Dynamic analysis of train–bridge system subjected to non‐uniform seismic excitations

Based on the theory of dynamic wheel–rail interactions, a dynamic model of coupled train–bridge system subjected to earthquakes is established, in which the non‐uniform characteristics of the seismic wave input from different foundations are considered. The bridge model is based on the modal comprehension analysis technique. Each vehicle is modelled with 31 degrees of freedom. The seismic loads are imposed on the bridge by using the influence matrix and exerted on the vehicles through the dynamic wheel–rail interaction relationships. The normal wheel–rail interaction is tackled by using the Hertzian contact theory, and the tangent wheel–rail interaction by the Kalker linear theory and the Shen–Hedrick–Elkins theory. A computer code is developed. A case study is performed to a continuous bridge on the planned Beijing–Shanghai high‐speed railway in China. Through input of typical seismic waves with different propagation velocities to the train–bridge system, the histories of the train running through the bridge are simulated and the dynamic responses of the bridge and the vehicles are calculated. The influences of train speed and seismic wave propagation velocity on the dynamic responses of the bridge–vehicle system are studied. The critical train speeds are proposed for running safety on high‐speed railway bridges under earthquakes of various intensities. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of train dynamics on seismic response of steel monorail bridges under moderate ground motion

This study is intended to investigate the seismic response of steel monorail bridges using three‐dimensional dynamic response analysis. We particularly consider monorail bridge–train interaction when subjected to ground motion that occurs with high probability. A monorail train car with two bogies with pneumatic tires for running, steering and stabilizing wheels is assumed to be represented sufficiently by a discrete rigid multi‐body system with 15 degrees of freedom (DOFs). Bridges are considered as an assemblage of beam elements with 6 DOFs at each node. Modal analysis is used for dynamic response analysis under moderate earthquakes. The seismic response of an advanced monorail bridge that adopts a simplified structural system and composite girders is investigated through comparison with seismic responses of a conventional bridge. The acceleration response of a monorail train is also calculated to investigate the effect of structural types of bridges on the train's dynamic response during earthquakes. Results show that the seismic responses of the advanced bridges are greater than those of the conventional monorail bridge because of the simplified structural system and increased girder weight that is attributable to composite girders of the advanced bridge. Moreover, the train on the advanced bridge shows greater dynamic response than that on the conventional bridge. Observations reveal that the dynamic monorail train system acts as a damper on the monorail bridge. That fact shows that the existing design, which considers a train as additional mass, yields a conservative result. Copyright © 2006 John Wiley & Sons, Ltd.     

Seismic performance evaluation of single damped‐outrigger system incorporating buckling‐restrained braces

The outrigger system is an effective means of controlling the seismic response of core‐tube type tall buildings by mobilizing the axial stiffness of the perimeter columns. This study investigates the damped‐outrigger, incorporating the buckling‐restrained brace (BRB) as energy dissipation device (BRB‐outrigger system). The building's seismic responses are expected to be effectively reduced because of the high BRB elastic stiffness during minor earthquakes and through the stable energy dissipation mechanism of the BRB during large earthquakes. The seismic behavior of the BRB‐outrigger system was investigated by performing a spectral analysis considering the equivalent damping to incorporate the effects of BRB inelastic deformation. Nonlinear response history analyses were performed to verify the spectral analysis results. The analytical models with building heights of 64, 128, and 256 m were utilized to investigate the optimal outrigger elevation and the relationships between the outrigger truss flexural stiffness, BRB axial stiffness, and perimeter column axial stiffness to achieve the minimum roof drift and acceleration responses. The method of determining the BRB yield deformation and its effect on overall seismic performance were also investigated. The study concludes with a design recommendation for the single BRB‐outrigger system.     

Seismic response controlled structure with Active Variable Stiffness system

The Active Variable Stiffness (AVS) system is proposed as a seismic response control system. It actively controls structural characteristics, such as stiffness of a building, to establish a non-resonant state against earthquake excitations, thus suppressing the building's response. It consumes a relatively small amount of energy and maintains the safety of the building in moderate to severe earthquakes. In order to accumulate practical data and investigate them, a building has been constructed as a trial. This paper describes the applied system, the control algorithm, verification of stiffness selection, results of tests for verifying system characteristics, some observed earthquake records and simulation analyses. Responses in controlled and uncontrolled states have been compared to show the effectiveness of the proposed system.     

Identification of soil–structure interaction effect in base-isolated bridges from earthquake records

Identification of system parameters with the help of records made on base-isolated bridge during earthquakes provides an excellent opportunity to study the performance of the various components of such bridge systems. Using a two-stage system identification methodology for non-classically damped systems, modal and structural parameters of four base-isolated bridges are reliably identified using acceleration data recorded during 18 earthquakes. Physical stiffness of reinforced concrete columns, dynamic properties of soil and foundation impedance are found by available theoretical models in conjunction with pertinent information from the recorded accelerographs. Soil–structure interaction (SSI) effect in these bridges is examined by comparing the identified and physical stiffness of the sub-structure components. It is found that SSI is relatively pronounced in bridges founded in weaker soils and is more strongly related to the ratio of pier flexural stiffness and horizontal foundation stiffness than soil shear modulus, G_s, alone. However, substantial reduction in G_s is observed for moderate seismic excitation and this effect should be taken into account while computing foundation impedance.     

Seismic response analysis of an interacting curved bridge–train system under frequent earthquakes

This paper establishes a scheme for the seismic analysis of interacting vehicle–bridge systems. The focus is on (horizontally) curved continuous railway bridges and frequent earthquakes. Main features of the proposed scheme are (i) the treatment of the dynamics in all three dimensions (3D), employing an additional rotating system of reference to describe the dynamics of the vehicles and a realistic 3D bridge model; (ii) the simulation of the creep interaction forces generated by the rolling contact between the wheel and the rail; and (iii) the integration of the proposed scheme with powerful commercial finite element software, during the pre‐processing and post‐processing phases of the analysis. The study brings forward the dynamics of a realistic vehicle–bridge (interacting) system during seismic shaking. For the (vehicle–bridge) case examined, the results verify the favorable damping effect the running vehicles have on the vibration of the deck. By contrast, the study stresses the adverse influence of the earthquake‐induced bridge vibration on the riding comfort but, more importantly, on the safety of the running vehicles. In this context, the paper unveils also a vehicle–bridge–earthquake timing problem, behind the most critical vehicle response, and underlines the need for a probabilistic treatment. Among the 20 sets of historic records examined, the most crucial for the safety of the vehicles are near‐fault ground motions. Finally, the study shows that even frequent earthquakes, of moderate intensity, can threaten the safety of vehicles running on bridges during the ground motion excitation, in accordance with recorded accidents. Copyright © 2016 John Wiley & Sons, Ltd.     

Hysteretic model development and seismic response of unbonded post‐tensioned precast CFT segmental bridge columns

The study investigated the cyclic behavior of unbonded, post‐tensioned, precast concrete‐filled tube segmental bridge columns by loading each specimen twice. Moreover, a stiffness‐degrading flag‐shaped (SDFS) hysteretic model was developed based on self‐centering and stiffness‐degrading behaviors. The proposed model overcomes the deficiency of cyclic behavior prediction using a FS model, which self‐centers with fixed elastic and inelastic stiffnesses. Experimental and analytical results showed that (1) deformation capabilities of the column under the first and second cyclic tests were similar; however, energy dissipation capacities significantly differed from each other, and (2) the SDFS model predicted the cyclic response of the column better than the FS model. Inelastic time‐history analyses were performed to demonstrate the dynamic response variability of a single‐degree‐of‐freedom (SDOF) system using both models. A parametric study, performed on SDOF systems subjected to eight historical earthquakes, showed that increased displacement ductility demand was significant for structures with a low period and low‐to‐medium yield strength ratio and reduced displacement ductility demand in these systems was effectively attained by increasing energy dissipation capacity. Copyright © 2008 John Wiley & Sons, Ltd.     

上海浦东国际机场T2航站楼弹塑性时程分析

上海浦东机场T2航站楼结构为复杂大跨混合结构,本文采用NosaCAD2005有限元程序建立结构分析模型,模型主要由非线性杆单元组成,包括梁、柱和二力杆单元,梁、柱采用三段变刚度杆模型,以受弯为主的梁单元截面弯矩-曲率关系采用二折线和三折线模型,柱和二力杆截面采用纤维模型。通过多遇和罕遇烈度下的弹塑性时程分析,研究了该结构的变形、内力、破坏情况的发展历程。计算结果表明,该结构可以满足"小震不坏,大震不倒"的设防要求。     

Performance-based semi-active control algorithm for protecting base isolated buildings from near-fault earthquakes

Base isolated structures have been found to be at risk in near-fault regions as a result of long period pulses that may exist in near-source ground motions.Various control strategies,including passive,active and semi-active control systems,have been investigated to overcome this problem.This study focuses on the development of a semi-active control algorithm based on several performance levels anticipated from an isolated building during different levels of ground shaking corresponding to various earthquake hazard levels.The proposed performance-based algorithm is based on a modified version of the well-known semi-active skyhook control algorithm.The proposed control algorithm changes the control gain depending on the level of shaking imposed on the structure.The proposed control system has been evaluated using a series of analyses performed on a base isolated benchmark building subjected to seven pairs of scaled ground motion records.Simulation results show that the newly proposed algorithm is effective in improving the structural and nonstructural performance of the building for selected earthquakes.     

Numerical analysis on seismic response of Shinkansen bridge-train interaction system under moderate earthquakes

This study is intended to evaluate the influence of dynamic bridge-train interaction (BTI) on the seismic response of the Shinkansen system in Japan under moderate earthquakes. An analytical approach to simulate the seismic response of the BTI system is developed. In this approach, the behavior of the bridge structure is assumed to be within the elastic range under moderate ground motions. A bullet train car model idealized as a sprung-mass system is established. The viaduct is modeled with 3D finite elements. The BTI analysis algorithm is verified by comparing the analytical and experimental results. The seismic analysis is validated through comparison with a general program. Then, the seismic responses of the BTI system are simulated and evaluated. Some useful conclusions are drawn, indicating the importance of a proper consideration of the dynamic BTI in seismic design.     

On the physical model of earthquake precursor fields and the mechanism of precursors’ time-space distribution — origin and evidences of the strong body earthquake-generating model

According to the requirement of the project “Establishment of the Physical Model of Earthquake Precursor Fields”, this paper elucidates the train of thinking for research on the project and some scientific problems which must be studied; the elucidation emphasizes that the core of this project is to study the conditions and processes of the generation of strong earthquakes. The paper first outlines the origin and development of the “strong-body earthquake-generating model” proposed by the author in the 1980’s; and then proves the reasonableness of the model from three aspects, namely: deep structures, mechanical analysis and rock fracture experiments. By studying the tomographic image for the northern part of North China, it can be seen that the sources of strong earthquakes are all distributed in high-velocity bodies, or in the contact zone between high-velocity and low-velocity bodies but nearer to the high-velocity body. It has been affirmed through studies of the mechanical models of hard and soft inclusions that the existence of a hard inclusion is an important condition for the high concentration of large amounts of strain energy. A lot of theoretical and experimental studies have been made to investigate the conditions for rock instability; the results have consistently indicated that rock instability, sudden fracture and stress drop would be possible only if the stiffness of the source body is greater than the environmental stiffness.     

基于含耗能梁段钢框筒侧向力分布的影响比较

含可更换剪切型耗能梁段钢框筒是一种新型消能减震结构,利用部分裙梁跨中耗能梁段集中塑性变形,方便震后快速替换和结构功能恢复。利用时程分析进行该结构截面的初选计算成本高,常用侧向力分布方式与时程分析的分析结果差异以及对该结构设计安全性的影响需要评估。利用SAP2000软件对1个30层含耗能梁段钢框筒进行了双向地震下的时程分析和五种侧向力分布方式的Pushover分析,并比较了"三水准"下的楼层位移、层间位移角、层剪力、层倾覆弯矩、性能点,以及大震下的柱轴力、塑性铰分布,并评价了各侧向力分布方式的影响和给出了该结构的一些设计建议。研究表明:各侧向力分布在含耗能梁段钢框筒的性能评估中有一定的参考价值,单一侧向力分布均不足以预估它的性能,宜考虑两种或多种侧向力分布来评估其性能;大震下各侧向力分布的最大层间位移角明显高于时程均值,各侧向力分布下结构的延性系数约为2;在含耗能梁段钢框筒的初步设计中,可根据均匀分布、SRSS分布、高度等效分布初选构件截面,最后宜采用时程分析对截面进行校核。     

Development of collapse-consistent loading protocols for experimental testing of steel columns

In order to effectively utilize results from quasi-static cyclic testing on structural components for the earthquake-induced collapse risk quantification of structures, the need exists to establish collapse-consistent loading protocols representing the asymmetric lateral drift demands of structures under low-probability of occurrence earthquakes. This paper summarizes the development of such protocols for experimental testing of steel columns prone to inelastic local buckling. The protocols are fully defined with a deformation- and a force-controlled parameter. They are generally applicable to quantify the capacity and demands of steel columns experiencing constant and variable axial load coupled with lateral drift demands. Through rigorous nonlinear earthquake collapse simulations, it is found that the building height, the column's local slenderness ratio, and ground motion type have the largest influence on the dual-parameter loading protocol indexes. Comprehensive comparisons with measured data from full-scale shake table collapse tests suggest that unlike routinely used symmetric cyclic loading histories, the proposed loading protocol provides sufficient information for modeling strength and stiffness deterioration in steel columns at large inelastic deformations.     

Modeling of RC columns strengthened with RC jackets

Constructing concrete jackets is a common technique when strengthening reinforced concrete (RC) columns, particularly in seismic regions. However, there are many uncertainties concerning the behavior of the composite specimen, particularly at the interface between the old and new concrete. In this paper, monotonic finite element (FE) analyses are performed to examine the behavior of strengthened columns under monotonic and cyclic loading. Through investigating two independent series of experimental results, it is demonstrated that monotonic FE analysis with appropriate assumptions can simulate both monotonic and cyclic loading conditions to a reasonable degree of accuracy. According to the results of this study, it is found that a simulation of the interface between the old and the new concrete is vital and cannot be ignored by simply considering a perfect bond at the interface. In the case of strengthened RC columns subjected to cyclic loading, strength degradation at the interface has to be included and can be effectively modeled by reducing the coefficients of friction and adhesion by using a proposed formula. Finally, the effect of jacket concrete shrinkage is simulated that leads to a reduced maximum load and stiffness of strengthened columns. Copyright © 2011 John Wiley & Sons, Ltd.     

Simplified design method and seismic performance of space trusses with consideration of the influence of the stiffness of their lower supporting columns

Static and dynamic force performance of two types of space truss structures i.e. square pyramid space truss (SPST) and diagonal on square pyramid space truss (DSPST), are studied to determine the effect of stiffness of their lower supporting members. A simplified model for the supporting columns and the equivalent spring mass system are presented. Furthermore, the feasibility of the simplified model is demonstrated through theoretical analysis and examples of comparative analysis of the simplified model with the entire model. Meanwhile, from the elastic analysis under frequently occurring earthquakes and elasto-plastic analysis under seldom occurring earthquakes subjected to TAFT and EL-Centro seismic oscillation it is shown that the simplified method can be encompassed in the results from the normal model. It also showed good agreement between the two methods, as well as greatly improved the computational efficiency. This study verified that the dynamic effect of the supporting structures was under considered in space truss design in the past. The method proposed in the paper has important significance for other space truss structures.     

Damage‐dependent vulnerability curves for existing buildings

Seismic behavior of damaged buildings may be expressed as a function of their REsidual Capacity (REC), which is a measure of seismic capacity, reduced by damage. REC can be interpreted as the median value of collapse vulnerability curves. Its variation owing to damage is a useful indication of increased building vulnerability. REC reduction, indicating the lowering of seismic safety after an earthquake (performance loss, PL), represents an effective index for assessing the need of seismic repair/strengthening after earthquakes. The study investigates the applicability of a pushover‐based method in the analysis of damaged structures for the case of existing under‐designed RC buildings. The paper presents a systematization of the procedure in an assessment framework that applies the capacity spectrum method based on inelastic demand spectra; furthermore, the vulnerability variation of a real building is investigated with a detailed case study. The behavior of damaged buildings is simulated with pushover analysis through suitable modification of plastic hinges (in terms of stiffness, strength and residual drift) for damaged elements. The modification of plastic hinges has been calibrated in tests on nonconforming columns. The case study analysis evidenced that, for minor or moderate damages, the original structural displacement capacity was only slightly influenced, but the ductility capacity was significantly reduced (up to 40%) because of the increased structure deformability. This implied performance loss in the range 10%–20%. For severe damages the PL ranged between 41% and 56%. Local mechanism types exhibit PL nearly double with respect to global mechanism types. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental investigation of railway train-induced vibrations of surrounding ground and a nearby multi-story building

In this paper, a field experiment was carried out to study train-induced environmental vibrations. During the field experiment, velocity responses were measured at different locations of a six-story masonry structure near the Beijing-Guangzhou Railway and along a small road adjacent to the building. The results show that the velocity response levels of the environmental ground and the building floors increase with train speed, and attenuate with the distance to the railway track. Heavier freight trains indu...     

高铁震源地震信号的挤压时频分析应用

我国每天有数千趟高铁列车驰骋在纵横交错的高铁线路上,构成了十分理想的均布震源,但寻找适合高铁震源地震信号的处理方法是充分挖掘信息的关键.传统的频谱分析结果表明高铁震源所产生的地震信号具有明显的窄带分立谱特征,但无法精确获得高铁震源地震信号的时频变化规律.本文首次将挤压时频分析这种分析工具引入到高铁震源地震信号处理中,对中国南方某高铁沿线采集到的高铁震源地震数据进行了分析.处理结果表明:利用挤压时频分析能够更加精确地刻画频率成分随时间的变化,能够利用单检波器精确刻画高铁列车的运行状态(匀速、加速等);同时利用挤压时频变换还可高精度地重构出所需频带的信号,为提取高铁震源地震信号的特征成分提供了一种有力工具.     

基于最小二乘支持向量机算法的高层建筑结构的强震抗毁性估计模型

采用现有的估计模型对混凝土建筑结构的抗毁性进行估计时,存在估计精度低、耗时长等问题。为此,提出一种基于最小二乘支持向量机的强震作用下混凝土高层建筑结构的抗毁性估计模型。该模型采用最小二乘支持向量机对混凝土结构强震损伤程度相关数据的训练样本进行训练,创建混凝土结构抗毁性估计模型;为了减少可能存在的模型误差,采用KLASSO调参模型对结构抗毁性估计模型中的参数进行调节和优化,得出可靠、稳定的强震作用下混凝土高层建筑结构抗毁性估计模型。仿真实验证明,该模型估计精度相对较高,可节省估计用时,为更好地提升建筑行业的安全检测工作效率提供很好的依据。     

Dynamic interaction of bridge–train system under non‐uniform seismic ground motion

The probability that an earthquake occurs when a train is running over a bridge in earthquake‐prone regions is much higher than before, for high‐speed railway lines are rapidly developed to connect major cities worldwide. This paper presents a finite element method‐based framework for dynamic analysis of coupled bridge–train systems under non‐uniform seismic ground motion, in which rail–wheel interactions and possible separations between wheels and rails are taken into consideration. The governing equations of motion of the coupled bridge–train system are established in an absolute coordinate system. Without considering the decomposition of seismic responses into pseudo‐static and inertia‐dynamic components, the equations of motion of the coupled system are formed in terms of displacement seismic ground motions. The mode superposition method is applied to the bridge structure to make the problem manageable while the Newmark‐β method with an iterative computation scheme is used to find the best solution for the problem concerned. Eight high‐speed trains running over a multi‐span steel truss‐arch bridge subject to earthquakes are taken as a case study. The results from the case study demonstrate that the spatial variation of seismic ground motion affects dynamic responses of the bridge–train system. The ignorance of pseudo‐static component when using acceleration seismic ground motions as input may underestimate seismic responses of the bridge–train system. The probability of separation between wheels and rails becomes higher with increasing train speed. Copyright © 2011 John Wiley & Sons, Ltd.