capable of predicting the dependency on time of the characteristic strength and energy dissipated of lead-rubber bearings. The theory is based on predicting the temperature of the lead core and relating the temperature to the strength. A much simpler theory is also presented based on neglect of heat conduction through the steel shim and end plates of the bearing. The theory is useful in predicting the cyclic behavior of lead-rubber bearings for simplified analysis, in extrapolating experimental data from one scale to another and in developing models for dynamic response history analysis of seismically isolated structures that account for the time-dependent mechanical properties of the bearings. A companion paper presents results of eight tests of six lead-rubber bearings that provide verification of the theoretical solution. [ABSTRACT FROM AUTHOR]

Conventional design of steel plate shear walls (SPSWs) assumes that 100% of the story shear is resisted by each infill panel. Following this approach, strength provided by the boundary frame moment resisting action, which provides the SPSW with overstrength, is neglected. While this design assumption has a positive impact on seismic performance of SPSWs, no analytical work has been done to quantify the magnitude of this overstrength in general terms. Such preliminary work is conducted in this paper. Based on plastic analysis of SPSWs, this paper investigates the relative and respective contributions of boundary frame moment resisting action and infill panel tension field action to the overall plastic strength of SPSWs, followed by a proposed procedure to make use of the strength provided by the boundary frame moment resisting action. Procedures for design of SPSWs having weak infill panels are also developed in this paper. Then, results from a series of time history analyses using validated models are presented to compare the seismic performances of SPSWs designed using different design assumptions. Future work needed to provide greater insight on SPSW designs is also identified. [ABSTRACT FROM AUTHOR]

Recent earthquakes have shown that research in earthquake engineering has to be focused on the assessment of vulnerability of existing constructions lacking appropriate seismic resisting characteristics. In fact, older buildings, designed and constructed until the late 1980s, without considering earthquake provisions, constitute a significant hazard in many cities of southern Europe. Therefore, the retrofit should be made in order to reduce the vulnerability, and, as a consequence, the risk to currently accepted levels. To this scope, the scientific community is developing more accurate methodologies in order to evaluate seismic performances of existing structures. Within this framework, the present paper aims at the evaluation of the mean annual frequency of exceeding a limit state of existing concrete frames by means of the probabilistic approach introduced by the Pacific Earthquake Engineering Research, adopting the application procedure suggested by Jalayer and Cornell and accounting for the uncertainties involved in the seismic response of structures. This procedure properly combines the probabilistic seismic hazard analysis with probabilistic seismic demand analysis and, finally, with the probabilistic seismic capacity analysis. In order to evaluate the seismic reliability of existing structures taking also into account for the model uncertainty, in this paper reference is made to experimental results derived from technical literature. In particular, three full-scale frames (bare frame, frame with brick infilled walls and frame with infilled walls reinforced with shotcrete) tested pseudodynamically at the ELSA Laboratory of Ispra have been considered. The developed analysis allowed to evaluate the seismic reliability of the bare frame, the influence of the infill panels, and, finally, the reliability of the retrofitting solution with shotcrete. [ABSTRACT FROM AUTHOR]

The majority of buildings and the vast majority of residential structures in North America are constructed using light-frame wood. Many of these structures are subjected to high winds along the eastern seaboard and gulf coast, and as a result routinely suffer damage resulting in financial losses. A relatively new paradigm in the field of earthquake engineering is performance-based design. This paper presents the concept of performance-based wind engineering for wood-frame buildings through the development and application of fragilities to form different owner/user performance expectations, namely, occupant comfort, continued occupancy, life safety, and structural integrity. The approach includes the development and application of fragility curves. An example analysis and design for a simple light-frame wood building for all four performance expectations is presented. The final design of the building needed to achieve the specified levels of structural performance are discussed for each performance expectation level. [ABSTRACT FROM AUTHOR]

This paper presents an observer designed under the assumption that differences between predicted and measured outputs arise from discrepancies between the real structural system and the nominal model used to represent it. The observer gain is independent of the assumed model error parametrization and proves to be the transpose of the state to output matrix of a state space formulation. The estimated state with the proposed observer is shown to be identical to that obtained by exciting the nominal model with the known input while adjusting the measured portion of the state to match the measurements at the start of every step. Numerical experiments suggest that the proposed observer can provide state estimates that are substantially more accurate than results predicted by projecting the measurements in a truncated modal space. [ABSTRACT FROM AUTHOR]

This paper continues to address the overarching goal to provide a more unified understanding of NiTi shape memory alloys intended for use in structural applications by attempting to link standard processing practice and basic materials characterization to the deformation behavior of large diameter bars. Results from cyclic tensile tests performed on large diameter Ni-rich polycrystalline NiTi bars are presented. Coupon specimens taken from deformation processed bars with diameters of 12.7, 19.1, and 31.8 mm are tested along with their respective full-scale specimens. The coupon tests results reveal small and highly variable differences between specimens taken from the different size bars. The full-scale specimen tests continue to show the presence of the R phase, but lack a Lüders-like transformation. A comparison of the results suggests that coupon specimens provide only limited information in terms of the full-scale behavior. Full-scale tests using an earthquake-type loading then show similar behavior to the tensile cyclic tests suggesting the ability to use NiTi in structural applications. Overall, this paper and Tyber et al. 2007 provide a multiscale analysis of NiTi shape memory alloys to be used by both material scientist and civil engineers in the development of applications for NiTi. [ABSTRACT FROM AUTHOR]

This paper presents a rigorous derivation of a previously known formula for simulation of one-dimensional, univariate, nonstationary stochastic processes integrating Priestly’s evolutionary spectral representation theory. Applying this formula, sample functions can be generated with great computational efficiency. The simulated stochastic process is asymptotically Gaussian as the number of terms tends to infinity. This paper shows that (1) these sample functions accurately reflect the prescribed probabilistic characteristics of the stochastic process when the number of terms in the cosine series is large, i.e., the ensemble averaged evolutionary power spectral density function (PSDF) or autocorrelation function approaches the corresponding target function as the sample size increases, and (2) the simulation formula, under certain conditions, can be reduced to that for nonstationary white noise process or Shinozuka’s spectral representation of stationary process. In addition to derivation of simulation formula, three methods are developed in this paper to estimate the evolutionary PSDF of a given time-history data by means of the short-time Fourier transform (STFT), the wavelet transform (WT), and the Hilbert-Huang transform (HHT). A comparison of the PSDF of the well-known El Centro earthquake record estimated by these methods shows that the STFT and the WT give similar results, whereas the HHT gives more concentrated energy at certain frequencies. Effectiveness of the proposed simulation formula for nonstationary sample functions is demonstrated by simulating time histories from the estimated evolutionary PSDFs. Mean acceleration spectrum obtained by averaging the spectra of generated time histories are then presented and compared with the target spectrum to demonstrate the usefulness of this method. [ABSTRACT FROM AUTHOR]