Seismic retrofit of square reinforced concrete piers by ferrocement jacketing

An experimental investigation was conducted to strengthen shear deficient reinforced concrete columns using ferrocement jacketing. Three scale model specimens, identical to the actual bridge piers, were tested. One of the piers was tested under as-built condition while the other two were strengthened with layers of wire mesh before being tested. All the specimens were subjected to a simulated seismic loading and constant axial load. It was observed from the experimental results that the ferrocement-jacketed specimens exhibited enhanced stiffness, strength, energy dissipation and ductility and the mode of failure changed from brittle shear failure to a ductile flexural failure. The control specimens failed by shear at a relatively low lateral displacement. A finite element model was developed and the results obtained from the numerical analysis compared well with the experimental results. A design methodology for strengthening piers with square/rectangular columns with inadequate shear strength using ferrocement jackets is also presented.     

Seismic performance of new-type box steel bridge piers with embedded energy-dissipating shell plates under tri-directional seismic coupling action

Accurate numerical models are necessary to evaluate the seismic performance and load-bearing mechanism of new-type box steel bridge piers with embedded energy-dissipating shell plates under tri-directional seismic coupling action. Numerical simulations of seismic performance under six types of tri-directional seismic coupling action was conducted. The effects of this stress on the seismic performance of the new-type steel bridge piers was evaluated through analysis of damage mode, hysteresis curve, skeleton curve, stiffness and strength degradation characteristic, and energy-dissipating capacity. This study also compared the numerical analysis with experimental results in order to validate the accuracy of the proposed finite element model. Based on this model, the range of relevant parameters expanded and 88 numerical specimens were analysed for seismic performance, producing further information about the influence of thickness and curvature of the embedded shell plate, spacing of transverse stiffening ribs of the shell, axial compression ratio, and slenderness ratio. Results showed that tri-directional seismic coupling action significantly affects the specimen’s deformation capacity; the embedded shell plate effectively improves the piers’ load-carrying and deformation capacity; and the thickness of the embedded shell plate, width-to-thickness ratio of the wall plate, axial compression ratio, and slenderness ratio significantly affect the seismic performance of the new-type steel bridge piers. To promote the ease of seismic design of new-type box steel bridge piers, this study used theoretical analysis and numerical simulation to calculate equations for the minimum height of the energy-dissipating zone of the bottom embedded shell plate. Finally, formulas were also established to calculate the relevant stability bearing capacity and displacement ductility factor of the new-type steel bridge piers under tri-directional seismic coupling action in order to improve their seismic design.     

基底摇摆隔震桥墩振动台试验与数值模拟研究

为了研究不同构造形式的基底摇摆隔震桥墩在不同水准地震作用下的响应规律和抗震性能，提出了设置高阻尼橡胶垫块和线性弹簧的两种基底摇摆隔震桥墩模型。通过振动台试验和数值模拟，对两种摇摆隔震桥墩的地震响应规律和抗震性能进行了对比研究。结果表明：两种基底摇摆隔震桥墩在不同水准地震作用后，桥墩均没有出现严重的破坏，其破坏特征主要表现为限位钢板的弯曲变形和提离约束部件的移位，桥墩呈现出良好的抗震性能；两种基底摇摆隔震桥墩相对于传统桥墩能够显著降低墩顶加速度和墩底应变响应，但墩顶水平位移响应也会相应增加，在摇摆隔震桥墩的设计上，应将墩顶水平位移作为主要设计参数；提出了两种基底摇摆隔震桥墩改进的Winkler两弹簧数值计算模型，通过与振动台试验结果对比，证明了该模型能够较好地模拟两种基底摇摆隔震桥墩的摇摆行为及其地震响应规律。     

Driving simulator experiment on the moving stability of an automobile under strong crosswind

In expanding expressway networks in Japan, various types of structures have been constructed, e.g., long span bridges and bridges with high piers. The expressway structures are well designed for the external dynamic forces, e.g., earthquakes and strong winds. However, for further safety promotion of the expressway networks, it is important to evaluate the drivers’ responses under strong dynamic disturbances. The present authors have investigated the moving stability of a vehicle under seismic motion based on both numerical simulation and virtual experiments using a driving simulator. Strong crosswind is considered as another factor that makes it difficult for drivers to control their vehicles. This study investigates the moving stability of a vehicle under strong crosswind based on numerical analyses and driving simulator experiments. To predict the future position of a moving vehicle including the reaction of a driver, the second-order predictable correction model is used in the numerical analyses. The results obtained from the numerical and experimental studies are compared and the validity of the driver model is discussed. It is expected that this research is helpful for the decision-making of expressway closure under strong wind and the design of wind barriers.     

V型墩预应力连续刚构桥结构动力分析和试验研究

义乌市宗泽大桥主桥为三跨预应力混凝土V型墩连续刚构桥。为了检测桥梁结构的动力性能 ,对该桥进行了动载试验。采用四边型板单元的空间有限元方法对其进行动力有关分析 ,并与试验结果进行比较。结果表明 :该桥以竖向弯曲振动为主 ,且实测频率比理论值大。冲击系数的大小与车辆行车速度的相关关系不明显     

基于CSC模型的UHPC构件侧向低速冲击分析

超高性能混凝土(ultra-high performance concrete,UHPC)较普通混凝土具有更优异的强度、韧性和耐久性,广泛应用于桥梁墩柱和建筑承重柱,而上述构件存在车(船)、滚石等侧向低速冲击的潜在威胁,为此,针对UHPC梁/柱构件在侧向冲击下的损伤破坏和动态响应进行数值仿真分析。现有商用模型中广泛采用的混凝土动态本构模型均基于普通混凝土开发,如混凝土损伤(K&C)模型和混凝土连续面帽盖(CSC)模型等。基于作者前期开展的UHPC单轴拉/压、三轴压缩和Hopkinson杆动态拉/压试验,以及已有UHPC双轴等压和静水压试验数据,系统标定了UHPC材料CSC模型的强度面、帽盖、损伤、应变率和硬化参数,给出了一组适用于UHPC的CSC模型参数确定方法。进一步基于LS-DYNA商用有限元分析软件,对已有四组钢管UHPC梁和钢筋UHPC梁/柱构件的落锤冲击试验进行数值模拟,通过对比落锤冲击力、梁/柱动态挠度响应和破坏模式,验证了所提出的CSC模型参数计算方法的适用性和正确性。同时,对冲击过程中刚性落锤与构件之间的作用过程及能量耗散进行了讨论。结果表明：平头落锤冲击下构件经历了惯性抵抗、变形响应、构件回弹和脱离四个阶段;球头落锤冲击构件的惯性抵抗阶段不明显;随着冲击能量的提高,钢管(筋)耗能占比逐渐增大。     

An assessment of the current Eurocode 1 design methods for building structure steel columns under vehicle impact

This paper presents a detailed assessment of the static and dynamic force requirements in Eurocode 1 for the design of steel columns under vehicle impact. Numerical simulations of steel columns under vehicle impact were carried out using the finite element package ABAQUS/Explicit. In these numerical simulations, the vehicle was represented by a spring–mass system which had been validated previously by the authors. The assessment results indicate that the equivalent static design force approach in Eurocode 1 is generally conservative for small and moderately sized columns that are typically used in low and medium multi-storey buildings (less than 10 storeys). For bigger columns, it is unsafe to use the Eurocode 1 equivalent static forces. It has also shown that it is acceptable to use a dynamic impulse to represent the dynamic action of vehicle impact on columns, but it is important that both the column and vehicle stiffness values should be included when calculating the equivalent impulse force–time relationship. It is also necessary to consider the two stages of behaviour of the impacting vehicle, before and after the column is in contact with the vehicle engine. This paper presents a method to implement these changes.     

FE modelling and fire resistance design of concrete filled double skin tubular columns

Concrete filled double skin tubular columns (CFDST) have excellent structural behaviour. They have been used as transmission towers and have potential to be used as building columns and bridge piers. Performance of the CFDST columns under ambient temperature has been well studied, whereas fire resistance of such columns is still a major concern. A summary of a series of fire tests on CFDST columns conducted by the authors is briefly presented in the paper. A finite element numerical model is developed to analyse the fire behaviour of CFDST columns, namely thermal and structural responses under fire exposure. The model is verified by the test results and then used to perform parametric analyses. Parameters which have significant effect on the fire behaviour of CFDST columns are identified. Based on the parametric studies, suggestions on the fire resistance design of such columns are made. Practical design tables are derived for the fire resistance design of some typical CFDST columns.     

Effect of approach span condition on vehicle-induced dynamic response of slab-on-girder road bridges

The present study investigates the effect of approach span conditions on a bridge’s dynamic response induced by moving vehicles. After developing a 3D bridge–vehicle interaction model for numerical prediction, a dynamic test on a full scale slab-on-girder bridge is conducted with dump trucks to validate the developed numerical methodology. A wooden plank is used to simulate the large faulting between the bridge deck and the approach slab. With consideration of the road surface profile and approach span condition, the predicted dynamic response of the bridge is compared to the experimental results, and they show a satisfactory agreement. The numerical model is also applied to investigate the effect of the approach span condition on the dynamic behavior of the bridge induced by the AASHTO HS20 truck. A parametric study is eventually conducted by changing the road surface condition and the faulting value. The faulting condition of the approach span is found to cause significant dynamic responses for the slab-on-girder bridges and to have a considerable effect on the distribution of impact factors along the transverse and longitudinal directions. Furthermore, impact factors obtained from the numerical analyses are compared with those values specified in the AASHTO codes.     

Parametric study of seismic performance of super-elastic shape memory alloy-reinforced bridge piers

One of the important measures of post-earthquake functionality of bridges after a major earthquake is residual displacement. In many recent major earthquakes, large residual displacements resulted in demolition of bridge piers due to the loss of functionality. Replacing the conventional longitudinal steel reinforcement in the plastic hinge regions of bridge piers with super-elastic shape memory alloy (SMA) could significantly reduce residual deformations. In this study, numerical investigations on the performance of SMA-reinforced concrete (RC) bridge bents to monotonic and seismic loadings are presented. Incremental dynamic analyses are conducted to compare the response of SMA RC bents with steel RC bents considering the peak and the residual deformations after seismic events. Numerical study on multiple prototype bridge bents with single and multiple piers reinforced with super-elastic SMA or conventional steel bars in plastic hinge regions is conducted. Effects of replacement of the steel rebar by SMA rebar on the performance of the bridge bents are studied. This paper presents results of the parametrical analyses on the effects of various design and geometric parameters, such as the number and geometry of piers and reinforcement ratio of the RC SMA bridge bents on its performance.     

小尺度立柱水动力系数的数值分析

采用MpCCI耦合器作为ABAQUS和FLUENT的数据交换平台,对不同截面形式桥梁墩柱结构受波浪场作用过程中的流目耦合现象进行数值模拟。计算结果表明,圆形截面与方形截面立柱在波流场中的波浪力拖曳力系数与传统的波浪力计算方法中采用的拖曳力系数相吻合,为后续多柱多截面桥梁基础在流固耦合问题上的扩展研究打下了一定的基础。     

Dynamic stress analysis for fatigue damage prognosis of long-span bridges

For fatigue damage prognosis of a long-span steel bridge, the dynamic stress analysis of critical structural components of the bridge under the future dynamic vehicle loading is essential. This paper thus presents a framework of dynamic stress analysis for fatigue damage prognosis of long-span steel bridges under the future dynamic vehicle loading. The multi-scale finite element (FE) model of the bridge is first developed using shell/plate elements to simulate the critical structural components (local models) and using beam/truss elements to simulate the rest part of the bridge (global model). With the appropriate coupling of the global and local models, the multi-scale FE model can accurately capture simultaneously not only the global behavior in terms of displacement and acceleration but also the local behavior in terms of stress and strain. A vehicle traffic load model is then developed for forecasting the future vehicle loading based on the recorded weigh-in-motion (WIM) data and using the agent-based traffic flow microsimulation. The forecasted future vehicle loading is finally applied on the multi-scale model of a real long-span cable-stayed bridge for dynamic stress analysis and fatigue damage prognosis. The obtained results show that the proposed framework is effective and accurate for dynamic stress analysis and fatigue damage prognosis.     

Photogrammetric measurements of RC bridge column deformations

The determination of the location of nonlinear response in structural systems is an important step to predict the performance of the system under different loading conditions. In bridge columns, these nonlinear deformations generally occur over a finite hinge length. A model of hinging behavior in reinforced concrete bridge columns will help guide proportioning, detailing and drift estimates for performance-based design. Data was collected during the NEESR investigation of the seismic performance of four-span large-scale bridge systems at the University of Nevada Reno that details deformations in column hinging regions during response to strong shaking events. A photogrammetry method was applied using a reference grid on the top and bottom column surfaces to record and analyze deformations in the plastic hinging regions. The method of application in this study holds several advantages over traditional sensors including that it is a remote visualization technique, inexpensive and simple to analyze the results. The surface deformations and rotations of a reinforced concrete bridge column under dynamic loading has been examined and compared with the results obtained from traditional instruments. The photogrammetry method performed very well to track the lateral and vertical displacements at the points on the grid surface as well as the deformed shape of the hinging regions, but the results of secondary calculations, such as rotations of the column, had limited success.     

Seismic performance of precast hollow bridge piers with different construction details

Currently the design scheme of precast hollow concrete bridge piers will be adopted in bridge design in China, but there is no code including specific design details of precast segmental piers in high seismic risk area. For comparative study of seismic performance of the hollow bridge piers which had different design details, six specimens of hollow section bridge pier were designed and tested. The specimens consist of the monolithic cast-in-place concrete bridge pier, precast segmental prestressed pier with cast-in-place joint and precast segmental concrete bridge pier with dry joints. Results show that all specimens have good displacement capacity. The bridge pier with bonded prestressed strands exhibits better energy dissipation capacity and higher strength. The un-bonded prestressed strand bridge pier displays less residual plastic displacement and energy dissipation capacity. The bridge pier with both bonded prestressed strands at the edge of the section and un-bonded in the center of the section not only exhibits more ductility capacity and less residual plastic displacement, but also shows better energy dissipation capacity. Compared with experimental results of prestressed bridge columns, analytical result demonstrates the developed numerical analysis model would provide the reasonable and accurate results.     

高墩大跨连续刚构桥地震反应研究

运用大型结构分析程序Midas／Civil在地震波作用下，对某一实际高墩大跨连续刚构桥的地震反应进行了数值模拟，并利用反应谱分析法分析了高墩大跨连续刚构桥在不同作用方向地震波作用下的内力变化，从而为剐构桥的抗震设计奠定了基础。     

Numerical simulation of concrete filled steel tube columns against BLAST loads

Concrete filled steel tubes (CFST) have been widely used in constructing high-rise buildings, arch bridges and factories for the past few decades. In this research, numerical studies were carried out to investigate the flexural behaviour of CFST columns under both static and dynamic loads. The numerical models were calibrated and validated against a number of experimental data where the proposed models showed very good agreement with the test results. The results indicated that CFST columns showed good resistance against flexural loads under both static and dynamic loading conditions and therefore it has the potential to be widely used in these areas where potential blast attacks or frequent earthquakes are expected. The verified numerical model can also be extended to predict performances of concrete-infilled steel tubes under different loading conditions.     

地震作用下宽箱鱼腹式连续梁桥地震响应分析

为了研究宽箱鱼腹式箱梁在地震作用下的动力特性,对哈尔滨市某立交桥进行动载试验,并用Midas Civil建立有限元模型,分析该桥的动力特性。通过对比理论数据与试验数据,验证模型准确性,在此基础上对模型施加地震荷载,进行非线性时程分析,研究宽箱鱼腹式连续箱梁桥在地震作用下的响应。结果表明:地震作用下宽箱鱼腹式连续梁桥主梁横向抗弯及抗扭性能较好,各阶模态变形以主梁竖弯和桥墩侧弯为主,桥梁墩高对结构的振动响应影响较大,矮墩承受较大的水平地震力,主梁在纵桥向刚度较大,导致主梁和桥墩构件纵桥向地震响应同步。该研究可以为相关类型桥梁抗震设计提供参考依据。     

盾构切削混凝土桥桩刀盘荷载分析

依托北京地铁12号线盾构直接切削西坝河桥16根800桥桩工程,通过三维数值模拟和理论推导,对盾构法清障掘进面荷载展开研究。通过三维动态模拟,分析单个刀具逐次切混凝土荷载变化规律。基于等效原理与单刀切削荷载,提出一种对切桩刀具数、推力及扭矩的估算模型。并将此估算模型用于计算苏州地铁直接切削广济桥掘进面荷载,对比分析计算结果与精确叠加值在推力、扭矩方面的平均误差分别为10%、3.3%,验证了该估算模型的正确性。应用本文模型对盾构穿越西坝河桥各轴桩位掘进面切桩荷载进行预测分析,指出切桩工况主要对扭矩造成影响。研究结果可为类似地层盾构清障工程中掘进面荷载计算提供参考。     

Prediction of vehicle-induced local responses and application to a skewed girder bridge

This paper proposes an innovative and flexible simulation method that predicts the dynamic responses of bridges induced by passing vehicles. The decoupled equations of motion of the vehicle-bridge system are derived from Lagrange equations and include the effect of road surface roughness, while the interaction forces between the two systems are calculated step by step, using Newmark’s method. This algorithm does not require a special finite element (FE) code and can be implemented with standard FE software and general numerical software such as ABAQUS and MATLAB, respectively. In order to illustrate the practicability of the method, an extensive case study is then presented in which some aspects of the dynamic behaviour of a skewed bridge monitored under vehicle-induced loads are investigated. After adjustment of the boundary conditions and the spectral roughness coefficient, good agreement is obtained between the bridge vibrations predicted by the numerical model and the field measurements. The validated model is further used to analyse the distinctive dynamic effects caused by the skewness. For that purpose, a reference non-skewed bridge model is prepared according to the same design as the original skewed bridge. The obtuse corner of the skewed bridge located near the loading path is found to be a critical region where the slab-negative moments, the girder stress near the sole plate and the bearing force are significantly greater than those in the reference bridge.     

Determination of the critical loading conditions for bridges under crossing trains

A procedure based on experimental and theoretical analyses to identify critical loading conditions on existing metallic railway bridges is presented. This method requires knowledge of the principal modal frequencies, and for this reason, a consolidated and simple procedure to study the bridge dynamics is herein explained. This consists of: preliminary studies; material and dynamic tests; and identification techniques to identify modal parameters and eventual non-linear behaviours. Generally the information collected can be used both to calibrate the bridge model and to obtain the refined frequency response function. In order to avoid high computational effort due to long time-history dynamic analyses by using the bridge model subjected to a series of train crossings, a new frequency domain approach for the identification of critical loading conditions is proposed. Evidence of the influence of the axle spacing and velocity of the vehicle on the dynamic magnification due to the train crossing is shown. The method is based on the construction of an excitation spectrum related to the train axle spacing and the velocity, given the weight of the vehicle. Comparison of the excitation spectrum with the frequency response function allows identification of the load patterns that bring the bridge to resonance conditions and might threaten bridge stability, bearing in mind continual changes in train technology.