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A method to calculate structural functionality for building structures based on structural natural frequency was proposed for seismic loading events. Structural functionality loss and recovery were determined by monitoring the change of structural natural frequency during the earthquake events or repair activities. A shape factor was introduced, structural functionality recovery function (SFRF), to consider the repair strategy and repair speed. As an example, this method was applied to obtain the structural functionality curve and seismic resilience of a half scale two-story reinforced concrete (RC) frame structure. This structure was subjected to a series of ground motions on a shake table and then repaired by carbon fiber cloth a total of four times. The results indicate that the SFRF is able to capture the recovery trend of a structure in the repair process. Meanwhile, a damage index-repair target (DI-RT) curve, representing the 5% difference between the proposed and traditional SFRFs, was used to investigate the impact of structural damage degree and repair target. The areas above the curve indicates that the difference between the proposed and traditional SFRFs cannot be ignored. [ABSTRACT FROM AUTHOR]

Pinching characterizes the hysteretic response of several structural systems. It is associated with a reduced dissipated hysteretic energy under cyclic loading and can significantly affect seismic performance, especially under repeated earthquakes. Although several scholars proposed advanced joint arrangements with reduced pinching, ordinary timber structures present pronounced pinching effects due to the local damage to the timber joints. This paper quantifies the impact of variable pinching on the seismic performance of a timber structural archetype. The authors modeled the hysteretic response of a light-timber framed assembly using an empirical hysteresis model and assessed the sensitivity of the displacement demand of the chosen archetype to pinching, number of earthquake repetitions, and spectral acceleration. The choice of an elementary structural archetype, rather than a more complex system, allows isolating the effects of pinching, which could otherwise be disguised by other phenomena, like force redistribution between structural assemblies due to plasticization. [ABSTRACT FROM AUTHOR]

This paper investigates the seismic response analysis of the 9-story SAC building equipped with pressurized sand dampers, a new type of low-cost energy dissipation device where the material enclosed within the damper housing is pressurized sand. The strength of the pressurized sand damper is proportional to the externally exerted pressure on the sand via prestressed steel rods; therefore, the energy dissipation characteristics of a given pressurized sand damper can be adjusted according to a specific application. The strong pinching behavior of pressurized sand dampers was characterized with a previously developed three-parameter Bouc-Wen hysteretic model that for this study was implemented in the open source code OpenSees with a C++ algorithm, and it was used to analyze the seismic response of the 9-story SAC building subjected to six strong ground motions that exceed the design response spectrum for all soil categories. The paper shows that for the family of strong ground motions used in this study, pressurized sand dampers with strength of the order of 5%–10% of the weights of their corresponding floors were able to keep the interstory drifts of the 9-story SAC building at or below 1%, while base shears and peak plastic hinge rotations were reduced in the damped configuration. Supplemental damping produced mixed results on floor accelerations; nevertheless, in most floors, peak accelerations were reduced. [ABSTRACT FROM AUTHOR]

Unbonded posttensioned controlled rocking masonry walls (PT-CRMWs) have been increasingly studied in the last decades due to their promising results regarding seismic resilience. However, implementing posttensioning (PT) has still some drawbacks, such as construction challenges, PT losses, and yielding during a seismic event. In response, this study investigates a newly proposed energy dissipation-controlled rocking masonry wall (ED-CRMW), which eliminates the use of unbonded posttensioned bars and relies instead on gravity loads to self-center the wall to its vertical plumb while incorporating an energy dissipation (ED) device to limit seismic displacements. The study presents a design approach for the proposed system, including the influence of higher mode effects. In this respect, a multispring macro model is developed using OpenSees and validated against recent experimental results by the authors. Next, as no distinct values are yet provided in ASCE 7, the seismic response modification factor is investigated using collapse risk analysis. Specifically, using the validated model, nonlinear static and dynamic analyses are performed to 20 ED-CRMW archetypes with different design configurations. The results demonstrate that the design objectives were achieved and that a seismic response modification factor of 7 assigned to the selected design configurations meets the FEMA P695 acceptance criteria for seismic collapse risk under the maximum considered earthquake (MCE). [ABSTRACT FROM AUTHOR]

The seismic vulnerability of existing RC framed buildings in seismic-prone areas requires affordable and practice-oriented solutions for their retrofitting. In this paper, the authors present a retrofitting solution for RC buildings based on the combined use of cross-laminated timber (CLT) panels and asymmetric friction connections (AFCs). The AFC connection is activated when the force level reaches the design threshold. The energy dissipation of the AFC increases the structural dissipation capacity and reduces the displacement demand. This research presents the outcomes of an experimental campaign on selected prototypes of these AFC connectors. The authors assess their dissipative capacity from cyclic load tests in four different connector arrangements and examine the contribution of aluminum shim layers. The first results highlight the significant dissipation potential of the AFC, although they also provide evidence of the notable sensitivity on the design and constructive details. The authors present a modeling approach to simulate the experimental results. [ABSTRACT FROM AUTHOR]

A strong mainshock may cause several aftershocks within a short interval. These aftershocks can make buildings damaged during the mainshock more vulnerable to collapse. Hence, it is critical to study the seismic responses of a structure during aftershock events following a major shock. The focus of this work was to investigate the seismic fragility of an emerging high-performance seismic-resistant system—the self-centering energy-absorbing dual rocking core (SEDRC) system—considering mainshock–aftershock sequences, and to compare SEDRC with traditional systems. First, three- and six-story SEDRC systems were designed following the direct displacement-based design method to show comparable maximum interstory drifts compared with those of the three- and six-story benchmark buckling-restrained braced frames (BRBFs), respectively, under the design-basis earthquake excitations. Second, 30 as-recorded mainshock–aftershock sequences were selected. The dynamic analyses and incremental dynamic analyses (IDAs) were conducted to study the seismic responses of the four buildings with the mainshock inputs alone and the mainshock–aftershock sequence inputs. The analysis results show that the designed SEDRC systems and BRBFs can obtain comparable performance in limiting the maximum interstory drifts (MID) responses, whereas the SEDRC systems are more efficient in limiting the maximum residual interstory drifts (MRD). Moreover, the SEDRC systems perform much better than BRBFs in resisting structural collapse. As expected, the aftershocks would increase the MID, but may increase or decrease the MRD of the SEDRC systems and BRBFs. Finally, the seismic fragilities of the designed systems were further investigated on the basis of the results from the IDAs in a probabilistic framework using a joint probability density function with the consideration of both MID and MRD. The advantages of the SEDRC systems in achieving excellent seismic collapse-resistant and self-centering capacity were explored through probabilistic analyses. [ABSTRACT FROM AUTHOR]

This paper analyzed damping ratios inferred from 1,335 seismic responses recorded in 154 instrumented buildings in California. These values were inferred using a parametric system identification technique in the time domain, and subjected to a series of reliability screening tests to retain only high-quality data. The resulting damping ratios conformed a data set of 1,037 high-quality values inferred exclusively from the seismic response of buildings, a database several times larger than previous studies of damping inferred from seismic response. The data set was analyzed using a linear mixed-effects statistical model to account for the fact that many of the data points were clustered, because they came from damping ratios in the same building shaken by various earthquakes. It was shown that damping decreases with increasing building height, which is the factor that best explained the relatively large variance observed in the data. Contrary to some previous recommendations, it was found that once the variation with height is taken into account, the primary structural building material is not statistically significant in the damping ratio of buildings subjected to earthquakes. However, when including the combined material and lateral resistant system as a factor in the statistical model, an additional 6% of the variance was explained. Results showed that steel buildings with moment-resistant frames have, on average, a slightly higher damping ratio than those with steel braced frames. The amplitude dependency of damping showed that there was no significant correlation between damping ratio and the overall lateral deformation demand in the building as measured by the peak roof drift ratio for amplitudes typically observed during moderate earthquake motions once a minimum level of amplitude is exceeded. [ABSTRACT FROM AUTHOR]

Ground motion intensity measures (IMs) provide a link between the probabilistic seismic hazard analysis and probabilistic structural response analysis. IMs that are well correlated with the structural response allow an estimation of the seismic response of the structure with low uncertainty (i.e., high efficiency), reducing the computational effort involved in the structural response analysis. In this paper, the efficiency of 10 different IMs for estimating the seismic response of wood-frame single-family houses is evaluated and compared. Six nonlinear models of one- and two-story houses with varying fundamental periods are analyzed. Based on the results, the 5%-damped average spectral pseudoacceleration at a period of 0.16 s is the recommended IM for estimating peak interstory drifts and peak roof accelerations in wood-frame houses. On the other hand, for collapse assessment of wood-frame houses the filtered incremental displacement with one pulse segment, a 4 Hz cut-off frequency, and a period of 0.5 s, is the most efficient IM, followed by peak ground velocity which is also a very efficient alternative. Finally, an expression for the spatial correlation of 5%-damped average spectral pseudoaccelerations is developed for use in regional seismic risk assessments. [ABSTRACT FROM AUTHOR]

Ronald Hamburger I congratulate the authors for their truly impressive and thorough empirical regression analyses using data from 151 lab tests in developing first-cycle envelope curves (backbones) for use in nonlinear component modeling. Backbones are dependent on the test data used in the formulation, and the authors note that the first-cycle envelope curves are load-history dependent. The purpose of this discussion is to supplement the authors' work by examining the influence of lab test load history on test results that in turn affect the derived backbones. [Extracted from the article]

Because significant damages to structures having structural irregularity in their plans were repeatedly observed during many past earthquakes, there have been great research efforts to evaluate their seismic vulnerability. Although most of the previous studies used simplified structural representations such as one-dimensional or two-dimensional models in the fragility analysis of plan-irregular structures, simple analytical models could not represent true seismic behavior from the complicated nonlinear coupling between lateral and torsional responses as the degree of irregularity increased. For space structures with high irregularity, more realistic representations such as three-dimensional models are needed for proper seismic assessment. However, the use of computationally expensive models is not practically feasible with existing approaches of fragility analysis. Thus, in this study, a different approach is adopted that can produce vulnerability curves efficiently, even with a three-dimensional model. In this approach, an integrated computational framework is established that combines reliability analysis and structural analysis. This enables evaluation of the limit-state faction without constructing its explicit formula, and the failure probability is calculated with the first-order reliability method (FORM) to deal with the computational challenge. Under the integrated framework, this study investigates the seismic vulnerability of space reinforced concrete frame structures with varying plan irregularity. Material uncertainty is considered, and more representative seismic fragility curves are derived with their three-dimensional analytical models. The effectiveness of the adopted approach is discussed, and the significant effect of structural irregularity on seismic vulnerability is highlighted. [ABSTRACT FROM AUTHOR]

To consider the effect of higher modes in predicting the seismic responses of midrise buildings, as well as the progressive changes in the dynamic characteristics during the nonlinear analysis, an adaptive force-based multimode pushover (AFMP) procedure is presented. This procedure is an adaptive version of the single-run multimode pushover (SMP) procedure that it is envisaged to be an enhancement of the previously proposed procedure. The procedure encompasses some adaptive pushover analyses. First, an adaptive single-mode pushover analysis using the first mode shape is performed. Moreover, one or two adaptive multimode pushover analyses are implemented by means of the enhanced lateral load distributions calculated by algebraically adding the instantaneous modal story forces. Therefore, the sign reversals of load vectors in the higher modes are considered. The results obtained through the adaptive single-mode and multimode pushover analyses are enveloped to compute the final seismic responses. It is demonstrated that the AFMP procedure can estimate with acceptable accuracy the seismic responses of midrise building frames. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the seismic response of a 0.6-scale three-story building with nonlinear viscous dampers under the design basis earthquake (DBE) and the maximum considered earthquake (MCE). The test structure consists of a moment-resisting frame (MRF) with reduced beam sections (RBS), a frame with nonlinear viscous dampers and associated bracing (called the DBF), and a gravity load system. The paper focuses on quantifying and assessing the seismic response of the test structure under the DBE and MCE. Three MRF designs were studied for 100, 75, and 60%, respectively, of the required base shear design strength according to ASCE 7-10. The DBF with nonlinear viscous dampers was designed to control the lateral drift demands. Earthquake simulations using ensembles of ground motions were conducted using the real-time hybrid simulation method. Experimental results show that a high level of seismic performance can be achieved under DBE and MCE ground motions, even for a building structure designed for as little as 60% of the design base shear strength required by ASCE 7-10 for a building structure without dampers. [ABSTRACT FROM AUTHOR]

A seismic demand model attempts to describe the behavior of a structure in terms of a set of predictor variables that represents the loading. For buildings, the most frequently used demand parameter and predictor variables are the maximum interstory drift ratio (MIDR) and the spectral accelerations of the ground motion at various modal periods, respectively. An adequate and optimal demand model should be independent of the suite of records that is used to calibrate it. It is shown that this is not the case with currently used demand models and that the dominant dynamic modes imposed by the ground motion suite have a significant effect on the model predictions. In this study, this influence is quantified in terms of the coefficient of partial determination. It is shown that the marginal contribution of the included variables in the demand model is dependent on the response mode that yields the MIDR. An alternative method of estimating the regression coefficients via Ridge estimation is discussed as an approach that minimizes the influence of the dominant mode on the demand model. The performance of the Ridge estimation is compared with the least squares (unbiased) counterpart using the cross-validation method. These findings have a major impact on the selection of ground motions for seismic assessment of structures. [ABSTRACT FROM AUTHOR]

This study presents an evaluation of drift demands and their associated uncertainties for nondeteriorating regular moment resisting frame structures subjected to ordinary ground motions (i.e., without near-fault effects). The only source of uncertainty considered is the uncertainty due to differences in the frequency content of the ground motions. The information presented in this study is deemed to be useful for preliminary design and seismic performance assessment in which the performance targets of interest are those related to damage and loss of function (downtime). Thus, the focus is on ductility levels that are not so large that they cause significant cyclic deterioration in the components of the structural system. The dependence of drift demands (the maximum roof drift, the average of maximum story drifts, and the maximum story drift over the height) on relative ground motion intensity, fundamental period, and number of stories is investigated. [ABSTRACT FROM AUTHOR]