Statistical analyses of effective lengths in steel arch bridges

This study conducts a quantitative investigation of the effective lengths of arch bridges using three-dimensional buckling and statistical analyses. Three analytical models of parabolic steel arch bridges including inclined, tied and deck-type arch bridges were studied. This paper indicates that changing bridge boundary conditions to force the global translation mode being the first mode can be used to obtain the effective lengths in the two local directions. Moreover, assuming a constant axial force of the arch to perform the buckling analysis is acceptable. Then, more than 25,000 three-dimensional buckling analyses with a broad range of bridge parameters were performed to obtain six statistical formulas with acceptable accuracy. The numerical results also indicate that the effective length estimated by the AASHTO specifications is conservative.     

曲线梁桥在车辆载荷下的动力响应研究

近年来随着我国公路交通的快速发展,曲线梁桥被大量工程采用.车辆过桥时的曲线桥振动涉及车辆三向载荷和桥梁弯扭耦合振动,有必要对其进行精确建模并深入研究.本文以某五跨连续曲线箱梁桥为背景,采用ABAQUS有限元软件建立该桥梁的模型,并利用Adams建立了三轴重型汽车整车模型,计算得到了不同工况下的轮胎力.通过编写基于Fortran语言的DLOAD和UTRACLOAD荷载子程序,将六个轮胎载荷作用于曲线桥上,分别进行了不同曲率半径、车速、载重和路面不平顺等条件下的曲线梁桥振动响应计算.研究表明:随着曲率半径的增加,桥梁跨中位移呈现略微下降的趋势;车辆行驶速度对跨中的横向位移及支座的支反力有较大影响;路面不平度等级越高,桥梁竖向挠度及弯矩的冲击效应越大.     

Stability and load-carrying capacity of three-dimensional long-span steel arch bridges

The behavior of several models of three-dimensional long-span steel arch bridges is investigated for evaluating the effects of various design parameters on both the strength and stability of these special structures. The major concerns in the design of a long-span steel arch bridge, from the structural safety point of view, are the yield and buckling failures. Different design parameters may affect the failure load for either type of failure in various ways. This study investigates how changes in certain design parameters would affect the behavior of steel arch bridges, which could lead to an optimum design of this type of bridge structures. The effects of the plate girder stiffness and arch bracing stiffness as well as the rise-to-span ratio and inclination of the arches towards each other are examined in this study. Both critical buckling load and the load-carrying capacity of each design alternative are investigated using the finite element method. All design alternatives are based on the latest AASHTO code for highway bridge design. It is concluded from this study that the inclined arch bridge using the maximum practical rise-to-span ratio (which is about 0.25) is the most favorable design. In addition, the increase in the stiffness of the plate girder does not reduce the bending moments in the arch ribs. However, providing a lateral bracing system with sufficient stiffness greatly reduces the out-of-plane bending moments and increases the load-carrying capacity and the critical buckling load of a long-span arch bridge.     

Design/analysis of curved box girder bridges

A computer program has been developed which will automatically design or analyze simple or multispan composite or non-composite steel box girder bridges for highway systems. Complete force and stress envelopes are presented in addition to comparative AASHTO code requirements. Influences due to distortion and warping are included in the analytical technique.     

基于板单元形函数的公路桥梁车桥耦合振动分析方法研究

为研究公路多片式梁桥的车桥耦合振动问题,提出一种基于矩形薄板形函数的车桥耦合振动分析方法.该方法以车轮与桥面接触点为界,将车桥耦合系统分为汽车与桥梁2个子系统,分别采用虚功原理与有限元法建立各自的运动方程,并通过车轮与桥面接触处的位移协调条件及车桥相互作用力的平衡关系相耦合,采用矩形薄板形函数实现车桥接触点位移与桥梁节点位移的联系以及车桥相互作用力的分配,通过迭代求解汽车和桥梁的运动方程得到其动力响应.根据分析方法的计算流程,编制了汽车 桥梁耦合系统的动力分析程序,并通过算例分析验证其可行性.研究结果表明,使用基于矩形薄板形函数的公路桥梁车桥耦合振动分析方法得到的车桥动力响应具有较好的精度,该方法具有广泛的适用性,可为多片式梁桥的车桥耦合振动分析提供一种新思路.     

Reliability validation of multigirder steel bridges designed by LRFD

The reliability index is examined for steel girder highway bridges designed by AASHTO load and resistance factor design (LRFD) Strength I limit state. The reliability analysis is based on the extensive stochastic finite element method (SFEM). The SFEM takes advantages of the conventional advanced first-order second-moment in that it considers the mechanic connection between the critical member and other members in the whole structure. The bridges are modeled as grillage beam systems. Basic design variables include sectional properties and various dead and live loads. The results obtained in noncomposite steel bridges indicate that the reliability index is very sensitive to the lateral distribution of live loads. Consequently, a simplified method is used in the reliability analysis of composite steel bridges. This simplified method can avoid the complex computation in SFEM yet achieve good accuracy. Due to overestimating the lateral distribution of live loads, the Strength I limit state in AASHTO LRFD specifications results in a conservative design for flexure but not for shear.     

Architecture of a coupled expert system for optimum design of plate girder bridges

A prototype knowledge-based expert system has been developed for optimum design of steel plate girders used in highway bridges. This expert system, called PG-BRIDGE1, is a coupled system in which AI-based symbolic processing is combined with the traditional numerical processing. Plate girders can be unstiffened or stiffened with single- or doublesided transverse stiffeners. They can be homogeneous or hybrid, made of high-strength flange plates and low-strength web plate. A mathematical optimization algorithm has been developed for minimum weight design of plate girders using the generalized geometric programming technique. The basis of design is the American Association of State Highway and Transportation Officials (AASHTO) specifications. The plate girders are subjected to the live (moving) loads of the AASHTO specifications. The knowledge base and symbolic processing has been developed using the Expert System Development Environment (ESDE). Numerical processing for structural analysis, optimization algorithm and graphics interface have been developed in FORTRAN 77.     

Wavelet domain analysis for identification of vehicle axles from bridge measurements

Bridge weigh-in-motion (B-WIM) is a process by which the axle and gross vehicle weights of vehicles travelling at highway speeds can be determined from instrumented bridges. The traditional method of attaching strain transducers to the soffit of the bridge and placing axle detectors on the road surface has been replaced here by using additional transducers underneath the bridge for axle detection and nothing-on-the-road (NOR). This paper presents a wavelet based analysis of strain signals and shows the efficacy of using wavelets in pattern recognition of these signals. The transformed signals are used to identify axle passage and hence the vehicle velocity and the axle spacing. In addition to numerically generated strains, signals acquired from such a NOR instrumentation of a bridge in Slovenia have been analysed by the method of wavelet transformation to extract axle position information that was not readily detectable using existing methods.     

Computer aided design of prestressed concrete highway bridges

The paper presents a computer aided design system for prestressed concrete highway bridges which, starting from few geometrical data, provides the complete geometry, prestressing steel, reinforcing steel, amount of materials and cost of all the bridge elements: deck, bearings, piers, abutments and foundations. Different configurations are devised, from short and medium to long-span bridges, accounting for different deck super-structures and erection methods. All the results are displayed on the computer screen and can be printed. The system provides also DXF files containing the general layout, cross-sections and prestressing arrangement of box girder bridges. This system allows, in a short time, an accurate design and an economical estimation of a particular bridge, taking into account the most important technical requirements. It is a useful decision-making tool for both design and administration engineers.     

Load distribution on highway bridges using ICES-STRUDL finite element analysis

The development of refined finite element models for the analysis of a concrete slab on steel beam highway bridges is presented in this paper. This paper summarizes the process by which a refined finite element analysis was applied to bridge superstructures using ICES-STRUDL. This process will assist bridge engineers and researchers in predicting the actual stress distribution and evaluating the load transfer to beams from designed vehicle loads on highway bridges.     

Analytical dynamic impact study based on correlated road roughness

The dynamic behavior of multigirder bridges under heavy trucks is investigated based on correlated road surface roughness. Four prestressed concrete bridges with span lengths ranging from 9.14 to 42.67 m (30 to 140 ft) are modeled as grillage beam systems. 3D nonlinear mathematical models for typical trucks are developed based on weigh-in-motion measurement data. These data were collected at two stations located on interstate highway 75 and 95, respectively, for a period of one week. There are a total number of truck counts of 21,444 processed in this study. The longitudinal road surface roughness is generated as correlated random processes along the deck transverse direction. Based on the results from field measurements, the spatial coherence function of these roughness profiles is approximately taken as a constant. Analytical results indicate that (1) the mean values of dynamic impact factors induced by heavy trucks are generally less than the values specified by the American Association of State Highway and Transportation Officials Specifications; and (2) the impact factors generally increase with the coefficient of correlation of road surface roughness.     

Analysis of slab-on-girder bridges

Grid models of three short-span steel girder bridges are developed and analyzed. The techniques used to develop grid models are discussed. Stresses and deflections from the grid analyses are compared to results of field load tests of the bridges. It is found for all three bridges that the grid analyses are able to reproduce the maximum measured stresses within 30%. The grid analysis results are also compared to results from the AASHTO wheel load distribution factor method for two of the bridges. The grid analysis results were found to match the measured results more closely in both cases.     

Computer simulation and field measurement of dynamic pavement loading

Two methods, i.e. computer simulation and field measurement, are used in this paper to investigate dynamic pavement loading (DPL) generated by vehicle–pavement interaction. A profilometer is used for measuring road surface roughness. Based on the power spectral density of the measured surface roughness, a computer simulation program is developed using quarter vehicle model. In field measurement methods, an experiment is designed to gain the time history of DPL. An IVECO vehicle is taken as a test vehicle and eight vibration cells were used to pick up vertical accelerations of vehicle body and axle. The test data are collected and recorded while the test vehicle is moving along 11 different pavement sections of highway and bridge at six different speeds. Statistical characteristics of vertical accelerations and DPL of the test vehicle are obtained and analyzed by means of random process theory. The result of computer simulation matches the result of field measurement very well. It is found that DPL is primarily concentrated between 1.8 and 14.8 Hz and coefficient of variation of DPL falls into the range of 5–35% of static vehicle load. An approximate relationship between coefficient of variation of DPL and vehicle speed and road surface roughness is established.     

Maximum Acceleration for the Vibration of Single Span Bridges with Even and Uneven Decks

The maximum acceleration response of even and uneven single span bridges is studied to find the effect of different influencing parameters. The bridge is modeled as a single span beam with even and uneven decks. The vehicle is modeled as a single degree of freedom sprung mass with constant speed. The unevenness is assumed to be a deterministic profile in the shape of a sinusoidal wave. The maximum acceleration responses considering the effect of varying bridge parameters and vehicle parameters are compared.     

An ergonomics approach to the problem of high vehicles striking low bridges

The incidence of high vehicles striking low bridges has increased considerably since about 1970. Now, between 400-500 such accidents occur every year. This study investigated two possible reasons for the accidents. These were drivers' knowledge of their vehicle heights, and drivers' understanding of the low bridge warning signs. Drivers' opinions of ways of preventing the accidents were also obtained. Only 12% of drivers were correct in their estimate of their vehicle height and 27% were within 3 in (76 mm) of the correct height. The majority of drivers made estimates which erred on the 'safe' side. 21% of drivers did not understand the road sign that shows 'Headroom at hazard ahead'. The ways of preventing high vehicles striking low bridges most popular with the drivers were those which provided them with information which was most directly relevant, ie, whether or not the vehicle would get safely under the bridge.     

Comparison of numerical techniques for 3D flutter analysis of cable-stayed bridges

This paper presents the results of a comparison study of the numerical techniques of structural and aerodynamic force models developed based on the spline finite strip method with the conventional finite element approach in three-dimensional flutter analysis of cable-stayed bridges. In the new formulation, the bridge girder is modelled by spline finite strips. The mass and stiffness properties of the torsional behaviour of complex bridge girder, which have a significant influence on the wind stability of long-span bridges, are modelled accurately in the formulation. The effects of the spatial variation of the aerodynamic forces can be taken into account in the proposed numerical model by distributing the loads to the finite strips modelling the bridge deck. The numerical example of a 423 m long-span cable-stayed bridge is presented in the comparison study. The accuracy and effectiveness of the proposed finite strip model are compared to the results obtained from the equivalent beam finite element models. The advantages and disadvantages of these different modelling schemes are discussed.     

横风下桥梁高度对高速列车交会性能的影响

为研究横风下桥梁高度对高速列车会车性能的影响,基于空气动力学和列车系统动力学,分析指数风分布下不同高度桥梁周围的流场,建立高速列车多体系统动力学模型,模拟横风下列车在不同高度桥梁上会车时的表面压力特性和气动载荷特性.将得到的气动力作为外加载荷作用于列车上,分析桥梁高度对高速列车会车安全性能的影响.结果表明:当列车在环境风下交会时,背风侧列车的气动力波动大于迎风侧列车的气动力波动;当监测点风速固定且桥梁高度小于15 m时,随着桥梁高度的增加,列车的气动载荷最大幅值和安全指标最大幅值均有所减小;当桥梁高度为15～30 m时,随着桥梁高度的增加,列车的气动性能和动力学性能基本保持不变.     

Trajectory planning and yaw rate tracking control for lane changing of intelligent vehicle on curved road

The lateral control for lane changing of intelligent vehicle on curved road in automatic highway systems was studied. Based on trapezoidal acceleration profile, considering the curvature difference between starting lane and target lane, a new virtual trajectory planning method for lane changing on curved road was presented, and the calculating formulas for ideal states of vehicle in the inertial coordinate system during a lane changing maneuver were established. Applying the predetermined trajectory, the re...     

Optimization of continuous steel plate girder bridges

The minimization method and structural optimization approach used in the SPGBROD program for the optimization of continuous steel plate girder highway bridges are briefly described. The standard optimal design formulation used in the program in discussed. An expression for the maximum deflection of continuous highway bridges is derived in order to form an appropriate deflection constraint equation. The results of some applications of the SPGBROD program are presented.