Seismic Demand Research Articles

Deformation behavior of rectangular underground structures in liquefiable deposits correlated to ground motion intensity measures

Rectangular underground structures in liquefiable deposits are susceptible to larger deformation during earthquake events. The intensity of earthquake motions, as one of the critical factors that would induce large deformation of underground structures in liquefiable deposits, however, was not received enough recognitions. In this paper, nonlinear dynamic analyses with a probabilistic seismic demand model (PSDM) were conducted for a two-dimensional liquefied soil-structure system, considering a variable thickness of liquefiable layer below the structure. The nonlinear soil behavior was simulated by the nonlinear constitutive model PDMY02. The constitutive parameters of saturated sand were calibrated by a slope model in the centrifuge test from LEAP-2017. Interstory drift ratio (IDR) and uplift ratio (UR) of underground structures were selected as engineering demand parameters (EDP). There were totally 18 recorded earthquake motions and 8 intensity measures (IMs) included for the PSDM. Numerical results show that the uplift behavior of underground structures is more sensitive to the variable thickness of liquefiable deposits compared to the horizontal drift of the structure. According to the performance of correlation, efficiency, practicality and proficiency, the velocity-related IMs are more appropriate than the acceleration-related IMs for the evaluation of seismic deformation behavior of underground structures. The deformation response as well as the adaptability of velocity-related IMs are further discussed and evaluated by considering more general cases including different buried depths and height-width ratios for rectangular underground structures.

Bayesian-optimized interpretable surrogate model for seismic demand prediction of urban highway bridges

Urban highway bridges are crucial for regional economic development and population mobility, but they are vulnerable to seismic hazards. Accurately predicting the seismic demands of bridges is essential. Several commonly-used methods for seismic demand estimates, such as cloud analysis, incremental dynamic analysis, and multiple stripe analysis, are computationally expensive and subject to theoretical assumptions and convergence issues, especially for portfolios of bridges. Machine learning techniques can be effective, but their lack of interpretability hinders understanding of the surrogate model's predictions. To address these challenges, this study develops a Bayesian-optimized interpretable ensemble learning surrogate model for predicting and interpreting the critical seismic demands of urban highway bridges.Thousands of continuous prestressed concrete girder bridges with typical geometric configurations in China are generated, and 120 ground motion records with different frequency, waveform, and duration characteristics are chosen. The seismic demand dataset is established based on nonlinear time-history analyses for urban highway bridges, accounting for different types of uncertainties. The surrogate models are developed based on the XGBoost ensemble learning method, with hyperparameters automatically and efficiently determined by Bayesian optimization technique. Compared to the random search and grid search methods, Bayesian optimization is approximately 8 times and 29 times faster, respectively, and it also achieves the highest prediction accuracy. Meanwhile, the relationship of each hyperparameter in the surrogate model is also revealed. The prediction results of the proposed model are compared with other machine learning models. The SHAP algorithm is subsequently used to explain the model predictions regarding the feature importance, global interpretations, and feature dependency analysis. The study quantifies the contribution of each structural feature and seismic intensity measure to the selected critical seismic demand and identifies the interaction effects between different input variables in the prediction.

Application of a Deep Learning Method to the Seismic Vulnerability Analysis of Cross-Fault Hydraulic Tunnels Based on MLE-IDA

Rapidly developed deep learning methods, widely used in various fields of civil engineering, have provided an efficient option to reduce the computational costs and improve the predictive capabilities. However, it should be acknowledged that the application of deep learning methods to develop prediction models that efficiently assess the nonlinear dynamic responses of cross-fault hydraulic tunnels (CFHTs) is lacking. Thus, the objective of this study is to construct a rational artificial neural network (ANN) prediction model to generate the mass data and fragility curves of CFHTs. Firstly, an analysis of 1080 complete nonlinear dynamic time histories via incremental dynamic analysis (IDA) is conducted to obtain the mass data of the drift ratio of the CFHT. Then, the hyper-parameters of the ANN model are discussed to determine the optimal parameters based on four examined approaches to improve the prediction capacity and accuracy. Meanwhile, the traditional probabilistic seismic demand models of the predicted values obtained by the ANN model and the numerical results are compared with the statistical parameters. Eventually, the maximum likelihood estimation couping IDA method is applied to assess the seismic safety of CFHTs under different damage states. The results show that two hidden layers, ten neurons, and the ReLU activation function for the ANN model with Bayesian optimization can improve the reliability and decrease the uncertainty in evaluating the structural performance. Moreover, the amplitude of the seismology features can be used as the neurons to build the input layers of the ANN model. It is found through vulnerability analysis that the traditional seismic fragility analysis method may overestimate the earthquake resistance capacity of CFHTs compared with maximum likelihood estimation. In practical engineering, ANN methods can be regarded as an alternative approach for the seismic design and performance improvement of CFHTs.

Effect of Steel Jacketing Thickness on Seismic Performance of Bridge

The bridges of Nepal are getting older and old bridges were designed without considering the seismic forces, hence have low seismic capacity. The capacity of these bridges needs to be enhanced and should perform well during seismic events. The jacketing technique can be used to upgrade the bridge's structural performance. This research paper mostly focuses on the seismic performance enhancement after the application of steel jacketing on the bridge pier. The variable that has been varied is the thickness of the steel jacket. The capacity of a bridge pier is evaluated using displacement-controlled nonlinear static analysis (Pushover). The time history load is applied to the structure to determine the seismic demand of the bridge. The quantification of the enhancement of the bridge structure after the application of Steel Jacketing is evaluated by plotting the fragility curve. The modeling of the bridge is done in CSI Bridge V20.2.0. The different damage state is defined using the strain values obtained from the pushover analysis. For different damage states, the capacity and demand value are used to obtain the probability of exceeding at different PGA levels. The fragility curve is developed using the First Order Second Order Method (FOSM). From the study, it is found, that the vulnerability of the bridge after the use of jacketing for extensive damage state, the probability of failure reduced from 28.22% to 14.24% at 1.0g PGA. Similarly, the vulnerability of the bridge after the use of jacketing for collapse damage state, the probability of failure decreased from 16.93% to 7.22% at 1.0 PGA

Evaluation of slab–wall connections in tunnel form concrete structures: A multi-level approach based on seismic demand and capacity

The seismic performance of an integrated tunnel-form concrete system relies heavily on the performance of walls, considering the safe design of slabs and the substantial length of in-place connections. However, despite ensuring suitable seismic behavior for slabs and walls, the lateral load resistance of the system depends on the capacity of connections between them, which has not received adequate attention in the existing technical literature and prescriptive codes. To address this gap, the present study focuses on the comprehensive evaluation of slab–wall connections in tunnel-form concrete systems. By analyzing 5-story and 10-story models, it was consistently observed that connections at lower levels are more vulnerable. Using the demand approach and considering the design basis earthquake (with a maximum acceleration of 0.35 g and a return period of 475 years) as the input excitation, the system exhibited a reliable immediate occupancy performance level with an estimated reliability of 100%. However, in taller structures, connections were predicted to experience cracking with a maximum demand to capacity ratio of 1.1. Applying the capacity approach and considering the earthquake corresponding to the immediate occupancy performance level in the system as the input excitation, the system achieved a reliable life-safety performance level with an estimated reliability exceeding 79%. However, in more than half of the building height, connections were predicted to experience cracking with a maximum demand to capacity ratio of 2. The results demonstrate that the existing shear-friction capacity adequately meets the demand of cracked connections in both approaches. Nevertheless, an evaluation of the shear-friction capacity demand ratio reveals that connections are undeniably one of the primary weaknesses of the tunnel-form concrete system, especially as the structure’s height, torsional effects, earthquake intensity, or allowable damage level increases. Therefore, special detailing is necessary to address this vulnerability.

Cyclic behavior of dual-steel beam-to-column welded flange-bolted web connections

Cyclic loading tests on dual-steel beam-to-column welded flange-bolted web connections were conducted to quantify their moment resistance, plastic deformation and energy dissipation capacities. The test program consisted of five one-sided connection specimens, where Q355 grade beams and Q690 grade columns were used, to study the effects of beam-to-column welded flange connection details and panel zone shear strength on the connection seismic performance. Two types of welded connection details were considered; one was the traditional complete-joint-penetration (CJP) welded connections by use of backing bars, and the other type was those with the bottom backing bar further reinforced by a fillet weld. Three column web thicknesses were designed to arrive at strong, intermediate and weak panel zones, respectively. It was found that the CJP weld with the backing bar reinforced only under the bottom beam flange produced satisfactory performance and accommodated plastic rotations larger than 0.03 rad, while a maximum plastic rotation of 0.04 rad could be developed in the high-strength steel panel zone before fracture occurred. These results evidenced that those dual-steel connections could still sustain high seismic deformation demands.

Seismic design and performance evaluation of hybrid braced frames having buckling-restrained braces and self-centering viscous energy-dissipative braces

Hybrid braced frames (HBFs) emerge as an innovative seismic-resilient system, synergizing the strengths of buckling-restrained braces (BRBs) and self-centering viscous energy-dissipative braces (SCVDBs). This novel system has the potential to simultaneously manage three key seismic demand parameters: peak inter-story drift (PID), residual inter-story drift (RID), and peak absolute floor acceleration (PFA). Nevertheless, a dedicated seismic design method for HBFs is yet to be developed. This research proposes a performance-based seismic design (PBSD) method specifically tailored for HBFs. The method's core relies on energy decoupling in the HBFs using a proposed energy distribution factor (η). To validate the proposed design method, sets of 4-, 8-, and 12-story braced frames are designed using varied η. A comprehensive seismic performance evaluation is conducted, utilizing nonlinear static and nonlinear time-history analyses. The findings indicate that the HBFs, designed utilizing different values of η, consistently meet predefined performance objectives. Within the scope of this study, the η value of 0.5 is shown to be optimal, enhancing the structural resilience of HBFs against PIDs and PFAs while exhibiting excellent self-centering performance comparable to the self-centering viscous energy-dissipative braced frame (SCVDF). Additionally, the HBFs demonstrate superior control over PFA compared to pure buckling-restrained braced frame (BRBF) and SCVDF.

Functional recovery evaluation of hybrid self‐centering piston‐based braced frames

AbstractSevere earthquakes possess formidable destructive potential, leading to substantial damage, widespread disruptions, and tragic loss of life. In response, researchers and policymakers strive to develop innovative solutions to quantify the seismic resilience of structures. This study aims to evaluate the post‐earthquake functional recovery of two types of braced frames: Self‐Centering Piston‐Based Braced Frames (SC‐PBBFs) and Buckling Restrained Braced Frames (BRBFs). The SC‐PBBFs are designed to mitigate structural damage by incorporating Self‐Centering Piston‐Based Bracings (SC‐PBBs) equipped with Shape Memory Alloy (SMA) bars and Friction Springs (FS). A set of building prototypes, representing low‐, mid‐, and high‐rise archetypes in seismic regions, are subjected to comprehensive analyses under 44 far‐field ground motions. This thorough examination incorporates seismic hazards, structural demands, and component damages to quantify the earthquake‐induced losses and repair timelines. The study findings indicate that BRBFs suffer more significant collapse losses than SC‐PBBFs. However, BRBF systems incur lower repair costs, mainly due to limited damage to acceleration‐sensitive non‐structural components. Additionally, the FEMA P‐58/ATC‐138 framework is employed to estimate re‐occupancy, functional recovery, and full repair time, identifying systems and components that exert a significant impact on functional recovery.

Response to discussion of “Seismic damage analysis due to near‐fault multipulse ground motion”

AbstractThe 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.

Effects of modeling assumptions on prediction of seismic demands of a single-story RC structure

This study investigates the seismic response of a single-story reinforced concrete (RC) structure subjected to strong ground motions. Effects of modeling assumptions used to idealize the reinforcement slip in beam-column joints and column footing are studied. For this purpose, the numerical model of a single-story, single-bay, three-dimensional asymmetric RC structure, tested on a shake table and its symmetric version, is analyzed. Two modeling approaches are considered to show the significance of rotation associated with the reinforcement slip. Bidirectional nonlinear time-history analyses are conducted using symmetric and asymmetric 3D models. In these analyses, 30 pairs of near-field ground motions, selected and scaled to match the target spectrum, are used. The findings indicate that the neglection of reinforcement slip in numerical model may result in an underestimation of almost 50% in story drift ratio demands.

Towards reliable seismic fragility assessment of highway bridges with oblong columns considering the drift-based capacity directionality effect

Highway bridges in seismic zones are commonly designed with oblong columns, featuring different force-displacement relationships and seismic capacities along different response directions. However, the state-of-art seismic fragility assessment treats seismic demand and capacity models as two independent models, which cannot capture the in-between directional dependence and correlation for oblong columns. This study develops direction-dependent seismic capacity limit state models and proposes a multi-step analysis framework to assess the seismic fragility of highway bridges with flexure-controlled oblong columns. Cyclic pushover analyses are conducted along different loading directions to identify direction-sensitive column drift ratios against four damage states. These drift ratios are utilized to regress a closed-form model, namely the directional capacity ratio model, to quantify the changes in drift capacities as a function of the column response angle. This model is integrated into an analysis framework to directly simulate the demand-capacity ratio (DCR) time history, where the peak value is utilized to assess the seismic fragility of the oblong column. The case study indicates that the most severe seismic damage to an oblong column is not necessarily along its principal axis. The proposed analysis framework outperforms existing approaches in having more reliable fragility estimates for the oblong column and bridge system.

Influence of Fluid Viscous Damper Stiffness on the Floor Acceleration Response of Steel Moment-Resisting Frames Under Far-Field Ground Motions

ABSTRACT The implementation of fluid viscous dampers has been proven as a feasible method to improve the seismic performance of buildings. However, the different variables involved in the damper’s design affect the structural response, especially in terms of seismic demand on non-structural elements. This paper presents a parametric study on the floor acceleration response of three case study buildings equipped with fluid viscous dampers through nonlinear time-history analysis. The results show that the different design parameters of fluid viscous dampers significantly modify the floor acceleration response, with some damper configurations yielding floor accelerations larger than those of the buildings without dampers.

Fragility Analysis of the Main Building–Coal Conveyor Trestle Interaction System of a Thermal Power Plant

Thermal power plants play a crucial role in the power system as critical lifeline infrastructure. In order to meet the production process requirements, the main building of a thermal power plant is often connected to a coal conveyor trestle. This study focuses on investigating the seismic interaction between the common three-row reinforced concrete frame-bent main building and the steel trestle in a circulating fluidized bed (CFB) unit. The objective is to assess the influence of the trestle on the main building and understand the failure mode of the trestle structure. The seismic interaction is analyzed through fragility analysis based on Incremental Dynamic Analysis (IDA). The results indicate that the trestle has minimal influence on the main building, except during the large deformation stage. The study identifies the failure mode of the coal conveyor trestle as excessive relative displacement along the longitudinal direction at the connection points, leading to collisions or falls. A seismic demand model based on longitudinal relative displacement is developed to obtain the fragility curve for the trestle structure. These findings offer valuable insights for assessing the seismic performance of thermal power plants.

Nonlinear Static Analysis of Building with Different Aspect Ratio


 
 
 
 The earthquake resistant design of structures requires that systems ought to maintain, adequately, any ground motions of an depth that would arise for the duration of their construction or in their regular use. However floor motions are unique inside the consequences they have got on structural responses. The most accurate evaluation method for structures subjected to strong ground motions is the time history analysis . This evaluation entails the integration of the equations of motion of a multi-degree-of-freedom system, MDOF, within the time domain the usage of a stepwise answer which will constitute the real reaction of a structure. This technique is time-eating even though for application in all sensible functions. The necessity for faster techniques that could make certain a dependable structural assessment or design of structures subjected to seismic loading brought about the pushover analysis.
 Pushover analysis is based totally on the belief that systems oscillate predominantly inside the first mode or inside the decrease modes of vibration at some stage in a seismic occasion. This ends in a reduction of the multi-degree-of-freedom, MDOF machine, to an equivalent single-degree- of-freedom, ESDOF gadget, with properties expected by a nonlinear static evaluation of the MDOF system. The ESDOF device is then eventually subjected to a nonlinear time- history analysis or to a response spectrum analysis with consistent- ductility spectra, or damped spectra. The seismic demands calculated for the ESDOF device are converted through modal relationships to the seismic demands of the MDOF machine.
 The objective of this thesis record is to emphasise the use of non-linear static procedure i.e pushover analysis a seismic overall performance assessment of R.C frames .
 
 
 

Response- and probability-based evaluation of spectrally matched ground motion selection strategies for bi-directional dynamic analysis of low- to mid-rise RC buildings

In this study, the effect of different strategies which consider various levels of constraints for spectrally matched ground motion (GM) selection on seismic responses of the buildings was evaluated. For this, six different three-dimensional buildings and three different local soil classes were considered. Various GM record sets were used for each strategy and local soil class pair to perform bi-directional nonlinear dynamic analyses of the buildings and maximum global and maximum inter-story drift ratio demands were obtained. To evaluate the efficiency of proposed strategies, the mean and dispersion of the demands were investigated. Then, the differences among the means of the seismic demands obtained for the strategies were evaluated using the analysis of variance method. Moreover, probability curves of the demands were constructed and compared. The results indicate that i) the mean of the demands generally used for code-based performance assessment can be estimated more consistently by the proposed strategies; ii) the supplemental constraints about spectral matching allow to control the dispersion of the spectral acceleration values of selected GMs and hence the dispersion of the demands; iii) using the appropriate one of the proposed strategies, GMs with desired dispersion of spectral accelerations can be acquired for probability-based performance assessment.

Seismic performance assessment of hydraulic tunnels considering oblique incoming nonstationary stochastic SV waves based on the generalized PDEM

An important aspect of a seismic performance assessment framework is to adequately consider the stochastic nature of SGMs. This requires an appropriate method for synthesizing random SGMs, a crucial step in conducting structural response analysis. Additionally, affected by topographic and geological conditions, the incident angle of SGMs is also uncertain and random, which may induce unexpected damage to structures. To date, a framework is presented to assess the seismic performance of hydraulic tunnels under stochastic obliquely incident SV waves. The framework incorporates the spectral representation method of SGMs and obliquely incident SV waves into stochastic dynamic analysis. To create the appropriate PDFs and CDFs for numerous performance indices, the generalized PDEM and equivalent extreme-value event are introduced. Subsequently, stochastic dynamic analysis and seismic performance assessment of the hydraulic tunnel are performed. Finally, the disparity between the hydraulic tunnel fragility curves generated using conventional linear regression and generalized PDEM is examined. The difference between vertically incident and obliquely incident SV waves is discussed. The results indicated that (1) different performance indices exhibit great differences in the stochastic dynamic response of structures and the failure probability of seismic performance evaluation; (2) compared with the traditional linear regression method, the probability of damage of hydraulic tunnels under strong SGMs may be overestimated; and (3) nonstationary stochastic obliquely incident SV waves can cause more seismic demand than nonstationary stochastic vertically incident SV waves under low/medium earthquake intensity levels for hydraulic tunnel.

Seismic fragility functions for earthquake-induced landslide risk assessment using identified optimal earthquake intensity measures

Seismic fragility analysis can relate the probability of unsatisfactory performance of slopes with increasing intensity of ground motions, which is the basic component of landslide hazard risk assessment. Determination of the optimal earthquake intensity measure (IM) is one of important prerequisite for seismic fragility analysis. Although a small number of studies have already performed seismic fragility analysis of slopes, the optimal IM for seismic fragility analysis of slopes have not been discussed and researched. In the present study, 15 IMs and two different engineering demand parameters (EDPs), including factor of safety (FOS) and Newmark permanent displacement (NPD), are selected for probabilistic seismic demand and seismic fragility analysis of slopes. The metrics of correlation, practicality, efficiency, and proficiency are adopted to identify the optimal earthquake IMs among the studied 15 IMs for two EDPs in seismic fragility analysis of slopes respectively. The results have found that the optimal IM is different for slope fragility analysis when different EDPs are selected. Acceleration spectrum intensity is the most optimal IM among the examined 15 IMs for seismic fragility analysis of slopes when FOS is adopted as the EDP. When NPD is selected as the EDP, root mean square of acceleration and velocity spectrum intensity are in general more appropriate than other IMs. In the last, the seismic fragility curves with regard to two EDPs and corresponding optimal IMs are derived for interpreting more properly slope seismic performance and earthquake-induced landslide risk.

Evaluation the effect of amplitude scaling of real ground motions on seismic demands accounting different structural characteristics and soil classes

Evaluation the effect of amplitude scaling of real ground motions on seismic demands accounting different structural characteristics and soil classes

Seismic acceleration demands in tall CLT buildings, predictive models and intensity measures

An accurate prediction of floor accelerations is crucial for estimating damage to contents and non-structural components in a building. Oversimplifying the nature of acceleration demands might result in biased estimates of building damage and consequently bias in the calculation of economic losses. However, given the relative novelty of multi-storey tall timber buildings, dedicated studies and models of their seismic acceleration demands are lacking. The need for these is stressed further when we recognise that the behaviour of walled timber structures is decidedly different from that of other conventional structural types. In this study, we apply modern data-driven approaches to evaluate efficient intensity measures (IMs) and develop regression models for predicting the peak floor acceleration (PFA) of multi-storey cross-laminated timber (CLT) buildings. Twenty-four IMs are evaluated and their prediction performance is compared. The sensitivity of acceleration demands to different IMs over a wide range of CLT buildings is investigated. We perform a systematic feature selection process using three different data-driven techniques. The selected features are then used to develop nine regression models to estimate PFA. Various modelling techniques, consisting of conventional (Linear and Polynomial regressions) as well as machine learning algorithms (Decision trees, Random forest, K-nearest neighbour, and Support vector regression) are used. The dataset used to train the models is obtained from numerical results of 69 CLT building models with variations in building height, panel fragmentation levels, and q-factors (ductility levels) subjected to a large set of strong earthquakes. After assessing the accuracy of our model predictions, their PFA estimates obtained are compared against previous research and design codes. Finally, simplified expressions for estimating peak floor accelerations in CLT structures are provided for practical purposes.

Impact of asymmetrical corrosion of piers on seismic fragility of ageing irregular concrete bridges

This article investigates the seismic fragility of ageing irregular multi-span reinforced concrete (RC) bridges. Different irregularity sources are considered, including: (i) substructure stiffness irregularity arising from the unequal-height piers, (ii) substructure stiffness irregularity arising from the spatially variable (asymmetrical) corrosion damage of piers and (iii) irregular distribution of effective tributary masses on piers of varying heights. To this end, a three-dimensional nonlinear finite element model is developed for multi-span RC bridges and verified against a large-scale shake table test results of a two-span concrete bridge specimen available in the literature. Nonlinear pushover, incremental dynamic and seismic fragility analyses are performed on three groups of two-span RC bridges with different configurations. Moreover, a time-dependent dimensionless local damage index is employed to evaluate the failure sequence and collapse probability of selected bridge layouts. The analysis results of the three studied irregularity sources show the considerable significance of spatially variable corrosion of bridge piers and substructure irregularity on the failure sequence of piers and seismic fragility of multi-span RC bridges. Furthermore, analysis outcomes show that uneven corrosion of piers triggers an unbalanced distribution of seismic ductility demands and irregular seismic response of equal-height multi-span RC bridges.