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Summary: This paper presents the authors' response to the discussion by Dean J. Maxam and Kumar K. Tamma of the paper titled "Development of a family of unconditionally stable explicit direct integration algorithms with controllable numerical energy dissipation." [ABSTRACT FROM AUTHOR]

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The discussion presents questions regarding the recommended damping scheme from the discussed paper and provides an alternative recommendation. The discussion also requests further explanation on behavioral differences between models incorporating the P-delta and corotational approaches that are presented in the paper. Responses to these questions are presented. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The paper under discussion presents a series of quasi-static tests used to examine the behavior of steel reinforced concrete (SRC) walls subjected to high axial force and lateral cyclic loading. A total of six wall specimens were designed, including five SRC walls and one reinforced concrete (RC) wall. In the 'Summary' section of the discussed paper, the authors state that: 'The use of SRC walls has gained popularity in the construction of high-rise buildings because of their superior performance over conventional RC walls'. The authors also proposed that, the SRC wall specimens showed increased flexural strength and deformation capacity relative to their RC wall counterpart. The discussion is prompted to rectify some statements and conclusions of the paper under discussion. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article presents the authors' response to John Hall's discussion of their article "Modeling viscous damping in nonlinear response history analysis of buildings for earthquake excitation.'' The authors discuss the use of the tangent stiffness matrix in Rayleigh damping, the limitations of linear viscous damping, and the viscous damper models for the damping matrix.

A response from the authors of the article "Development of a family of unconditionally stable explicit direct integration algorithms with controllable numerical energy dissipation" in the Vol. 43, 2014 issue is presented.

This paper proposes a hybrid data‐driven and physics‐based simulation technique for seismic response evaluation of steel Buckling‐Restrained Braced Frames (BRBFs) considering brace fracture. Buckling‐Restrained Brace (BRB) fracture is represented by cumulative plastic deformation capacity. A dataset, consisting of 95 past BRB laboratory tests and 120 simulated BRB responses generated using the finite element method, is first developed. An Artificial Neural Network‐based (ANN) predictive model is then trained using the training dataset to estimate the cumulative plastic deformation of BRBs. The prediction capability of the ANN‐based predictive model is validated using the training dataset and an existing regression‐based predictive model. In the second part of the paper, an hybrid simulation technique combining the data‐driven model and physics‐based numerical modeling is presented to conduct the nonlinear time history analysis, followed by 1) validation against a full‐scale BRBF testing and 2) demonstration of the proposed simulation technique using a six‐story BRBF. The results confirm that the proposed predictive model can predict the BRB fracture with sufficient accuracy. Furthermore, the hybrid data‐driven physics‐based simulation technique can be used as a powerful tool for dynamic analysis of BRBFs considering BRB fracture. [ABSTRACT FROM AUTHOR]

A response from the author of the article "Seismic behavior and modeling of steel reinforced concrete (SRC) walls" in the previous issue is presented.

The paper under discussion presents a detailed study on the reduction of pounding force on buildings due to expansion joints being filled with rubber. From shake table experiments and numerical simulations, the authors of the paper concluded that the rubber can reduce the maximum pounding force and hence the pounding damage to buildings. However, the writers of this short communication observed some significant issues in the experimental results as well as the numerical simulations. These observations are presented and raise questions about the validity of the results and the subsequent conclusions. [ABSTRACT FROM AUTHOR]

SUMMARY Three main topics including the floor motion action mechanism, the test frame design, and the target spectrum simulation presented in the paper are discussed specifically. Floor motion action mechanism is critical in understanding the seismic performance of architectural nonstructural components. Seismic sensitiveness and earthquake response properties of the nonstructural components should be considered in the design of the test frame for the shaking table test. Target spectrum simulation is also a challenging job in the shaking table test, in which dynamic characteristics of the specimen, performance of the shaking table facilities, and the control techniques should be all considered. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Evaluation of Building Period Formulas for Seismic Design," by Oh-Sung Kwon and Eung Soo Kim in a 2010 issue.

SUMMARY It seems that the explicit KR-α method (KRM) is promising for the step-by-step integration because it simultaneously integrates unconditional stability, explicit formulation, and numerical dissipation together. It was shown that KRM can inherit the numerical dispersion and energy dissipation properties of the generalized-α method (GM) for a linear elastic system, and it reduces to CR method (CRM) if ρ∞ = 1is adopted, where ρ∞ is the spectral radius of the amplification matrix of KRM as the product of the natural frequency and the step size tends to infinity. However, two unusual properties were found for KRM and CRM, and they might limit their application to solve either linear elastic or nonlinear systems. One is the lack of capability to capture the structural nonlinearity, and the other is that it is unable to realistically reflect the dynamic loading. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Damage assessment of tall buildings after an earthquake is important for efficient postearthquake management due to social and economic reasons. Structural health monitoring (SHM) system enables rapid, remote, and objective condition assessment for tall buildings by controlling dynamic properties of structures. However, tracking only the changes in dynamic properties of tall buildings may not be sufficient for damage assessment. In this paper, changes in modal frequencies and maximum interstory drift ratio are investigated as damage assessment indicators because they can be obtained by analyzing vibration data recorded by SHM system. On the other hand, limited number of sensors are used due to economic reasons. Therefore, in this paper, firstly, a unique methodology on development and optimization of nonlinear simplified model for tall buildings is presented to estimate responses of noninstrumented floors from instrumented floors. After that, new threshold values are suggested for changes in dynamic properties and interstory drift ratios to reliably decide performance level of structures after earthquakes. Finally, the proposed method was validated with vibration record of a real damaged building. [ABSTRACT FROM AUTHOR]

This paper explores the use of Artificial Neural Networks (ANN) for the rocking problem. The paper adopts rigid rocking blocks of different sizes and slenderness, which undergo rocking motion without sliding and bouncing when subjected to recorded earthquakes. This research focuses on the cases where the blocks overturn or safely return to their initial (rest) position at the end of the ground shaking. An ANN model is trained to efficiently categorise the response into overturning or safe rocking using the structural parameters, ground motion characteristics, and the coefficient of restitution as input. The results show the substantial contribution of velocity and frequency characteristics of the ground motion to overturning. In addition, ANN is used to predict the response amplitude and identify the most critical input variables that govern safe rocking. The analysis reveals that rocking amplitude is governed by a combination of duration, frequency, and intensity characteristics of the ground excitation. Interestingly, the maximum incremental velocity (MIV), a novel intensity measure for the rocking literature, shows a substantial correlation with the rocking amplitude. In this context, this paper proposes closed‐form expressions using the most influential input variables to provide a quick, yet adequately accurate, response prediction. Finally, this study pays special attention to the contribution of the coefficient of restitution, which, in general, is less critical to the peak safe rocking response, while it becomes more important to the overturning response. [ABSTRACT FROM AUTHOR]

This paper discusses the results of a series of hybrid earthquake tests on a full‐scale reinforced concrete (RC) building with masonry infills. The prototype was a five‐story structure representing the vulnerable part of a typical RC building in Southern Europe, with beams stronger than the columns and masonry infill walls weaker than the surrounding frame elements. The specimen was subjected to a sequence of unidirectional earthquake simulations of increasing intensity up to conditions of significant damage to the infills, using the pseudodynamic (PsD) testing method with substructuring. The input ground motion was a real earthquake recording, slightly modified in amplitude and frequency to match the elastic design code spectrum. The physical substructure of the hybrid model consisted of the first story of a two‐story mock‐up structure built in the European Laboratory for Structural Assessment (ELSA); the second story ensured realistic boundary conditions at the top of the first one. The characteristics of stories two to five were simulated by a numerical finite‐element model developed in OpenSEES and updated throughout the test sequence using data obtained from preceding tests. The experiments were terminated with the onset of a soft‐story mechanism at the first story of the physical substructure for an earthquake with a peak ground acceleration of 0.3 g. The paper summarizes the key characteristics of the specimen and the major observations from the hybrid tests, illustrating the evolution of structural/nonstructural damage and the cyclic hysteretic building response. The attainment of significant damage limit states is correlated with experimentally defined engineering demand parameters and ground‐motion intensity measures for the performance‐based seismic assessment of buildings. Data and observations from these experiments add substantially to our understanding of the effects of masonry infills on the seismic behavior of RC‐framed structures. [ABSTRACT FROM AUTHOR]

Impedance matching is a novel approach to executing model‐in‐the‐loop (MIL) simulations. The concept, key features, and sample applications of this approach have been described in a series of publications. This paper advances theory and implementation for impedance‐matching MIL by: (1) developing a feedback linearization technique for implementing MIL for nonlinear virtual systems, (2) systematically characterizing MIL performance‐stability tradeoffs using three design‐oriented criteria—performance: defined as closeness of the controlled‐actuator impedance to the virtual‐boundary impedance; control effort: low controller response at high frequencies to reduce sensitivity to measurement noise and uncertainties in the actuator model; and stability: pursued using passivity of the controlled actuator system, and (3) assessing, through experimentation, the robustness of two ways to estimate feedback reaction force from the test article. These fundamental advancements to MIL are described using a one‐dimensional configuration consisting of a fluid‐filled cylindrical vessel as the physical test article and a uniaxial hydraulic shake table controlled to imitate different seismic isolation systems at the base of the vessel. [ABSTRACT FROM AUTHOR]

The physical parameter identification of the dynamic mechanical model, such as stiffness identification, provides some valuable information for detecting post‐earthquake damage to building structures. During an earthquake, tracking changes in stiffness on the skeleton curve can be effective. It would also be helpful as an approximate evaluation if the method could be applied to structures with arbitrary poly‐linear hysteresis characteristics. However, previous research has not identified any poly‐linear hysteresis characteristics in a unified formulation. This paper proposes a new stiffness identification method in the time domain for building structures with any poly‐linear hysteresis characteristics using sparse modeling. The validity of the proposed method was investigated through numerical simulations and a full‐scale shaking table test. [ABSTRACT FROM AUTHOR]

Decision‐makers and stakeholders require a rapid assessment of potential damage after earthquake events in order to develop and implement disaster risk reduction strategies and to respond systematically in post‐disaster situations. The damage investigated manually after an earthquake are complicated, labor‐intensive, time‐consuming, and error prone process. The development of fragility curves is time consuming and unable to predict the damage for wide classes of structures since it considers few structural properties and only one seismic characteristic. Furthermore, the nonlinear finite element method cannot be utilized for numerous buildings because it involves more time and money. This paper presents the machine learning (ML)‐based seismic damage prediction of RC buildings. It is found that some of the research works only considered seismic parameters or structural parameters to train the ML models and predict the structural damage assessment. However, these ML models may not fully reveal the underlying complexity of the relationship between input parameters and building performance. As a result, their applicability will be limited. This paper evaluates the feasibility of using ML techniques such as K‐nearest neighbor, random forest, decision tree, support vector machine, and artificial neural network to rapidly predict earthquake‐induced reinforced concrete building damage considering both the structural properties and ground motion characteristics. The machine learning models are trained using the simulation results. Due to lack of real earthquake damage datasets or limited access, most of the research works used Scikit Learn train_test_split function to randomly split the entire datasets into training and testing datasets and the performance of the proposed ML technique are evaluated using the testing datasets. However, in this study, the performances of different ML models are evaluated using real earthquake damage datasets of RC buildings collected after 2015 Nepal earthquake. The overall accuracy on testing datasets suggests the capability of machine learning algorithms in successfully predicting the seismic damage of reinforced concrete buildings in quick time with reasonable accuracy. This study is beneficial in emergency response and recovery planning after an earthquake. [ABSTRACT FROM AUTHOR]

After a strong earthquake, criteria are needed to determine whether buildings are safe to reoccupy based on observable damage. This paper presents a simulation‐based methodology to identify relevant damage indicators and safety thresholds for building structures. Prior knowledge of the most relevant damage indicators and their thresholds can increase the accuracy and confidence of post‐earthquake evaluations. Current practice to translate observable damage into a tagging decision relies on qualitative guidelines based on past earthquake experience and judgment, which may be susceptible to speculation and interpretation. In addition, past experience may not be relevant to newer structural systems and to large or complex (e.g., high‐rise) buildings. To augment past observations and data from structural component tests, nonlinear dynamic analyses can be used to estimate the collapse safety of structures with simulated damage. Technologies to execute these simulations have matured over the years, although to date they have not been systematically applied to evaluate the destabilizing effects of simulated damage on collapse safety. In this paper, a methodology is presented to use numerical simulations of damage to identify and evaluate relevant damage indicators that can be quantitatively related to safety thresholds. Damage indicators are selected based on their reliability in estimating the structural safety and their sensitivity to modeling uncertainty, that is, where the preferred indicators are insensitive to variability in the structural materials and model parameters. The safety threshold for each damage indicator is selected to maximize accuracy in post‐earthquake building assessments. The methodology is demonstrated through an application study of ductile reinforced concrete frame buildings. Results show that aggregated indices of structural component damage (e.g., aggregated over the floor of a building) outperform other damage indicators based on peak or residual drifts or simpler percentages of damaged components. Subject to agreement of a number underlying assumptions, this methodology can be applied to a wider variety of structures to improve post‐earthquake evaluation guidelines. [ABSTRACT FROM AUTHOR]

Lessons from recent earthquakes have provided a tough reality check of the traditional seismic design approach and technologies, highlighting the urgent need for a paradigm shift of performance‐based design criteria and objectives toward low‐damage design philosophy and technologies for the whole building system. Modern society is asking for "earthquake proof" resilient buildings that are able to withstand seismic events without compromising their functionality. The EU‐funded SERA (Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe Project) project discussed in this paper provided the opportunity to develop and validate within the European context an integrated seismic low‐damage prototype, including main structure and non‐structural elements, for the next generation of high‐performance buildings. This paper presents an overview of the research, involving three‐dimensional shake table tests of a two‐storey 1:2 scaled timber‐concrete post‐tensioned dissipative low‐damage structure "dressed" by earthquake‐resistant gypsum/masonry partitions and glass/concrete facades. Specimen details, construction and assembly phases, test setup, and experimental results are discussed. After many cycles of input motions at increasing levels of seismic intensity (higher than Collapse Prevention Limit State), the integrated building system exhibited a very high seismic performance. The experimental campaign carried out at the National Laboratory of Civil Engineering in Lisbon confirmed the unique potential of low‐damage technologies and the opportunity for their widespread implementation into design practice. [ABSTRACT FROM AUTHOR]

The paper under discussion proposes a framework to evaluate ground motion selection and modification procedures and illustrates its application for two different procedures as applied to a non-degrading bilinear inelastic single-degree-of-freedom system. This discussion focuses on providing additional context that this writer feels is needed in relation to both the proposed framework and also its specific application in the paper, which are important for the conclusions made by the authors. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Integral abutment bridges (IABs) are becoming the solution of choice in the low to mid‐length ranges because of their low cost compared with traditional solutions and their good performance under seismic actions. The main drawback of these bridges is the need to consider soil‐structure interaction to assess their performance, a problem that is more pronounced for actions implying horizontal deck movements, such as temperature or the specific focus of this paper, that is, seismic action. In IAB design, simplified models are often used, where soil‐structure interaction is modeled by means of beams on non‐linear Winkler springs for the evaluation of seismic behavior. This paper, starting from an existing non‐linear dynamic model (NLDM) that describes IABs longitudinal seismic response, derives two equivalent static models: one non‐linear and the other linear, for displacement‐ or force‐based design respectively. A parametric study is carried out to assess the static models performance in terms of the main design internal actions versus the NLDM. Finally, the assessed model errors are discussed in the context of partial factors safety format. [ABSTRACT FROM AUTHOR]

This discussion is based on the paper by Chen et al. in 2023 (hereafter referred to as "the original paper/authors"). In their study, the original authors conducted a series of analyses using nonpulse, single‐pulse, and multipulse ground motion records, evaluating their impact on a frame structure, a slope, and a gravity dam. Their key finding suggests that multipulse ground motion leads to more severe structural damage compared to nonpulse and single‐pulse ground motions. However, it is important to note that the seismic damage analysis of the gravity dam in this paper does not adhere to state‐of‐the‐practice recommendations. Consequently, drawing a definitive conclusion regarding the influence and importance of multipulse ground motion records on the seismic response of concrete dams requires further justification. This necessitates the incorporation of high‐fidelity numerical models and probabilistic performance evaluation. We will discuss the significance of modeling assumptions, specifically addressing the dam–rock dynamic interaction in crack propagation and failure in dams. [ABSTRACT FROM AUTHOR]

The authors thank the discusser for the attention and interests on our previous work, entitled "Seismic damage analysis due to near‐fault multipulse ground motion" (referred to as the original paper/work in the following text). To demonstrate the increased seismic demands required by multipulse ground motions compared to non‐ and single‐pulse ground motions, three cases were illustrated in the original work, including frame structures, a soil slope and a concrete dam. The discusser, Dr M.Amin Hariri‐Ardebili, raised concerns on the seismic response of the dam, together with the optimal intensity measure of ground motions. Specifically, four subissues are involved, including effectiveness of the numerical model of dam, the damage index for dam, the selection strategy for input ground motions, and the ground motion intensity measures. Detailed responses to these issues are provided. In short, the main conclusion in the original paper that the multipulse ground motions potentially cause more severe damage compared to non‐ and single‐pulse ground motions is reliable. [ABSTRACT FROM AUTHOR]

The reliability of non‐linear dynamic analysis aimed to predict the seismic performance of structural and geotechnical systems, as well as their dynamic interaction, is significantly affected by the selection of suitable input motions. Several procedures for selecting actual earthquake records compatible with the seismic hazard at the site of interest and for evaluating synthetic accelerograms consistent with a seismological framework are available in the literature. However, the degree of uncertainty affecting these approaches might lead to unreliable performance predictions especially for strongly non‐linear problems, such as those involving the response of soils to cyclic and dynamic loading. In this vein, the paper presents a procedure for generating fully non‐stationary ground motions ensuring energy compatibility with a target motion. Two different approaches have been introduced: i) the time window method based on the central finite difference approach and ii) the simplified intensity‐compatible approach in which a closed form expression is provided to evaluate a modulating function that depends on the Arias intensity and on the strong motion duration of a target motion. To highlight the reliability and the accuracy of the proposed procedure, several sets of spectrum‐compatible artificial accelerograms, generated starting from a rock outcropping motion, were used as input motions in a series of one‐dimensional site response analyses. The analysis results are presented and discussed in the paper highlighting the influence of the main features of the proposed generation procedure on the variability of the computed site response. [ABSTRACT FROM AUTHOR]

A realistic performance‐based seismic loading protocol called generated sequential ground motion (GSGM) has been developed in this paper. GSGM is a ground motion fabricated from segments of real recorded ground motions that could enable the introduction of performance‐based seismic assessment and design to experimental testing in setups such as shaking table testing. It can also significantly reduce the number of nonlinear time history analyses required in performance‐based seismic design. The protocol optimizes the behavioral information output of an experimental test or numerical analysis by incorporating dynamic demands corresponding to design limit states with different probabilities of exceedance (i.e. 10%, 5%, and 2% in 50 years) in a single record. In addition, since the segments are matched to relevant target spectra, the number of ground motions required to estimate the mean response is reduced. This paper presents the algorithm developed to produce the GSGM. The capability of the GSGM to replicate the structural responses produced by code‐compliant suites, and a suite of 100 ground motions as a more robust estimation of the actual response is investigated. The results of the case study bridge pier show that the drift variation of the GSGMs compared to code‐compliant suites is within 10%. Compared to the estimate of the actual response, the drift variation of GSGMs and the code‐compliant suites is 20% and 15%, respectively, and the damage variation is 30% and 15%, respectively. Furthermore, considering other relevant intensity measures when producing GSGMs can reduce these variations. This study suggests that the GSGM can replicate structural responses of the current code procedures. [ABSTRACT FROM AUTHOR]

The earthquake‐induced displacement of sloping soil mass is an important indicator of co‐seismic landslide initiation. In this paper, an improved Newmark displacement model that considers the accumulation of dynamic pore water pressure (DPWP) in the soil caused by both vertical and horizontal ground motions is proposed. The model can quantitatively describe the dynamic changes of the seismic yield acceleration of near‐saturated infinite soil slopes. Three different types of ground motion time histories are selected to compare the performance of the proposed Newmark displacement model, and the influence of DPWP accumulation on the slope yield acceleration and on the seismic displacement is obtained. The seismic slope displacement analyses indicate that the weakening effect of slope yield acceleration caused by bidirectional earthquake excitation‐induced DPWP is more obvious than when only considering the horizontal ground motion, when the slip surface soils are in near‐saturated state. The effect of initial saturation (Sr0) on the DPWP accumulation caused by vertical ground motion is also investigated. Furthermore, the accumulated seismic displacement can be reasonably explained by the frequency distribution characteristics of the ground motions. Finally, the numerical results of this paper show that the seismic displacement model seldomly considering the effect of DPWP, or only considering the DPWP induced by horizontal ground motion, can significantly underestimate the displacement value when the slip surface soils are in a near‐saturated state. [ABSTRACT FROM AUTHOR]

With growing interest in rocking structures, it is important to quantify the effects of ground motion processing schemes on rocking response. To this end, this paper studied the influence of different ground motion correction schemes and parameter values on the rocking displacement spectrum. When the problem is treated on an individual ground motion basis, then it seems that ground motion correction does have an influence on the rocking response, especially for more slender blocks. This influence is larger for causal filtering. However, no specific trend related to the cut off period of the filter can be observed (at least for cut off periods longer than or equal to 10 s) or on the type of the recording device (analog or digital). On the other hand, when treating the problem statistically (by comparing the statistics of the response due to sets of ground motion, not a single ground motion), the effect is significantly reduced: The processing schemes do not induce any significant bias to the rocking response and the motion‐to‐motion variability seems more important than the ground motion correction method. This conclusion applies to both analog and digital records, both causal and acausal filters, and to all near field pulse like, near field no pulse like, and far field records. [ABSTRACT FROM AUTHOR]

Prior to implementing retrofitting measures for seismic action, it is necessary to evaluate the global capacity of unreinforced masonry (URM) buildings. Even with simplified assumptions, equivalent frame (EF) modeling adequately captures global responses and failure mechanisms in existing buildings, making it a popular modeling strategy among structural engineers. However, macro‐elements employed in the EF modeling of URM walls consider in‐plane (IP) and out‐of‐plane (OP) behaviors separately by decoupling their interaction and require independent verification for OP failure involving limit analysis. Such decoupling of interaction is justifiable if proper wall‐wall/wall‐floor connections and rigid‐diaphragm action of slabs are ensured; however, OP failure is likely a result of inadequate connections. Multiple components of ground motion excitation and plan eccentricity in buildings can activate bidirectional interaction in such circumstances. Due to OP damage, the interaction reduces the full IP strength of a URM wall, resulting in overestimating its lateral capacity. This paper proposes a frame‐like 3D macro‐element incorporating the effect of OP action on the IP shear response of URM piers under static and monotonic lateral loads. Only two parameters modifying IP shear stiffness and capacity are required to account for the interaction. Analytical expressions for the interaction parameters are proposed from a detailed micro‐modeling study. The paper also demonstrates, within the EF modeling, the applicability of the proposed macro‐element for seismic analysis of regular URM shear walls with openings. [ABSTRACT FROM AUTHOR]

The objective of this paper is to study the elastic seismic response of simplified building models that include considerations of the vertical lateral force resisting system (walls) and the horizontal lateral force resisting system (floor diaphragms) through parametric study. The assumption of rigid diaphragms is often used in the seismic design of buildings; however, research suggests that the diaphragm may influence the fundamental building period and the seismic building response. In this paper, a simplified model is presented for single and multi‐story buildings utilizing two degrees of freedom per story for the vertical system, for example, the walls, and one degree of freedom per story for the floor diaphragm. The number of stories, the stiffness of the walls and diaphragm(s), and the mass distribution between the walls and diaphragm are varied to represent a large range of potential building compositions. Eigen analyses of the models indicate that the wall and diaphragm interact when at similar periods resulting in elongation of the overall building period. Response of elastic time‐history analyses of the building models are presented in this paper where it is shown that the force demands in both the wall and diaphragm(s) are dependent on the relative stiffness of the walls and diaphragm(s), and the mass‐distribution between these two systems. In the companion paper "Wall‐Diaphragm Interactions in Seismic Response of Building System II: Inelastic Response and Design" the parametric building study is extending to nonlinear time‐history analyses including different levels of assumed inelasticity in both the walls and diaphragm. [ABSTRACT FROM AUTHOR]

This paper investigates the collapse risk of seismically isolated buildings that are designed by the procedures of the ASCE/SEI 7‐16 standard for sites within 5 km of the active fault that controls the hazard. The study is based on six‐story perimeter frame buildings designed with special concentrically braced frames for a location in California. The seismic isolation systems considered in this study are comprised of either: (i) triple friction pendulum bearings with high friction coefficients at the sliding interfaces, (ii) triple friction pendulum bearings with low friction coefficient at the sliding surfaces and enhanced with fluid viscous dampers, or (iii) triple friction pendulum bearings with low friction coefficients at the sliding surfaces. The paper demonstrates that the seismically isolated buildings designed per Section 17.3.3 in ASCE/SEI 7‐16 standard, but with either increased isolator displacement capacity or increased superstructure strength by comparison to the minimum required, can achieve an acceptable collapse risk. It is also demonstrated that the seismic isolation systems that have the best collapse performance for far‐field motions are not necessarily the best for the near‐field pulse‐like ground motions. [ABSTRACT FROM AUTHOR]

The article presents the response of A. M. Reinhorn, G. Maddaloni, and K. P. Ryu on their study on the simulation of floor response spectra in shake tables. The authors clarified that floor amplification could be represented by functions related to the floor elevation. It mentions that the design of the test frame for the ceilings were illustrated to control the response in a test specimen using shake tables. It adds that oil column, noise, and seismic mass were indicated in a system diagram.

A response by Oh-Sung Kwon and Eung Soo Kim to a letter to the editor about their article "Evaluation of Building Period Formulas for Seismic Design," in a 2010 issue is presented.

A letter to the editor about the article "Real-time hybrid testing using the unconditionally stable explicit CR integration algorithm," by Cheng Chen, James M. Ricles, Thomas M. Marullo and Oya Mercan that was published in the 2009 issue.

An elastic parametric study of simplified single‐ and multi‐story building models presented in a companion paper shows that seismic building response depends on the period(s) of the vertical lateral force resisting system (vLFRS), the period of the diaphragm (i.e. the horizontal LFRS, or hLFRS) and the mass distribution between the walls and floors. This paper extends the study to include the potential for inelasticity (ductility) in both the v‐ and hLFRS and examines the impact of this inelasticity on the building response. Increased ductility in the vLFRS reduces vLFRS forces, but to what extent are hLFRS (diaphragm) demands reduced? Similarly, ductile hLFRS presumably reduce hLFRS forces, but what about vLFRS forces? Past work has shown that hLFRS forces are difficult to predict. The building model responses indicate wall‐diaphragm interactions may occur between higher modes of the vertical system and the rigid diaphragms causing increased force demands. Ductility demands are observed to be driven by the element (wall or diaphragm) with the larger inelasticity. Significant ductility demands are observed for short period buildings. A simplified formula for an effective ductility seismic force response modification coefficient for the horizontal LFRS is proposed that considers force reductions from both the inelastic vertical and horizontal LFRS. [ABSTRACT FROM AUTHOR]

Servo‐hydraulic shake tables are widely used for simulating earthquake shaking in a laboratory environment. Control procedures for shake‐table testing and the associated mathematical models are well documented. An evaluation of such models revealed nuances regarding actuator control, which led to the development of the simple, easy to implement, robust shake‐table controller described in this paper. This controller design recognizes that (i) differential pressure feedback in actuator control is highly beneficial in reducing the consequences of hydraulic‐related nonlinearities and other modeling uncertainties, (ii) the bandwidth over which differential pressure feedback is useful is limited by the sampling frequency of the chosen digital controller, (iii) a linear model predicts shake‐table response with high fidelity across a broad frequency range for a carefully chosen differential pressure gain and a sufficiently large controller sampling frequency, and (iv) shake‐table transfer functions derived from such a linear model are highly effective in designing a feedforward controller. Further, and perhaps most importantly, the controller utilizes real‐time feedback of the reaction force from the test article to account for table‐test article interaction. The three clear advantages of the proposed shake‐table controller are (i) the test‐article dynamics are decoupled from the control design, (ii) the need for offline/online iterative tuning, which is often ground motion‐ and test article‐specific, is minimized, and (iii) control procedures for shake tables can be standardized, all of which are validated in this paper through a series of experiments performed on a uniaxial hydraulic shake table. [ABSTRACT FROM AUTHOR]

This paper proposes alternative seismic design approaches for steel moment‐resisting frames (MRFs) that improve their performance and reduce the number of undesirable one‐story and two‐story yield mechanisms that form under seismic loading, compared to MRFs designed using the conventional strong‐column‐weak‐beam (SCWB) design approach. The alternative design approaches are capacity‐design approaches that directly compare story shear force demands from nonlinear time‐history analyses (NTHA) with corresponding shear force capacities in design iterations to avoid one‐story and two‐story mechanisms. To implement the capacity‐design approach, the NTHA use special capacity‐controlled numerical models for design, in which the one‐story and two‐story shear force design demands are limited by the intended yield mechanisms of the MRF. Unlike the SCWB approach, the alternative design approaches directly address the cause of undesirable one‐story and two‐story mechanisms. The paper presents NTHA results for a set of MRFs, where some were designed using a conventional approach (including SCWB) and some were designed using the alternative approaches. The increases in nominal steel weight of the MRFs designed using the alternative approaches are relatively small compared to the weight of the MRF designed using the conventional SCWB approach. Compared to the MRF designed using the SCWB approach, the MRFs designed using the alternative design approaches have improved seismic performance with reduced tendency to form one‐story and two‐story mechanisms, more uniform story drifts, reduced maximum story drift, and improved collapse performance. [ABSTRACT FROM AUTHOR]

As structures are built taller and more slender, their response becomes increasingly sensitive to dynamic loads that are induced by the buildings' higher‐frequency vibration modes. This leads to a more complex seismic response of high‐rise structures when compared to the seismic response of low‐rise structures that are primarily governed by their fundamental modes of vibration. This paper presents the results of extensive shake table testing and finite element analyses of a small‐scale, 1.5‐meter‐tall shaking table specimen that was designed and scaled to experimentally capture the higher‐mode effects of a 125‐meter‐tall reference tall building. The test specimen is comprised of a simplified superstructure with uniform mass and stiffness representing the main structure of the full‐scale reference tall building, and a base‐rocking mechanism to represent the moment‐limiting effect of the inelastic plastic‐hinging mechanism at the base of the reference building. Using the methodology proposed in this paper, the scaled specimen was shown to exhibit similar seismic response characteristics, including the corresponding higher‐mode effects, along the height of the structure as those predicted numerically on the full‐scale reference building. Results of the shaking table tests experimentally provided further evidence that relying only on a moment‐limiting mechanism at the base of a cantilever structure is insufficient in limiting peak seismic loads due to higher‐mode effects. In addition, by comparing test results with predictions obtained using several previously proposed analytical methods, the paper demonstrated that predicting shear force amplifications due to higher‐mode effects is still challenging. The methodology developed in this study can be used to design other similar small‐scale shaking table tests for the development of new analytical methods to predict higher mode effects and experimentally validate the efficiency of new high‐performance systems developed to mitigate higher‐mode effects on tall and slender structures and more generally to assess the ability of these systems to achieve enhanced seismic resilience. [ABSTRACT FROM AUTHOR]