Seismic Performance Assessment Research Articles

Seismic behavior and damage assessment of two historical fortified masonry palaces with corner towers

Recent earthquakes have highlighted that historical fortified masonry constructions may suffer extensive damage, even under low-to-moderate seismic actions, and corner towers may be one of the most vulnerable structural elements. An accurate assessment of the structural seismic performance is one of the most effective tools to deeply understand and identify the main structural weaknesses of such a building typology. To this aim, the need to properly simulate the dynamic behavior of large complex masonry buildings can strongly limit the application of simplified analysis methods widely used in common practice and largely presented in the literature. The objective of this study is to provide a comprehensive numerical insight into the earthquake response and seismic vulnerability of historical fortified masonry palaces with corner towers using non-linear dynamic analyses and a macro-modelling FE-based approach, which is able to take into account the complex interactions between different macro-elements and the characteristics of the seismic action. After a knowledge phase of the geometrical and constructive features of the two palaces under study, detailed three-dimensional FE models have been developed and predictive non-linear dynamic analyses have been performed to assess damage patterns and identify the most critical macro-elements. The numerical analyses highlight that the seismic response and damage distributions are significantly influenced by the geometrical features and main dynamic properties of the two palaces. A fundamental role is also played by the interactions of the different macro-elements with the adjacent structural parts. The results of the non-linear dynamic analyses point out that the two palaces are highly vulnerable to seismic actions, highlighting the onset of possible local collapse mechanisms and recurrent damage concentrations. For both the palaces, the most critical elements are the corner towers that present remarkable cracks patterns along the height, in the connection regions with the adjacent walls, in the upper part and in the vaults. Widespread damage is also observed in the macro-elements that are characterized by high slenderness, large openings and small walls thickness, and in the large vaults of the two palaces. A clear correlation between large displacements and high values of energy density dissipated by tensile damage is generally observed for the main critical macro-elements of both the palaces. The main outcomes presented in this study may also represent a useful insight to improve the knowledge and better understand the earthquake response and seismic vulnerability of similar historical fortified masonry palaces located in the same region, providing valuable information for practical applications in seismic risk assessment and mitigation at territorial scale.

Seismic Fragility Functions for Non-Seismically Designed RC Structures Considering Pounding Effects

The proposed study develops fragility functions for non-seismically designed reinforced concrete structures considering different pounding configurations. The study addresses an existing research gap, since large-scale seismic risk assessment studies involving the seismic performance assessment of building portfolios usually do not involve fragility functions accounting for the possibility of pounding. The selected structures include configurations involving different separation distance values and exhibiting floor-to-floor pounding, floor-to-column pounding, pounding between structures with a significant height difference, and pounding between structures with a significant mass difference. The behaviour of these pounding configurations was analysed using incremental dynamic analysis and compared with that of the corresponding control cases (i.e., individual structures with no interaction with other structures). The results indicate the type of failure mechanism that contributes to the global collapse of the different configurations and the influence of the separation distance. Results highlight the main differences between the expected performance of different pounding configurations with respect to the occurrence of the failure mechanism that governs their collapse. Finally, results indicate that large-scale seismic risk assessment studies should consider fragility functions accounting for different pounding configurations when the possibility of pounding is not negligible, except in cases involving floor-to-floor pounding.

Seismic performance assessment of a masonry building under earthquakes induced by geothermal power plants operation

Geothermal power plants (GPPs) are at the center of attention for affording the required electricity of the communities as a green resource. By developing these infrastructures, in the surrounding area, the occurrence of repetitive low-to-moderate earthquakes has been observed as an important side effect. This undesired vibration can cause some levels of disturbance to the operation of these buildings. The main objective of this research paper is to investigate the effects of induced earthquakes by the GPPs operation on the performance of a masonry building from two distinct points of view: structural behavior and occupants’ comfort. In this regard, a three-story masonry building located in Germany is considered as a sample of common type of residential buildings. By using the three-dimensional finite element analysis approach and considering the nonlinear behavior of brick walls at a macro level, the damage states of the building are obtained via a numerical pushover analysis. Afterward, using 25 high-intensity recorded accelerograms due to GPPs activity, the building performance is investigated. The responses highlight that the studied building does not suffer from significant structural damages. However, by considering different existing criteria and thresholds in the literature, the experienced vibration by the building occupants can be classified as disturbing for their comfort.

Seismic Performance and Collapse Safety Assessment of Post-Tensioned Hybrid Precast Concrete Infill Wall-Frames and Comparison with Reinforced Concrete Infill Wall-Frames

ABSTRACT Post-tensioned hybrid (PH) precast concrete wall-frame buildings provide excellent seismic performance, by reducing structural damage and residual drifts. In the present study, the use of PH precast concrete walls, as partial infill walls in low-rise reinforced concrete (RC) moment-resisting frames is evaluated and compared with RC infill wall (RIW) frames with a similar structural configuration. For this purpose, the seismic performance and collapse safety of 4-story post-tensioned hybrid precast concrete infill wall (PIW) frames and RIW frames with different frame shear ratios are studied. Following the FEMA P695 methodology, fragility curves are generated, the collapse margin ratio is determined, and then the adjusted collapse margin ratio of each frame is compared with acceptable adjusted collapse margin ratio . The results indicate that, peak normalized floor displacements, inter-story drifts, and the column chord rotation demand of the PIW frames are for the most part slightly larger than the corresponding RIW frames but the PIW frames show better seismic performance in reducing the residual inter-story drifts than RIW frames, under design earthquake level and risk-targeted maximum considered earthquake level ground motions. Although a slight decrease in the is observed with increasing , for both PIW and RIW frames, exceeds the indicating that the PIW frames show satisfactory collapse performance.

Comparative Seismic Performance Assessment of Reinforced Concrete Frame Structures with and without Structural Enhancements Using the FEMA P-58 Methodology

Adding energy dissipation devices to reinforced concrete (RC) frame structures is a commonly adopted structural enhancement in seismically active regions. In this paper, a state-of-the-art seismic performance assessment is applied to a typical fixed-base RC frame structure designed based on the current Chinese code. Two additional structural enhancements, including equipping buckling restrained braces (BRB) and designing as a base-isolated structure, are investigated. Nonlinear response history analyses were performed to assess the structural performance parameters under four different seismic hazard levels (i.e., frequently occurring earthquake, design level earthquake, maximum considered earthquake, and very rare earthquake). The seismic performance is quantified in terms of repair times, repair costs, and casualties. The intensity-based assessment method is used, and a comparative analysis is performed for each performance measure. The results show that a base-isolated structure and BRB frame structure can each effectively reduce the repair cost and repair time compared with a fixed-base frame, as the repair mostly come from nonstructural components. In addition, the casualties in the base-isolated structure are the lowest of the three structures. It should be noted that the acceleration response of the BRB frame structure is the largest among the three structures, and that its acceleration-sensitive components are seriously damaged, causing the most casualties.

Influence of Optimal Intensity Measures Selection in Engineering Demand Parameter of Fixed Jacket Offshore Platform

This research identifies the significant optimal intensity measures (IM) for seismic performance assessments of the fixed offshore jacket platforms. A four-legged jacket platform for the oil and gas operation is deployed to investigate the seismic performance. The jacket platform is applied with nonlinearly modeled using finite element (FE) software OpenSees. A total of 80 ground motions and 21 different IMs are incorporated for numerical analyses. Nonlinear time-history analyses are performed to obtain the jacket structure’s engineering demand parameters (EDP): peak acceleration and displacement at the top of the structure. Four important statistical parameters: practicality, efficiency, proficiency, and coefficient of determination, are then calculated to find the significant IMs for seismic performance of the jacket structure. The results show that acceleration-related IMs: effective design acceleration (EDA), A95 parameter, and peak ground acceleration (PGA) are optimal IMs, and the acceleration-related IMs have good agreements with the acceleration-related EDP.

Development of a New Cyclic Loading Protocol for Seismic Performance Assessment of Steel Moment Connections

ABSTRACT Given the high level of seismic activity across the Middle East and particularly Iran, loading history data and respective seismic records in the region are required to formulate regional loading protocols for proper estimation of seismic behavior of structural components in accordance with construction conditions in the area. This study aims to propose such a loading protocol for the seismic performance assessment of steel moment connections in both real and laboratory conditions. A study is done on all the earthquakes that took place in the region and more than 2000 modified records of earthquakes that occurred in Iran during the past four decades to prepare an appropriate list of far-field records for the region. Subsequently, nonlinear time history analyses were performed for 7-, 12-, and 20-story steel buildings and construction conditions in the region and damage parameters were obtained. With different analytical, statistical and numerical analyses on the damage parameters resulted in target values for formulating the loading protocol for the region. Finally, an appropriate loading protocol was proposed to evaluate the moment connections (including reduced beam section connections and welded unreinforced flange-welded web moment connections) considering the construction conditions of the structures as well as the seismic history of the region.

Comparative seismic performance assessment of RC and RC/ECC hybrid frame structures: a shake table study

Comparative seismic performance assessment of RC and RC/ECC hybrid frame structures: a shake table study

Machine-learning interpretability techniques for seismic performance assessment of infrastructure systems

Machine-learning has recently gained considerable attention in the earthquake engineering community, as it can map the complex relationship between the expected damage and the input parameters. It is often necessary to understand the reasons for the behavior and predictions of the machine-learning model. This paper addresses this issue through interpretable machine-learning approaches such as partial dependence plots, accumulated local effects, and Shapely additive explanations. The evaluation of these approaches is carried out (1) at a component level by analyzing the shear strength predictions by a machine-learning model and (2) at a regional level through the machine-learning model for the regional damage assessment of bridges in California. The comparison helps to identify (1) the proper implementation of these approaches for the efficient use of machine-learning models and (2) key influential variables and thresholds that govern the prediction of the machine-learning models.

Prediction Equations for Out-of-Plane Capacity of Unreinforced Masonry Infill Walls Based on a Macroelement Model Parametric Analysis

In the seismic performance assessment of reinforced concrete (RC) frames, a reliable estimation of the capacity of unreinforced masonry (URM) infill walls is of utmost importance to ensure structural safety conditions. With particular attention to the out-of-plane (OoP) capacity of URM infill walls after in-plane (IP) damage, the issue of defining reliable analytical prediction models for the assessment of the capacity is an ongoing study. In this paper, empirical equations are proposed for the evaluation of the infilled frame’s OoP capacity, with or without IP damage, based on an extensive numerical parametric analysis, focusing on the influence of the key parameters that govern the mechanical model. The OoP capacity of URM infill walls, considering the variation in their geometrical and mechanical properties, was evaluated by using a macroelement model. The OoP strength was found to be largely influenced by the compressive strength, slenderness ratio, aspect ratio, and, additionally, level of IP damage. The reduction of OoP strength and stiffness due to IP damage was largely governed by the strength and the slenderness ratio of the URM infill wall. The reliability of the proposed model was also proved by comparisons with experimental results and some of the analytical models already available in the literature. The proposed equations provide reliable estimates of the OoP capacity by strongly indicating the suitability of the adopted macroelement model in capturing the OoP response of URM infills.

Simplified Modeling for the Seismic Performance Assessment of Automated Rack-Supported Warehouses

AbstractA reduced-order modeling approach is proposed for the linear and nonlinear analysis of automated rack-supported warehouse (ARSW) structures under seismic loads. Steel ARSWs are massive stru...

Seismic performance assessment of steel frames with slack cable bracing systems

Slack cable collapse prevention system is a cost-effective and simple method for seismic upgrading of existing structures. In this study, the effectiveness of adding slack cables to 2, 4, 8, and 12-story steel frames are assessed. The pushover analyses were performed to evaluate the general behavior of the original and braced frames. Considering 22 pairs of far-field ground motion records per FEMA P695, the nonlinear time-history analyses, as well as Incremental Dynamic Analyses (IDAs), were conducted. The maximum compression force of the first story columns, base shear demand, and the Collapse Margin Ratio (CMR) were determined and compared for original and braced frames. The fragility curves were developed and compared for the structures. Obtained results show that the slack cables postpone the collapse of the frames without increasing the initial stiffness of the structure. The average of maximum values of column axial force for the frames with slack cables are close to original frames, while it has a considerable increase in typical cable brace system cases. All original frames exceed the 10% probability when subjected to Maximum Considered Earthquake (MCE). However, the probability of collapse for the braced structures in MCE decreased significantly to less than 10%. A significant improvement in the collapse safety could be observed in the braced frames. The slack cable technique has demonstrated almost similar performance to the typical cable braces and even superior protection in terms of structural column axial forces and base shear.

Compression and In-plane Seismic Behaviour of Ashlar Three-leaf Stone Masonry Walls

ABSTRACT There is a lack of knowledge regarding the parameters needed for the effective seismic performance assessment of historical stone masonry buildings. The paper presents the results of an extensive experimental campaign consisting of four compression and fifteen in-plane cyclic shear tests on three-leaf ashlar stone masonry walls and its constituents. The morphology, level of vertical load, and testing boundary conditions were systematically varied, and their influence on the load-bearing and deformation capacities, stiffness, ductility and energy dissipation was analysed. Good consolidation of the inner core enables in-plane failure mechanism of the walls to occur without decisive out-of-plane damage. The boundary conditions applied significantly influence the failure modes and large deformation capacities obtained, whereas transverse connections in the case of a shear failure mechanism do not significantly influence the overall lateral in-plane response of walls.

Loading protocols for seismic performance evaluation of buckling-restrained braces in RC frames

The selection of a proper loading protocol for seismic performance evaluation of structural dampers poses quite a challenge at the very first step of quasi-static cyclic tests. Existing loading protocols for buckling-restrained braces (BRBs) are mainly developed on the basis of the seismic responses of BRB-steel frame systems. However, the behavior of a BRB in reinforced concrete frames (RCFs) differs markedly from that in the steel frames. In this study, a set of loading protocols were constructed to provide a reference for seismic performance assessment of BRBs in RCFs. The methodology for the development of loading protocols was illustrated and a series of BRB-RCFs varying in building heights and story shear resisted by BRBs were designed. An extensive analytical investigation of seismic responses of BRBs under far-field, near-fault, and long-duration earthquakes was systematically evaluated and quantified. Based on the rainflow counting method, the control parameters in terms of numbers of cycles, amplitudes, and residual core strains were determined to construct loading sequences. The effectiveness of the proposed loading protocols was discussed and verified through comparisons with existing loading sequences and time-history analysis results of a validated BRB-RCF model. It is indicated that the proposed loading protocols can conservatively reflect the actual seismic damage demands with a reasonable agreement.

Seismic performance assessment of a super high-rise twin-tower structure connected with rotational friction negative stiffness damper and lead rubber bearing

In this paper, a novel rotational friction negative stiffness damper (RFNSD) composed of negative stiffness device (NSD) and rotational friction dampers (RFDs) is proposed to develop flexible connection for improving the seismic performance of an asymmetrical super high-rise twin-tower connected structure. The prototype structure is rigidly connected by long-span steel truss, and shaking table test has shown that the rigid connection between the towers and the truss corridor generally cause buckling of steel truss members and structural damage on the connected floors. To mitigate seismic responses of the truss corridor and the towers, the rigid connection is replaced by flexible ones using the proposed RFNSD and lead rubber bearing (LRB). The working principle of RFNSD is introduced and the theoretical force-displacement model is derived. The numerical model for the proposed flexible connection is presented and detailed three-dimensional finite element models for the rigidly and flexibly connected structures are established. Then by nonlinear time history analysis, seismic responses of the models under three-directional excitations are analyzed, and the effect of flexible connection’s design parameters is discussed. The results show that the developed flexible connection can obviously mitigate the dynamic responses and structural damages. As the stiffness of the pre-tensioned spring in NSD increase, the dynamic response of the steel truss connection corridor would be further decreased. The RFDs can effectively control the increased deformation of the flexible connection caused by the NSD, and promotes the energy dissipation capacity. The model with the flexible connections presents good seismic performance, indicating the effectiveness of the proposed RFNSD.

Predicting the Maximum Seismic Response of the Soil-Pile-Superstructure System Using Random Forests

ABSTRACT Seismic fragility analysis has been considered an efficient method for seismic performance assessment of soil-pile-superstructure systems (SPSSs). However, seismic fragility analysis based on widely used numerical methods often requires a significant investment of time. In this study, a new approach based on the random forest technique, which can be applied to fragility analysis, is proposed to accurately and efficiently predict the maximum seismic response of SPSSs. Moreover, based on the random forest technique, the velocity RMS is found to exhibit a stronger correlation with the maximum seismic response of SPSSs in liquefiable soils.

Seismic performance assessment of steel moment-resisting frames with self-centering viscous-hysteretic devices

This study evaluates the seismic performance of the steel frame with self-centering viscous-hysteretic devices (SC-VHD frame) and investigates the effect of design parameters of the SC-VHD, preload, loading stiffness, unloading stiffness and viscous damping ratio, on seismic performance through conducting nonlinear static pushover analysis, fragility analysis and risk assessment on 4-, 8-, and 12- story SC-VHD frames with different design parameters. Results indicate that the maximum normalized base shear and the ultimate roof drift ratios of the SC-VHD frames increase by more than 13.3% and 42.9%, respectively, compared with the conventional frames. The SC-VHD frames have acceptable low probabilities of collapse and probabilities exceeding considered residual drift under the maximum considered earthquake (MCE) and during a 50-year period. Accordingly, the most sensitive parameter regarding the probabilities of collapse is loading stiffness, followed sequentially by unloading stiffness, viscous damping ratio and preload. While for the probability exceeding considered residual drift under the MCE, the parameters of ring springs, preload, loading stiffness and unloading stiffness, have a significant effect on the 4- and 8-story SC-VHD frames, and the viscous damping ratio of the viscous damper has the most significant effect on the 12-story SC-VHD frame. For the probability exceeding considered residual drift during a 50-year period, the most sensitive parameter is the viscous damping ratio.

Post-fire hysteretic and low-cycle fatigue behaviors of Q345 carbon steel

A series of material tests are carried out to study the cyclic loading behavior of Q345 carbon steel after fire. A total of 60 specimens are examined, which are heated to 500, 750 or 1000 °C, then cooled by air cooling, water spray cooling or water immersion cooling, followed by either incremental-amplitude cyclic loading or constant-amplitude low-cycle/extremely low-cycle fatigue (LCF/ELCF) loading. The typical fracture failure mechanism of the specimens is analyzed by scanning electron microscope (SEM) and metallurgical microscopy (MM). The material parameters of Ramberg–Osgood model, Masson–Coffin model and a nonlinear combined hardening model are calibrated to facilitate the assessment of the residual seismic performance of the steel after fire. Among other important findings, the test results show that water immersion cooling with a rapid cooling speed following a medium or large fire (heated to 750 °C or 1000 °C) have a significant impact on the cyclic behavior of the Q345 steel. In these cases, the formation of martensite with high strength and poor ductility results in an increase in the cyclic stress, a decrease in the ductility and a sharp reduction of the fatigue life. These phenomena indicate that the seismic performance of steel structures may be significantly compromised after rapid cooling from a medium or large fire. Other heating-cooling processes have less pronounced effects on the hysteretic and low-cycle fatigue properties of the material.

Lifetime risk-based seismic performance assessment of buildings equipped with supplemental damping and base isolation systems under probable mainshock-aftershock scenarios

This research attempts to investigate the efficacy of different passive vibration control systems, from both technical and economic points of view, to mitigate the lifetime seismic risk of typical buildings under probable mainshock-aftershocks sequences via a novel probabilistic framework. In this regard, three separate common building models are considered, including 5-, 10-, and 15-story intermediate steel moment-resisting frame buildings. These models are designed optimally with/without passive vibration control systems, including hysteretic damping, linear viscous damping, and base isolation systems as independent alternatives. Next, for the hazard modeling, all active faults located in the greater Tehran area are taken into account to simulate the earthquake scenario. Afterward, probable earthquake scenarios during the 50 years of buildings’ life-spans are generated randomly, including the events, as well as their corresponding synthetic stochastic accelerograms. In the next step, responses of buildings and their cumulative losses are calculated under the whole scenarios considering various damage types such as structural, non-structural, and content-related. In the end, by using the Monte-Carlo simulation method, the seismic risk of different building alternatives is estimated. Interestingly, the application of each of the considered vibration control devices leads to a significant reduction in lifetime losses (both physical and economic). It is revealed that the viscous damper has the highest efficacy among different systems. Importantly, by neglecting aftershocks' effects, the estimated lifetime risk will be underestimated by about 27 to 57% below the expected value. Finally, among the active faults in the greater area of Tehran, the North Tehran, Kahrizak, and Mosha faults have the highest contribution in the estimated lifetime risk of buildings.

Seismic acceleration demand and fragility assessment of storage tanks installed in industrial steel moment-resisting frame structures

Recent seismic events highlighted the importance of non-structural elements in seismic assessment and performance-based earthquake engineering. When referring to industrial facilities, storage tanks represent one of the most critical components for the continuous functionality of industrial and building plants after seismic events. At the same time, the dispersion of dangerous or inflammable materials, due to their collapse, could become a safety issue in terms of both human life and environmental impact. This study focuses on the seismic performance assessment of a liquid-storage tank installed in an industrial steel moment-resisting frame building. The performance is assessed in terms of fragility curves, that are provided for the meaningful limit states that affect the liquid-storage tank and considering several intensity measures. The results related to the structural performance are also discussed in detail in terms of fragility functions and floor response. The assessment is performed through nonlinear dynamic analyses using two different modelling approaches to evaluate the structural and non-structural performance. The first modelling approach explicitly accounts for the tank-structure interaction, while in the second one the tank is only modelled considering its seismic mass. The results show the importance of the modelling assumptions to accurately estimate the seismic demand on liquid-storage tanks and corresponding fragility, which is calculated in terms of different intensity measures (IM): average ground spectral acceleration, peak floor acceleration, and floor spectral accelerations. Peak floor acceleration, drift profiles, and absolute acceleration and relative displacement floor response spectra are instead scrutinised for what concerns demand. The comparison with the code formulations available in the literature for estimating the seismic demand to non-structural elements pointed out their inaccuracy for the analysed liquid-storage tank and the need for further efforts to develop more accurate procedures. Furthermore, the outcomes indicate that the IM adopted for secondary components, i.e. peak floor acceleration, may not always be the optimal one hence additional attention should also be paid to the definition of updated fragility curves for non-structural elements, identifying and adopting more suitable IMs.