Time History Analysis Research Articles

A numerical investigation into the behaviour of cable-stayed bridges under deck explosions

This paper explores the behaviour of cable-stayed bridges (CSBs) when subjected to intentional explosion events. An example CSB was proposed and analysed using a three-dimensional (3D) finite-element (FE) model; a nonlinear time-history analysis taking into account the geometric and material nonlinearities was conducted. Six blast scenarios were considered; the explosion took place on the bridge deck. Response quantities, such as forces in cables, movements of deck and pylons, states of stress in main girders, and reactions on bearings and pylon foundations were examined. The critical blast scenario for each of these quantities was identified. Some design measures for mitigating cable failure were proposed and examined. The results of analyses showed that considering several blast scenarios for the design and evaluation of CSBs is mandatory. Non-symmetric (relative to the bridge longitudinal axis) blast loading scenarios are generally more critical than symmetric ones. Increasing the area of some long cables in the main span, and increasing spacing of the cables nearby the pylon together with strengthening the main girder nearby the pylon could be useful measures to reduce failure potential. This study may help better understand the response of CSBs to extreme events.

EFFECT OF MECHANICAL PROPERTIES OF FILLING MATERIAL ON STATIC AND DYNAMIC BEHAVIOR OF MASONRY ARCH BRIDGES

The present study examined the impacts of the mechanical properties of the filling material on the seismic behaviour of masonry arch bridges (MAB). A bridge model that did not exist was selected to achieve this objective. Using this model, bridge models with different filling material properties were created in the SAP2000 computer program. Modal analysis and linear time history analysis (THA) were conducted on the aforementioned models to ascertain the filling material's influence on the bridge's dynamic behavior. The findings of the modal analysis indicated that an increase in the density of the filling material increased in the period, while an increase in the elasticity modulus led to a decrease in the period. As a result of linear THA, it was determined that as the density of the filling material increases, the displacements and stresses increase, and as the elastic modulus increases, the displacements and stresses decrease. As a result of static analysis, it was determined that as the density of the filling material increases, the displacement and stress values increase, and as the elastic modulus increases, these values decrease.

Seismic performance of continuous rigid-frame bridges affected by flood-induced scour

River-crossing bridges in high-intensity seismic regions can be vulnerable to the combined action of earthquake and flood hazards; in particular, flood-induced scour of the substructure can have a notable influence on the seismic behavior of bridge structures. Currently, long-span continuous rigid-frame bridges are widely used to cross large rivers worldwide, yet related studies on their seismic performance under flood-induced scour have been lacking. This paper focuses on the effects of time-varying flood-induced scour on the seismic performance of long-span continuous rigid-frame bridges incorporating complex thin-walled reinforced concrete piers with pile group foundations. A detailed finite element (FE) model for a representative bridge structure is developed and the scour depth risk of the bridge is evaluated under several flood events for different return periods. The influence of flood-induced scour on the pile-soil interaction is examined throughout the bridge service life. Detailed seismic fragility assessment is carried out through nonlinear time-history analyses using a large suite of 100 seismic records. Particular focus is given to evaluate the time-varying scour effects on the pile and soil deformations as well as on the component and system level seismic fragility functions. It is shown that the total flood-induced scour depth exhibits a nonlinear increasing trend with the increase in service time, particularly in the initial 10 years of the bridge service life. The deformations of the scoured piles, within a depth of 20 m, are also shown to increase significantly with the increase in service time. The results indicate that the scour has a pronounced effect on both the component and system level seismic fragility functions. Importantly, although the piles (or pile groups) are typically designed to remain elastic under seismic loading, they are shown to be subjected to significant inelastic demands and governing damage levels as a result of time-varying flood-induced scour effect. Overall, this study provides a methodology to assess the time-varying seismic fragility of the scoured long-span rigid-frame bridges with complex thin-walled reinforced concrete piers, which can enhance the multi-hazard time-varying seismic resilience assessment for bridge structures with similar configurations.

Effect of infill walls on the seismic performance of a severely damaged substandard RC building during the February 6, 2023, Kahramanmaras earthquake sequence

On February 6, 2023, two catastrophic earthquakes with moment magnitudes of Mw 7.7 and Mw 7.6 struck southern cities of Türkiye, occurring only nine hours apart. Spectral accelerations obtained from some of the recorded ground motions exceeded the design spectrum specified in the Turkish Building Earthquake Code (TBEC 2018) for the maximum credible earthquake level. This has prompted a review of seismic design practices within the framework of TBEC 2018. To address this concern, this study evaluates the performance of a reinforced concrete (RC) building with a ribbed slab that sustained heavy damage, according to official damage assessments, after the February 6th earthquake sequence. Numerical models were developed both with and without infill walls to assess their influence on the building’s response. Time history analysis and static pushover methods were used for its seismic performance assessment. Time history analyses were conducted under ground motions recorded at three different stations in close proximity to the investigated building. The inclusion of infill walls in the numerical model significantly influences the seismic performance analysis results. Peak floor accelerations of the building are determined to be higher at infilled model compared to the bare frame. The distribution of damaged columns in the actual building aligns well with the analysis results of the numerical model that includes infill walls. Notably, the numerical analysis using the ground motion record of the closest station to the building most accurately represents the actual damage distribution observed after the earthquakes. Finally, while the inclusion of infill walls in the model increases the lateral stiffness of the structure, it was also observed that displacement-dependent results obtained in the nonlinear time history analysis, such as relative story drifts, could increase depending on the selected ground motion record. This highlights the complex interaction between the infill walls, modal properties of the building, and the dynamic characteristics of the earthquake record.

Dynamic model and performance assessment of inter-story isolation system with supplement inerter (IISI)

The hybrid control combining the conventional seismic isolation and tuned mass damper inerter is recently gaining popularity for the seismic protective strategy. This paper presents a simplified dynamic model of the inter-story isolation system with a supplement inerter (IISI) for seismic performance assessment. The dynamic characteristics, such as modal frequencies, mode shapes, damping ratios, and participation factors, as well as the seismic response spectrum, were studied considering the importance of the equivalent linear model for seismic design. The vibration characteristic formula of the IISI was derived using a simplified 2-degree-of-freedom (2DOF) model. The influence of the calculated parameters of the model on the vibration characteristics was analyzed. To understand the isolation control mechanism, the response transfer function in the frequency domain was derived, and the effects of model parameters on the deformation amplitude amplification factor of the superstructure and substructure were analyzed. Based on equivalent linear properties, a seismic response prediction formula based on the response spectrum method is provided and verified by time history analysis (THA). The effect of soil-structure interaction (SSI) on the simplified 4-DOF model was also studied. The seismic responses and effectiveness of the IISI were evaluated using a Multi-degree-of-freedom (MDOF) model example. The research results demonstrate that the addition of an inerter changes the vibration characteristics of the traditional isolation system. The supplement inerter is effective in controlling the seismic response of the IISI, and the established analysis method can be used to analyze the seismic response of the IISI by incorporating additional inerter mounted in the isolation layer. The hybrid control strategy shows better effectiveness in reducing displacement in the isolation layer.

In-plane Rotation Response of Skewed Simply Supported Bridges Considering Multi-point Pounding Effect

Previous earthquake events have shown that the in-plane rotation of skewed bridges can induce multi-point pounding at longitudinal expansion joints and transversely between the decks and shear keys. These pounding phenomena may result in damage to girders and excessive deck movement. To explore the interaction between multi-point pounding and in-plane rotation response of decks in multi-span skewed simply supported bridges under seismic excitation, simplified equations for estimating bi-directional pounding forces were derived based on the force equilibrium principle. Finite-element models of skewed simply supported bridges incorporating pounding effects were developed, and time-history analyses were conducted to investigate the influence of skew angle, expansion joint width, and shear key capacity on the seismic response of bridges. The analytical results demonstrate the accuracy of the simplified pounding force estimation equations. The interaction mechanism indicates a positive feedback loop between multi-point pounding and in-plane rotation response, in which the two phenomena mutually amplify the responses. Parametric analysis reveals that the maximum seismic response can occur at a skew angle of 30°, an expansion joint width of 10cm, or a shear key capacity exceeding 20%. With increasing expansion joint width and shear key capacity, the multi-point pounding effect and in-plane rotation response can be mitigated. However, an excessive expansion width may induce greater deck displacements, and a higher shear key capacity can lead to damage in the piers.

Optimal intensity measures and probabilistic fragility assessment for the long-span aqueduct structure with four-column bents

The intensity measure (IM) is a key factor in determining the accuracy of seismic performance assessment, which can represent the power of ground motion. However, the optimal IMs selection for long-span aqueduct structures with four-column bents has not been investigated in the previous study. This study aims to evaluate the optimal IMs for use in probabilistic seismic demand model (PSDM) and propose the scalar- and vector-valued fragility methods of the long-span aqueduct structure. To achieve this goal, taking the long-span aqueduct structure with four-column bents in the Central Yunnan Water Diversion Project in Southwest China as a typical case, a series of nonlinear dynamic time history analysis are conducted. Then, the 21 commonly-used IMs are tested and evaluated based on the different metrics (e.g. correlation, efficiency, practicality and proficiency). The optimal vector-valued IMs for the fragility analysis of the long-span aqueduct structure with four-column bents is proposed. Meanwhile, the PSDMs of optimal vector-valued IMs are also established and compared. Finally, the scalar- and vector-valued fragility functions are developed in terms of the optimal IMs. A method for seismic fragility analysis of the long-span aqueduct structure with four-column bents based on vector-valued IMs is proposed. The numerical results reveal that peak ground acceleration (PGA), peak pseudo acceleration spectrum (PSA), root-mean-square of acceleration (Arms) and characteristic intensity (Ic) are relatively appropriate IMs for seismic performance evaluation of the long-span aqueduct structure with four-column bents. In particular, PGA is considered to be the optimal IM due to its highest correlation, better efficiency, practicality and proficiency. The scalar-valued fragility curves can only describe the impact of the single IM on the damage probability of the aqueduct structure, which may overestimate or underestimate its damage probability. Furthermore, the vector-valued IMs can significantly increase the fitting ability of the PSDMs. The fragility surfaces are superior to scalar-valued fragility curve due to the vector-valued IMs can more accurately describe the ground motion information. In summary, the findings of this study highlight the significance of proposing the optimal IMs and developing vector-valued fragility surfaces when evaluating the seismic performance of the long-span aqueduct structure with four-column bents.

Resistance of eccentric braced steel frames against progressive collapse and overload factor

Due to the possibility of sudden removal of the main structural members, which are the results of various reasons such as fire and explosion, it is required to reduce the damage as much as possible via a comprehensive understanding of the structural behavior affected by members' failure. The degree of damage directly depends on the type of lateral and gravity load resisting system. The present study intends to explore progressive failure in nine six-story five-bay steel frames with three types of eccentric braced frames. These braced frames were performed by nonlinear time history analysis. The structural behavior and failure progress against the omission scenario of column and braces with different arrangements were analyzed. Then, since the preliminary analysis cannot predict the residual strength of frames against progressive failure, vertical incremental dynamic analysis is utilized to determine the overload factor. The results of the analysis showed that the removal of the middle columns set the stage for more critical situation compared to the corner columns. Also, if the removal scenario occurs in the higher stories, the probability of starting failure from the braces will be more than that of columns.

Study on the Shock-Absorption Performance of Isolation Systems in High-Rise Vertically Irregular Double-Story Structures

(1) Research background: The aim of this study was to explore the seismic response of vertically irregular high-rise buildings using a double-layer isolation system. (2) Methods: A 24-story vertically irregular high-rise frame-shear wall structure was designed, and the finite element model of the double-layer isolation structure was established, as well as the models of the seismic structure, the foundation isolation structure, and the story-separated seismic structure. A dynamic time–history analysis of these models under rare ground motion was carried out. (3) Results: The double-layer isolation system has the best isolation effect, followed by the foundation isolation structure, and finally the interlayer structure. The double-layer isolation system can increase the natural vibration period of the structure by 1.25 times, reduce the displacement angle of the layer by about 74.3%, reduce the acceleration of the top layer by about 82.3%, reduce the base shear force by about 59.68%, reduce the overturning moment of the bottom layer by about 68.89%, and reduce the torsion angle of the top layer by about 89.68%. (4) Conclusions: The double-layer isolation system can effectively reduce the overall seismic response of the structure and effectively control the torsional response of the structure, which makes it feasible for application.

Effects of Soil–Structure Interaction on the Seismic Response of RC Frame–Shear Wall Building Structures Under Far-Field Long-Period Ground Motions

This paper focuses on the effect of soil–structure interaction (SSI) on the seismic response of high-rise RC frame–shear wall structures under far-field long-period ground motions. Elastic–plastic time–history analyses were performed using ABAQUS. The effects of the ground motion type, soil type, and structural frequency on the seismic response are analyzed and quantitatively evaluated. On this basis, the influence mechanism of SSI on the seismic response under far-field long-period ground motions is discussed and revealed through a ground motion spectrum analysis. The results show that the consideration of the SSI effect leads to an increase in the displacement response and a decrease in the shear response. The SSI coefficient of the base shear is all less than 1, ranging from 0.5 to 1. The SSI effect under far-field long-period ground motions is more pronounced than that under ordinary ground motions. The shear force reduction in the current code may not be applicable to the structural design considering the SSI effect under far-field long-period ground motions. The displacement response amplification of the SSI effect on loess soil (Site 2) is more remarkable than that on sand soil (Site 1). The SSI effect can reduce the structural frequency, especially for the structures with fewer floors on the softer soil site. The “bimodal characteristic” of the acceleration response spectrum for far-field long-period ground motions may lead to shear force amplification when SSI is considered.

A direct energy-based design method for damping control reinforced concrete structure: methodology and application

Energy-based seismic design, which integrates both the accumulated hysteretic energy and plastic deformation of the structure, provides a more comprehensive evaluation of structural seismic performance compared to other performance-based seismic design methods. In damping control structures, the distribution of hysteretic energy is clearly defined, with the expected positions for energy dissipation and damage concentrated in the dampers. This facilitates the application of an energy-based design method in such structures. This research presented a novel direct energy-based design (DEBD) method for damping control reinforced concrete (RC) structures, following the principle that the energy dissipation capacity of the structural members and dampers exceeds the hysteretic energy dissipation demand. With this principle, an energy-based damage index, which is directly correlated with structural damage state, was introduced. Subsequently, a detailed energy-based design process was provided. To achieve the desired seismic performance, the required energy dissipation capacity of dampers was determined using a pre-select damage index, and thereby, identifying the design parameters of the dampers. Finally, to validate the feasibility of the proposed design method, an 8-story RC frame with friction dampers was chosen as an example. The energy dissipation capacity and damage state of the designed structure were evaluated through nonlinear time-history analyses, and the results demonstrate the successfully achievement of the predefined seismic performance.

Direct loss-based seismic retrofit of reinforced concrete frames

AbstractIn earthquake-prone areas, structures not compliant with modern design codes significantly contribute to seismic risk. Therefore, risk mitigation strategies (e.g., seismic retrofit) should be employed to reduce the expected economic and human losses. This paper introduces a procedure for the design of retrofit solutions for reinforced concrete (RC) frame buildings to achieve - rather than be bounded by - a desired target level of earthquake-induced loss for a given site-specific seismic hazard profile. The presented methodology is “direct” because the designer and/or client can set a loss target in the first step of the procedure and no design iterations are virtually required. Direct loss-based seismic retrofit (DLBR) relies on a simplified loss assessment methodology enabled by a surrogate probabilistic seismic demand model. This defines the probability distribution of seismic deformation demand of single degree of freedom (SDoF) systems conditioned on different shaking intensity levels. The proposed design methodology enables designers to account for risk/loss-based considerations from the conceptual/preliminary design phase, thus facilitating the choice among different retrofit solutions. Starting from two under-designed case-study buildings, four illustrative applications of the procedure are provided. They involve considering different economic expected annual loss targets and different retrofit solutions involving the addition of RC walls and RC column jacketing. Benchmark loss estimates are calculated using non-linear time-history analyses of refined, multi-degree-of-freedom models showing satisfactory results: the simplified loss estimate introduces an overestimation maximum equal to 15.4% among the four illustrative applications.

Investigation of the effects of mainshock-aftershock sequences on the dynamic responses of pipeline considering soil-pipeline interaction

Pipelines are important structural elements that are frequently used today to meet many infrastructures needs such as drainage, natural gas or water transmission. In this context, the usability of such structures, which are important elements of infrastructure systems, especially after disasters such as earthquakes, is of great importance. For this reason, within the scope of this study, a parametric investigation of the seismic behaviors of a natural gas pipeline system under mainshock-aftershock sequences have been carried out, specifically taking into account the soil-natural gas pipeline interaction (SNGPI) in the help of finite element model (FEM) proposed. Before developing the model of SNGPI system proposed using solid element, the fundamental mode frequencies of the pipeline system modeled using the solid element for the verification have been compared with those of obtained from the pipeline system modeled using the beam element and the analytical solutions. After verification of proposed model is demonstrated, SNGPI system has been modeled and its fundamental modes have been compared with mode frequencies of soil stratum obtained from well-known simple analytic solutions. After this stage, the dynamic analyses of natural gas pipeline (NGP) system in the time domain have been carried out using four different soil systems and four different mainshock-aftershock sequences. The results of the nonlinear time-history analyses have been investigated in terms of the stress and the displacement responses. Parametric evaluations show that the greatest displacements and the stresses occurring at the considered nodes of NGP system may be importantly affected from mainshock-aftershock sequences and soil stiffness changes. As the soil stiffness decreases, both the peak stresses and displacements increased significantly. On the other hand, the same responses obtained under mainshock loadings, which have relatively lower peak ground acceleration (PGA)/peak ground velocity (PGV) ratio compared to aftershock loadings, are generally larger than those obtained under aftershock loadings.

Displacement-Based Seismic Design of Multi-Story Resistance Capacitance-Coupled Shear Wall Buildings with Energy-Dissipation Dampers

This research aims to apply the displacement-based design method (DBDM) for the seismic design of reinforced concrete-coupled shear wall buildings equipped with energy dissipation dampers. The DBDM offers design simplicity by focusing on structural design based on a target design displacement, where the building converts into a single degree of freedom (SDOF) system. The implementation of dampers aims to reduce repair costs and downtime for buildings following significant seismic events. Two types of dampers are utilized in this study: metallic damper and viscoelastic damper. The DBDM procedure begins with determining the target displacement, which corresponds to the specific story drift ratio of the structural system, using a nonlinear static pushover analysis. For the structural wall system considered in this study, a target drift ratio of 1/250 is selected due to the inherent rigidity of the structure. The effective damping factor is then determined from the average energy absorption, which is based on the ductility factor of each structural member. Additionally, the effective period of the building is obtained from the displacement spectrum of the design-level earthquakes. Finally, the required damper shear capacity for the SDOF system is calculated based on the target deformation and effective stiffness. The design earthquakes are generated from the acceleration response spectrum for Level 2 earthquakes, as specified in the Japanese seismic code, utilizing three different sets of phase information: Kobe, El Centro, and random phase records. The effectiveness of the DBDM is scrutinized through a comparison with results obtained from time history analysis. The results obtained for 6-, 12-, and 18-story RC-coupled shear walls with energy dissipation dampers indicate that the proposed design methodology effectively meets the specified design objectives.

Study on the Influence of Wind Load on the Safety of Magnetic Adsorption Wall-Climbing Inspection Robot for Gantry Crane

The maintenance of the surface of steel structures is crucial for ensuring the quality of shipbuilding cranes. Various types of wall-climbing robots have been proposed for inspecting diverse structures, including ships and offshore installations. Given that these robots often operate in outdoor environments, their performance is significantly influenced by wind conditions. Consequently, understanding the impact of wind loads on these robots is essential for developing structurally sound designs. In this study, SolidWorks software was utilized to model both the wall-climbing robot and crane, while numerical simulations were conducted to investigate the aerodynamic performance of the magnetic wall-climbing inspection robot under wind load. Subsequently, a MATLAB program was developed to simulate both the time history and spectrum of wind speed affecting the wall-climbing inspection robot. The resulting wind speed time-history curve was analyzed using a time-history analysis method to simulate wind pressure effects. Finally, modal analysis was performed to determine the natural frequency and vibration modes of the frame in order to ensure dynamic stability for the robot. The analysis revealed that wind pressure predominantly concentrates on the front section of the vehicle body, with significant eddy currents observed on its windward side, leeward side, and top surface. Following optimization efforts on the robot’s structure resulted in a reduction in vortex formation; consequently, compared to pre-optimization conditions during pulsating wind simulations, there was a 99.19% decrease in induced vibration displacement within the optimized inspection robot body. Modal analysis indicated substantial differences between the first six non-rigid natural frequencies of this vehicle body and those associated with its servo motor frequencies—indicating no risk of resonance occurring. This study employs finite element analysis techniques to assess stability under varying wind loads while verifying structural safety for this wall-climbing inspection robot.

A rcGAN-based surrogate model for nonlinear seismic response analysis and optimization of steel frames

The combination of the surrogate model and optimization algorithm to solve structural optimization problems is an efficient way to lower computational costs and reduce time consumption. However, the development of surrogate models for structural analysis frequently faces challenges due to limited datasets. To tackle this issue, this paper presents a surrogate model capable of training on limited datasets while simultaneously predicting multiple concerned indicators, and demonstrates its effectiveness in performance assessment and design optimization through two seismic design case studies. Specifically, an improved model architecture based on the conditional Generative Adversarial Network (cGAN) is proposed. The feasibility of this surrogate model for seismic response analysis and optimization is initially demonstrated using an existing planar frame case. Subsequently, to validate the suitability of the surrogate model for Nonlinear Time History Analysis (NTHA) tasks, the proposed approach is applied to optimize a 3D steel frame equipped with nonlinear viscous dampers. Herein, a three-objective optimization problem is formulated, employing the Non-Dominated Sorting Genetic Algorithm (NSGA-II), driven by the trained rcGAN, to identify the Pareto front. The optimum design is subsequently selected from this front utilizing a multi-criteria decision-making technique. The outcomes from three optimization tests indicate that our approach effectively enhances the seismic performance of the frame while achieving substantial economic benefits, ultimately reducing the construction cost of the benchmark structure by up to 31.1 %.

Theoretical and numerical study of the thermo-mechanical coupling effect on the fluid viscous damper

The fluid viscous damper (FVD) is a typical passive energy dissipation device applied to civil engineering structures for vibration control. However, the heat generated during its operation will alter the properties of the fluid, thereby affecting the damping force. This study explores the thermo-mechanical coupling effect on the performance of the FVD. A theoretical model is developed based on fluid dynamics and thermodynamics to reflect the interaction between the real-time damping force and temperature of the FVD. Computational fluid dynamics (CFD) simulations are performed to investigate the impact of the thermo-mechanical coupling effect on the hysteresis performance of the damper and validate the proposed calculation method. The dynamic behavior and vibration mitigation effectiveness of the FVD considering the thermo-mechanical coupling effect are examined based on time history analysis on a single-degree-of-freedom and a multi-degree-of-freedom system. The results indicate that the increased temperature will lead to a reduction in the damping force, while the degraded force will in turn slow the temperature rise. Long-duration and high-intensity excitations can significantly amplify the impact of the thermo-mechanical coupling effect, thus it is essential to be considered in designing dampers for loads in the service stage and major earthquakes. The thermo-mechanical coupling effect on the supplemental damping ratio of the damper is greater than that on structural response control effectiveness, thereby it cannot be neglected when the damping ratio is used as the design criterion for FVDs.

Monorail guideway structures performance under seismic loads

Monorail Guideway Structures (MGWS) is a kind of railway that moves at high speed rather than trains. Cairo Monorail Projects was considered in this research work. This research investigates the seismic performance of MGWS using pushover analysis (PA) in SAP2000. Based on the results of PA, the hinges were formed in piers prior to beams. The performance of MGWS was determined considering varies parameters including span length, pier height, pier cross-section, reinforcement ratio, concrete compressive strength and stirrups diameter. Establishing the shear and torsion over strength ratio (OSR) is required to protect MGWS elements from brittle failure. In addition to using PA, Time history analysis (THA) was also conducted using SAP2000. The results from both methodologies of analysis were compared and envelope values for the OSR for shear and torsion were determined. Shear and torsion OSRs were determined implementing the basic concepts of the AASHTO Guide Specifications for LRFD Seismic Bridge Design (AASHTO 2022) and were compared to the values calculated from the SAP2000. This comparison was executed in both longitudinal and transverse directions, considering the same parameters for the pushover analysis. The OSR results were calculated using PA and the THA.

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

Predicting the building damage due to earthquakes has persistently been a challenge. Various ground motion Intensity Measures (IMs) through correlation analysis with Engineering Demand Parameters (EDPs) have long been employed for structural response prediction. However, considering several Machine Learning (ML) techniques and a comprehensive set of scalar and vector-valued IMs has not been entirely undertaken, especially in the context of special concentrically braced frames. In addressing these limitations, this study employs a blending ensemble learning method along with new IMs extracted in the time-frequency domain and three EDPs, including peak story drift ratio (PSDR), peak floor acceleration (PFA), and peak floor velocity (PFV). Time history analysis is performed using a set of 1126 far-field ground motions and 57 IMs extracted from ground motions in the time domain, frequency domain, time-frequency domain, and spectral domain. Also, some special IMs are proposed to capture ground motion's time and frequency nonstationary characteristics. Four base models—Random forest, Bayesian ridge regression, classification and regression tree, and K-Nearest neighbors—have been used to build a blended ensemble model. The findings showed that the XGBoost meta-model better predicted PSDR, PFA, and PFV, obtaining a coefficient of determination (R2) of 0.901, 0.962, and 0.961, respectively. A prediction accuracy greater than 90 % was achieved using the proposed vector-valued IM (including the mean of instantaneous amplitude, the area under the square of acceleration, and peak ground acceleration) for PSDR (R2 = 90.02 %), PFA (R2 = 94.75 %), and PFV (R2 = 94.41 %). Furthermore, the results showed that the new IMs extracted from the instantaneous amplitude and frequency perform well in predicting EDPs.

Response analysis of a long-span cable-stayed bridge with ultra-high piles subjected to near-fault ground motions considering deep-water, sedimentation, local site, and wave-passage effect

The objective of this study is to examine the dynamic response behavior of a long-span cable-stayed bridge with ultra-high piles subjected to near-fault ground motions, comprehensively considering deep-water, sedimentation, local site, and wave-passage effects. Firstly, a 3D finite element (FE) model of the long-span cable-stayed bridge with ultra-high piles (Approximately 105 m) and a tower height of 216.4 m was established using Midas software. The deep-water, sedimentation, local site, and wave-passage effects were synthetically considered in this FE model. The FE model incorporates the sag effect of the stayed cable and the pile-soil interaction, enabling a detailed seismic analysis. Secondly, the examined near-fault ground motions with long-period velocity pulses were selected from the PEER database according to the design acceleration response spectrum with a fortification intensity of VIII degrees. Finally, nonlinear time history analyses of the selected long-span cable-stayed bridge, subjected to spatial near-fault ground motions including local site effect and wave-passage effect, were conducted, and the responses of critical design sections and points in structures were examined and evaluated. The results demonstrate that long-period velocity pulses can significantly affect the structural responses, while deep-water and sedimentation effects do not have a significant impact on the dynamic responses of long-span cable-stayed bridges. For the local site effect, the softer the soil at the support site and the greater the difference in soil conditions at the support, the larger the structural response. Regarding the wave effect, the structural response will increase or decrease depending on the magnitude of the wave speed and the span length between towers.