Time-varying seismic fragility analysis of durability damage of high-tensile reinforcement ECC bridge pier

The deterioration of the performance of offshore bridges is particularly prominent due to the complex natural environment,including the coupling effects of earthquake and seawater erosion.In particular,bridge piers are the main energy-consuming and load-bearing components,so that excellent seismic capacity of bridge piers is the key to avoiding bridge damage.Although earthquake resistant behavior of ordinary reinforced concrete bridge piers(ordinary pier)can be improved by increasing the section size and reinforcement ratio of piers,the improvement of the earthquake resistant behavior is limited.To further improve the earthquake resistant behavior of bridge piers,high-tensile reinforcement engineered cementitious composite(ECC)bridge piers are utilized and time-varying seismic fragility analysis are conducted in this study.The refined model of a bridge pier is built by OpenSees.First,the influence of ECC replacement height on pier curvature is analyzed to determine the reasonable ECC height.Then,the time-varying fragility analysis of high-tensile reinforcement ECC piers(ECC composite piers)with durability damage are evaluated considering the time-varying law of materials.Four damage states,slight damage,moderate damage,extensive damage and complete collapse,are utilized in the study.These fragility curves indicate the durability damage can debase the earthquake resistant behavior of piers continually,the exceedance probability of the same state of destruction increases with the increase of peak ground acceleration(PGA)and service time of pier.The results also indicate that the corrosion level of chloride ion to pier is small during the early service period,and the bridge pier vulnerable curve is similar to that of the new bridge pier.As the level of chlorine ion corrosion deepens,transcendental probability is increased.Compared with the ordinary pier,the exceedance probability in each limit state of ECC composite piers is significantly reduced.The proposed ECC composite pies leads to better realistic time-varying earthquake resistant behavior.

An extended multiple-support response spectrum method incorporating fluid-structure interaction for seismic analysis of deep-water bridges

The effects of ground motion spatial variability(GMSV)or fluid-structure interaction(FSI)on the seismic responses of deep-water bridges have been extensively examined.However,there are few studies on the seismic performance of bridges considering GMSV and FSI effects simultaneously.In this study,the original multiple-support response spectrum(MSRS)method is extended to consider FSI effect for seismic analysis of deep-water bridges.The solution of hydrodynamic pressure on a pier is obtained using the radiation wave theory,and the FSI-MSRS formulation is derived according to the random vibration theory.The influence of FSI effect on the related coefficients is analyzed.A five-span steel-concrete continuous beam bridge is adopted to conduct the numerical simulations.Different load conditions are designed to investigate the variation of the bridge responses when considering the GMSV and FSI effects.The results indicate that the incoherence effect and wave passage effect decrease the bridge responses with a maximum percentage of 86%,while the FSI effect increases the responses with a maximum percentage of 26%.The GMSV and FSI effects should be included in the seismic design of deep-water bridges.

Earthquake simulation test of circular reinforced concrete bridge column under multidirectional seismic excitation

Structures behave multi-directionally when subjected to earthquake excitation. Thus, it is essential to evaluate the effect of multidirectional loading on the dynamic response and seismic performance of reinforced concrete bridge columns in order to develop more advanced and reliable design procedures. To investigate such effects, a 1/4 scaled circular reinforced concrete bridge column specimen was tested under two horizontal and one vertical components of a strong motion that has long duration with several strong pulses. Damage progress of reinforced concrete columns subjected to strong excitation was evaluated from the test. The test results demonstrate that the lateral force response in the principal directions become smaller than computed flexural capacity due to the bilateral flexural loading effects, and that the lateral response is not significantly affected by the fluctuation of the axial force because the horizontal response and axial force barely reached the maximum simultaneously due to difference of the predominant natural periods between the vertical and the horizontal directions. Accuracy of fiber analyses is discussed using the test results.

Study of Nonlinear Seismic Response and TMD Primary Control of the Cable-Stayed Bridge Section of the Third Macao-Taipa Bridge

The practical design of the cable-stayed bridge of the 3rd Macao-Taipa bridge is investigated by the finite element analysis program ANSYS, and 3-D elements BEAM188 and BEAM4 are adopted to create a dynamic calculation model. In order to analyze the material nonlinear seismic response of the cable-stayed bridge, the nonlinear behaviors of the ductile plastic hinges of the bridge towers are taken into account by employing the nonlinear rotational spring element COMBIN40. To simulate a major earthquake, three earthquake records were chosen using a wave-choosing program and input into the bridge structure along longitudinal and transversal directions. Comparisons of the linear and nonlinear seismic responses of the cable-stayed bridge are performed. In addition, a study of TMD primary control is carried out using element MASS21 and element COMBIN14, and it is indicated that the effects of mitigation monitoring are evident.

Study of Vertical Seismic Response of Concrete Self-Anchored Suspension Bridges

Based on the variational prineiple of incomplete generalized potential energy with large deflection, the vertical nonlinear vibrational differential equation of self-anchored suspension bridge is presented by taking the effect of coupling of flexural and axial action into consideration. The linear vertical equation is obtained by omitting the nonlinear term, and the pseudo excitation method(PEM). Taking the self-anchored concrete suspension bridge over Lanqi Songhua river for an example, the expected peak responses of main beam, towers and cables are calculated. And the seismic spatial effects on vertical seismic response of self-anchored suspension bridges are discussed.

Implications of seismic pounding on the longitudinal response of multi-span bridges-an analytical perspective

Seismic pounding between adjacent frames in multiple-frame bridges and girder ends in multi-span simply supported bridges has been commonly observed in several recent earthquakes.The consequences of pounding include damage to piers,abutments,shear keys,bearings and restrainers,and possible collapse of deck spans.This paper investigates pounding in bridges from an analytical perspective.A simplified nonlinear model of a multiple-frame bridge is developed including the effects of inelastic frame action and nonlinear hinge behavior,to study the seismic response to longitudinal ground motion.Pounding is implemented using the contact force-based Kelvin model,as well as the momentum-based stereomechanical approach.Parameter studies are conducted to determine the effects of frame period ratio,column hysteretic behavior,energy dissipation during impact and near source ground motions on the pounding response of the bridge.The results indicate that pounding is most critical for highly out-of-phase frames and is not significant for frame period ratios greater than 0.7.Impact models without energy dissipation overestimate the displacement and acceleration amplifications due to impact,especially for elastic behavior of the frames.Representation of stiffness degradation in bridge columns is essential in capturing the accurate response of pounding frames subjected to far field ground motion.Finally,it is shown that strength degradation and pounding can result in significant damage to the stiffer frames of the bridge when subjected to large acceleration pulses from near field ground motion records.

A Comparative Analysis between the Spanish and Portuguese Seismic Codes: Application to a Border RC Primary School

The Iberian Peninsula is close to the Eurasia-Africa plate boundary resulting in a considerable seismic hazard.In fact,the southwestern Iberian Peninsula is affected by far away earthquakes of long-return period with large-very large magnitude.A project named PERSISTAH(Projetos de Escolas Resilientes aos SISmos no Território do Algarve e de Huelva,in Portuguese)aims to cooperatively assess the seismic vulnerability of primary schools located in the Algarve(Portugal)and Huelva(Spain).Primary schools have been selected due to the considerable amount of similar buildings and their seismic vulnerability.In Portugal,the Decreto Lei 235/83(RSAEEP)is mandatory while in Spain,the mandatory code is the Seismic Building Code(NCSE-02).In both countries,the Eurocode-8(EC-8)is recommended.Despite the fact that both regions would be equally affected by an earthquake,both seismic codes are significantly different.This research compares the seismic action of Ayamonte(Huelva)and Vila Real de Santo António(Portugal).Both towns are very close and located at both sides of the border.Moreover,they share the same geology.This analysis has been applied considering a reinforced concrete(RC)primary school building located in Huelva.To do so,the performance-based method has been used.The seismic action and the damage levels are compared and analysed.The results have shown considerable differences in the seismic actions designation,in the performance point values and in the damage levels.The values considered in the Portuguese code are significantly more unfavourable.An agreement between codes should be made for border regions.

Seismic Design Strategy of High Pier Bridge

China’s infrastructure construction has been continuously improving in recent years,especially its highway construction,which spans from north to south and connects east to west.Some special areas are also interconnected through bridges,but constructing highway bridges through complex terrains or across valleys and mountain gullies presents significant challenges,requiring an increase in the height of bridge piers.These bridge piers generally reach tens or even hundreds of meters in height.Furthermore,the construction of these high-pier bridges is becoming increasingly widespread.Not only do they pose greater construction challenges,but they also have higher requirements for seismic resistance.This article primarily analyzes the characteristics of high-pier bridges and proposes seismic design schemes,calculation methods,and design strategies to enhance the construction quality of high-pier bridges.

Seismic response analysis of continuous rigid frame bridge considering canyon topography effects under incident SV waves

To evaluate the importance of the canyon topography effects on large structures, based on a rigid frame bridge across a 137-m-deep and 600-m-wide canyon, the seismic response of the canyon site is analyzed using a two-dimensional finite element model under different seismic SV waves with the assumptions of vertical incidence and oblique incidence to obtain the ground motions, which are used as the excitation input on the pier foundations of the bridge with improved large mass method. The results indicate that canyon topography has significant influences on the ground motions in terms of inci- dent angle. The peak ground acceleration values vary greatly from the bottom of the canyon to the upper comers. Under ver- tical incident SV waves, at the upper comers of canyon the peak ground accelerations greatly increase; whereas the peak ground accelerations diminish at the bottom comers of canyon. Under oblique incident SV waves, the shaking of the canyon slope perpendicular to the incidence direction is much more severe than that of the opposite side of canyon. And the ground surface has been characterized by larger deformations in the case of oblique incident waves. It is also concluded that the low piers and frame of the continuous rigid frame bridge ape more sensitive to the multi-support seismic excitations than the flexible high piers. The canyon topography as well as the oblique incidence of the waves brings the continuous rigid frame bridge severe responses, which should be taken into account in bridge design.

Numerical investigation of the effects of soil-structure and granular material-structure interaction on the seismic response of a flat-bottom reinforced concrete silo

In this work,a numerical study of the effects of soil-structure interaction(SSI)and granular material-structure interaction(GSI)on the nonlinear response and seismic capacity of flat-bottomed storage silos is conducted.A series of incremental dynamic analyses(IDA)are performed on a case of large reinforced concrete silo using 10 seismic recordings.The IDA results are given by two average IDA capacity curves,which are represented,as well as the seismic capacity of the studied structure,with and without a consideration of the SSI while accounting for the effect of GSI.These curves are used to quantify and evaluate the damage of the studied silo by utilizing two damage indices,one based on dissipated energy and the other on displacement and dissipated energy.The cumulative energy dissipation curves obtained by the average IDA capacity curves with and without SSI are presented as a function of the base shear,and these curves allow one to obtain the two critical points and the different limit states of the structure.It is observed that the SSI and GSI significantly influence the seismic response and capacity of the studied structure,particularly at higher levels of PGA.Moreover,the effect of the SSI reduces the damage index of the studied structure by 4%.

Study on time-varying seismic vulnerability and analysis of ECC-RC composite piers using high strength reinforcement bars in offshore environment

As the main seismic component of a bridge,seismic damage to the bridge pier has a greater effect on its subsequent service.In the offshore chloride environment,the issues(e.g.,reinforcement bar corrosion and attenuation of concrete strength)of piers caused by chloride ion seriously curtail the normal service life and deteriorate the anti-seismic property of bridge structures.The engineered cementitious composite(ECC)-reinforced concrete(RC)composite pier with high strength reinforcement bars(HSRB)is expected to solve the above problems.This study aims to clarify the time-varying seismic vulnerability(SV)of the HSRBECC-RC composite pier during its full life cycle(FLC).Based on OpenSees,the refined finite element analysis models of RC pier,ECC-RC composite pier,and HSRBECC-RC composite pier have been established.Moreover,using the nonlinear time-path dynamic analysis method,the influence of chloride ion erosion on the time-dependent seismic vulnerability(SV)of these different piers in different service life and different peak ground acceleration(PGA)were analyzed from a dynamic point of view.The research shows that the exceeding probability(EP)of the same damage level increases with the enhancement of service time and PGA and with the increase of destruction,the exceeding probability(EP)of slight damage(DL-1),moderate damage(DL-2),serious damage(DL-3),and complete collapse(DL-4)decreases in turn;the corrosion degree of chloride ion to piers is small during the early service period,the time-varying vulnerability curve of the bridge piers is almost the same as that of a new bridge,and during later service,as the extent of chloride ion corrosion deepens,exceeding probability(EP)under severe damage(DL-3)and complete collapse(DL-4)is increased,and the seismic performance is significantly enhanced.

Seismic Analysis for Rigid-Framed Prestressed Reinforced Concrete Bridge in Tianjin Light Railway

The seismic analysis of a rigid-framed prestressed concrete bridge in Tianjin Light Railway is performed. A 3-D dynamic finite element model of the bridge is established considering the weakening effect caused by the soft soil foundation. After the dynamic characteristics are calculated in terms of natural frequencies and modes, the seismic analysis is carried out using the modal response spectrum method and the time-history method, respectively. Based on the calculated results, the reasonable design values are finally suggested as the basis of the seismic design of the bridge, and meanwhile the problems encountered were also analyzed. Finally, some conclusions are drawn as: 1) Despite the superiority of rigid-framed prestressed concrete bridge, the upper and lower ends of the piers of the bridge are proved to be the crucial parts of the bridge, which are easily destroyed under designed earthquake excitations and should be carefully analyzed and designed; 2) The soft soil foundation can possibly result in rather weakening of the lateral rigidity of the rigid-framed bridge, and should be paid considerable attention; 3) The modal response spectrum method, combined with time-history method, is suggested for the seismic analysis in engineering design of the rigid-framed prestressed concrete bridge.

Seismic Performance of Bridges with Different Pier Heights： Longitudinal Analysis of an Existing Bridge

This paper is dedicated to the study of the seismic performance of an existing RC （reinforced concrete） bridge localized in a region of moderate seismicity. The bridge has six spans and piers with very different heights, three of which are monolithically connected to the deck. To understand the roles of the different pier sizes in the overall behavior, several analyses were carried out in the longitudinal direction： （1） linear dynamic approach; （2） non-linear static approach; （3） non-linear dynamic approach. Linear dynamic analysis was made in order to design the bridge for the ultimate limit state considering the largest value of the ductility factor. No safety verification was made for the other loads. Using non-linear static analyses, sensitivity was performed to check the influence of reinforcement quantities of each pier on the overall behavior of the bridge under Lisbon seismic action. For the non-linear dynamic approach, a series of strong motion records compatible with the EC-8 spectrum for Lisbon area were generated. The very same combinations of reinforcement quantities were studied. Comparisons between static and dynamic non-linear analysis were made to confirm the validity of the first one in the case under analysis, where the period of vibration is quite high.

Damper placement for seismic control of super-long-span suspension bridges based on the first-order optimization method

To ensure the anti-earthquake performances of super-long-span suspension bridges, effective devices should be employed to control the seismic response of key sections. In this paper, four kinds of assessment functions for seismic response control effect are formulated based on the mechanism of seismic response control with dampers and the seismic response characteristics of long-span suspension bridges. A new optimal placement method of dampers using penalty function and first-order optimization theory is then proposed. Runyang suspension bridge (RSB) with a main span of 1490 m is then taken as an example. After seismic response time-history analyses on RSB using different placements of dampers, the analysis results are optimized by employing the optimal placement method and the optimal placements of dampers with the four assessment functions are then achieved respectively. Comparison of the four optimal control effects show that different assessment functions can lead to different optimal placements when the number of dampers is certain, but all placements of dampers can reduce the seismic response of RSB significantly. The selection of assessment functions and damper optimal placement should be determined by the structural characteristics and by what is considered in the structures. Results also show that the first-order optimization is an effective method on determining the optimal placement of dampers.

Simplified Method and Influence Factors of Vibration Characteristics of Isolated Curved Girder Bridge

The isolated curved girder bridge's vibration characteristics play a major part in the seismic responses of structures and anti-seismic properties.A clear analytic relationship between design parameters and the system's vibration characteristics could be established by its simplified dynamic analysis model,making it convenient for providing a reference to the optimization of design and safety analysis.A double-mass six-degree-of-freedom model for curved girder bridges with isolation bearings installed at the top of the bridge piers is built and a simplified analysis method for the vibration characteristics of the system is provided.Combined with the Matlab programming,the influences of radius of curvature,central angle,bridge deck width and damping ratio of the isolation layer and circular frequency of the isolation layer of isolated curved girder bridges on the pseudo-undamped natural circular frequency(called pseudo-frequency for short)and system damping ratio are systematically analyzed,and the sensitivity of vibration characteristics of isolated curved girder bridges is studied.The results show that the vibration characteristics of isolated curved girder bridges can be reflected well with this simplified model and calculation method.The pseudo-frequency of curved girder and system damping ratios increases with the increase of the isolation layer.The third-order vibration characteristic is more sensitive to the parameters of a curved girder,and the first-order vibration characteristic is sensitive to both central angle and radius of curvature to some extent while insensitive to the width of the bridge deck.Furthermore,the second-order vibration characteristic is not sensitive to the parameters of a curved girder.

Comprehensive Optimal Control on Seismic Response of a Single-Tower Self-Anchored Suspension Bridge

Earthquake may cause severe damage to all kinds of bridge such as the falling down of the girder; therefore,effective measures should be employed to control the seismic displacement. In this paper,the method of comprehensive optimal control,com-bined with analytic hierarchy process,is employed to investigate the seismic response control of the Nanjing Jiangxinzhou Bridge,which is a single-tower self-anchored suspension bridge （SSSB）. Also,3-dimensional nonlinear seismic response analyses are con-ducted. Three types of practical connection measures for seismic response control of SSSB are investigated,and the optimal pa-rameters of the connection devices are achieved by this method. Results show that both the elastic connection devices and the damp-ers with rational parameters can reduce the seismic displacement of the bridge effectively,but the elastic connection devices will in-crease the seismic force of the tower. When all factors are consid-ered,the optimal measure is by using the elastic connection devices and the dampers together. These results can provide references for seismic response control of SSSBs.

Probability-based practice-oriented seismic behaviour assessment of simply supported RC bridges considering the variation and correlation in pier performance

Probability-based seismic performance assessment of in-service bridges has gained much attention in the scientific community during the past decades. The nonlinear static pushover analysis is critical for describing the seismic behaviour of bridges subjected to moderate to high seismicity due to its simplicity. However, in existing analysis methods,the generation of pushover curve needs tremendous amount of computational costs and requires skills, which may halter its application in practice, implying the importance of developing practice-oriented analysis method with improved efficiency. Moreover, the bridge pier performance has been modelled as deterministic, indicating that the variation associated with the pier material and mechanical properties remains unaddressed. The correlation in the performance of different piers also exists due to the common design provisions and construction conditions but has neither been taken into account. This paper develops a simplified pushover analysis procedure for the seismic assessment of simply supported RC bridges. With the proposed method, the pushover curve of the bridge can be obtained explicitly without complex finite element modelling. A random factor is introduced to reflect the uncertainty in relation to the pushover curve. The correlation in the pier performance is considered by employing the Gaussian copula function to construct the joint probability distribution. Illustrative examples are presented to demonstrate theapplicability of the method and to investigate the impact of variation and correlation in bridge pier behaviour on the seismic performance assessment.

Integrated framework for seismic fragility assessment of cable-stayed bridges using deep learning neural networks

The increasing intensity of strong earthquakes has a large impact on the seismic safety of bridges worldwide.As the key component in the transportation network,the cable-stayed bridge should cope with the increasing future hazards to improve seismic safety.Seismic fragility analysis can assist the resilience assessment under different levels of seismic intensity.However,such an analysis is computationally intensive,especially when considering various random factors.The present paper implemented the deep learning neural networks that are integrated into the performance-based earthquake engineering framework to predict fragility functions and associated resilience index of cable-stayed bridges under seismic hazards to improve the computational efficiency while having sufficient accuracy.In the proposed framework,the Latin hypercube sampling was improved with additional uniformity to enhance the training process of the neural network.The well-trained neural network was then applied in a probabilistic simulation process to derive different component fragilities of the cable-stayed bridge.The estimated fragility functions were combined with the Monte Carlo simulations to predict system resilience.The proposed integrated framework in this study was demonstrated on an existing single-pylon cable-stayed bridge in China.Results reveal that this integrated framework yields accurate predictions of fragility functions for the cable-stayed bridge and has reasonable accuracy compared with the conventional methods.

Seismic stability of reinforced soil walls under bearing capacity failure by pseudo-dynamic method

In order to evaluate the seismic stability of reinforced soil walls against bearing capacity failure,the seismic safety factor of reinforced soil walls was determined by using pseudo-dynamic method,and calculated by considering different parameters,such as horizontal and vertical seismic acceleration coefficients,ratio of reinforcement length to wall height,back fill friction angle,foundation soil friction angle,soil reinforcement interface friction angle and surcharge.The parametric study shows that the seismic safety factor increases by 24-fold when the foundation soil friction angle varies from 25°to 45°,and increases by 2-fold when the soil reinforcement interface friction angle varies from 0 to 30°.That is to say,the bigger values the foundation soil and/or soil reinforcement interface friction angles have,the safer the reinforced soil walls become in the seismic design.The results were also compared with those obtained from pseudo-static method.It is found that there is a higher value of the safety factor by the present work.

Seismic damage analysis of the outlet piers of arch dams using the finite element sub-model method

This study aims to analyze seismic damage of reinforced outlet piers of arch dams by the nonlinear finite element （FE） sub-model method. First, the dam-foundation system is modeled and analyzed, in which the effects of infinite foundation, contraction joints, and nonlinear concrete are taken into account. The detailed structures of the outlet pier are then simulated with a refined FE model in the sub-model analysis. In this way the damage mechanism of the plain （unreinforced） outlet pier is analyzed, and the effects of two reinforcement measures （i.e., post-tensioned anchor cables and reinforcing bar） on the dynamic damage to the outlet pier are investigated comprehensively. Results show that the plain pier is damaged severely by strong earthquakes while implementation of post-tensioned anchor cables strengthens the pier effectively. In addition, radiation damping strongly alleviates seismic damage to the piers.