装配式空心钢管混凝土拱桥可行性研究

为减小大跨度钢管混凝土拱桥自重,提高大跨度钢管混凝土拱桥的施工便利性,提出使用预制空心钢管混凝土构件代替实心钢管混凝土构件作为大跨度钢管混凝土拱桥拱肋的新思想。该文采用有限元分析方法对某特大桥进行了试设计研究,建立空心钢管混凝土拱桥模型和实心钢管混凝土拱桥模型,在不同工况组合条件下,对两者拱肋内力、挠度进行了分析比较,使用现有规范的计算公式进行承载力验算。结果显示:空心钢管混凝土方案与原实心钢管混凝土方案相比,拱肋各杆轴力有明显减少,不同杆件、不同主拱圈截面弯矩有减少亦有增加,不同方案对挠度的影响不大,空心钢管混凝土构件均满足承载力要求。分析结果表明空心钢管混凝土代替钢管混凝土的新思想具有可行性,可以减小大跨度拱桥整体自重,减少混凝土用量,降低拱肋上、下弦杆轴力,在提高大跨度拱桥整体力学性能和经济性方面具有一定优势。     

天津安阳桥设计关键技术

该文介绍了天津安阳桥设计的若干关键技术。天津海河安阳桥桥梁建筑艺术设计优美,造型独特,是天津滨海新区中心商务区的新地标,是桥梁建筑艺术与桥梁结构的完美结合。安阳桥为大跨度空间钢网拱桥,软土地基上大跨度拱桥水平推力是一个技术难题。安阳桥主拱为空间钢网拱,主拱刚度较弱,主拱和主梁的刚度匹配,空间主拱的设计,是另一个技术难题。安阳桥为空间拱桥,安阳桥的抗震和抗风性能又是一个值得研究的课题。     

基于虚拟激励法的大跨度斜拉拱桥随机响应

通过建立空间结构有限元模型,利用一种计算效率很高的随机振动理论—虚拟激励法对大跨度斜拉拱桥的随机振动地震响应进行了研究。将该桥的动力特性以及由施加于该桥纵向激励、纵＋竖向激励、横＋竖向激励、纵＋竖＋横向激励所得到的随机振动地震响应,与相同跨径的钢管混凝土拱桥进行对比分析,可以得到：大跨度斜拉拱桥中斜拉索的存在改善了主拱肋拱脚附近的受力,提高了拱桥的抗震性能。     

基于虚拟激励法的大跨度斜拉拱桥随机响应

通过建立空间结构有限元模型,利用一种计算效率很高的随机振动理论-虚拟激励法对大跨度斜拉拱桥的随机振动地震响应进行了研究.将该桥的动力特性以及由施加于该桥纵向激励、纵 竖向激励、横 竖向激励、纵 竖 横向激励所得到的随机振动地震响应,与相同跨径的钢管混凝土拱桥进行对比分析,可以得到大跨度斜拉拱桥中斜拉索的存在改善了主拱肋拱脚附近的受力,提高了拱桥的抗震性能.     

拱肋内倾角对大跨度钢箱提篮拱桥动力特性及地震响应影响的分析

为研究大跨度钢箱提篮拱桥拱肋内倾角对其动力特性及其地震响应的影响,该文以目前中国最大跨度的南广高速铁路肇庆西江特大桥为工程背景,基于Ansys大型结构分析通用程序建立空间有限元模型,并对计算结果进行对比分析,得出结论:对于大跨度钢箱提篮拱桥,增大拱肋内倾角对于增大结构刚度是有利的,但是在地震作用下也会增加结构的部分内力,降低拱肋的面内极限承载力.因此,在大跨度钢箱提篮拱桥的设计与施工中应综合考虑拱肋内倾角的影响.同时,为考虑不同步激励对大跨度钢箱提篮拱桥地震响应的影响,进一步分析了行波作用下桥梁的地震响应.     

拱式拱上结构钢筋混凝土拱桥极限承载力分析

本文在现有文献资料的基础上进行理论分析和试验研究，将拱式拱上结构钢筋混凝土拱桥平面内承载力分析化为框架问题，考虑几何材料非线性及塑性较的形成，对短期静力荷载作用下影响极限承载力的各主要因素进行了分析。分析表明：大跨长拱桥极限承载力受拱上结构控制，拱上结构验算应考虑主拱变形的影响；小跨径拱桥联合作用显著，应考虑拱上结构对承载力的提高。考虑联合作用可以平衡拱上结构和主拱圈之间的安全度，使主拱圈最省。本文的分析成果可供新建拱桥设计和已建拱桥承载力评定参考。     

考虑河谷场地效应的大跨度拱桥的地震响应分析

为研究V型河谷场地效应对大跨度钢管混凝土拱桥的地震响应影响,以某大跨度钢管混凝土拱桥为工程背景并简化V型河谷场地模型,建立河谷-拱桥有限元模型,讨论在SV波作用下对桥梁的地震响应影响。结果表明:由于地震荷载是均匀作用在场地,且河谷-拱桥有限元模型是轴对称模型,因此得到的拱桥主拱圈的内力和位移响应趋势是对称分布;不同地震波作用下得到的主拱圈内力和位移响应大小不同,这和拱桥拱脚与场地连接部位的地震动强度和地震波的频谱特性有关;在进行桥梁抗震设计时,SV波作用下拱桥关键部位应重点关注。     

落步溪大桥178m劲性骨架混凝土拱桥关键技术研究

宜万铁路落步溪大桥是国内最大跨度(178m)的双线铁路劲性骨架混凝土拱桥.对该桥拱轴线系数的取值,梁、拱和立柱匹配刚度等设计关键技术建立有限元模型进行计算分析,得出了大跨度拱桥的拱轴线系数,梁、拱和立柱匹配刚度的计算原则和方法.     

局部视线遮挡下拱桥线形测量及其对承载力的影响

针对既有拱桥主拱线形测量过程中存在局部视线受遮挡的情况,介绍了一种新的主拱线形测量方法——辅助测量法,并基于此分析了主拱线形测量对其承载力的影响。研究表明:(1)采用该方法能够方便且精确地获取主拱的完整线形;(2)主拱线形对既有拱桥承载力评定具有显著影响,在对既有拱桥进行承载力评定时需要准确获取主拱的实际线形。     

大跨度钢管混凝土拱桥的动力特性分析

通过ANSYS对2座钢管混凝土拱桥例进行动力特性分析,探讨了拱上建筑形式、拱肋倾角、横撑形式和横撑刚度对大跨度钢管混凝土拱桥的动力特性的影响,对深入认识钢管混凝土拱桥动力特性有一定的参考价值。     

Fatigue design for plug/ring type gas welded joints of sts301l including welding residual stresses

This paper presents a fatigue design method for plug and ring type gas welded joints, which incorporates welding residual stress effects. A non-linear finite element analysis (FEA) was first performed to simulate the gas welding process. The numerically predicted residual stresses of the gas welds were then compared to experimental results measured using a hole drilling method. In order to evaluate the fatigue strength of the plug and ring type gas welded joints, a stress amplitude (σ _a ) _R taling the welding residual stress of the gas weld into account was introduced and is based on a modified Goodman equation incorporating the effect of the residual stress. Using the stress amplitude (σ _a ) _R , the ΔP-N _f relations obtained from fatigue tests for plug and ring type gas welded joints having various dimensions and shapes were systematically rearranged into (σ _a ) _R -N _f relations. It was found that the proposed stress amplitude (σ _a ) _R could provide a systematic and reasonable fatigue design criterion for the plug and ring type gas welded joints.     

Non-fragile multi-objective static output feedback control of vehicle active suspension with time-delay

This paper presents an approach to design a delay-dependent non-fragile H_∞/L₂–L_∞ static output feedback (SOF) controller for active suspension with input time-delay. The control problem of quarter-car active suspension with actuator time-delay is formulated to a H_∞/L₂–L_∞ control problem. By employing a delay-dependent Lyapunov function, new existence conditions of delay-dependent non-fragile SOF H_∞ controller and L₂–L_∞ controller are derived, respectively, in terms of the feasibility of bilinear matrix inequalities (BMIs). Then, a procedure based on linear matrix inequality optimisation and a hybrid algorithm of the particle swarm optimisation and differential evolution is used to solve an optimisation problem with BMI constraints. Design and simulation results of non-fragile H_∞/L₂–L_∞ controller for active suspension show that the designed controller not only can achieve the optimal performance and stability of the closed-loop system in spite of the existence of the actuator time-delay, but also has significantly improved the non-fragility characteristics over controller perturbations.     

Measurement of soot oxidation with No<Subscript>2</Subscript>-O<Subscript>2</Subscript>-H<Subscript>2</Subscript>O in a flow reactor simulating diesel engine DPF

Understanding the mechanism of carbon oxidation is important for the successful modeling of diesel particulate filter regeneration. Characteristics of soot oxidation were investigated with carbon black (Printex-U). A flow reactor system that could simulate the condition of a diesel particulate filter and diesel exhaust gas was designed. Kinetic constants were derived and the reaction mechanisms were proposed using the experimental results and a simple reaction scheme, which approximated the overall oxidation process in TPO as well as CTO. From the experiments, the apparent activation energy for carbon oxidation with NO₂-O₂-H₂O was determined to be 40±2 kJ/mol, with the first order of carbon in the range of 10∼90% oxidation and a temperature range of 250∼500°C. This value was exceedingly lower than the activation energy of NO₂-O₂ oxidation, which was 60±3 kJ/mol. When NO₂ exists with O₂ and H₂O, the reaction rate increases in proportion to NO₂. It increases nonlinearly with O₂ or H₂O concentration when the other two oxidants are fixed.     

Incorporating insights from signal optimization into reservation-based intersection controls

Reservation-based intersection control for autonomous vehicles has the potential to make greater use of intersection capacity. Indeed, previous studies on the first-come-first-served (FCFS) policy (which prioritizes vehicles by order of their reservation request) have shown improvements over optimized signals. However, in certain situations, such as asymmetric intersections, FCFS easily performs worse than signals. To address this issue, we propose two new reservation policies, WEIGHTED and PHASED. WEIGHTED weights vehicle delay by signal timings, and PHASED simulates a signal but allows red phase turning movements that will not cause a collision. We test these policies on a city network and an arterial bottleneck intersection subnetwork and show that PHASED performs better than WEIGHTED in some scenarios, and vice versa. Furthermore, we show that using a combination of PHASED and WEIGHTED can perform better than using either one alone for the entire network. Results show that these policies provide effective and easily implemented alternatives to FCFS for reservations.     

Evaluation of a vehicle directional control with a fractional order PD<Superscript>μ</Superscript> controller

In this paper, a novel controller, the fractional order PD^μ controller, is designed to improve the performance of the driver-vehicle system. First, fractional calculus and fractional order PI^λD^μ controller are introduced. A control algorithm for vehicle directional control using the fractional order PD^μ controller is then presented. Based on preview-follower theory, the on-line tuning method of the fractional order PD^μ controller is designed. By comparing simulated and experimental results, the validity and robustness of the proposed fractional order PD^μ controller in the closed loop system are verified. Finally, comprehensive evaluations are performed between the systems with the fractional order PD^μ controller and with an integer PD controller. The results demonstrate that the use of the fractional order controller leads to an improvement of the performance of the driver-vehicle system.     

Assessment of a semi-Hertzian method for determination of wheel–rail contact patch

Wheel–rail contact calculations are essential for simulating railway vehicle dynamic behavior. Currently, these simulations usually use the Hertz contact theory to calculate normal forces and Kalker's ‘FASTSIM’ program to evaluate tangential stresses. Since 1996, new methods called semi-Hertzian have appeared: 5 Kik, W. and Piotrowski, J. A fast approximate method to calculate normal load at contact between wheel and rail and creep forces during rolling. Paper presented at the 2nd Mini-conference on Contact Mechanics and Wear of Rail/Wheel Systems. July29–31, Budapest.  [Google Scholar] 7 Ayasse, J. B., Chollet, H. and Maupu, J. L. 2000. Paramètres caractéristiques du contact roue-rail. Rapport de Recherche INRETS n225, ISSN 0768–9756 (in French) [Google Scholar] (STRIPES). These methods attempt to estimate the non-elliptical contact patches with a discrete extension of the Hertz theory. As a continuation of 2 Ayasse, J. B and Chollet, H. 2005. Determination of the wheel–rail contact patch in semi-Hertzian conditions. Vehicle System Dynamics, 43(3) [Google Scholar], a validation of the STRIPES method for normal problem computing on three test cases is proposed in this article. The test cases do not fulfill the hypothesis required for the Hertz theory. Then, the Kalker's FASTSIM algorithm is adapted to STRIPES patch calculus to perform tangential forces computation. This adaptation is assessed using Kalker's CONTACT algorithm.     

Solving the K-shortest paths problem in timetable-based public transportation systems

Finding the K-shortest paths in timetable-based public transportation systems is an important problem in practice. It has three typical variants: the K-earliest arrival problem (K-EAP), the K-shortest travel time problem (K-STTP), and the K-minimum number of transfers problem (K-MNTP). In this article we show that these problems can be solved efficiently by first modeling the timetable information with the time-expanded approach, then applying the Martins and Santos (MS) algorithm. Then we model the timetable information with the time-dependent approach and propose a modified version of the MS algorithm for solving the K-EAP. Experimental results on real-world data show that for K smaller than 100, which is enough for most applications, the execution times of the MS algorithm for the problems in the time-expanded model are less than 100 ms on a server with a 1.86-GHz central processing unit (CPU) and 4 GB of memory. For solving the K-EAP the modified MS algorithm in the time-dependent model is even more efficient (about three times faster for K ≤ 100) than the original algorithm in the time-expanded model. Our results imply the great potential of the MS algorithms in practical transportation service systems.