Seismic Response Of Bridges Research Articles

Does vehicle‐bridge interaction resemble the effect of tuned‐mass dampers on bridges during earthquakes?

AbstractIn many seismic studies, the coupled vehicle‐bridge system is treated as a tuned‐mass damper (TMD)‐bridge system, and unsurprisingly, the vehicle usually reduces the seismic bridge response. The current study challenges this common belief. To this end, it investigates the influence of running vehicles on the seismic performance of bridges. Specifically, it compares the effect of vehicle‐bridge interaction (VBI) to that of a TMD on bridges subjected to earthquakes. The discussion explores the underlying physical mechanisms of VBI and TMD, and highlights the superficial similarities and the substantial differences between them. In this context, the study presents pertinent numerical simulations for a set of natural earthquake records.

Seismic isolated bridge performance evaluation and design proposal using artificial neural network

AbstractSeismic isolators such as rubber bearings and other dampers are critical components of seismic design. The hysteresis behavior of such bearings is complicated, and engineers are using a bilinear model or equivalent linearization method in design practice. The response evaluation and initial design parameter assumptions are highly dependent on engineers' expertise and need repeated analysis. Therefore, this study proposed a machine learning‐based approach to conduct bridge seismic isolation performance evaluation and design parameters proposal without repeating the nonlinear simulations. The training data were generated by conducting a nonlinear time history analysis of the bridge structure model with input design earthquakes. Four trained three‐layer neural network models could perform bridge seismic response evaluation, predict the structure's seismic response, and suggest design proposal using some input parameters.

Contribution of vertical ground motion on seismic response of multi-span simply-supported T-girder RC bridges in the presence of corrosion-fatigue degradation

Highway bridges, located in heavy traffic and corrosive environments, are prone to corrosion-fatigue degradation, due to which material properties of steel and concrete in bridge girders get altered and effective area of rebars reduces resulting in reduced flexural stiffness of girders. Consequently, exposed bridges become weaker to resist earthquake loads, particularly for the ones having three significant translational components. It is, therefore, important to evaluate life-long performance of bridges that suffer from corrosion-fatigue degradation and are subjected to seismic events having substantial vertical ground motions (VGMs). Such a threatening scenario for seismic safety of bridges has not been explored yet. The current study demonstrates the confronting role of corrosion-fatigue degradation and VGM on bridge seismic response through a representative multi-span RC bridge in Gujarat, India, and required information on corrosion, traffic, and seismic activities is acquired from appropriate sources. The degradation mechanism is modeled as a coupled phenomenon of pitting corrosion of rebar and traffic-induced fatigue stresses that give rise to fatigue cracks at deep pit locations of rebars in girders. Developed numerical model of the bridge composes of all essential features to accurately capture the gradual degradation along life-span and fluctuations in response of key vulnerable bridge components under horizontal and vertical excitations. Results suggest that ignoring the impact of this degradation mechanism and VGM can lead to higher seismic vulnerability of bridges and endanger their safety under future earthquakes.

Effects of structural symmetry of introduced polyether diol on low temperature tolerance of laminated polyurethane bearings in bridges

Laminated seismic isolators are installed on highway bridges worldwide to minimize the risk of seismic collapse. In recent years, Laminated Polyurethane Bearing (LPB) has gained immense popularity in the field of large-span bridge construction due to its advantages such as ultra-high bearing capacity, low cost, and simplicity of production. However, Polyurethane (PU) elastomers of LPB undergo cold hardening, which reduces the ability of LPB to protect bridges from seismic damage in freezing regions. In this study, four kinds of polyether diols with varied chemical symmetry were added to PU consisting of PTHF, TDI, and MOCA, respectively. The introduced polyether diols include polytrimethylene ether diol (POTG) and polytetrahydrofuran (PTHF) with symmetric linear structures, and poly(oxypropylene) (PPG) and 3-methyl-tetrahydrofuran/tetrahydrofuran co-polyether diol (3MTHF) with asymmetric structures. The microscopic characterization performance tests and low-temperature mechanical experiments were conducted to investigate the effect of structural symmetry of added polyether diol on the low-temperature tolerance of LPB. Results prove that due to the significant structural irregularity of the chains, the 3MTHF-based PU exhibits the least amount of microphase separation and the lowest elastic modulus among all specimens, yielding the best low-temperature tolerance of corresponding LPB. It was further discovered that the Bouc-Wen model with proper parameters can accurately simulate the lateral response of the 3MTHF based LPB at different temperatures. Finally, the seismic responses of bridges isolated by 3MTHF based LPB were investigated and compared with those of the bridges with the conventional PTHF based LPB under near-fault earthquake loadings at low temperatures. The results shows that 3MTHF significantly enhances the horizontal flexibility of the LPB, thus improving the effectiveness of the isolation system in low-temperature environments.

Influence of seawater depth on offshore ground motion characteristics and seismic responses of sea-crossing cable-stayed bridges

This paper studies the effect of seawater depth on offshore earthquake motion characteristics and seismic response of bridges. By analyzing the offshore seismic data recorded by the K-NET during 2006–2021, the horizontal amplification coefficient spectrum and V/H spectral ratio of offshore ground motions were compared for various offshore stations at different seawater depths. Moreover, a numerical model simulating the propagation process of seismic waves in the seabed was developed to investigate the effects of seawater depth and site conditions on offshore ground motions. Finally, a site-seawater-pile foundation-cable-stayed bridge coupling model was created to study the influence of seawater depth on the seismic responses of sea-crossing cable-stayed bridges. The results reveal that the vertical response spectrum of offshore ground motion in deeper seawater is lower for periods longer than 0.3 s. The numerical models reveal that seawater has a suppression effect on the P wave near the resonance frequency of the seawater layer. Due to the hydrodynamic effect, the longitudinal bridge seismic response is significantly amplified. The amplification effect becomes more obvious with an increase in seawater depth. Therefore, it is important to consider the influence of the seawater layer in the seismic design of sea-crossing bridges.

Influence of canyon topography amplification effect and shielding effect on bridge seismic response

Influence of canyon topography amplification effect and shielding effect on bridge seismic response

Shaking table tests and numerical studies on the seismic behaviors of FPB in railway continuous beam bridges

Friction pendulum bearings (FPBs) were extensively used in recent years in railway beam bridges located in the earthquake-prone regions of China. While the efficiency of FPB and reliability of constitutive models have been demonstrated by many experimental studies, the seismic behaviors of FPB in continuous beam bridges in real earthquakes have rarely been investigated. Therefore, a 1/10-scale three-span railway beam bridge isolated by FPB was tested utilizing a 10.1 m × 8.1 m shaking table with six DOFs. The seismic responses of the bridge were analyzed in terms of phenomena, displacement, acceleration, and strain. Different sliding behaviors of the FPB at each pier cap appear because of the interaction with different damaged mid piers. Obvious uplift of the girder ends occurs due to the spherical surface of the FPB, which is evidenced by the measured vertical displacement of the bearings. Numerical simulation based on OpenSees indicates that the FPB element with the suggested friction coefficient model can well reproduce the peak and residual displacements of the FPB. A comparison of calculated and measured acceleration responses reveals that both damaged piers and FPB can filter out the higher frequencies of the input motion. The seismic responses of bridges isolated by the FPB and flat sliding bearing (FSB) were presented based on the validated model under PGAs from 0.2 g to 1.5 g. The FPB dissipates more earthquake energy with small peak and residual displacements, embodying better performance than that of the FSB due to the restoring capacity.

Comparative Analysis of Isolation Effects of Laminated Rubber Bearing and Composite Rubber Bearing Used in Bridges with Different Pier Heights

In order to reveal the vibration isolation performance of new composite rubber bearings (CRBs), this paper establishes a numerical model of composite rubber bearings based on SAP2000, and studies the seismic response of bridges supported by LNB and CRB at different pier heights. The results show that compared with LNB, CRB can effectively reduce the shear force and bending moment of the pier without increasing the structural displacement.Compared with LNB, the advantages of CRB in isolation performance vary little with pier height, which indicates that CRB has broad application prospects..

Seismic performance assessment of a sea-crossing cable-stayed bridge system considering soil spatial variability

Soil spatial variability at different supports is vital in the seismic performance assessment of large-span structural systems, including sea-crossing cable-stayed (SCCS) bridges. This study systematically investigates the influences of soil spatial variability on the seismic performance of SCCS bridges. In particular, the uncertain sites considering soil spatial variability are developed based on the random field theory and Latin Hypercube Sampling technique. The refined 3D finite element model of a representative SCCS bridge considering soil-structure interaction (SSI) is created in ABAQUS, and the spatially varying seafloor seismic motions (SVSSMs) with soil uncertainties are stochastically simulated. The tornado diagram sensitivity analysis method is leveraged to study the relative sensitivity of each soil property on the dynamic responses of the SCCS bridge. Finally, the component and system fragility curves are developed with and without considering soil spatial variability. The results show that soil spatial variability can significantly influence the SVSSMs and SSI, and lead to large variability of bridge seismic responses. The uncertainties of soil shear modulus and density have the most evident effects on the seismic responses of SCCS bridges. Furthermore, it is also found that neglecting the soil spatial variability would underestimate the component and system seismic fragility of SCCS bridges.

Influence of Near Fault Earthquakes with Forward Directivity and Fling Step on Seismic Response of Steel Box-Girder Bridge

The existing bridge seismic design guidelines that rely on the ground acceleration in the far fault zone,ignore the potential impact of near fault forward directivity and fling-step effects on the bridge structures. In the current study probabilistic seismic damage evaluation of a continuous four-span box girder bridge under the impact of near-fault forward directivity and fling step effect is studied employing the fragility analysis. The incremental dynamic analysis is used to construct the fragility curves which shows a range of damage states from minor to collapse for the different damage metrics and for the considered peak ground acceleration varying between 0.1g and 1.2g. Damage metrics such displacement pier ductility, rotational pier ductility and displacement of girder are used to develop the fragility curves and the probabilistic seismic damage model. To evaluate the bridge vulnerability, a probabilistic seismic damage assessment is performed using an ensemble of forward directivity and an ensemble of fling-step comprising permanent ground offset. The suggested probability-based earthquake damage framework is anticipated to be a well-versed model able to estimate the seismic damages to the continuous box girder bridges while taking into account the variation of near fault earthquakes. The findings show that, even at low PGA values the forward directivity and the fling-step ground motions represent a significant risk to the bridge.

Study on the Basic Performance Deterioration Law and the Application of Lead Rubber Bearings under the Alternation of Aging and Seawater Erosion

Lead rubber isolation bearings are well-recognized as a common and effective means to mitigate the seismic responses of bridges. However, rubber isolation bearings used in offshore bridges are extremely vulnerable to the action of the alternation of aging and seawater erosion caused by weather conditions, wind, waves, and other factors. Meanwhile, the deterioration law and application of lead rubber bearings subject to the effect of aging and seawater erosion cycles are not clear. Thus, aging and seawater erosion cycles testing on both lead rubber isolation bearings (LRB) and rubber materials were carried out. The parameters for the Mooney–Rivlin model of the rubber material used in LRBs were determined and the time-varying law of basic performance of LRBs was obtained based on test results of LRBs and their rubber material. Then, the determined rubber material parameters were applied into the finite-element model of LRBs to verify the basic performance degradation law of the LRBs. Finally, the obtained basic performance degradation law of LRBs was substituted into the finite model of offshore bridges to investigate the impact of the property degradation of LRBs on their seismic performance. The time-varying law of seismic performance of offshore bridge structures was also studied based on finite element analysis. The results show that both the horizontal and vertical stiffness of LRBs increase with the alternating of aging and seawater erosion time, and the horizontal and vertical stiffness increase by 16.1% and 24.3%, respectively, during the 120-year service period. Additionally, the Mooney–Rivlin model parameters of the LRB rubber material are also significantly affected by the alternating of aging and seawater erosion. Additionally, the results also indicate the deterioration of LRBs has a great influence on the anti-seismic performance of offshore bridge structures. After 120 years of service of offshore bridge isolation bearings under the alternating of aging and seawater erosion, the maximum displacement of the pier top of the offshore bridges, the maximum bending moment at the pier bottom, and the maximum displacement of the rubber bearing increased by 14.2%, 6.6%, and 9.1%, respectively. The findings of this paper play an important role in the seismic behavior study and the life-cycle performance analysis of offshore traffic projects such as sea-crossing bridges in marine environments. At the same time, they also lay a theoretical foundation for the performance analysis of rubber isolation bearings and offshore bridge structures under the alternation of aging and seawater erosion cycles.

Study on influence of longitudinal pier height difference on seismic response of bridge

Study on influence of longitudinal pier height difference on seismic response of bridge

Influence of the Pier-abutment-deck interaction on the Seismic Response of Bridges Equipped with FPS

This work regards the analysis of the seismic response of bridges isolated with single concave friction pendulum devices, including or neglecting the presence of the rigid abutment. Two six degree-of-freedom models are considered for the two cases, in order to represent the response of the elastic reinforced concrete pier and of the infinitely rigid reinforced concrete deck. The behavior of the friction pendulum isolators accounts for the non-linear dependency of the friction coefficient on the sliding velocity. The comparison is carried out by including the aleatory uncertainty in the seismic input (i.e., accounting for different natural records with different characteristics) and by varying the modelling properties within a parametric analysis. Finally, by solving the equations of motion in nondimensional form, the difference between the two models are deepened in terms of influence of the seismic isolation.

Seismic response analysis of long-span continuous girder bridge considering fluctuating friction of bearing

Under the combined action of horizontal and vertical earthquakes, separation-pounding of bridge beam ends and bearings occurs, which adversely affects the overall mechanical behaviour of any bridge. Based on D'Alembert's principle, this study proposes a theoretical analysis method to verify the separation of bridge beam ends and bearings, which is substantiated by the measured data. A three-span continuous steel-box-girder bridge was selected as the research object, and finite element models (FEMs) using the bilinear bearing and friction bearing models were established. The numerical models were verified by comparing the simulation results with the theoretical calculations. A comparative study on the seismic response of continuous girder bridges with different bearing models was conducted, and it was found that the friction bearing model is better for simulating the whiplash effect of long-span continuous girder bridges. The results indicate that the peak pounding force generated by the separation of the beam end and bearing is 1.74 times the weight of the beam end. Moreover, the whiplash effect causes the tension and compression stress states of the side span of the main beam to reverse and drastically reduce the compressive stress of the middle span by 70%. Finally, it is recommended that the friction bearing model which is able to realistically simulate the seismic response of the bridge more accurately be used to simulate bearings with large axial force fluctuations.

Semi-Active Control of Seismic Response on Prestressed Concrete Continuous Girder Bridges with Corrugated Steel Webs

To improve the seismic capacity of prestressed concrete (PC) continuous girder bridges with corrugated steel webs (CSWs), suitable damping control measures can be used to effectively reduce the seismic response of the bridge. Based on the semi-active control theory, the semi-active control system of a three-span PC continuous girder bridge with CSWs is designed, and the semi-active control system program of the three-span PC continuous girder bridge with CSWs is compiled by MATLAB. The time–history curves of damper energy consumption of active optimal control algorithm and three different semi-active control algorithms are compared and analyzed, as are the time–history curves of main girder displacement, acceleration, and pier internal force with or without semi-active control. The study shows that the rational determination of the weight matrix coefficient can make the active control achieve a better vibration absorption effect and economy. The semi-active control algorithm of Hrovat has the best vibration absorption effect, which is closest to that of the active optimal control algorithm. Under the state of semi-active control, the average vibration absorption rate of displacement and acceleration of the main girder with CSWs are 71% and 20%, respectively. The time–history curve of bending moment and shear force in the pier bottom is similar, and the average vibration absorption rate of bending moment and shear force at the bottom of pier #2 is 70%. At the same time, the average vibration absorption rate of bending moment and shear force at the bottom of pier #3 is between 42% and 48%. The semi-active control measure has a good vibration absorption effect on the overall seismic response of the PC continuous girder bridges with CSWs. This study provides a certain reference for the seismic reduction and isolation design of composite structure bridge with CSWs.

Seismic behaviors of PCIC piers-supported bridge structures to spatially varying ground motions

Damages to bridge piers were repeatedly observed in many previous strong earthquakes, resulting in disruptions to traffic and impairing the functionality of road network. Extensive studies have been carried out to improve the seismic resistance of bridge piers so as to enhance the seismic performances of bridge structures. In a recent study, an innovative pendulum-type column-in-column (PCIC) system was proposed to reduce seismic induced vibrations of bridge piers. This study extends the previous study on investigating the seismic performances of PCIC piers-supported bridge structures subjected to spatially varying ground motions (SVGMs). Three-dimensional (3D) finite element (FE) models of a typical 5-span continuous bridge supported by the conventional piers and PCIC piers are developed in the ABAQUS software in the present study, and numerical simulations are performed to evaluate the dynamic responses of bridges with conventional and PCIC piers. It is demonstrated that the PCIC piers can effectively mitigate the seismic responses of bridge structures. The SVGMs tend to amplify seismic responses of bridges, therefore need be considered when evaluating the seismic responses of multi-span bridges. The results demonstrate the great potentials of the applications of PCIC piers for seismic-resistant design of bridge structures.

Self-Centering Prestressed Concrete Pier Considering the Effect of Vertical Earthquake Motions with External Aluminum Dissipators

A prototype self-centering prestressedconcrete (SCPC) bridge pier andconventional reinforced concrete (RC) pier with similar backbone curves are designed and modeled. The objective of this study is to investigate the seismic performance of the SCPC bridge pier considering the effect of vertical earthquake ground motions. Under a severe vertical earthquake motion, the RC pier damage is much greater than the SCPC pier. The SCPC bridge pier shows a great capability in reducing residual drift at the top of the structure, therefore, the probability of bridge survival is increased. In this study, the external aluminum bars were used to reduce the seismic energy impacts on the bridge pier structure. In addition, the averages of the maximum and residual drifts of bridge piers under a set of 20 earthquake ground motion records impact with different vertical-to-horizontal peak acceleration ratios on the bridge seismic response are presented. The results are compared with the case of horizontal-only excitations, to clarify the effect of the vertical earthquake on the SCPC and RC bridge pier. Hence, the designers can find good solutions for structures in earthquakes resistance.

Optimization of the seismic response of bridges using variable‐width joints

AbstractAn aspect of seismic design of bridges that has hardly received proper attention so far is the appropriate selection of joint gaps. End gaps define the boundary conditions of the bridge and affect its dynamic response; their proper design can lead to an improved structural performance under dynamic actions. The idea of the ‘Dynamic Intelligent Bridge’ is explored here, wherein current bridge joints that have a fixed width are substituted by variable‐width joints and, under seismic loading, the joint gap is optimised either with a one‐off adjustment, or continuously (in real time) through semi‐active control. In all cases, a novel device is used that permits this improved behaviour of the joints, the moveable shear key (MSK), a device for blocking the movement of the bridge deck, which has the possibility to slide, hence varying the size of the existing joint gap. In this context, the effect of gap size on the seismic response of bridges is assessed herein and a methodology is put forward for optimising this size, using a number of criteria such as maintaining the functionality of the bridge for moderate earthquakes, and ensuring the safety of the bridge and its users under earthquakes stronger than that used for design.

Research on semi-active control of long and large-span continuous beam bridge vibration reduction considering system fault tolerance

In order to reduce the seismic response of long and large-span continuous beam bridge, this paper carried out a study on vibration reduction control of long and large-span continuous beam bridge, and magnetorheological dampers are used to provide control force for the control scheme. Based on the LQR classic optimal active control algorithm, a semi-active control algorithm considering system fault tolerance is proposed. When some dampers fail, the fault-tolerant control algorithm provides compensation output to the control system, so that the control system can still maintain the expected control effect. The actual engineering example of a long and large-span continuous beam bridge is selected, and a finite element analysis program is written. The semi-active vibration reduction control of the long-span continuous beam bridge is calculated and analyzed in various combinations of working conditions. The calculation results show that the method in this paper has achieved good results in controlling the seismic response of the bridge structure.

Rapid Seismic Evaluation of Continuous Girder Bridges with Localized Plastic Hinges.

In seismic assessment of continuous girder bridges, plastic hinges form in bridge piers to dissipate seismic energy through nonlinear restoring forces. Considering temporal and spatial variations of ground motions, seismic evaluation of the bridges involves nonlinear stochastic vibration and expensive computation. This paper presents an approach to significantly increase the efficiency of seismic evaluation for continuous girder bridges with plastic hinges. The proposed approach converts nonlinear motion equations into quasi-linear state equations, solves the equations using an explicit time-domain dimension-reduced iterative method, and incorporates a stochastic sampling method to statistically analyze the seismic response of bridges under earthquake excitation. Taking a 3 × 30 m continuous girder bridge as an example, fiber beam-column elements are used to simulate the elastic–plastic components of the continuous girder bridge, and the elastic–plastic time history analysis of the continuous girder bridge under non-uniform seismic excitation is carried out. Results show that the computation time is only 5% of the time of the nonlinear time history approach while retaining the accuracy. This study advances the capability of rapid seismic assessment and design for bridges with localized nonlinear behaviors such as plastic hinges.