Multi-span Simply Supported Bridges Research Articles

Seismic applicability analysis of high-speed railway multi-span simply-supported bridges based on simplified model

Seismic applicability analysis of high-speed railway multi-span simply-supported bridges based on simplified model

Reduction of the Longitudinal Seismic Response of High-Speed Railway Multi-Span Simply-Supported Bridges by the Track Constraint

ABSTRACT The longitudinal seismic response reduction in railway bridges is worthy of attention because it relates to the engineering cost. It is difficult to further explore the reduction effect because the complexity of traditional analysis model leads to the low efficiency in parametric analysis. In this paper, the track structure was simplified, and a simplified calculation model was established. The parametric analysis considering the span number and pier height on the simplified model seismic responses was carried out. The results showed that the reduction effect was extensive and there was a great internal force transferred to the subgrade-track structure.

Seismic fragility analysis of multi-span steel truss railway bridges in Turkey

In this study, seismic fragility analysis of multi-span steel truss bridges still giving service in railway network of Turkey was aimed. For this purpose, two representative multi-span steel truss bridges were selected in Turkish railway lines. A detailed three-dimensional inelastic finite element (FE) model for each bridge was created using commercial FE software. These models were used to perform non-linear time history analyses for each of the selected 30 ground motions scaled to 10 different peak ground acceleration (PGA) values to assess seismic demands of the bridges. To develop fragility curves, probabilistic seismic demand models (PSDMs) were defined. The most appropriate ground motion intensity measure (IM) for PSDMs of both bridges was determined among 11 IMs and the PGA was found as the optimal IM. Finally, the fragility curves for both the components and structural systems of the bridges were developed. The results clearly showed that the multi-span continuous (MSC) steel truss bridge is more vulnerable than the multi-span simply supported (MSSS) steel truss bridge, and for both bridge types, steel bearings are the most vulnerable components. Additionally, top wind braces for the MSC bridge as well as transverse beams and truss vertical members for the MSSS bridge were found as the most vulnerable superstructure members.

Influence of Bearing Types and Design Code Advances on Seismic Vulnerability of Simply Supported Highway Bridges

ABSTRACT Multi-span simply supported (MSSS) highway bridges are one of the most common bridge types across the world and have several vulnerable components, including bearings, piers, and abutments. Although several past studies have evaluated the seismic response and fragility of common multi-span simply supported bridges, there is negligible research that explores the influence of bearing types, and non-ductile failure modes of bridge piers on the performance of older non-seismically designed simply supported bridges. Additionally, a better understanding of seismic risk to highway transportation systems necessitates the exploration of design code advances and subsequent impact on the seismic vulnerability of MSSS highway bridges. Consequently, this study also focuses on developing and comparing fragility curves for the older design era non-seismically designed, and modern era seismically designed MSSS bridges. High-fidelity three-dimensional (3-D) analytical models, which account for the nonlinear behavior of different components, including non-ductile failure modes of bridge piers, are developed. Deterministic seismic response assessment reveals a higher seismic demand on bridge pier for MSSS bridges with steel bearings as compared to those with elastomeric bearings. The bridge component and system fragility curves are developed with a suite of ground motions representative of the seismic hazard of the case-study region. Results reveal the significant vulnerability of older non-seismically designed MSSS bridge with steel bearings due to the non-ductile failure of the bridge pier. The vulnerability of the bridge is significantly reduced with the adoption of modern seismic design and detailing practices.

Performance Evaluation of Chinese High-Speed Railway Bridges Under Seismic Loads

The multi-span simply supported (MSSS) box girder bridge is the most used structural form for the high-speed railway (HSR) in China. In structural design, it is required that the MSSS bridge system has high stiffness and low deflection under the operation loads. With the expansion of the HSR network to regions that are seismically active, the seismic performance of MSSS bridges in these regions is an issue of great concern. In this study, the performance-based earthquake engineering (PBEE) methodology originally developed to quantify the seismic performance of buildings and bridges has been adopted to quantify the seismic performance of the HSR MSSS bridges in China. Typically, a four-span MSSS bridge used in China’s Sichuan–Yunnan HSR lines has been extensively assessed by the PBEE approach. This study is the first of its kind to systematically identify and quantify the damage states, repair actions, repair costs and travel delay losses for China’s HSR MSSS bridge system. The results reveal that the financial loss from the MSSS bridge system is highly dependent on the anchorage capacity of the fixed bearings. Overall, the costs of travel delay outweigh those for structural repair. Most of the financial loss can be attributed to the functional loss of the track-slab components and bearings of the HSR MSSS bridge system.

Seismic vulnerability and loss assessment of an isolated simply-supported highway bridge retrofitted with optimized superelastic shape memory alloy cable restrainers

Restrainers, being of relatively low cost and easy to install, are often used to prevent unseating of bridge spans. The potential of using superelastic shape memory alloy (SMA) restrainers in preventing such failure has been discussed in the literature; however, the impact of such smart restrainers with optimized configurations in reducing the failure probability of bridge components and system as well as the long-term economic losses given different earthquake scenarios has not been investigated yet. This study presents a probabilistic seismic fragility and long-term performance assessment on isolated multi-span simply-supported bridges retrofitted with optimized SMA restrainers. First, SMA restrainers are designed following the displacement-based approach and their configuration is optimized. Then, seismic fragility assessment is conducted for the bridge retrofitted with optimized SMA restrainers and compared with those of the original bridge and the bridges with elastic restrainers (steel and CFRP). Finally, long-term seismic loss (both direct and indirect) are evaluated to assess the performance of the retrofitted bridges in a life-cycle context. Results showed that among three considered restrainers, SMA restrainers make the bridge less fragile and help the system lower long-term seismic loss. The design event (DE, 2475-year return period) specified in Canadian Highway Bridge Design Code (CHBDC, CSA S6-14 2014) may underestimate the long-term seismic losses of the highway bridges. Under DE, the damage probability of the bridge retrofitted with optimized SMA restrainers experiencing collapse damage is only 0.7%. Under the same situation, its expected long-term loss is approximate 17.6% of that with respect to the unretrofitted bridge.

Vibration control of bridges under simultaneous effects of earthquake and moving loads using steel pipe dampers

This study aims to develop a practical methodology based on the eigenfunction expansion method to assess the effects of simultaneous action of vertical earthquake excitation and moving vehicle loads in single-span and multi-span simply-supported bridges. While the effects of vertical earthquake ground motions are generally ignored in common design practice, it is shown that the influence of simultaneous vertical earthquake excitation and vehicle loads can considerably affect the structural response of the bridge, especially in near-field earthquakes with high amplitude vertical components. To address this issue, a novel vibration suppression system is proposed using steel pipe dampers and its reliability is investigated for a wide range of bridge flexural rigidity under seven different earthquake records. The results indicate that the proposed system can significantly (up to 75%) suppress the vertical vibrations generated in the bridge, especially for the systems with lower flexural rigidity. For the same maximum deflection limits, application of pipe dampers could reduce the required flexural rigidity of the bridge (up to 50%), and therefore, lead to more economic design solutions with lower structural weight.

Simplified moment-curvature relationship in analytical form for circular RC sections

The behaviour of regular multi-span simply-supported bridges is strongly dependent on the behaviour of its piers. The response of a pier is governed, in general, by different mechanisms: flexure, shear, second order effects, lap-splice of longitudinal bars or their buckling. The flexural behaviour is an important part of the problem, and it can be characterised through the equivalent plastic hinge length and the Moment-Curvature law of the fixed end. In this paper, a procedure to calculate the Moment-Curvature relationship of circular RC sections is proposed which is based on defining the position of few characteristic points. The analytical formulation is based on adjusted polynomial functions fitted on a database of fibre-based analyses. The proposed solution is based on three parameters: dimensionless axial force, mechanical ratio of longitudinal reinforcement, geometrical ratio of transverse reinforcement. A benchmark case is presented to compare the solution to a FEM non-linear analysis. Even if it is based on few input data, this solution allows to have good indicators on the material performances (e.g. yielding, spalling, etc). For these reasons, the proposed approach is deemed to be particularly effective in performing quick yet accurate mechanics-based regional-scale assessment of bridges.

Modeling the impact of corrosion on seismic performance of multi-span simply-supported bridges

The corrosion of steel rebar negatively affects the serviceability and capacity of RC bridges and increases their vulnerability in earthquakes. Most of existing numerical models rely on either solid elements with a detailed corrosion damage model, involving impractical computational costs, or fiber beam elements with an incomplete corrosion damage model, requiring careful justification. A time-dependent corrosion damage model based on fiber beam elements was herein proposed as a numerical tool conserving both computational efficiency and appropriate accuracy. The proposed corrosion damage model comprehensively incorporates most of the potential corrosion-induced damage patterns on reinforced concrete, including cross-section loss, ductility degradation and compressional buckling of rebar; deterioration of cover concrete and core concrete; and deteriorated strain penetration effect. This corrosion damage model was implemented in OpenSees via fiber beam elements in which the strain penetration effect was simulated by the Bond_SP01 material with the Zero Length element. The accuracy of corrosion damage model was validated with existing experimental data of cyclic loading tests on corroded RC columns. A multi-span simply supported (MSSS) bridge was selected to showcase how to implement the proposed corrosion damage model in the time-dependent seismic fragility analysis of RC bridges. A sensitivity analysis was conducted to illustrate the roles of different corrosion damage patterns in altering seismic fragility of RC bridges. It revealed that the corrosion-induced deterioration of strain penetration and rebar yield strength significantly increase the seismic fragility of the corroded MSSS bridge.

Safety and Stability of Light-Rail Train Running on Multispan Bridges with Deformation

AbstractThis study investigated the safety and stability of light-rail trains that run on multispan simply supported bridges (MSSBs) and have experienced some settling and girder deformation caused by both foundation settlement and girder deflection/camber. A three-dimensional dynamic nonlinear finite-element model for a light-rail train track–MSSB interaction system, which took into account rail irregularities, girder deformation, wheel–rail contact, and coupling effects, was developed. A case study analyzed a four-car light-rail train rolling on a MSSB, and the relationships between the girder deformation and running performance under various speeds were obtained. The results indicate that speed is the dominant factor that contributes to the safety and stability of the light-rail train when girder deformation is present. In addition, the influence of girder deformation was found to be greater on safety than on stability. In real applications, it is recommended to pursue advanced monitoring and evaluatio...

Seismic Fragility Assessment of Skewed MSSS-I Girder Concrete Bridges with Unequal Height Columns

Multi Span Simply Supported Bridges (MSSS) are categorized among the most vulnerable bridge classes and their vulnerability increases when different sources of irregularities such as skewness as well as columns height differences are included. Different sources of irregularities make the irregular bridge more complicated in case of dynamic response than regular bridges, and therefore a comprehensive study should be implemented to explore the effect of different irregularities on seismic performance of bridges individually and jointly. This paper explores the effect of skewness and unequal height columns on the seismic response of MSSS-I girder concrete bridges commonly constructed in Central and Southeastern United States (CSUS). The scope of the study is limited to tree spans which are the most prevalent spans in this class of bridges. The results show that the component fragilities become more sensitive to column height ratio with increase in the bridge skew angle particularly in longitudinal direction. The study of the combined effects of skewness and column height ratio on the bridge system fragility also reveals that the column height ratio has negative effect on the fragility of bridge system in all damage states and different skew angles but this effect increases by increasing the skewness as well as damage state of interest.

Domino-type progressive collapse analysis of a multi-span simply-supported bridge: A case study

Hongqi Viaduct, a multi-span simply-supported bridge in Zhuzhou city, Hunan Province, China, collapsed progressively during the mechanical demolishing of the bridge on May 17, 2009. Totally nine spans collapsed in the accident and it is a typical domino-type progressive collapse. The accident resulted in the loss of 9 lives and 16 injuries. Investigations were conducted after the accident to determine the cause of the unexpected progressive collapse. This paper is aimed at presenting a summary of the bridge before and after the incident, the demolishing plans and field investigations after the accident. To better understand the cause and mechanism of the progressive collapse, a numerical simulation is carried out. A detail 3D finite element (FE) model is developed by using the explicit FE code LS-DYNA. The bridge components including the bridge slabs, wall-type piers, longitudinal and transverse reinforcement bars are included in the model. The non-linear material behaviour including the strain rate effects of the concrete and steel rebar are considered. The model is used to simulate the bridge collapse induced by demolishing, and the domino-type progressive collapse of the bridge is clearly captured. Based on the numerical results, the reason for the failure is discussed and better understood. Finally, the possible mitigation methods of such progressive collapses of multi-span viaducts are suggested.

Performance evaluation of natural rubber seismic isolators as a retrofit measure for typical multi-span concrete bridges in eastern Canada

More than 46% of the 2672 multiple-span bridges in the Province of Quebec (Canada) are concrete girder bridges. Due to the advanced age and the lack of seismic detailing, these bridges may be vulnerable to earthquake events. In an effort to prevent an interruption of the transportation network, which could be catastrophic for Quebec, a comprehensive research program was conducted whose aims were to assess the seismic vulnerability of typical bridge classes retrofitted with natural rubber seismic isolator devices through the development of fragility curves. The understanding of the impact of various modeling parameters on structural-component responses is the first step in a forward-vulnerability assessment of bridges in Quebec. This paper presents part of a comparative study using detailed three-dimensional nonlinear models that was conducted to assess the longitudinal and transverse responses of multi-span continuous (MSC) and multi-span simply supported (MSSS) concrete bridges in their as-built and retrofitted configurations using different synthetic ground motions (SGM) for the eastern part of Canada. Deterministic responses in terms of column curvature demand, abutment footing deformations, and abutment wall deformations are provided for the longitudinal and transverse directions of bridge models. The influences of various modeling parameters were assessed using analysis of variance (ANOVA) and design-of-experiments (DOE) principles to perform screening of 12 structural parameters. This study revealed that the most important modeling parameters that affect critical components responses of MSC and MSSS bridges are the isolator effective stiffness, the abutment stiffness, and the gap between abutment and deck, in addition to the variation in gross bridge geometry and ground-motion contents. This screening study also gives an indication that the variation in other modeling parameters such as structural damping and skew angle affect the seismic response of MSC and MSSS bridges and should be considered carefully in a seismic-vulnerability assessment for these portfolios of concrete bridges. In addition, it was found that the use of seismic isolation devices effectively reduces the curvature demand placed on columns but has a negative impact on the deformation demand placed on abutment walls.

A new scheme for the seismic retrofit of multi-span simply supported bridges

There are two alternative strategies that a designer may adopt and combine when faced with the retrofitting of a bridge: (a) the increase in the capacity or (b) the reduction in the actions of the structure. In this article, a new scheme, based on the second strategy, is proposed for the retrofit of existing multi-span simply supported (MSSS) bridges. The reduction in the actions of the bridge was mainly achieved by utilising an external restraining system consisting of I-shaped steel piles driven in the backfill soil and a slab that is the pile-cap of the piles. The restraining system was preliminarily designed and assessed in an existing MSSS bridge system, whose deck slab was made continuous. The existing and the retrofitted bridge were analysed by means of non-linear dynamic time history analysis and their response was compared in terms of serviceability and earthquake resistance performance. The study showed that the retrofitting scheme enhanced effectively the earthquake resistance of the existing bridge.

Longitudinal Seismic Response Analysis of MSSS Bridge in Qinghai-Tibet Railway

This paper presents the results of seismic behavior analysis of a multi-span simply supported (MSSS) bridge in Qinghai-Tibet Railway. The main goal is to examine the effects of frozen soil condition and wave passage on seismic behavior of MSSS Bridge. A 2D FE model was established by ANSYS software in order to evaluate the effects of modeling, in which bearings and pounding effects were also considered. Results indicate that frozen soil condition has an important effect on the seismic response in longitudinal direction; wave passage can influence the seismic response of MSSS Bridge within a certain range of seismic wave travelling velocity.

Three-dimensional nonlinear seismic performance evaluation of retrofit measures for typical steel girder bridges

Steel girder bridges are common bridges in North America which have exhibited considerable vulnerabilities in past earthquake events. This paper conducts nonlinear time history analysis using detailed three-dimensional models of typical multi-span simply supported and multi-span continuous steel girder bridges to evaluate the effectiveness of various retrofit strategies. Restrainer cables, steel jackets, shear keys, and elastomeric isolation bearings are assessed for their influence on the variability and peak longitudinal and transverse response of critical components in the bridges. The results indicate that different retrofit measures may be more effective for each class of bridges. For example, the restrainer cables are effective for the multi-span simply supported (MSSS) bridge, yet not the multi-span continuous (MSC) bridge; shear keys improve the transverse bearing response in the MSC bridge but are not effective in the MSSS bridge which exhibits less transverse vulnerability; and elastomeric bearings improve the response of the vulnerable columns in both the MSSS and MSC bridges yet lead to increased abutment demands in the MSC bridge. The study reveals that while a retrofit may have a positive influence on the targeted component, other critical components may be unaffected or negatively impacted. This lends support to vulnerability assessments that consider the impact of retrofit on system vulnerability reflecting the contribution of multiple components.

Inelastic seismic response of stiffening systems and development of demand spectrum: Application to MSSS bridges

AbstractA stiffening system is a system that increases its stiffness as it goes under large displacements. Such behavioural characteristic can result from constitutive behaviour or at the structural level often from closure of gaps between various components (sub‐systems) of the structure. An example of the latter situation is multi‐span simply supported (MSSS) bridges under horizontal earthquake ground motion. Unlike softening systems, stiffening systems have not been studied. In addition to the need for more understanding of the seismic response of stiffening systems, there is a need to develop response spectrum that can be used in design. Several parameters including gap size and ratios of sub‐systems stiffness, strength, and mass control the behaviour of a stiffening system. In this study, a simplified stiffening model is developed and over 367 000 cases are analysed to investigate the nonlinear stiffening behaviour and pounding. Parameters considered also include ground motion characteristic. Results are evaluated and compared in terms of displacement and dissipated hysteretic energy. Parameter study results show that, on average, the displacement response is lower for stiffening systems, however, they dissipates higher hysteretic energy, due to higher yield cycles and yield excursions, and can possibly sustain more damage than a bilinear, elastic–plastic system. Using parameter study database, design response spectrum for stiffening systems is also proposed and its practical application is demonstrated through its application to an MSSS bridge. Results of this study goes beyond MSSS bridges and will have application for many structural systems where response is characterized by a stiffening behaviour. Copyright © 2007 John Wiley & Sons, Ltd.

Seismic behavior and capacity/demand analyses of three multi-span simply supported bridges

This paper presents the results of an analytical study on the seismic response of three Multi-Span-Simply-Supported (MSSS) bridges in New Jersey. The main goal is to determine the capacity/demand ratio for various components in order to evaluate the seismic vulnerability and to develop retrofit strategies. Another important objective is to investigate the effect of those response characteristics that are unique to this class of bridges on their seismic performance. Furthermore, the effect of modeling approach and appropriateness of pushover analysis using existing demand curve are also addressed considering the stiffening-interaction between the bridge and the abutments. The investigation includes detailed nonlinear time history analyses of three actual bridges as representatives of typical 2, 3, and 4 span bridges, which are common in New Jersey and the Eastern United States in general. Both 2-D and 3-D models were employed in order to evaluate the effect of modeling. Several parameters prove to have an important effect on the seismic response of MSSS bridges, such as soil–structure interaction, impact between adjacent spans, steel bearings, and plasticity at pier columns. Therefore, the seismic response of MSSS bridges is evaluated in light of a comprehensive parametric study based on these factors and quantified through capacity/demand ( C / D ) ratios for critical elements. Furthermore, the research needs related to the seismic evaluation, retrofit, and design of MSSS bridges are also discussed.

Seismic Response of Multiple Span Steel Bridges in Central and Southeastern United States. I: As Built

The seismic response of typical multispan simply supported (MSSS) and multispan continuous steel girder bridges in the central and southeastern United States is evaluated. Nonlinear time history analyses are conducted using synthetic ground motion for three cities for 475 and 2,475-year return period earthquakes (10 and 2% probability of exceedance in 50 years). The results indicate that the seismic response for the 475-year return period earthquake would lead to an essentially linear response in typical bridges. However, the seismic response for a 2,475-year return period earthquake resulted in significant demands on nonductile columns, fixed and expansion bearings, and abutments. In particular, pounding between decks in the MSSS bridge would result in significant damage to steel bearings and would lead to the toppling of rocker bearings, which may result in unseating of the bridge deck.

Effects Of Impact On The Seismic Response Of MSSS Bridges

This paper presents results of a study on the effect of impact on seismic response of Multi-Span Simply-Supported (MSSS) bridges. The investigation includes detailed dynamic analysis of three actual bridges as representatives of 2,3, and 4 span bridges, which are common in the Eastern United States. Furthermore, using a Stiffening Single-Degree-Of-Freedom (S-SDOF) model a series of parametric study are performed. The objectives are to better quanti~ the effect of impact on the seismic performance of MSSS bridges and to provide the knowledge base for development of design guidelines within a performancebased framework. Several damage criteria, namely displacemen~ dissipated hysteretic energy, and low-cycle fatigue darnage index are considered. It is shown that on the average displacement dem&ds are lower for S-SDOF systems, consistent with pushover analysis based on current seismic codes. However, considering other damage criteria, it is quite possible for an S-SDOF system to sustain more damage than an elastic-plastic system. Design implications and the needs for future research are also discussed.