香溪长江公路大桥斜拉索施工技术及安全措施研究

斜拉索安装是斜拉桥施工的关键环节,其施工质量直接影响桥梁安全性。香溪长江公路大桥索塔采用倒Y型结构,锚固区空间有限,斜拉索在塔端无法同步、分级对称张拉作业,根据斜拉索重量、长度、张力荷载等参数,对比斜拉索塔、梁两端作业空间和施工特点,不同索号选用了不同的安装方式。针对斜拉索退扭现象,在梁端和塔端分别采用消除扭转或限制扭转的牵引张拉设备,确保斜拉索施工质量及安全。     

预应力钢拉杆在斜拉索锚固中的应用

文章结合某大跨度斜拉桥,针对预应力钢绞线加预应力钢拉杆的斜拉索锚固方式,运用空间有限元方法对预应力混凝土空心矩形索塔节段进行应力分析,探讨预应力钢拉杆在斜拉索锚固中的作用,为斜拉桥锚固结构设计提供参考。     

斜拉桥中斜拉索的安装技术

对于斜拉桥施工来说,斜拉索安装、张拉及调试要求严格,如何保证斜拉索安装质量,从而保证各索受力均衡,满足设计要求线形是主桥施工的一大难点。结合以往工程经验,分析斜拉索施工难点,提出对策,探讨斜拉索安装的具体措施,为同类工程提供参考借鉴。     

斜拉桥中斜拉索施工技术探讨

对于斜拉桥来说,斜拉索施工质量直接决定着斜拉桥质量。针对某斜拉桥中斜拉索布置为双索面、扇形密索体系的特点,总结了该工程斜拉索施工工艺,同时鉴于超长索塔部安装起吊过程中摆动幅度很大,提出可行的处理措施。     

金江金沙江大桥平行钢绞线斜拉索安装技术

通过攀西高速公路(攀枝花—西昌)金江金沙江大桥斜拉索施工实践,重点介绍了平行钢铰线斜拉索的安装工艺及张拉控制,并对斜拉索安装过程中的一些问题进行了论述。     

钢锚梁索塔锚固区单节段有限元受力分析

文章结合平南相思洲大桥工程实例,运用有限元软件对该桥索塔锚固区不平衡索力最大的节段模型进行计算,分析索塔锚固区水平荷载传递途径及受力特点。结果表明:钢锚梁与牛腿的连接方式对混凝土塔壁产生的拉应力最小;在不平衡索力作用下,特别是断索工况,混凝土塔壁会存在拉应力集中的现象,设计时应在索塔锚固区混凝土适当加强钢筋与预应力筋的布置。     

独塔斜拉桥施工阶段索塔锚固区局部应力分析

通过ANSYS大型通用有限元软件,对某跨径布置为180m+110m+46m的双索面独塔斜拉桥,进行各施工阶段工况下索塔锚固区局部应力情况的计算和分析。对该独塔斜拉桥选取索塔上部索区的4个节段,考察其截面正应力的分布规律,以发现独塔斜拉桥索塔锚固区位置的受力机理,用于指导设计和施工,供专业技术人员参考。     

鄂东长江公路大桥斜拉索安装技术

随着斜拉桥跨度的增加,作为主要受力构件之一的斜拉索的长度、直径和重量也不断增加,这给斜拉索施工带来了较大的安全风险及工艺控制难度.鄂东_长江公路大桥是一座主跨近千米的混合梁斜拉桥,结合其北岸主桥上部构造施工.介绍了该桥斜拉索安装的主要施工方法和技术特点.     

炳金大桥斜拉索安装

斜拉索安装关键在于施工计算、斜拉索PE护套的保护和施工安全，本文主要就斜拉索安装的基本方法、施工计算和专用工具作了一定的介绍。     

基于傅里叶变换的斜拉索振动频率识别研究

文章基于乌江二桥拉索振动频率监测实践，应用傅里叶变换的方法对斜拉索振动传感器实时采集到的监测信号进行分析。为保证实测拉索基频索力值的准确性，采用峰值一功率谱频差法和峰值一倒频谱分析法分别识别拉索的基频，并将二者识别的结果进行了比较。     

Traffic and emissions impact of congestion charging in the central Beijing urban area: A simulation analysis

Congestion charging is being considered as a potential measure to address the issue of substantially increased traffic congestion and vehicle emissions in Beijing. This study assessed the impact of congestion charging on traffic and emissions in Beijing using macroscopic traffic simulation and vehicle emissions calculation. Multiple testing scenarios were developed with assumptions in different charging zone sizes, public transit service levels and charging methods. Our analysis results showed that congestion charging in Beijing may increase public transit use by approximately 13%, potentially reduce CO and HC emissions by 60–70%, and reduce NOx emissions by 35–45% within the charging zone. However, congestion charging may also result in increased travel activities and emissions outside of the charging zone and a slight increase in emissions for the entire urban area. The size of charging zone, charging method, and charging rate are key factors that directly influence the impact of congestion charging; improved public transit service needs to be considered as a complementary approach with congestion charging. This study is used by Beijing Transportation Environment and Energy Center (BTEC) as reference to support the development of Beijing’s congestion charging policy and regulation.     

Analysis of Work Zone Traffic Behavior for Planning Applications

Abstract

Understanding work zone traffic behavior is important for the planning and operation of work zones. The objective of this paper is to develop a mathematical model of work zone traffic flow elements by analyzing the relationships between speed, flow, and density that can be used to estimate the capacity of work zones. Traffic flow data were collected from 22 work zone sites on South Carolina interstate highways. The scatter plots of the collected data demonstrate that the relationship between speed and density does not follow Greenshields’ linear model. A non-linear hyperbolic model was developed to describe the relationship between speed and density. Using this model the capacity of a work zone was estimated to be 1550 passenger cars per hour for 2-lane to 1-lane closures. Adjustments to this capacity value to consider other types of vehicle as well as the work zone intensity are provided. Highway agencies can use this estimated capacity along with anticipated traffic demand to schedule work zone operations to avoid long periods of over-saturation.

The tapered approach to work zone lane closures used by South Carolina is similar to methods used in work zones throughout the world. The authors believe that the methodology described in this paper for modeling work zone traffic as well as estimating work zone capacity is transferable to other countries. The conversion of actual volumes to passenger car equivalents may have to be modified due to the significant differences in traffic makeup between the United States and other countries.     

Incorporating work zone configuration factors into speed‐flow and capacity models

This study aims to develop work zone speed‐flow and capacity models, which incorporate work zone configuration factors including the number of work zones, geometrical alignment, work zone speed limit, and work zone length. On the basis of the traffic data from six work zone sites with various work zone configurations, two nonlinear traffic speed and flow models including work zone configuration factors are developed for the uncongested and congested traffic conditions, respectively. A work zone capacity model is proposed on the basis of the two models. The three models can further be used to examine the effects of work zone configuration factors on the speed‐flow relationship and capacity at work zones. Results show that traffic speed, traffic flow, and work zone capacity increase with the posted speed limit. Traffic speed under uncongested conditions decreases with the geometric alignment, the number of work zones, work zone length, and heavy vehicle percentage. Under congested conditions, the increase of the number of work zones is found to exhibit a larger negative impact on the traffic flow than the increase of geometric alignment. The number of work zones is also found to have the largest negative impacts on work zone capacity, followed by the geometric alignment. Short work zone length exhibits a relatively minor contribution to increasing work zone capacity. Copyright © 2014 John Wiley & Sons, Ltd.     

An improved cellular automata model for heterogeneous work zone traffic

This paper aims to develop an improved cellular automata (ICA) model for simulating heterogeneous traffic in work zone. The proposed ICA model includes the forwarding rules to update longitudinal speeds and positions of work zone vehicles. The randomization probability parameter used by the ICA is formulated as a function of the activity length, the transition length and the volumes of different types of vehicles traveling across work zone. Compared to the existing cellular automata models, the ICA model possesses a novel and realistic lateral speed and position updating rule so that the simulation of vehicle’s lateral movement in work zone is close to the reality. The ICA model is calibrated and validated microscopically and macroscopically by using the real work zone data. Comparisons of field data and ICA for trajectories, speed and speed–flow relationship in work zone show very close agreement. Finally, the proposed ICA model is applied to estimate traffic delay occurred in work zone.     

Optimal subwork zone operational strategy for short‐term work zone projects in four‐lane two‐way freeways

Roadside trees in Singapore are regularly trimmed for the purpose of traffic safety and roadside tree‐trimming project is one typical type of short‐term work zone projects. To implement such a short‐term work zone project, contractors usually divide an entire work zone into multiple subwork zones with the uniform length. This paper aims to determine an optimal subwork zone strategy for the short‐term work zone projects in four‐lane two‐way freeways with time window and uniform subwork zone length constraints. The deterministic queuing model is employed to estimate total user delay caused by the work zone project by taking into account variable traffic speeds. Based on the user delay estimations, this paper proceeds to build a minimization model subject to time window and uniform length constraints for the optimal subwork zone strategy problem. This paper also presents a variation of the minimization model to examine the impact of unequal subwork zone length constraint. Since these minimization models belong to the mixed‐integer non‐differentiable optimization problems, an iterative algorithm embedding with the genetic simulated annealing method is thus proposed to solve these models. Finally, a numerical example is carried out to investigate the effectiveness of the proposed models. Copyright © 2010 John Wiley & Sons, Ltd.     

断层破碎带隧道衬砌静力稳定性分析

结合一实际工程,选取包括断层破碎带和断层影响带在内的沿隧道纵向300m的计算区域,用八节点六面块体单元将计算区域离散化,采用三维弹塑性静力有限元法模拟分析隧道各个施工阶段,以及建成后围岩和衬砌的受力与变形状态。通过分析比较可知:(1)断层破碎带处的坑道变形和围岩塑性区均明显比非断层破碎带处要大;(2)由于断层破碎带的影响,初期支护、二次衬砌内力的增加幅度约为10%～30%。     

节理岩体隧道围岩稳定性判定指标合理性研究

隧道围岩失稳模式和稳定性判据一直是工程界争论的焦点,迄今没有科学合理的标准,常以洞周位移或塑性区经验值作为稳定性判定指标。洞周位移受围岩弹模、隧道形状等因素影响,而且不同部位变形值差异很大,很难找到统一标准;以塑性区作为稳定性判据优于以位移作为判据,围岩塑性化反映连续介质宏观塑性流动力学动态,而不能用于量化判定由优势结构面控制节理岩体破坏的隧道稳定性。文章结合细观节理形态和变化,通过UDEC离散元程序,研究节理岩体隧道失稳模式及量化的稳定性判定指标,探讨了细观结构机制和宏观力学行为关系。结果表明:(1)结构面极大地削弱岩体力学性质及其稳定性,结构面变形与强度性质对于隧道稳定性起着关键控制性作用;(2)节理岩体隧道扰动区可划分为脱落区、张开区和剪切滑移区,其中脱落区表征围岩失稳模式,张开区围岩处于脱落临界状态,即塌方潜在区域;(3)剪切滑移区是诱发围岩发生渐进性破坏主因,提出将剪切滑移区作为节理岩体隧道稳定性判定指标具有严格力学依据,可以定量化评价围岩稳定程度。最后,以在建兰渝铁路木寨岭隧道为例,对比了锚杆支护前后力学效应,验证了以剪切滑移区作为节理岩体隧道稳定性判定指标的可靠性、合理性和现实性。     

Safety impacts of signalized lane merge control at highway work zones

Lane closures due to highway work zones present many challenges to the goal of ensuring smooth traffic operations and a safe environment for both drivers and workers. Late merge behavior at a work zone closure is a dangerous behavior that impacts the traffic conflicts upstream of work zone closures. This paper analyzes the safety impacts of using a signalized lane control strategy at the work zone merge points. To achieve the objective of this research, a field study has been conducted at a highway work zone to collect traffic and driver behavior data, and a two-stage, simulation-based approach is used to analyze the safety impacts of implementing a signalized lane merge control strategy at the studied work zone. In the first stage, micro-simulation models are developed and calibrated based on field data to generate vehicle trajectories. In the second stage, the U.S. Federal Highway Administration’s Surrogate Safety Assessment Model is employed to identify potential conflicts under different traffic conditions. The paper concludes that a proposed signal control device could significantly reduce lane-change conflicts at work zone merge points. In addition, recommendations on the signal cycle length and timing splits are provided.     

小曲率薄壁热煨弯管前过渡区支撑器

文中指出了小曲率、薄壁感应热煨弯管前过渡区出现的成型问题,分析感应加热弯曲时前过渡区的受力状况和变形稳定性,从加强前过渡区钢管热弯曲时的稳定性出发,设计了伸缩自如、支撑力大、自身质量轻、装卸方便、通用性强的前过渡区支撑器。由应用前后的对比可知,前过渡区出现的问题得到根本解决。     

考虑生态环境效应的止水帷幕设计方法初探

当隧道旁穿大型水体工程时,常将隧道与水体之间的止水帷幕设计为具有一定开口的结构型式,止水帷幕开口的大小直接关系到其止水能力以及对周边地下水环境的影响程度。文章依托实际工程,采用数值模拟的方法,探讨了止水帷幕开口大小(埋深和密度)对降水效果及水位回升时间的影响。结果表明:(1)止水帷幕的开口大小对水位降深的影响可分为无影响区、渐变区和突变区三个区域;对水位恢复的影响可分为渐变区和突变区;(2)止水帷幕埋深越大,降水效果越好,但回水时间越长;悬挂部分帷幕布置密度越大,降水效果越差,回水时间越短。综合降水效果、回水时间、施工成本等因素,止水帷幕设计参数的选取应落在渐变区内;(3)结合依托工程水文地质条件,给出了该工程止水帷幕设计参数值,即埋深应在14~20 m内,布置密度在0~0.8内,并通过工程应用验证了其有效性。