Seismic Design Of Bridges Research Articles

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.

Nonlinear seismic response analysis of long-span railway cable-stayed bridges crossing strike-slip faults

Active faults along railways in the mountainous regions of western China pose significant challenges to bridge safety. To ensure the safe operation of long-span railway bridges under complex geological conditions, this study investigates the synthesis of artificial ground motions for bridges crossing strike-slip faults and analyzes their nonlinear seismic response. First, we develop a theoretical method for simulating high- and low-frequency seismic motions using a finite fault and an equivalent velocity pulse model. Next, using a specific long-span railway cable-stayed bridge as a case study, we construct a nonlinear finite element model with OpenSees software. Finally, we assess the seismic response of key bridge components considering various crossing angles, seismic amplitudes, fault rupture directivity, and fling-step effects. The results show that the crossing angle significantly influences the seismic response, with longitudinal and transverse responses exhibiting opposite patterns. Additionally, the scaling factor of seismic motion significantly affects bridge response. For bridges crossing strike-slip faults, the longitudinal response exhibits a sudden increase in displacement due to instantaneous velocity pulses, while the transverse response shows notable residual displacement influenced by the fling-step effect. However, the critical section curvatures of bridge towers and piers remain within the elastic range across all crossing angles, indicating that controlling large displacement deformations is crucial for the seismic design of bridges crossing strike-slip faults.

Seismic analysis of bridge with buckling‐restrained brace posttensioned concrete pier

AbstractA two‐span bridge built with a two‐column pier consisting of unbonded posttensioned precast concrete columns and a buckling‐restrained brace (BRB) is analyzed using a three‐dimensional nonlinear numerical model. Seismic damage to the pier is eliminated through rocking of the posttensioned columns and seismic energy dissipation by the BRB. The numerical model is calibrated with experimental results of posttensioned columns and BRB structural elements. Seismic assessment of the bridge pier is performed using the ratio of BRB axial force to base shear as the parameter of interest. Limits for the seismic performance of the bridge pier are established by means of nonlinear static analysis using OpenSees. Bidirectional ground motions are used to perform probabilistic hazard analysis through nonlinear time history simulations. Three damage limit states are defined in this research: the activation point of posttensioning bars, the maximum base shear capacity or onset of concrete spalling, and collapse defined as the state at 20% loss of maximum base shear capacity. The analysis results are formulated into fragility curves for the three damage states as well as the residual drift. The fragility curves could be used for preliminary seismic bridge design. The analysis shows that the BRB dissipates significant seismic energy and the posttensioned concrete columns reduce residual displacements so that the bridge pier can remain functional after severe earthquakes. The fragility approach for designing bridge piers constructed with posttensioned concrete columns and BRB elements is a significant improvement over conventional seismic bridge design and can contribute to functional recovery after severe earthquakes.

Dynamic responses of large-diameter variable-section group-piles subjected to shaking-table tests with varying scour depths

Scouring leads to soil loss around piles, which, in turn, changes the ground-vibration characteristics and influences the seismic performance of bridges. In this study, the Xiang’an Bridge was used as a reference for constructing a large shaking-table test model to investigate the dynamic characteristics of the pore-pressure ratio of saturated sandy soils, accelerations, and bending moments of the piles, as well as the horizontal displacements of the pile-top at scouring depths of 10, 20, and 32 cm, with ground-vibration intensities ranging from 0.10-0.45 g. The results indicated that as the scour depth increased, the pile acceleration of the group piles increased and changed abruptly at the variable cross-section and soil-stratum interface. The peak values of the horizontal displacement of the pile-top and bending moment of the pile exhibited an increasing trend. As the ground-shaking intensity increased, the pore-pressure ratio of the saturated sandy soil, pile acceleration of the group piles, horizontal displacement of the pile-top, and bending moment of the pile body gradually increased, whereas the base frequency of the pile foundation gradually decreased. This study can serve as a reference for the seismic design and reinforcement of scour bridges in areas prone to seismic activity.

Reliability polynomial chaos metamodel for the dynamic behaviour of reinforced concrete bridges

The approximation of complex engineering problems and mathematical regressions serves as the authentic inspiration behind the artificial intelligence metamodeling methods. Among these methods, polynomial chaos expansion, along with artificial neural networks, has emerged at the forefront and become the most practical technique. Previous studies have highlighted their robust capabilities in solving complex problems and their wide utilization across numerous applications, particularly in structural analysis, optimization design problems, and predictive models of uncertainty outcomes. The aim of this article is to present a methodology that introduces their implementation of for structural engineering, primarily focusing on reinforced concrete bridges. The proposed approach consists of demonstrating the applicability of the polynomial chaos to evaluate the dynamic behavior of two-span reinforced concrete bridges through a predictive model of natural vibration properties for eigenvalues modal analysis. Subsequently, response spectral method is conducted according to the Moroccan guide for bridge seismic design and the prescription of the EUROCODE 8 within the context of reliability assessment using Monte Carlo simulation. The efficacy of the proposed approach is illustrated by a comparison between the predicted vibration properties and the resulting values obtained through finite element modal analysis and artificial neural networks. The polynomial chaos process is based on a collected dataset of multiple reinforced concrete bridges sourced from technical studies offices and the Regional Administration of the East, affiliated with the Moroccan Ministry of Equipment and Water. Finally, this work contributes to the field by enhancing predictive modeling and reliability evaluation for bridge engineering using artificial intelligence metamodels.

Study on unseating prevention for multi-union long simply supported girder bridges under near-fault ground motions

Girder shifting is a common form of seismic damage for girder bridges. Unseating could occur when the displacement of the girder is too large, especially for bridges near faults, because the velocity impulse effect leads to greater displacement responses of structures. Setting metal dampers between girders and piers is a useful way to control the seismic behavior and reduce the risk of unseating. Since metal dampers are inevitably exposed to the erosive service environments, their mechanical properties may degrade due to corrosion. In this paper, a U-shaped metal damper made of stainless steel instead of mild steel (i.e., U-shaped stainless steel damper, which could be named simply as USSSD) is proposed and applied to the seismic reduction design of girder bridges. First, the finite element model (FEM) of the USSSD is built by the ABAQUS, and its force-displacement relationship is obtained based on the skeleton curve, which is fitted by the trilinear kinematic strengthening model. Then, a multi-union long simply supported girder bridge is taken as an example. The FEM of the adopted bridge is established via the Midas Civil to verify the seismic mitigation effect of the proposed USSSD excited by near-fault ground motions. The numerical analyses demonstrate that the unseating may occur without the use of the USSSDs. The relative displacement between the girder and pier is effectively controlled by the USSSDs, and the reduction is more than 50 %. When the bridge is equipped with the USSSDs, both the curvature ductility coefficient of the pier bottom and the maximum drift of the pier tip increase by a limited amplitude, which do not cause additional damage to the piers.

Development of strength reduction factors for performance-based seismic design of bridges in far-fault seismic regions

In this paper, strength reduction factors (R-factors) for performance-based seismic design of bridges in far-fault seismic regions are developed. Response spectrum analyses (RSA) and nonlinear time history analyses (NTHA) of simplified bridge models with piers of circular and rectangular sections having several substructure-superstructure connections are performed for wide ranges of design parameters and pier displacement ductilities based on target performance levels are obtained. Subsequently, a set of equations representing R-factors is proposed by performing linear regression analyses on the data obtained from the analyses. The accuracy of the proposed equations is investigated by performing error performance analyses, which indicated R-factors with mean error values close to zero. Furthermore, a simple application procedure of the proposed R-factor equations is presented and explained in detail through various sample bridges designed to achieve the performance objectives recommended by AASHTO LRFD, Eurocode, and the Canadian Highway Bridge Design Code (CSA). Eventually, a comparison between the estimated R-factors and those suggested by design codes is presented. The results showed that AASHTO LRFD recommends conservative R values for single-column bents, while it provides overestimated R values for multiple-column bents. Indeed, it is found that Eurocode recommends conservative R values for piers of limited-ductile behavior and relatively high R values for piers of ductile behavior. Therefore, it is concluded that the R-factors suggested by design codes might result in performance levels not intended in design.

Point Estimation-Based Dynamic Reliability Analysis of Beam Bridges under Seismic Excitation Considering Uncertain Parameters

Beam bridges, as the primary structural form of medium and small-sized bridges, are extensively utilized for road and railway crossings over rivers and valleys. Ensuring their reliability during earthquakes is crucial not only for maintaining traffic flow but also for mitigating the seismic impact on the economy and society. Considering earthquake intensity and uncertain parameters, this paper proposes an innovative method for assessing the seismic reliability of simply-supported beam bridges under three different levels of seismic design: minor, moderate, and major earthquakes. The proposed method first estimates the probability of encountering three typical earthquake intensities during the design life of simply-supported beam bridges based on crowd intensity, benchmark intensity, and major earthquake intensity. It then introduces uncertain parameters and employs the point estimation method to calculate the probability of bridge passage under specific earthquake intensities. Finally, it combines these earthquake intensities to calculate the overall seismic reliability of simply-supported beam bridges. The effectiveness and efficiency of this method are demonstrated through calculations for a three-span, double-degree-of-freedom simply-supported beam bridge, and validated using Monte Carlo simulations. This research provides solid theoretical support for seismic assessment, design, and intensity-based reliability analysis of simply-supported beam bridges.

Effect of material characteristics of lead rubber isolators on seismic performance of box girder bridge

Near-field (NF) earthquakes have distinct ground motions, forward directivity pulses, and fling-step motions, causing structural responses to differ from far-field (FF) earthquakes. Seismic isolation is regarded as a developed and successful technology that may be applied to enhance a structure’s functionality and safeguard it against catastrophic earthquake effects. The variation in mechanical properties of seismic isolation also significantly influences bridge seismic response. The study investigates the influence of lead rubber (LRB) isolators and the characteristics of ground motions on seismically isolated bridges, aiming to determine optimal parameters for minimal earthquake response. Key parameters include ground motion characteristics, characteristic strength (Q), and isolator flexibility. The study modeled the force-deformation behavior of isolators using bilinear behavior, reflecting the Bouc-Wen hysteric model. CSI Bridge was used to model seismically isolated steel box girder bridges, with eight natural accelerograms assessing a 2% probability of exceedance in 50 years. The peak responses of pier displacement (MPD), isolator hysteric energy (HED), base shear, and deck acceleration are chosen as the response parameters for the comparison. To evaluate the response parameters, the earthquake data are scaled to the three studied peak ground acceleration (PGA) levels of design level (0.2 g), extreme level (0.4 g), and rare-extreme level (0.8 g). The findings offer insight on the relevance of isolator stiffness and its influences on the seismic performance of isolated bridges. The study identifies minimum values for pier displacement, hysteric energy, deck acceleration, and base shear at specific Q/weight sustained by isolator (W) and time period (T) values. Recommendations are made for the preliminary seismic isolation design of bridges with LRB isolators, highlighting the importance of PGV to PGA ratio in earthquake damage assessment.

A simplified weak coupling dynamic analysis method for running safety evaluation of train on bridges under earthquake excitation

This study proposes a simplified analysis method that couples the bridge and train-track subsystem in a weak form to facilitate the dynamic analysis of the train-track-bridge coupled system (TTBS) under earthquakes. The method includes three main steps: (i) performing dynamic analysis of the bridge under seismic conditions to obtain the response of the bridge deck; (ii) interpolating the bridge displacement beneath each wheelset based on the train's velocity, departure time, and the initial positions of the wheelsets; and (iii) assessing the running safety of the train by incorporating the interpolated bridge response as track irregularity into the train-track coupled system. Steps (i) and (iii) can be analyzed separately using finite element and multibody dynamics software, eliminating the need to create a complex TTBS model that is challenging to achieve within a single software platform. Additionally, based on the method’s assumptions, the earthquake excitation on the train can be separated into the seismic inertial effect and seismic-induced bridge deformation, enabling a quantitative analysis of the impact of these two types of excitations on train safety. Taking a 10-span simply supported bridge and a long-span cable-stayed bridge as examples, the proposed method’s assumptions are verified by comparing its results with those obtained from a complex TTBS model. Furthermore, the impact characteristics of inertial effects and seismic-induced bridge deformation on train safety for these two types of bridges are analyzed. The proposed method offers robust support for seismic design of bridges and facilitates a comprehensive analysis of the mechanisms through which seismic excitations affect train safety.

Field observations on the damage to road bridges after the 2023 Turkey Earthquake

A series of large-scale earthquakes occurred on February 6 in southern Turkey. The authors had the opportunity to join the Japan Disaster Relief (JDR) Expert Team and visit several damaged areas in Turkey from March 10 to 12, 2023. This article highlights damage cases of a road tunnel and several road bridges the authors observed around Antakya, Nurdağı, and Malatya. From the features of the observations, this article discusses the following three items for further study in the seismic design of road bridges: (1) seismic details for robustness, (2) seismic responses of bridges with longer natural periods, and (3) post-event inspection.

Prediction and correlations estimation of seismic capacities of pier columns: Extended Gaussian process regression models

Assessing the seismic capacity of pier columns is a crucial element in the performance-based seismic design of bridges. Such assessment necessitates a probabilistic approach to accurately determine the marginal probability distributions of seismic capacities and to characterize the dependencies among these variables. In response to this need, this paper employs Multi-Output Gaussian Process Regression (MO-GPR), a probabilistic machine learning method, to jointly model the multiple seismic capacities of pier columns. We initially introduce a probabilistic seismic capacity model that utilizes MO-GPR for pier columns and validate its predictive accuracy in comparison to Bayesian linear regression and existing empirical methods. Subsequently, the methodology is augmented by the integration of hierarchical modeling within the MO-GPR framework, resulting in a Multi-Output Hierarchical Gaussian Process Regression (MO-HGPR) model that effectively estimates intraclass correlation coefficients for specific types of datasets. It is postulated that these correlation coefficients also reflect correlations associated with multiple components of the real structure. This study employs MO-HGPR and MO-GPR separately to investigate the potential correlations of seismic capacities among pier columns and distinct limit states. The results demonstrate that the MO-GPR model exhibits superior prediction accuracy and more effectively portrays uncertainty compared to existing empirical models. Moreover, the correlations of seismic capacities among piers and limit states are both robust and significantly impact the seismic fragility of bridges. This finding highlights the essential nature of considering capacities correlations in seismic fragility or risk assessment processes.

NONLINEAR SIMULATIONS TO EVALUATE THE CODE-BASED RESPONSE MODIFICATION FACTOR FOR SEISMIC DESIGN OF SLAB-ON-PILE STRUCTURE

Slab on Pile (SOP) structure using concrete spun pile (CSP) is frequently constructed for highway or railway infrastructures in Indonesia. However, some previous studies showed that spun piles have low energy dissipation and ductility. Therefore, spun pile application as bridge piers, particularly in high seismic locations such as Indonesia, needs additional consideration. The response modification factor (R) in the SOP elastic seismic design needs to be carefully considered since this parameter reflects the ability of the structure to dissipate energy through inelastic behavior. The work discussed in this paper primarily concerns the evaluation of the R-value based on the Indonesia seismic bridge design code, SNI 2833-2016, which is applied to SOP seismic design. The study provided an alternative reference for engineers in the seismic design of a SOP structure. Preliminary elastic design of SOP structures demonstrated that the number of piles and structural flexibility is significantly affected by the R-values consideration. In addition, the pinching hysteresis captured from the nonlinear dynamic analysis results emphasized the limited capability of an SOP structure in dissipating energy under seismic excitation. Moreover, the spun pile concrete material, especially in the pile-to-pile head connection, was observed to have an earlier failure. This study strongly suggested using an R-value of 1.5 to achieve a high seismic performance SOP structure with little need for aftershock retrofitting, even though this would necessitate much more spun piles. However, some further research could be conducted to develop the high seismic performance but economical design of SOP structures.

Reconstruction and validation of ground motions across dip-slip faults: an application to response analysis of a long-span suspension bridge

Recent seismic events have unequivocally highlighted the susceptibility of fault-crossing bridges to the synergistic effects of ground surface vibrations on either side of the fault plane and the tectonic dislocations arising from fault-induced surface ruptures. This study delineates both seismic and parametric response analyses of fault-crossing suspension bridges, employing a straightforward yet efficacious method for simulating desired ground motions near fault-rupture zones. Herein, we introduce a user-friendly method to incorporate predicted fault-induced displacements, accounting for both fling-step and directivity effects, into processed ground motion chronologies, enabling the generation of dip-slip fault ground motions. The accuracy and efficacy of the proposed method are affirmed by juxtaposing the generated ground motions with the observed ones (MGM). An exhaustive parametric analysis, addressing factors like fault-crossing location, fault-crossing angle, and frequency components of fault-crossing ground motions, of a suspension bridge over a rupture fault, is executed using the fashionable ANSYS software. This study provides clear and specific guidelines for the seismic design of suspension bridges traversing rupture faults.

A non-linear static analysis for the seismic design of single-span integral abutment bridges

Integral abutment bridges are characterised by a monolithic connection between the deck and the abutments. Because of this connection, the seismic behaviour of the entire structure tends to be controlled by its interaction with the surrounding soil, and especially with the approach embankments. To date, methods for the seismic design of this type of bridges are still characterised by substantial uncertainties, mostly because of insufficient understanding of the dynamic response of the soil–structure system. This paper provides a contribution to the interpretation of the seismic behaviour of integral abutment bridges, focusing on a single-span structural scheme that has been receiving significant attention in recent years. The dynamic interaction between the bridge and the soil is studied with global numerical models of the soil–bridge system developed in OpenSees and subjected to a variety of ground motions. The results of the dynamic simulations, interpreted also with the aid of a modal analysis of the system, are used to develop and finally validate a simplified design procedure. This procedure is based on the capacity spectrum method, aimed at evaluating the maximum deformation and internal forces in the structure produced by the longitudinal component of the seismic motion that typically dominates the design of integral bridges.

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Equivalent static methods for seismic design of straight integral abutment bridges

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

Track-bridge deformation relation and interaction of long-span railway suspension bridges subject to strike-slip faulting

During earthquakes, the long-span railway bridges crossing active faults are more vulnerable because of the combined effects of pulsed ground motions and surface dislocations. To study the track-bridge deformation and interaction of long-span railway suspension bridges crossing the strike-slip faults, the refined finite element model of a ballasted track-bridge-pile-soil coupled system was established using the nonlinear finite element software ANSYS/LS-DYNA. A detailed and systematic numerical simulation was conducted from the soil cracking and compression during the ground surface rupture, pile–soil interaction, and three-dimensional track constraints to track-bridge deformation relationships and interactions. One-dimensional wave propagation theory was employed to derive the ground motions on the bedrock according to ground surface-measured seismic records. The influences of the fault-crossing angle (FCA) and permanent ground rupture displacement (PGRD) on the seismic responses and track-bridge interaction were analysed by considering the pile–soil interaction and site response effect. A method for calculating the track curvature radius based on track deformation is presented to evaluate the running traffic conditions of the trains. Additionally, the stability of the ballast bed was estimated using the track-bridge relative displacement. The conclusions drawn can be applied in practical seismic design and train running safety assessment of long-span railway suspension bridges crossing the strike-slip faults.

Shaking table experiment study of a multi-tower cable-stayed bridge with consideration of seismic pounding effect between the main bridge and approach bridge

In this study, a 1/100-scale shaking table experiment was designed and conducted for a multi-tower cable-stayed bridge in order to investigate its seismic response characteristics with consideration of seismic pounding between the main and approach bridges. The test parameters include the expansion gap size and period ratio between the main bridge and the approach bridge. Both the near-field and far-field ground motions were selected to excite the model. Test results indicate that the seismic response of multi-tower cable-stayed bridges is very sensitive to the gap size and a reasonable gap size of expansion joint can mitigate the pounding effect on structural response. In addition, a period ratio close to 2:1 resulted in the most significant pounding effect and should be avoided in the design stage to reduce the collision risk. Moreover, seismic pounding could significantly amplify the relative displacement between the pier and girder of the main bridge elevating the risk of girder unseating. The test results can provide a valuable reference for the seismic design of cable-stayed bridges with multi-tower.

Shaking-Table Tests for Seismic Response of Arch Foot of a Long-Span Arch Bridge on Sand-Gravel Soil Sites Considering SSI Effect

ABSTRACT The seismic performance of arch bridges is dependent on the strength of bridges and the built-on soil site types. To investigate the influence of soil-structure interaction (SSI) on the seismic response of an arch-foot arch bridge with a sand-gravel soil site, several shaking-table tests for a 1/90 downscaled arch-foot model placed on sand-gravel soil were conducted based on the engineering prototype of the third Pingnan Bridge with a long-span concrete-filled steel-tube (CFST) arch bridge. The test results showed the following: (1) The seismic acceleration response of both the sand-gravel soil site and arch foot were amplified, which is related to both the non-linear dynamic behavior of sand-gravel soil and frequency-spectrum characteristics of the input seismic waves. (2) The sliding displacement of the arch foot under strong ground motions increased accompanied with a settlement of the soil surface. However, the safety risk of the arch foot may be underestimated in seismic design. (3) The dynamic shear stress-strain loops of sand-gravel soil exhibited a high-energy dissipation capacity, and the energy-transfer mechanism at the interface between the model soil and arch foot was integrated. The results obtained are expected to provide insights into the dynamic interaction behavior of the gravel soil and arch bridge systems and the seismic design of arch bridges built on sand-gravel soil sites in practical engineering.