Seismic Demand Research Articles

Refined probabilistic seismic demand modeling of high-speed railway bridge under near-fault hanging-wall effects and velocity pulse effects by a novel ground motion selection approach

Refined probabilistic seismic demand modeling of high-speed railway bridge under near-fault hanging-wall effects and velocity pulse effects by a novel ground motion selection approach

Optimization of a novel lateral energy dissipation system for cable-stayed bridge with short piers based on seismic vulnerability analysis

Cable-stayed bridges with short piers are susceptible to becoming the structural weak link in seismic resistance during strong earthquakes. Traditional lateral restraint systems, such as fixed and sliding bearing systems, may impose substantial lateral forces and displacement demands, affecting the entire bridge's seismic safety. A butterfly-shaped steel plate damper has been developed and integrated into a lateral energy dissipation system along with elastoplastic cables to address this. Given the significant computational challenges and the complexity of identifying the optimal parameters for the energy dissipation system, this paper combines the probabilistic seismic demand model (PSDM) with the response surface method (RSM) to propose the seismic vulnerability fitting optimization method (SVFOM). Based on SVFOM, utilizing a central composite design (CCD), 17 analysis scenarios that account for the parameter variations of the lateral energy dissipation system are established. By developing response surface functions for bearing damage (ys) and pier damage (yp) through the seismic response fitting of the structure across all scenarios, we determined the optimal parameters for the lateral energy dissipation system to minimize damage to both bearings and piers. The finite element model validation analysis, which demonstrated significant reductions in pier displacement and the probability of bearing damage, confirms the effectiveness of the SVFOM. Optimized parameters showed that the new lateral energy dissipation system can significantly enhance the lateral seismic performance of cable-stayed bridges with short piers. Compared to scenarios without energy dissipation and with lateral sliding bearings, they demonstrated that this optimized system reduces the relative displacement of the piers and girders by 56 % and the probability of complete bearing failure by 87 % while maintaining pier damage within acceptable limits. This optimized system offers a valuable reference for the seismic design of similar bridge structures.

Probabilistic seismic demand analysis for bridges based on earthquake scenarios

The current probabilistic seismic demand analysis of structures predominantly considers the correlation between the ground motion intensity measure (IM) and structural seismic demand, but fails to effectively capture regional source characteristics. It is essential to integrate earthquake engineering with seismic response of structures using source parameters to quantify regional ground motion uncertainties and determine appropriate IMs. This study presented a probabilistic seismic demand analysis method for structures based on earthquake scenarios, characterized by 1) utilizing the stochastic finite-fault method to simulate ground motions at a specific site instead of employing multiple seismic waves from different source areas, and 2) incorporating the correlation between IMs and the key indicator of source parameters, stress drop, into the probabilistic seismic demand analysis. Taking a continuous girder bridge as an example, the performance of the stress drop and 14 individual IMs in predicting the longitudinal seismic demand and reflecting source characteristics was evaluated. The results revealed that it was difficult to establish a reliable relationship between the stress drop and structural seismic demand. Owing to the complexities of ground motion and structural parameters, the individual IMs were challenging to effectively capture their characteristics simultaneously. Therefore, composite IMs have been proposed to cover the characteristics of both the source and seismic demand. The optimal solutions were derived using a multi-objective genetic algorithm, which exhibited desirable capabilities in both aspects, providing a comprehensive guide for the seismic performance assessment of regional transportation networks.

Development of a novel rotational metallic damper as a dissipative connector in rocking steel core systems: Cyclic behavior and seismic demand

Rocking systems with stiff rocking cores have been proposed as a promising solution for mitigating concentrations of story drift and enhancing structural seismic resilience. This study introduces a novel rotational metallic damper, termed the rotational steel rod damper (RSRD), developed for use in rocking steel core systems to improve energy dissipation capacity. The configuration, working mechanism, and application of the RSRD in rocking steel core systems are described. Three critical energy-dissipating elements, low-yield-point steel rods with different edge shapes, were isolated from the RSRD and tested to validate the efficacy of an optimal hourglass shape, defined through cubic equations, in enhancing low-cycle-fatigue performance. Two RSRD specimens were then tested and analyzed, focusing on failure modes, cyclic behavior, rotational strength, and energy dissipation. Both specimens demonstrated positive and stable hysteretic performance and energy dissipation capacity, with maximum equivalent viscous damping ratios of 0.51 and 0.53. Subsequently, structural models of seven steel frames were developed in OpenSees for case studies. Nonlinear response history analyses were performed under 20 ground motion records scaled to DBE and MCE levels. Dynamic behaviors, particularly the seismic demand on RSRDs, were examined. Numerical results confirmed the efficacy of the RSRD in mitigating inter-story drift. The location of the pivoting point of the rocking core significantly influenced the rotational demand on the RSRD. The proposed RSRD presents an innovative energy-dissipating alternative for the development of rocking steel core systems.

Machine-learning-based models for predicting seismic demands of SCBFs based on scalar and vector-valued intensity measures

Machine-learning-based models for predicting seismic demands of SCBFs based on scalar and vector-valued intensity measures

Seismic response of rocking bridge systems under three-dimensional ground motions

Compared to theoretical models, finite element methods provide greater versatility for dynamic response analyses of rocking bridges, especially when considering the influences of various nonlinear boundary conditions. A finite element modeling method based on fiber section elements for three-dimensional seismic analyses of rocking bridges is developed in this paper. This method solves the problem of energy dissipation and stiffness determination of the rocking interface. Based on the proposed modeling method, considering nonlinear boundary conditions (such as abutment-soil interaction, impact effect, and pile-soil interaction), the seismic responses of rocking bridges, including free rocking, prestressed rocking and prestressed rocking with dampers, under the excitation of three-dimensional ground motions are analyzed. The results show that: after reasonable design, the prestressed rocking bridge with dampers exhibits similar seismic responses to the cast-in-place bridge, and maintains a good self-centering ability. The responses of all the rocking bridges under bi-directional loading are greater than those under unidirectional loading. In contrast, vertical ground motion's influence on the response of the rocking bridges is minimal. Ignoring the pile-soil interaction significantly underestimates the seismic demand of the evaluated bridges, especially the free rocking bridge and rocking bridge with prestressed tendons only.

Exploring the potential of rigid polyurethane foam waste in structural lightweight concrete

The structural lightweight concrete is gaining significant interest in the research community due to its reduced dead load. The reduction in the self-weight not only lowers the gravity load but can also lower the seismic demands for the structural members and hence can potentially reduce the overall cost. This study examines the feasibility of developing a sustainable structural lightweight concrete by utilizing rigid polyurethane foam waste as coarse aggregates (5–10 mm). The silica fume was incorporated as a cement replacement to enhance the compressive strength of the mix. A total of three composite mix formulations consisting of polyurethane foam, cement-coated polyurethane foam, and pumice (control specimens) as coarse aggregates were tested. The testing was performed for workability, compressive strength, flexural strength, elastic modulus, absorption, permeable voids, chloride-ion penetration, freeze and thaw resistance, and drying shrinkage. The results achieved for elastic modulus, chloride ion penetrability, and drying shrinkage, were meeting the minimum requirements of the standards making this composite suitable for the structural application. The results revealed that uncoated polyurethane based lightweight aggregate concrete resulted in an air-dry density of 1829 kg/m3 with the corresponding compressive strength of 19.5 MPa and flexural strength of 2.78 MPa at 28 days. Besides, the polyurethane-based lightweight concrete also showed lower internal structure damage against freeze and thaw action, along with improved thermal conductivity.

Seismically induced torsional amplification in limited ductile buildings

This article deals with the seismic demand on limited ductile buildings featuring plan asymmetry. When the yielding occurs in a structural wall positioned at the edge of the building remote from the centre of resistance (CR), the position of the CR would shift even further away from the wall, causing an additional, and momentarily, increase in torsion. The undesirable shift in the position of the CR is usually shortlived and would reverse as other walls in the building also surpass the yield limit. However, the limited ductile construction (typical of low to moderate seismicity regions) can be vulnerable. This additional amplification in torsion can only be captured by Incremental Dynamic Analyses (IDA), but not by elastic analyses nor by nonlinear analyses of high ductility demand. Thus, the phenomenon as described is not widely known in spite of torsion being a well researched topic. In this study, parametric studies employing IDA of limited ductile buildings of different structural configurations were undertaken to capture the trends and develop recommendations for guiding structural design.

Parameter-normalized probabilistic seismic demand model considering the structural design strength for structural response assessment

The Probabilistic Seismic Demand Model (PSDM) is a crucial component of the performance-based seismic design framework when establishing the relationship between the ground motion intensity measure (IM) and the engineering demand parameter (EDP). The definitions of IMs and EDPs introduce varying degrees of uncertainty into the PSDM and notes different fragility or hazard analysis results. In accordance with the elastic limit state of the structural seismic response, this study normalizes two key parameters, the IM and EDP, within the PSDM. Normalized EDP (EDPN) is the ratio of the structural response to the elastic limit state of the structure, as defined by the onset of the strength yielding of the main structural element. Similarly, the IM (IMN) is normalized based on corresponding ground motions (scaled) that cause the structure to offer an elastic limit state response. This means that structural design strength is considered in IMN following the construction of a parameter-normalized PSDM. The study examined two typical isolated bridges presented their hazard curves with IMN. The results show that IMN can unify the efficiency and sufficiency of different IMs and reduce uncertainty in the PSDM. The assessment error of the structural elastic limit state for its design strength had little effect on the parameter-normalized PSDM, so the model is robust. Additionally, the IMN outperformed traditional IMs for efficiency and sufficiency in most instances.

Implementación de Disipador de Energía, TADAS

El Salvador is a country with high seismic demand, so the design and construction processes of buildings today areaimed at reducing the vulnerability caused by earthquakes, as part of the philosophy of damage mitigation and correct structural performance, there are Advances in detailing and construction techniques, so the use of deformation. energy dissipation systems is a safe way to prevent damage at a reasonable economic cost compared to the use of other more complex and sophisticated technologies. In El Salvador, the implementation of the TADAS (Triangular plate Added Damping And Stiffness) energy dissipation system has been implemented in a pioneering way and on a small scale, in the case of a two-story building, structured with Steel frames with ordinary detailing. The first level corresponds to parking, so the TADAS devices have only been installed in a longitudinal direction, while the second level corresponds to various uses of meeting people in meeting rooms and office work, so architectural issue the existence of windows with a view not interrupted by structural elements turned out to be a condition for not installing TADAS on that level. The final result meets the requirements of the ASCE-7-16 standard in deformation control, and prevention of structural damage due to the ductility that TADAS provides to the global structure. All the structural elements satisfy resistance and service requirements given by AISC-ANSI-36016. ILIA: Investigaciones Latinoamericanas en Ingeniería y Arquitectura, No. 01, 2024: 103-107.

Random‐positioned‐sampling effect on probabilistic seismic demand modeling of modularized suspended buildings with free‐standing objects and architectural function regioning

AbstractThe definition of the targeted engineering demand parameters (EDPs) is important to probabilistic seismic demand modeling (PSDM), which produces probability density functions of EDPs conditioned on seismic intensity measure (IM). The targeted EDPs are usually defined at the group level to account for multiple components/units. Thus, they are affected by the considered range of units, i.e., the sample positions. For instance, the maximum peak floor acceleration (PFA) within the whole building differs from the maximum among only the important positions related to seismic loss. Additional uncertainties are induced in the PSDM of PFA if the sample positions vary when architectural function and non‐structural elements change. In this study, the aforementioned influence is termed random‐positioned‐sampling (RPS) effect, and it is investigated by targeting a modularized suspended building, which features the tuning mechanism, multiple major modes, uneven response envelopes, and notable non‐structural‐object‐structure interactions (NSOSI). Results show that the RPS effect lowers the maximum‐based group‐level EDP and increases the dispersion within the EDP sample sets, indicating that conventional PSDMs without considering the RPS effect are biased. The significance of the influence is positively correlated to the position‐wise coefficient of variation of EDP but negatively correlated to the density of sample positions. The combined influence of the NSOSI and the RPS effect is two‐sided for PSDM. The NSOSI amplifies the RPS effect via enlarging position‐wise dispersion of EDP, whereas, the RPS effect waives part of the detrimental scattered contributions from NSOSI. Overall, the IM performance is handicapped, even with IM optimization. However, it can be compensated if architectural function region information is acquired beforehand since the sample positions are restrained.

Uncertainty and Latin Hypercube Sampling in Geotechnical Earthquake Engineering

A soil–foundation–structure system (SFSS) often exhibits different responses compared to a fixed-base structure when subjected to earthquake ground motion. Both kinematic and inertial soil–foundation–structure interactions can significantly influence the structural performance of buildings. Numerous parameters within an SFSS affect its overall response, introducing inherent uncertainty into the solution. Performing time history analyses, even for a linear elastic coupled SFSS, requires considerable computational effort. To reduce the computational cost without compromising accuracy, the use of the Latin Hypercube Sampling (LHS) technique is proposed herein. Sampling techniques are rarely employed in soil–foundation–structure interaction analyses, yet they are highly beneficial. These methodologies allow analyses determined by sampling to be conducted using commercial codes designed for deterministic analyses, without requiring any modifications. The advantage is that the number of analyses determined by the sampling size is significantly reduced as compared to considering all combinations of input parameters. After identifying the important samples, one can evaluate the seismic demand of selected soil–foundation–bridge pier systems using finite element numerical software. This paper indicates that LHS reduces computational effort by 60%, whereas structural response components (translation, rocking) show distinct trends for different systems.

Seismic Vulnerability Indices of Facades of Colonial Houses in the Historic Center of Morelia, México

Evaluating the seismic vulnerability of facades of historic masonry buildings is essential not only for their significant historical and heritage value, but also to evaluate the safety of this type of construction. This work applies a simplified methodology to assess the seismic vulnerability of the facade of masonry buildings in the historic center of Morelia, Michoacán, México. The historic center of Morelia was declared a World Cultural Heritage Site by UNESCO in 1991. On the facades, there is ornamentation with sculptural and vegetal decorative elements. The methodology involved conducting visual inspections to identify the location, type of structure, construction materials, doors, windows, balconies, cornices, ironwork, pediments, niches, and sculptures, among other characteristic elements of colonial architecture. The seismic demands were determined specifically for the city’s historic center based on a recent seismic hazard assessment of Morelia. Based on the methodology and the compiled database, characterized vulnerability indices were defined for the different damage scenarios that buildings may present. Results indicate that earthquakes with intensities greater than VIII on the Modified Mercalli scale risk collapsing heritage masonry buildings’ facades.

Direct loss‐based seismic design of low‐rise base‐isolated reinforced concrete buildings

AbstractThis paper proposes a procedure to design low‐rise base‐isolated structures achieving a specific target level of earthquake‐induced loss (e.g., dollars, downtime) while complying with a predefined minimum level of structural reliability. The procedure is “direct” since the target loss is specified at the first step of the process, and virtually no design iterations are required. Direct loss‐based design (DLBD) is enabled by a simplified loss assessment module involving: (1) surrogate probabilistic seismic demand models representing the probability distribution of peak horizontal displacements and accelerations on top of the isolation layer conditional on different ground‐motion intensity levels; (2) approximations of the superstructure response; (3) simplified consequence models for isolation system and superstructure based on damage‐to‐loss ratios (economic loss or repair time); (4) simplified consequence models for acceleration‐ and drift‐sensitive non‐structural components, based on storey loss functions of a potential inventory of components. Given some basic geometrical parameters of the superstructure, DLBD provides the isolation system's force‐displacement curve and the required superstructure's strength complying with a selected loss target. The members' structural detailing follows the principles of direct displacement‐based design, sectional analysis, and the general theory of base isolation. The procedure is illustrated by designing six reinforced concrete wall buildings (two‐, three‐, and four‐storeys) base isolated with lead rubber bearings, to achieve predefined targets of expected repair time. Repair time is benchmarked against a more refined method adopting a cloud‐based non‐linear time history analysis, finding a maximum underestimation of 17%, thus confirming the dependability of DLBD. Such error is almost entirely attributable to the simplified estimation of peak floor accelerations, and it could be potentially eliminated by refining such estimation.

Multidimensional Seismic Fragility Study of Intake Towers Based on Incremental Dynamic Analysis

Assessing the fragility of intake towers using a single damage index does not allow for accurate evaluation of the potential for structural damage under seismic conditions. In this study, based on the probabilistic seismic demand analysis method, the effects of ground motion intensity on maximum displacement, local damage index, and global damage index are considered, and the seismic fragility of an intake tower structure is analyzed. First, 10 natural ground motion records were selected from the ground motion database (PEER) and 2 artificial seismic waves were synthesized. These seismic waves were amplitude-modulated for incremental dynamic analysis (IDA). The trends of the IDA curves were analyzed to divide the performance levels of the intake tower structure. Furthermore, a two-dimensional fragility curve for the intake tower structure was plotted in this study. The maximum displacement in the direction of parallel flow and the damage index were taken into account in the two-dimensional fragility curve. The results show that, under the designed seismic acceleration, the two-dimensional fragility curve for the intake tower structure was lower than the one-dimensional curve. This indicates that the seismic design based on the one-dimensional performance index was unstable. This provides a theoretical reference for seismic optimization design and the strengthening of intake towers. Therefore, it is recommended to use multidimensional fragility analysis to study the seismic performance of intake tower structures in seismic design.

Developing and evaluating a risk-informed decision support system for earthquake early warning at a railway bridge

Earthquake early warning (EEW) systems provide timely information on the arrival of strong seismic waves at a site. Such information can help mitigate the consequences of earthquakes on the operation of infrastructure assets. EEW-informed mitigation actions should stem from risk-based decision-making protocols, and EEW benefits should be evaluated for the range of possible rupture scenarios that affect an asset of interest. This paper addresses these challenges specifically for railway bridges by: (1) developing a risk-informed EEW decision support system (DSS) for these assets; and (2) quantifying the effectiveness of the proposed EEW-DSS in mitigating seismic risks for railway bridges across relevant rupture scenarios. The proposed EEW-DSS combines information on site-specific seismic hazard, time-dependent EEW algorithm outputs, probabilistic seismic demand modeling, damage/derailment fragilities, and seismic loss models. These modeling components compose a multi-criteria decision-making framework. Value of information theory is then proposed to estimate the loss-mitigation benefits of the EEW-DSS, accounting for varied stakeholder risk priorities as well as dynamic lead-time/accuracy tradeoffs related to EEW performance. A railway bridge with multiple piers is adopted for the case study, which demonstrates the importance of risk-based, uncertainty-informed decision-making to the overall effectiveness of EEW in potentially reducing seismic losses.

Pounding impact on seismic demands for adjacent irregular buildings with collinear alignment eccentricity

This research aims to evaluate the impact of pounding on seismic demands for neighboring irregular buildings with collinear alignment eccentricity and provide valuable recommendations for seismic design. To achieve this, a numerical simulation is conducted to calculate the effects of pounding on the seismic response requirements in different scenarios where two irregular adjacent buildings with eccentric center of mass are considered, plan irregularity is reflected with eccentricities between the rigidity center and mass center of the building’s superstructure. Adjacent buildings with three different heights involve four-, eight-, and twelve-story buildings with moment-resisting frame (MRF) structural system. To ensure reliable estimation of engineering seismic demands, three different ground motions, which are fully compatible with the design spectrum, are applied to different adjacent building configurations. A nonlinear time history analysis is performed to determine the response demands for different adjacent buildings with collinear alignment eccentricity, such as displacement, inter-story drift, story shear force, impact force, and acceleration responses. The Engineering Design Parameters (EDP) are thoroughly examined to gain a comprehensive understanding of the structural behavior and performance of the adjacent irregular buildings. The findings hold for all these scenarios, suggest that the colinear eccentricity of the irregular building in the closing/convergence direction, promotes the pounding and increases the number of impacts, while the eccentricity in the opening/divergence direction, reduces the pounding probability and the number of impacts between adjacent buildings. Moreover, the findings highlight the impact of eccentricity on peak acceleration responses and emphasize the importance of considering eccentricity in assessing the dynamic response of adjacent buildings with insufficient separation.

Seismic fragility analysis of long-span rigid-frame bridge on mountainous soft clay site

In order to assess the damage condition of bridge components for a large-span rigid bridge in a soft clay site in a mountainous area in China southwest, a finite element model of a large-span rigid bridge is established based on the OpenSees software, and the joint probability density distribution function of the ground motion strength and seismic demand and the marginal distribution function of the ground motion are introduced into the kernel density function. As a basis to get the method of calculating the fragility of the bridge members, and the method is verified for its feasibility, on this basis, the damage condition of the bridge components are analyzed, and finally the damage condition of the bridge system are analyzed by the first-order bounds method and the improved PCM method (IPCM). The results showed that: (1) Kernel density method (KDE) can effectively calculate the damage probability of each component, for example, under ground motions with PGA equal to 0.2 g, the probability of slight damage of the 1# pier is 29%, that of the intermediate consolidation pier (2# pier ~ 4# pier) is about 90%; the probability of slight damage of the 1# bearing is 48%, and that of the 2# bearing is 87%. (2) Reasonable value of the expansion joints can effectively reduce the probability of main beam collision. In this investigation, the value is taken as 0.18 m ~ 0.24 m. (3) The bridge system is more likely to be damaged than a single component in the system, and the damage probability of a single component cannot be used as a criterion for the bridge system in the actual working condition. Comparing the first-order boundary law with the IPCM method, the IPCM method has higher accuracy.

Seismic performance of skewed bridges with uniform and non-uniform scour

Seismic safety of highway bridges is one of the critical issues for the functionality of transportation lifelines after severe earthquakes. Skewed highway bridges are found to be more vulnerable due to the irregular distribution of seismic demands on the bridge components. Moreover, scour induced loss of soil material and hence reduction in lateral support around the foundation piles can amplify the seismic effects on the structural components of water crossing bridges. A numerical study was conducted to investigate the seismic performance of skewed and straight highway bridges with varying scour depths and two different scouring types around the bridge piles. Analytical models of straight (0°) and 45° skewed bridges were created using the OpenSees program and a series of nonlinear response history analysis was carried out under the effect of recorded strong ground motions. In the first scouring type which was called as Case-1, scour depth was assumed the same around all piles and varied uniformly. In Case 2, two different non-uniform scouring types with linearly varying scour depth around the piles were investigated. The uncertainty in the earthquake ground motion excitation direction of the two horizontal components was also studied by considering the variable incidence angle of ground motion pairs. The maximum seismic demands of the members at different ground motion incidence angles were evaluated and compared to the demands obtained for the critical ground motion incidence angles suggested by Caltrans. Superstructure displacement, curvature demands of bridge column and shear force demands of pile elements are the seismic demand parameters examined within the scope of the study and were compared for each scour condition for both straight (0°) and 45° skewed bridge.

Sufficiency assessment of intensity measures for natural and spectral-matched ground motion records

A correct Intensity Measure (IM) selection is essential for Performance-Based Earthquake Engineering (PBEE) applications, as any probabilistic seismic demand model (PSDM) depends significantly on the IM. If a single IM can describe the complexity of the corresponding ground motion record, it can be defined as sufficient in an absolute sense. However, this is unlikely because a single number should be able to inform on the frequency content, the amplitude, the duration, the energy content, etc. For this reason, literature studies have defined sufficiency in a relative sense to investigate whether one IM is more sufficient (i.e., more informative) than another in predicting the structural response. This work explores the relative sufficiency of eight scalar IMs through Nonlinear Response History Analyses (NRHAs) using two sets of 20 pairs of ground motion records. Both sets are spectrum-compatible and consist of unscaled natural and spectral-matched records. Also, both Cloud and Incremental Dynamic Analysis procedures are used. This study demonstrates that Cloud analysis cannot be used in its conventional form to study sufficiency when spectral-matched accelerograms are used. When natural accelerograms are employed, the results clearly indicate the existence of a sufficient IM among those selected. Conversely, it is more difficult to define the relative sufficiency of the IMs for spectral-matched records because the operation of record adjusting leads to similar structural demands. This result could question either the validity of using spectral-matched accelerograms for PBEE due to the lack of aleatory variability in the structural demand or the necessity of having a sufficient IM when a PSDM is fitted in a PBEE analysis using spectral-matched accelerograms.