Combined with the mechanical behaviors of concrete arch ring web and the material properties of ultra-high performance concrete(UHPC),the prefabricated assembly UHPC butterfly web was proposed to replace the cast-in-place concrete web.Subsequently,a new type of concrete arch structure with UHPC butterfly web was developed to reduce the self-weight and construction difficulties.The Wumengshan Bridge with a span of 270 m was taken as the prototype,the UHPC butterfly web was used to replace the steel truss web of the original steel truss-concrete composite arch ring,then a trial design was carried out for this new type of concrete arch bridge.The research results show that in the construction process,the stresses in the arch ring at the maximum cantilever stage and the completion of cast-in-place of the middle box top and bottom plates are within allowable limits,and the first-order elastic overall stability coefficients are 12.02 and 4.12,respectively.The strength,overall strength-stability,and deformation verifications of the arch ring all meet the requirements of specifications.Compared with the steel truss-concrete composite arch ring,the weight increased by UHPC is similar to that reduced by steel,and the self-weight of the trial design arch ring only increases by 5％.However,the material cost reduces by 21％.Additionally,the out-of-plane bending stiffnesses of arch foot and vault sections in the trial design arch ring increase by 25％and 32％,respectively,and axial forces of critical sections only increase by 3.8％-6.2％.Due to the optimization on the arch axis coefficient,the bending moments of arch foot and vault sections reduce at most by 37.0％and 22.5％,respectively.Compared with the prototype bridge,the natural vibration frequency of the trial design arch bridge is larger with the maximum increment of only 8.5％,which has little effect on the dynamic characteristics of the arch bridge.In summary,the research results have good theoretical significance and practical application values for promoting the technical progress of concrete arch bridges.7 tabs,11 figs,28 refs.
Ground motion is categorized into near fault zone and across fault zone where impulsive component is included. The impulsive component usually causes larger damage than that by far-fault ground motion. To build a Benchmark model platform for cable-stayed bridges across-fault region for comparative analysis, the paper proposes a way combining the finite fault source model. In the paper, the finite fault source model was conducted based on the site Qiongshan earthquake. After the geological structural parameters were determined, forward modeling of near site earthquake was carried out, and the observation points were obtained using numerical simulation. Then, the analysis results were compared with the pulse characteristic parameters of similar grade of recording ground motion. Additionally, the ground motion near-fault region was analyzed to validate the finite fault source model.
为了准确分析水分对水泥基材料性能的影响,从水分传输机理、孔结构对水分传输的影响以及水分传输的表征方法等方面系统总结了水泥基材料水分传输的研究进展,并对水泥基材料水分传输的研究发展趋势进行了展望.结果表明:水泥基材料在水分传输的驱动力主要来自渗透作用、扩散作用和毛细作用;连通孔作为水泥基材料水分传输的通道,其临界孔隙率、孔隙分布以及孔径大小等均会影响水分传输的速率;水泥基材料中水分传输虽然可以利用传统试验方法与现代无损测试方法对其进行研究,但是这些手段需要人工多次测量,不仅耗费大量的时间且误差较大,利用不同的数值模拟方法分析水泥基材料水分传输能够获得较好的结果.此外,目前对于水分在水泥基材料内部的传输,大多数研究都忽略渗透作用以及扩散作用的影响,而只是把毛细作用力作为水分传输的驱动力;且利用数值模拟的方法分析水泥基材料的水分传输时大多是在分子尺度上进行研究,并将水分视为一维传输.未来水泥基材料水分传输的研究首先是要系统的考虑水分传输的3个驱动力;其次,研究水分传输时最好采用多维的数值模型;最后,应当寻求更为先进的数值模拟方法分析水泥基材料的水分传输.
为研究大粒径钢渣在基层中的适用性,采用大粒径沥青混合料级配设计方法将不同比例的钢渣与碎石掺配,分析不同水泥掺量(质量分数,下同)和成型方法对水泥稳定大粒径钢渣基层混合料(CSLS)最佳含水率和最大干密度的变化规律,并对不同成型方法和结构类型的CSLS进行无侧限抗压强度、间接抗拉强度、抗压回弹模量等测试,研究养生龄期、水泥掺量、成型方法、结构类型对CSLS力学特性的影响规律.研究结果表明:振动压实法下骨架密实和悬浮密实结构CSLS的平均最大干密度分别为重型击实法下的1.023倍和1.013倍,重型击实法下骨架密实和悬浮密实结构CSLS的平均最佳含水率分别为振动压实法下的1.111倍和1.223倍;养生龄期对CSLS的强度特性有正向影响,呈非线性增长的趋势;水泥掺量从4.0％增大至6.0％,CSLS的7 d无侧限抗压强度平均增长25.9％,28 d间接抗拉强度平均增长39.6％,90 d抗压回弹模量平均增长22.4％;成型方法对CSLS的路用性能影响较大;对于悬浮密实(骨架密实)结构CSLS,振动成型试件的7 d无侧限抗压强度、28 d间接抗拉强度、90 d抗压回弹模量分别比静压成型试件相同指标高109.9％、122.8％、54.2％(108.5％、117.4％、52.9％);2 种成型方法下,悬浮密实结构 CSLS 的力学性能均略高于骨架密实结构,其中振动成型下,悬浮密实结构CSLS的7 d无侧限抗压强度、28 d间接抗拉强度、90 d抗压回弹模量分别比骨架密实结构相同指标高14.8％、10.6％、8.6％.
为解决现有匝道连续分流间距规定未考虑匝道设计速度及车辆换道紧急程度,导致匝道设计速度较高时相邻出口间距不足车辆紧急换道的问题,开展匝道连续分流间距研究.首先,基于车辆运行特征并考虑换道安全性,将驾驶人在匝道连续分流区的操作过程划分为4个阶段:减速过程、标志认读过程、等待过程和换道过程.其次,基于实测车辆运行轨迹,提出了考虑换道紧急程度的sigmoid换道轨迹模型,并通过拟合优度检验证明了该模型对匝道连续分流区的适用性.最后,分析了间距模型中参数的取值,提出了匝道连续分流最小间距推荐值.结果表明:sigmoid换道模型对于匝道中车辆左换道和右换道的拟合优度分别可达97.83％和96.63％,拟合精度较高,能够准确描述匝道连续分流区的换道行为.提出的间距计算模型符合车辆行驶特点,与轨迹吻合度高;当匝道设计速度在小于60 km/h和大于60 km/h时,匝道连续分流最小间距分别受主线设计速度和匝道设计速度控制,设计速度较高的匝道所需间距明显更长.与《公路路线设计规范》(JTG D20-2017)和《公路立体交叉设计细则》(JTG/T D21-2014)中规定值相比,当匝道设计速度小于60 km/h时,间距推荐值与规定值相近;当匝道设计速度大于60 km/h时,规定值偏小.提出的最小间距推荐值,可为设计人员对该指标的灵活设计提供参考.
