平转桥梁转动体系受力分析

转动体系在转体施工过程中受力集中且往往存在偏心现象,其受力安全性直接攸关转体施工的成败,分析转动体系受力状态对确保桥梁转体施工具有重要意义。在明确桥梁转体工程转动体系常见受力状态的基础上,以实际工程为背景建立转动体系局部仿真模型,对上转盘、下转盘、球铰及球铰加劲肋进行详细的受力分析。结果表明:无偏心状态球铰接触应力由内向外先增大后减小,最大接触应力出现在球铰边缘附近;各部分Von Mises应力及下转盘竖向正应力随偏心程度的加剧呈一侧增大一侧减小;下转盘偏心方向两侧的混凝土竖向正应力差值随偏心程度的增大而增大,工程上可据此估计不平衡力矩。     

上跨铁路转体桥梁设计与施工关键技术

深圳市外环高速公路上跨广深铁路桥梁采用两跨预应力混凝土变高度T形刚构箱梁,跨径为2×82.5 m,桥面宽33 m,平面转体法施工,转体角度72.342.,转体结构悬臂长度为2×73.5 m,转体重量为2.4万t,刷新了中国铁路广州局集团管辖范围内转体桥梁宽度和重量记录.在该桥试转体阶段,通过称重试验、试转试验和点动试验,为正式转体提供了技术参数,确保了转体顺利进行.该桥的建成保证了深圳市外环高速公路按计划顺利通车,为我国大吨位转体桥梁设计与施工积累了宝贵经验.     

马官营特大桥上跨成昆铁路桥梁转体施工技术研究

桥梁转体施工是解决新建高速公路与既有铁路"公铁交叉"问题的主要技术措施之一,该技术可以最大限度地减少桥梁施工过程对既有铁路运营干扰,因而得到工程界的青睐,但是桥梁转体施工过程中的风险不容小觑。合理的转体系统组成以及转体施工关键技术参数是确保桥梁转体施工成功的关键。本文以武易高速马官营特大桥上跨成昆铁路施工为例,结合施工现场与转体跨线桥施工的特点,对转体跨线桥桥梁施工的转体系统组成以及转体牵引力、设备配置进行探究。工程实践表明:由于采用技术措施得当,转体跨线桥工程如期如质完成,并为类似工程提供了参考。     

在役预应力混凝土桥梁预应力检测技术——现状、技术难点与展望

随着我国桥梁建设的突飞猛进,占75%以上的预应力混凝土桥梁的预应力损失病害问题日益突出。本文通过对在役预应力混凝土桥梁预应力无损检测技术和局部破损检测技术现状的研究分析,指出当前在役预应力混凝土桥梁预应力检测技术存在的技术难点,提出采用部分区域局部破损检测和大范围无损检测相结合的方法提高对在役预应力混凝土桥梁持久应力的测试精度,并建议通过在预应力钢筋中埋设智能传感器对在役预应力混凝土桥梁的持久应力进行长期监测。     

沪杭客专海杭特大桥上承式拱桥转体施工关键技术研究

对沪杭客专海杭特大桥上跨石大公路88m+160m+88m自锚上承式拱桥的转体施工关键技术进行研究。通过对桥梁进行称重、试转试验,验证了转体系统的可靠性,为正式转体提供了科学依据。并对转体系统关键构造及工序提出了改进措施,保证了该桥顺利施工。     

邹城转体斜拉桥转盘结构受力分析

随着桥梁转体吨位不断增加,转盘及墩塔结构的受力越来越大,对其安全造成很大威胁,因而对转盘和墩塔结构进行详细的局部受力分析变得非常重要.该文结合山东邹城斜拉桥转体设计方案,采用Ansys软件建立了包括转盘、牵引盘、牛腿、撑捧脚、上部横梁以及部分塔柱的三维有限元模型,对牛腿结构、开槽底部以及上转盘底部混凝土及钢板等受力进行详细的分析.结果表明:1)牛腿和主墩的凹角处存在应力集中,需要加密配筋;2)合理的主墩开槽尺寸可以减少混凝土用量,但开槽需保证应力传递流畅并避免局部应力集中;3)上转盘底部混凝土存在受力不均匀现象,尤其在偏载情况下比较明显,需要包裹厚钢板使受力趋于均匀,以保证转体安全.     

多点支撑转体系统球铰受力特性模型试验研究

球铰作为桥梁转体系统的关键承力构件,其受力特性对桥梁转体安全至关重要。该文以跨襄阳北编组站大桥为对象,开展多点支撑转体系统球铰受力特性模型试验,详细分析承力支腿数量、桥梁转动速度、轨道平顺性和风荷载对球铰应力的影响,探讨不同工况下球铰应力的变化规律。试验结果表明：增加承力支腿数量可以使上、下球铰受力更为均匀;在转动加速阶段,球铰受加速度效应影响显著,在匀速转动阶段,上球铰的应力变化随着转体角度的增大逐渐增大,而下球铰受力较为均匀,建议转速控制为0.02～0.04 rad/min;轨道不平顺会增大球铰应力变化,随着不平顺度的增大,球铰应力变化也随之增大;在风荷载作用下,下球铰受力较为均匀,而上球铰应力变化随着转动角度的增大而增大,应避免在高风速下进行转体。     

基于齿轮齿轨传动的斜拉桥多点支撑转体系统设计及应用

跨襄阳北编组站大桥为转体斜拉桥,转体时梁面以上塔高73 m,最大转体重量32 000 t,为提高转体过程中桥梁的抗倾覆稳定性,设计了基于齿轮齿轨传动的多点支撑转体系统。转体系统主要由转动系统(中心球铰、常规撑脚、滑道、齿条)及辅助支撑系统(驱动承力支腿、电气控制系统)组成。中心球铰设计最大承载28 000 t, 6个驱动承力支腿总设计承载6 000 t,通过6个驱动承力支腿的齿轮啮合齿轨实现桥梁转体。该转体系统通过降低中心球铰承受的竖向荷载,改善了承台及桩基的受力状态;转体过程中6个驱动承力支腿实时与滑道保持接触状态,提高了转体桥梁的抗倾覆稳定性。对转动结构和辅助支撑系统受力进行计算,结果表明该转体系统受力满足要求。工程实践验证了该转体系统的可靠性。     

小榄水道特大桥钢管混凝土拱竖向转体施工设计与分析

小榄水道特大桥为中承式钢管混凝土拱桥,采用"先梁后拱"、竖向转体施工方法。笔者主要介绍竖转体系、缆索吊装系统、锚固系统、竖转实施及其施工要点,以期为同类桥梁施工提供参考。     

小兴浪混凝土开口薄壁箱拱桥平转施工技术

文章主要阐述混凝土开口薄壁箱拱桥梁平转施工过程中的技术控制技术要点,重点从转盘施工控制,转体混凝土重平衡控制,钢绞线扣索系统控制,平衡转体施工控制,转体安全措施及注意事项,结构固定及合拢段施工等几个方面进行阐述,并进行总结,为今后同类桥梁施工和设计提供借鉴。     

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.     

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.     

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.     

Designing H ∞/GH 2 static-output feedback controller for vehicle suspensions using linear matrix inequalities and genetic algorithms

This paper presents an approach to design the H _∞/GH ₂ static-output feedback controller for vehicle suspensions by using linear matrix inequalities (LMIs) and genetic algorithms (GAs). Three main performance requirements for an advanced vehicle suspension are considered in this paper. Among these requirements, the ride-comfort performance is optimized by minimizing the H _∞ norm of the transfer function from the road disturbance to the sprung mass acceleration, while the road-holding performance and the suspension deflection limitation are guaranteed by constraining the generalized H ₂ (GH ₂) norms of the transfer functions from the road disturbance to the dynamic tyre load and the suspension deflection to be less than their hard limits, respectively. At the same time, the controller saturation problem is considered by constraining its peak response output to be less than a given limit using the GH ₂ norm as well. A four-degree-of-freedom half-car model with active suspension system is applied in this paper. Several kinds of H _∞/GH ₂ static-output feedback controllers, which use the available sprung mass velocities or the suspension deflections as feedback signals, are obtained by using the GAs to search for the possible control gain matrices and then resolving the LMIs together with the minimization optimization problem. These designed H _∞/GH ₂ static-output feedback controllers are validated by numerical simulations on both the bump and the random road responses which show that the designed H _∞/GH ₂ static-output feedback controllers can achieve similar or even better active suspension performances compared with the state-feedback control case in spite of their simplicities.     

Robust <Emphasis Type="Italic">H</Emphasis><Subscript>∞</Subscript> preview control of an active suspension system with norm-bounded uncertainties

A robust H _∞ preview control is investigated for an active suspension system with look-ahead sensors. The uncertain system is described by a state-space model with linear nominal parts and additional nonlinear time-varying norm-bounded uncertainties. Proof of robust stability and a feedback-type robust H _∞ preview controller are derived by augmenting the dynamics of the original system and previewed road input. As, however, the augmented previewed road input gives the system a much larger dimension than the original system, much more computation time is required for solving of Riccati equations. To resolve this problem, a decomposed robust H _∞ preview controller is proposed. Robust stability and performance variations for system uncertainties are shown using a numerical example of a quarter-car model.