Seismic response of skewed RC box-girder bridges

It is critical to ensure the functionality of highway bridges after earthquakes to provide access to important facilities. Since the 1971 San Fernando earthquake, there has been a better understanding of the seismic performance of bridges. Nonetheless, there are no detailed guidelines addressing the performance of skewed highway bridges. Several parameters affect the response of skewed highway bridges under both service and seismic loads which makes their behavior complex. Therefore, there is a need for more research to study the effect of skew angle and other related factors on the performance of highway bridges. This paper examines the seismic performance of a three-span continuous concrete box girder bridge with skew angles from 0 to 60 degrees, analytically. Finite element （FE） and simplified beam-stick （BS） models of the bridge were developed using SAP2000. Different types of analysis were considered on both models such as： nonlinear static pushover, and linear and nonlinear time history analyses. A comparison was conducted between FE and BS, different skew angles, abutment support conditions, and time history and pushover analysis. It is shown that the BS model has the capability to capture the coupling due to skew and the significant modes for moderate skew angles. Boundary conditions and pushover load profile are determined to have a major effect on pushover analysis. Pushover analysis may be used to predict the maximum deformation and hinge formation adequately.

Dynamic finite element model updating of prestressed concrete continuous box-girder bridge

The dynamic finite element model （FEM） of a prestressed concrete continuous box-girder bridge, called the Tongyang Canal Bridge, is built and updated based on the results of ambient vibration testing （AVT） using a real-coded accelerating genetic algorithm （RAGA）. The objective functions are defined based on natural frequency and modal assurance criterion （MAC） metrics to evaluate the updated FEM. Two objective functions are defined to fully account for the relative errors and standard deviations of the natural frequencies and MAC between the AVT results and the updated FEM predictions. The dynamically updated FEM of the bridge can better represent its structural dynamics and serve as a baseline in long-term health monitoring, condition assessment and damage identification over the service life of the bridge .

Free Vibration Analysis of RC Box-Girder Bridges Using FEM

The free vibration analysis of simply supported box-girder bridges is carried out using the finite element method.The fundamental frequency is determined in straight,skew,curved and skew-curved box-girder bridges.It is important to analyse the combined effect of skewness and curvature because skew-curved box-girder bridge behaviour cannot be predicted by simply adding the individual effects of skewness and curvature.At first,an existing model is considered to validate the present approach.A convergence study is carried out to decide the mesh size in the finite element method.An exhaustive parametric study is conducted to determine the fundamental frequency of box-girder bridges with varying skew angle,curve angle,span,span-depth ratio and cell number.The skew angle is varied from 0°to 60°,curve angle is varied from 0°to 60°,span is changed from 25 to 50 m,span-depth ratio is varied from 10 to 16,and single cell&double cell are used in the present study.A total of 420 bridge models are used for parametric study in the investigation.Mode shapes of the skew-curved bridge are also presented.The fundamental frequency of the skew-curved box-girder bridge is found to be more than the straight bridge,so,the skew-curved box-girder bridge is preferable.The present study may be useful in the design of box-girder bridges.

Simulation of Temperature Field in Original Segment of Concrete Box-Girder Bridge

Temperature field and its variation with time are necessary for analyzing the thermo-mechanical performance of mass concrete structures at their early ages. This paper carries out a temperature field simulation analysis for an original segment of a real box girder bridge with the finite element software ANSYS. Two representative exothermic rate models are used to describe the heat- releasing process caused by the cement hydration in concrete. The exothermic rate model that conforms to reality more closely is recognized by comparing the simulation results with the data gathered from the optical fiber temperature sensors pre-embedded in the original segment. The air temperature and wind velocity that constitute thermal boundary conditions are determined in the light of the local meteorological department and correlative research achievements of recent years. Moreover, the consideration for the steel formwork acting as a barrier to heat loss is also proved to be beneficial to improve the simulation effect.

Performance-based seismic assessment of skewed bridges with and without considering soil-foundation interaction effects for various site classes

The seismic behavior of skewed bridges has not been well studied compared to straight bridges. Skewed bridges have shown extensive damage, especially due to deck rotation, shear keys failure, abutment unseating and column- bent drift. This research, therefore, aims to study the behavior of skewed and straight highway overpass bridges both with and without taking into account the effects of Soil-Structure Interaction （SSI） due to near-fault ground motions. Due to several sources of uncertainty associated with the ground motions, soil and structure, a probabilistic approach is needed. Thus, a probabilistic methodology similar to the one developed by the Pacific Earthquake Engineering Research Center （PEER） has been utilized to assess the probability of damage due to various levels of shaking using appropriate intensity measures with minimum dispersions. The probabilistic analyses were performed for various bridge configurations and site conditions, including sand ranging from loose to dense and clay ranging from soft to stiff, in order to evaluate the effects. The results proved a considerable susceptibility of skewed bridges to deck rotation and shear keys displacement. It was also found that SSI had a decreasing effect on the damage probability for various demands compared to the fixed-base model without including SSI. However, deck rotation for all types of the soil and also abutment unseating for very loose sand and soft clay showed an increase in damage probability compared to the fixed-base model. The damage probability for various demands has also been found to decrease with an increase of soil strength for both sandy and clayey sites. With respect to the variations in the skew angle, an increase in skew angle has had an increasing effect on the amplitude of the seismic response for various demands. Deck rotation has been very sensitive to the increase in the skew angle; therefore, as the skew angle increased, the deck rotation responded accordingly. Furthermore, abutment unseating showed an increasing trend due to an increase in skew angle for both fixed-base and SSI models.

The effect of different intensity measures and earthquake directions on the seismic assessment of skewed highway bridges

In this study the probable seismic behavior of skewed bridges with continuous decks under earthquake excitations from different directions is investigated. A 45° skewed bridge is studied. A suite of 20 records is used to perform an Incremental Dynamic Analysis （IDA） for fragility curves. Four different earthquake directions have been considered： -45°, 0°, 22.5, 45°. A sensitivity analysis on different spectral intensity measures is presented; efficiency and practicality of different intensity measures have been studied. The fragility curves obtained indicate that the critical direction for skewed bridges is the skew direction as well as the longitudinal direction. The study shows the importance of finding the most critical earthquake in understanding and predicting the behavior of skewed bridges.

A New Method on Resolving the Rotation in the Plane of Skew Bridges

The rotation of skew bridges in the plane is a common phenomenon in engineering. Traditional measure is to setup pins or limiting displacement with lateral bearings, but the result is not satisfactory. In order to solve this problem, the reason for the rotation in the plane is found by philosophy analysis and an idea regarding the application of slantleg frame skew bridges without abutment is brought forward in this paper. Theory and engineering practices indicate that slant-leg rigid frame bridges without abutment can restrain the rotation of skew bridges in the plane to the utmost extent because of its structural characteristics and can fundamentally solve the tough defect of skew bridges.

Prediction of Skewed Bridge Behaviors with Arbitrary Boundary Conditions—— Theoretical Approach and Its Design Application

In this paper, we report on an analytical solution for beam-type skewed highway bridges subjected to truck loading. To confirm the analysis derivation and the solution obtained, the moment and shear responses to the design truck load are acquired using the analytical method for a number of typical US highway bridges and compared with those from numerical finite element method （FEM） analysis. In addition, the lateral distribution factors for moment and shear used in routine design are investigated based on comparison of the analytical approach and FEM. The analytical solution is shown in good agreement with the FEM result. Furthermore, the relevant provisions in the American Association of State Highway Transportation Officials＇ （AASHTO＇s） LRFD Bridge Design Specifications are also discussed here for comparison, particularly with respect to design application. It is observed that the design code specified load distribution factor may not predict well, especially for shear and/or severe skew.

河道斜交桥梁壅水及流场特性分析

圆端桥墩是平原河道内一种常见的桥墩型式,为探究斜交圆端桥墩不同布置方式引起的壅水特性和水流流态变化,建立三维数值模型,采用SIMPLE算法耦合k-ε紊流模型求解N-S方程组,应用VOF法追踪自由液面,分析了单个桥墩壅水特性、绕流流场和升阻力系数随斜交角度变化的规律。研究结果表明:下游墩前壅水高度最大,壅水长度最长,上游墩前冲高值最大;水流绕流经过上游桥墩后偏向下游桥墩侧,桥墩垂直桥轴线布置方式绕流形成的壅水叠加效应更明显;斜交桥梁布置采取圆端桥墩时,桥墩顺水流布置,可有效减小阻水宽度与壅水高度,弱化流场结构变化。

Development of the applicability of simplified Henry’s method for skewed multicell box-girder bridges under traffic loading conditions

Concrete precast multicell box-girder(MCB) bridges combine aesthetics with torsional stiffness perfectly.Previous analytical studies indicate that currently available specifications are unable to consider the effect of the twisting moment(torsional moment) on bridge actions.In straight bridges the effect of torsion is negligible and the transverse reinforced design is governed by other requirements.However,in the case of skewed bridges the effect of the twisting moment should be considered.Therefore,an in-depth study was performed on 90 concrete MCB bridges with skew angles ranging from 0° to 60°.For each girder the bridge actions were determined under the American Association of State Highway and Transportation Officials(AASHTO) live load conditions.The analytical results show that torsional stiffness and live load positions greatly affected the bridges' responses.In addition,based on a statistical analysis of the obtained results,several skew correction factors are proposed to improve the precision of the simplified Henry's method,which is widely used by bridge engineers to predict bridge actions.The relationship between the bending moment and secondary moments was also investigated and it was concluded that all secondary actions increase with an increase in skewness.

斜风作用下超大跨跨海斜拉桥典型施工状态抖振响应研究

为研究风偏角和风速对超大跨跨海斜拉桥典型施工状态抖振性能的影响,以黄茅海大桥为背景,通过气弹模型风洞试验对斜风作用下该桥边塔最大单悬臂、中塔最大双悬臂、边塔最大双悬臂3种典型施工状态的抖振响应进行分析,并对基于气弹模型风洞试验和《公路桥梁抗风设计规范》(JTG/T 3360-01—2018)的等效静阵风荷载进行对比。结果表明:超大跨跨海斜拉桥各典型施工状态抖振响应最不利风偏角为0°~30°,各典型施工状态在各风偏角下的抖振响应与风速呈二次函数关系;各典型施工状态下竖向抖振响应主要由主梁一阶对称竖弯模态贡献,横向和扭转抖振响应主要由桥塔一阶横弯模态贡献;与基于气弹模型风洞试验的等效静阵风荷载相比,基于规范计算的等效静阵风荷载偏不安全,建议进一步研究超大跨跨海斜拉桥的等效静阵风荷载。

竖向地震动对斜交连续梁桥的影响研究

为充分了解竖向地震动对斜交连续梁桥的影响,以某3×30m斜交连续梁桥为背景,利用OpenSees软件建立考虑碰撞效应的计算模型,采用时程分析法对比研究了在两种地震动(水平双向地震动和三向地震动)输入工况下对桥梁支座、碰撞效应,以及桥面位移、桥面转角的影响。分析结果显示:考虑竖向地震动后,全桥支座的纵、横向剪切力均有增长,各支座竖向力的变化幅度均很明显,尤其以桥台处支座最为显著;桥台处支座更容易出现剪切、挤压破坏或脱空;由于竖向地震动作用,支座的临界剪切力增大,使其约束作用增强,导致桥面纵、横向位移减小,主梁与桥台、挡块之间的碰撞效应明显减弱,桥面的旋转程度呈现较大降低。

小角度斜交上跨铁路异型T构桥受力分析研究

随着铁路大规模的建设,线路间的小角度斜交交叉穿越不可避免。当桥下净空受限时,常用的门式刚构方案存在不适用性。本文结合西十高铁西安东站动走线上跨西十正线工程,将门式墩与小T构梁结合,采用空间异型框架T构梁桥满足净空受限情况下的线路间小角度斜交跨越。建立了全桥三维整体模型、纵向计算模型、横梁局部模型等有限元模型,通过不同模型间的比较,分析了异型框架T构梁桥的纵、横向受力计算方法,对纵向模型、局部横梁模型的适用性进行了论证,并对常用的局部横梁模型进行刚度修正,提出了修正刚度后的局部横梁模型。修正后的横梁局部模型受力明确,计算结果与三维空间模型一致,可满足设计计算要求。

空心板桥跨中横向分布系数分析

为探索空心板桥横向分布系数的变化规律及影响因素,采用有限元分析软件Midas Civil 2020建立空心板桥的有限元模型,研究宽跨比及斜交角对装配式空心板桥横向分布系数的影响。结果表明:车辆荷载作用下,随着空心板桥宽跨比的增大,各板横向分布系数整体减小,车辆荷载作用的偏载侧板的横向分布系数变化较非偏载侧平缓;随着斜交角的变大,偏载侧板横向分布系数变大,非偏载侧板的横向分布系数变小;空心板桥斜交角不大于20°时,偏载侧各板横向分布系数增量均小于5%,在实际工程中可近似忽略,超过30°时对荷载分配影响较大,分析时不可忽略。

涉河斜交桥梁壅水特性分析

通过建立二维数学模型,模拟研究了涉河斜交桥梁在不同斜交角度下的壅水及水动力特征。模拟结果表明:在河道宽深比偏小的情况下,保持桥跨不变,随着桥墩布置与水流垂向夹角增大,桥前最大壅水和建桥前后的流速差呈增大趋势,且斜交角越大,增大趋势越强。流速偏转角则随斜交角度的增大先增大后减小,极大值出现在45°左右。工程建设前后桥墩周围流速差的分布规律随斜交角变化,当斜交角度小于等于45°时,工程前、后的流速增大区主要集中在桥孔和近河道两岸的下游地带;当斜交角大于45°时,工程前、后流速变化区主要集中在河道两岸近岸地带及下游桥墩墩周,下游桥墩一侧的近岸上游地带以及上游桥墩一侧的近岸下游地带变化区域显示出较强的对称性。研究成果可为桥梁布设、桥梁壅水、桥梁冲刷和护岸等工程措施提供借鉴。

斜弯T梁桥横隔板布置力学性能研究

目前,针对斜弯T梁桥横隔板布置的研究较少,为研究横隔板布置对桥梁力学性能的影响、优化斜弯桥横隔板布置,文章结合桥梁博士梁格模型,对不同横隔板道数、不同跨径及不同中隔板布置方式的正交、斜交桥梁开展受力分析。研究表明,25 m跨T梁布置2道隔板为宜,30 m、40 m跨T梁布置3道中横隔板为宜;对于正交、斜交桥梁,采用中隔板正布方式,受力性能均优于采用中隔板斜布。

装配式斜转正桥梁结构受力分析

受桥下道路条件及经济因素影响,斜转正桥梁的应用越来越广泛。斜转正桥梁同一跨各片梁的长度差异较大,通常受到弯扭耦合作用,受力情况比正交桥梁复杂得多,进行桥梁设计时需要分析每片梁的受力情况。文章以广东某高速公路项目为背景,针对高速公路装配式斜转正桥梁建立梁格模型进行受力分析,进而指导斜转正桥梁设计,通过实际项目案例验证装配式斜转正桥梁在高速公路建设中的可行性,旨在为今后类似项目提供参考。

斜交铁路荷载对框架桥应力的影响性分析

以某跨度为9.0m的框架桥为实际工程背景,采用MIDAS FEA NX建立三维实体有限元模型,对框架受列车单双线荷载、列车荷载中线与框架纵向中线的斜交角度(分别考虑0°、10°、20°、30°、45°,共5种情况)等力学性能影响因素进行数值分析,对比各个工况下的应力结果,从而确定框架最不利荷载情况。研究结果表明:当斜交角度相同时,双线列车荷载对框架顶板和竖墙产生的拉应力和压应力更大;当列车荷载中线与框架纵向中线的斜交角度由0°增至45°,角度等于20°时,框架顶板和竖墙的拉应力和压应力最大。

斜弯T梁桥横隔板配筋优化研究

为研究多种跨径斜弯T梁桥的横隔板力学性能,优化横隔板的配筋布置,文章针对T梁跨径、T梁结构形式及中隔板布置方式,采用桥梁博士建立梁格模型开展横隔板受力分析。研究表明,25 m、30 m、40 m长的跨梁桥斜交30°T梁正布横隔板与正交T梁正布横隔板易出现最大不利荷载和最大裂缝,采用不同布置方式的横隔板力学性能有一定的差异,但其选配配筋接近,在实际设计中按最不利情况选配钢筋,既可保障结构安全,又能提高工程经济效益。该研究成果可为同类型的斜弯桥设计提供参考。

斜交连续箱型钢混组合梁受力性能分析

文章以深圳外环高速一座(47+47)m斜交连续箱型钢混组合梁为工程背景,采用Midas Civil有限元软件分别建立单梁模型和梁格模型,对比分析了结构支反力、变形及纵横向应力变化情况,给出了两种模型的受力特性差异,得出单梁法不能准确反映横向各纵梁之间差异的结论。同时分析构造设计对主梁受力的变化的影响,结论可作为同类型桥梁设计的指导。