Segmental Bridges under Combined Torsion, Bending and Shear

Segmental bridges with unbonded prestressed tendons have some advantages, such as the weather independence and the corrosion protection of prestressing tendons. This paper analyzed the behavior of a prestressed segmental bridge with unbonded tendons under combined loading of torsion, bending and shear. According to the experiment research, a modified skew bending model was developed to calculate the bearing capacity of segmental bridges subjected to combined bending, shear and torsion. The finite element method was used to investigate the deflection behaviors of such structure, also to check the theoretical model. The theoretical and FEM research results were compared favorably with the test results from Technical University of Braunschweig, Germany. Finally, suggestion for the design and construction of segmental bridges with external prestressing was made.

Web Shear Strengthening Technique of Deep Precast Prestressed Hollow Core Slabs under Truck Loads

Precast prestressed Hollow Core Slabs (HCS), are one of the famous and widely used slabs for concrete structures all over the world and widely implemented in the Middle East. HCS are used in industrial, commercial, residential buildings, as well as, in the parking structures. This paper succeeded to present new special details for deep HCS to enhance and strengthen the web shear strength capacity of HCS 400 and 500 mm depths respectively at the open parking area. This is subjected to heavy truck wheel loads so as to achieve the LRFD Code’s requirements. However, it is noticed many web shear cracks of HCS are used at parking area at many projects in Gulf Region. On the other hand, ACI318-14 permits no shear reinforcement in prestressed HCS thickness of less than 12.5 in (320 mm). The paper presents experimental tests program, to verify the numerical finite element of deep HCS under maximum design uniform loads, in addition to the new strengthening techniques. New strengthening techniques succeed to enhance the web shear capacity by significant percentage, due to the new details for HCS 400 by 68% up to 256% increasing of the web shear capacity compared to the ordinary HCS section. Also, HCS 500 shear capacity is enhanced with different percentages of strengthening techniques by 55%, up to 197% based on the different cases of strengthening. Furthermore enhancing deep HCS shear performance;the new techniques have an advantage of an easy execution at the site;casting with structural topping, otherwise the preparation can be done in precast factory before site handover, which saves time and cost compared to the others traditional strengthening techniques.

Shear Behavior of Novel Prestressed Concrete Beam Subjected to Monotonic and Cyclic Loading

Prestressed steel ultrahigh-strength reinforced concrete(PSURC) beam is a new type of prestressed concrete beam, which not only has a considerable compressive strength attributed to the ultrahigh strength concrete, but also ensures a certain degree of ductility at failure due to the existence of structural steel. Five of these beams were monotonically tested until shear failure to investigate the static shear performance including the failure pattern, loaddeflection behavior, shear capacity, shear crack width and shear ductility. The experimental results show that these beams have superior shear capacity, crack control ability and shear ductility. To study the shear performance under repeated overloading, seven PSURC beams were loaded in cyclic test simultaneously. The overall shear performance of cycled beams is similar to that of uncycled beams at low load level but different at high load level. The shear capacity and crack control ability of cycled beams at high load level are reduced, whereas the shear ductility is improved. In addition, the influences of variables including the degree of prestress, stirrup ratio and load level on the shear performance of both uncycled and cycled beams were also discussed and compared, respectively.

Shear behavior of ultra-high-performance concrete beams prestressed with external carbon fiber-reinforced polymer tendons

The ultra-high-performance concrete(UHPC)and fiber-reinforced polymer(FRP)are well-accepted high-performance materials in the field of civil engineering.The combination of these advanced materials could contribute to improvement of structural performance and corrosion resistance.Unfortunately,only limited studies are available for shear behavior of UHPC beams reinforced with FRP bars,and few suggestions exist for prediction methods for shear capacity.This paper presents an experimental investigation on the shear behavior of UHPC beams reinforced with glass FRP(GFRP)and prestressed with external carbon FRP(CFRP)tendons.The failure mode of all specimens with various shear span to depth ratios from 1.7 to 4.5 was diagonal tension failure.The shear span to depth ratio had a significant influence on the shear capacity,and the effective prestressing stress affected the crack propagation.The experimental results were then applied to evaluate the equations given in different codes/recommendations for FRPreinforced concrete structures or UHPC structures.The comparison results indicate that NF P 18-710 and JSCE CES82 could appropriately estimate shear capacity of the slender specimens with a shear span to depth ratio of 4.5.Further,a new shear design equation was proposed to take into account the effect of the shear span to depth ratio and the steel fiber content on shear capacity.

Experimental study on shear behavior of prestressed reactive powder concrete I-girders

As a new generation of concrete,RPC(Reactive Powder Concrete)has attracted great research attention for its ultra-high strength and high durability.In the present paper,experimental results from tests on eight prestressed RPC I-section girders failing in shear are reported herein.The beams with RPC of 120 MPa in compression were designed to assess the ability to carry shear stress in thin webbed prestressed beams with stirrups.The test variables were the level of prestressing,shear span-depth ratio(a/d)and stirrup ratio.Shear deformation,shear capacity and crack pattern were experimentally investigated in detail.With regard to the shear resistance of the test beams,the predictions from three standards(AFGC,JSCE and SIA)on the design of UHPC structures were compared with the experimental result suggesting that the experimental strength is almost always higher than predicted.RPC,as a new concrete,was different from normal concrete and fiber reinforced concrete.Further study should be needed to develop an analytical method and computation model for shear strength of RPC beams.

Shear design of high strength concrete prestressed girders

Normal strength prestressed concrete I-girders are commonly used as the primary superstructure components in highway bridges. However, shear design guidelines for high strength PC girders are not available in the current structural codes. Recently, ten 7.62 m （25 feet） long girders made with high strength concrete were designed, cast, and tested at the University of Houston （UH） to study the ultimate shear strength and the shear concrete contribution （Vc） as a function of concrete strength （f＇c）. A simple semi-empirical set of equations was developed based on the test results to predict the ultimate shear strength of prestressed concrete I-girders. The UH-developed set of equations is a function of concrete strength （√f＇c）, web area （bwd）, shear span to effective depth ratio （a/d）, and percentage of transverse steel （Pt）. The proposed UH-Method was found to accurately predict the ultimate shear strength of PC girders with concrete strength up to 117 MPa （17000 psi） ensuring satisfactory ductility. The UH-Method was found to be not as overly conservative as the ACI-318 （2011） code provisions, and also not to overestimate the ultimate shear strength of high strength PC girders as the AASHTO LRFD （2010） code provisions. Moreover, the proposed UH-Method was found fairly accurate and not exceedingly conservative in predicting the concrete contribution to shear for concrete strength up to 117 MPa （17000 psi）.

预应力UHPC槽形节段与整体式混凝土板组合梁受剪性能

将预制的UHPC槽形节段通过干缝连接和预应力张拉形成槽形梁,再与整体现浇的混凝土板组合成的组合梁,称为预应力UHPC槽形节段与整体式混凝土板组合梁(PUCS-MCS组合梁)。它是一种能充分发挥不同材料的性能、施工方便且整体性能好的新型桥梁结构。为探究其抗剪性能,开展了9根模型梁的试验。分析了接缝数、接缝处剪力键数、剪跨比、UHPC钢纤维体积率、配箍率和纵筋率等参数对试件变形、破坏模式、抗剪承载力的影响;基于试验研究结果,提出了PUCS-MCS组合梁抗剪承载力计算方法。结果表明:PUCS-MCS组合梁均为剪压破坏,所有梁在开裂前的荷载-挠度曲线差异不大,在开裂后刚度不断下降;PUCS-MCS组合梁的抗剪承载力随接缝处剪力键数、UHPC钢纤维掺量、配箍率和纵筋率的增大而增大,随干接缝数量增加和剪跨比的增大而减小,其中影响最显著的是干接缝和剪力键,影响最小的是钢纤维掺量和配箍率,因此PUCS-MCS组合梁可不配箍筋,并可采用较低钢纤维掺量的UHPC。

新型预应力混凝土钢管桁架叠合梁抗剪性能有限元分析

为解决施工现场中现有装配式混凝土叠合梁、梁柱结点钢筋相互影响的问题,设计一种新型预应力混凝土钢管桁架叠合梁。为进一步研究该叠合梁的抗剪性能,共设计6个叠合梁、3个整浇梁进行ABAQUS有限元模拟,分析其破坏特征机理、荷载–跨中挠度曲线等,研究试件剪跨比、底板厚度参数对抗剪性能的影响,以及新型预应力混凝土钢管桁架叠合梁与整浇梁的抗剪性能对比。数值模拟分析结果显示,新型叠合梁与整浇梁均为剪切破坏,在底板厚度相同的情况下,随着剪跨比的增大,叠合梁的极限承载力略微降低。此外,预制高度增加会导致叠合梁的极限承载力减小。叠合梁表现出与整浇梁相似的受剪性能,随着剪跨比增加,叠合梁相对于整浇梁表现出更好的抗剪性能。综合而言,新型预应力混凝土钢管桁架叠合梁具有良好的抗剪性能。

部分预制预应力型钢混凝土梁受力性能试验与设计方法研究

为简化现场施工工序,创新将预应力技术与装配式技术集成应用于型钢混凝土结构中,提出部分预制预应力型钢混凝土(PPPSRC)梁。通过5个梁试件的受弯性能试验及5个梁试件的受剪性能试验,研究了预应力施加顺序、预应力度、预应力筋高度及预制混凝土种类对PPPSRC梁的破坏形态和截面应力发展的影响,并结合试验结果对各试件的裂缝发展规律、承载及变形能力进行了分析研究。研究结果表明:预应力施加于梁预制部分或施加于整个梁对PPPSRC梁受力性能影响较小,不同预应力施加顺序的试件开裂荷载与峰值荷载差值均在5%以内;预应力度和预制部分混凝土种类对PPPSRC梁的抗裂性能影响显著,其中PPPSRC梁的开裂荷载相较于普通型钢混凝土梁最高可提高166%,而预制部分采用超高性能混凝土相比预制部分采用普通混凝土的试件开裂荷载可提高33%。基于试验结果建立了适用于PPPSRC梁的受弯、受剪承载力以及开裂荷载的计算公式,计算结果与试验结果吻合较好。

体外预应力UHPC无腹筋梁抗剪性能试验研究

为研究体外预应力超高性能混凝土(Ultra-high Performance Concrete,UHPC)无腹筋梁的抗剪性能,设计了3片体外预应力UHPC无腹筋梁,剪跨比分别为1.44、2.56、3.67,采用四点加载的方式进行抗剪性能试验,获得了试验梁的荷载-位移关系、荷载-应变关系、破坏形态以及极限抗剪承载力。试验结果表明:体外预应力UHPC无腹筋梁的抗剪破坏方式均表现为脆性破坏,随着剪跨比的增大,试验梁破坏形态依次表现为斜压破坏、剪压破坏、剪拉破坏;剪跨比越大,斜裂缝的数量越少、倾角越小,试验梁的极限抗剪承载力越小,且减小趋势变缓。基于极限平衡法推导了体外预应力UHPC无腹筋梁的抗剪承载力计算公式,验算了14片无黏结预应力UHPC梁的抗剪承载力,该公式适用性良好。

基于预应力扩散的变截面箱梁剪应力计算方法

文中在变截面箱梁剪应力计算传统方法的基础上,考虑轴力变化产生的附加剪应力,并提出预应力扩散的概念,引入预应力扩散函数,运用楔形弹性体理论求解,建立了基于预应力的扩散的变截面箱梁剪应力计算方法.以某特大桥中跨悬浇段为例,对比使用传统计算方法和本文计算方法的计算结果发现:在根部附近轴力变化对剪应力影响很大,在悬臂自由端附近影响较小;在施工阶段中传统计算方法会大大低估截面中的剪应力和主拉应力,因此不能忽略轴力变化对剪应力的影响.

斜截面抗剪强度上限值和预应力混凝土梁最小配筋率计算理论研究

文章遵循基本力学原理,从结构理论出发,推导修正后的混凝土梁斜截面抗剪强度上限值理论与公式,首次给出考虑斜箍筋特殊效应后的斜截面抗剪强度上限值的理论与方法;抗剪实验梁结果证明所提出的抗剪强度上限值理论与方法的正确性;基于预应力束应力全过程分析,首次推导并提出了预应力混凝土梁双值最小配筋率理论与计算方法,明确了预应力混凝土梁最小配筋率存在两个临界点,合理的预应力混凝土梁配筋率在两个临界点形成的范围之内,计算实例证明预应力混凝土梁双值最小配筋率理论的正确性。

预应力混凝土梁-型钢混凝土柱新型框架节点受剪承载力计算方法

梁柱节点受剪承载力计算是混凝土框架结构节点抗震设计的关键点之一,由于节点剪力传递机理与构造的复杂性,目前尚未形成完善的节点受剪承载力计算理论。该文阐述了预应力混凝土梁-型钢混凝土柱新型框架节点的受力机理,并基于桁架模型和斜压杆模型,提出了一种同时考虑预应力筋与型钢贡献的节点受剪承载力计算方法。开展了新型节点受力性能拟静力试验,分别选取了梁端破坏与节点剪切破坏两种破坏形式的节点试验数据,对所建立的新型节点受剪承载力计算方法进行了验证评估,结果表明,该文提出的预应力混凝土梁-型钢混凝土柱框架节点承载力计算方法具有较好的精度。

变电站装配式柱下独立基础设计方法

为进一步推动变电站模块化建设,文章以变电站工程中现浇混凝土柱下独立基础为原型,分析其受力特点和基础形式,进行基础装配式分块和连接设计,并通过ABAQUS有限元模拟和相关规范公式验证所设计装配式基础是否满足承载力和抗裂要求。研究结果表明:分块设计方案较为合理,可以满足工厂制作方便、运输及吊装要求;预应力-抗剪键的连接方式适用于装配式基础,所设计的预应力筋和抗剪键满足基础接缝面的抗弯、抗剪承载力和抗裂要求,并且具有一定的安全储备。

基于MCFT理论的PC空心板梁抗剪强度分析

为研究预应力混凝土空心板梁的抗剪强度,基于6次预应力混凝土空心板梁抗剪强度试验,对板梁斜裂缝扩展、极限抗剪强度开展分析,基于修正斜压场理论(MCFT),建立了板梁理论计算模型,研究了预应力混凝土空心板梁箍筋间距的等效间距法确定原则,对比试验数据,验证了其有效性并分析弯剪组合效应对抗剪强度的影响,针对预应力、配筋率、钢筋和混凝土强度等不同参数开展分析。结果表明:加载点位置抗剪强度计算值与试验抗剪强度的比值为0.71,剪跨中点位置抗剪强度计算值与试验抗剪强度的比值为0.99,支座位置纯剪状态下抗剪强度计算值与试验抗剪强度的比值为1.11,考虑弯矩后,板梁抗剪强度削弱,剪跨中点位置计算值与试验值更为接近;预应力混凝土空心板梁在弯剪组合状态下,全黏结预应力钢筋数量由2根提高到10根,抗剪强度提高21.7%;随预应力筋数量的增多,有效预应力大小对抗剪强度的影响更为显著,当弯矩为100 kN·m时,有效预应力由186 MPa增加到1395 MPa的过程中,2根预应力筋抗剪强度提高10.2%,6根预应力筋抗剪强度提高15.3%,10根预应力筋抗剪强度提高20.3%。

装配式预应力混凝土框架梁柱压接接缝抗剪性能试验与承载力计算方法研究

梁柱压接接缝抗剪性能对保证装配式预应力混凝土框架整体性能至关重要,为研究预压应力作用和梁端弯矩作用对其抗剪性能和承载力的影响,进行了11个预应力压接接缝试件和3个预应力压接接缝受弯矩作用试件的抗剪性能试验。试验结果表明:预加力能显著地增加接缝的抗剪承载能力,截面预应力分布对承载力有明显影响;预压应力均匀分布时,其极限剪应力和残余剪应力与均匀压应力之间均呈线性正相关关系;预压应力偏心分布时,预加力偏心距越大,其极限承载力较相同均匀预加力接缝降低越显著;接缝受梁端弯矩作用时,弯矩使接缝截面压力增加,接缝截面开裂前,压力合力偏心距减小,进而提高接缝的抗剪承载力;但接缝截面开裂后,压力合力偏心距增加,其抗剪承载力出现降低,接缝截面处于受弯极限状态时,抗剪承载力降至最低。提出了梁柱压接接缝考虑预应力作用和梁端弯矩作用的抗剪承载力计算方法。

采用浅铰缝的横向预应力空心板桥受力性能

为了消除铰缝病害对装配式空心板桥的不利影响,提出了一种采用浅铰缝的横向预应力装配式空心板桥方案。通过对一跨跨径13 m的空心板桥足尺模型的试验和非线性有限元分析,研究荷载作用下的桥梁受力性能。试验结果表明,浅铰缝结合面法向黏结强度为弱侧混凝土轴心抗拉强度的40%;结合面的切向黏结强度为弱侧混凝土轴心抗压强度的1.1%。试验过程中铰缝和新旧混凝土结合面保持完好,空心板先于铰缝破坏失效。采用浅铰缝的横向预应力装配式空心板桥的破坏模式为空心板破坏,铰缝不再是空心板桥受力的薄弱环节。有限元计算结果表明,横向预应力大大减小了铰缝结合面的法向拉应力。空心板桥的浅铰缝结合面发生的是剪切破坏而不是弯拉破坏。参数分析结果表明,施加横向预应力时,预应力不宜小于预应力钢筋强度标准值的45%。

飞机荷载桥梁装配式主梁横向新型连接方案及其静动力性能分析

针对既有装配式主梁铰缝连接强度弱、湿连接施工复杂等问题,充分考虑飞机荷载桥梁荷载集度大、空间受力显著等特点,提出一种剪力键和横向预应力筋混合连接的装配式主梁连接方案。该方案通过剪力键与键槽实现相邻主梁拼接,采用横向预应力筋为接缝界面提供压应力储备,具有结构整体性好、施工方便等优点。以某机场滑行道桥为对象,基于ABAQUS平台建立新型连接装配式主梁的非线性数值模型,开展静、动力学性能分析以验证方案的可靠性,揭示了剪力键位置、数量、高度及初始预应力对主梁力学行为和抗震性能的影响规律。结果表明:飞机静载作用下,该方案能够满足规范对于主梁挠度限值的要求且具有可观的安全储备。增设跨中剪力键及增加其数量可显著降低主梁跨中挠度和弯矩;相较于仅设置梁端剪力键,加设3道跨中剪力键可使静载下力学响应分别降低19.92%、23.35%,使地震下力学响应分别降低17.29%、40.12%。剪力键倾角和高度对主梁受力影响较小,增大横向预应力筋初始张拉力可有效提高主梁接缝界面的预压应力,静载、地震下的最大增幅分别为45.31%、46.51%。研究成果可为飞机荷载桥梁的主梁拼装提供重要的技术支撑,并可拓展应用于重载公路、铁路桥梁。

缓黏结预应力钢绞线用胶黏剂固化指标试验研究

近年来缓黏结预应力技术因其优异特性在预应力结构领域深受欢迎。缓黏结预应力技术的关键材料是缓黏结预应力钢绞线,技术原理是通过胶黏剂固化后将钢绞线与周围的混凝土融为一体,从而增加结构的黏结锚固性能。当前学术界和工程界对胶黏剂固化指标的研究较少,本文主要对胶黏剂常见的4种固化检测指标进行试验研究,包括邵氏硬度、拉伸剪切强度、抗压强度和弯曲强度试验。结果表明:胶黏剂的4种固化指标达到最大值时对应的固化时间接近相同,所以4种固化指标具有一致性;胶黏剂固化后邵氏硬度最大值的离散系数最小(0.013),邵氏硬度特征值(80 D)是胶黏剂固化完成的最佳固化评定指标。

薄壁墙式墩结构装配式方案及其抗震性能分析

针对既有柱式墩预制拼装技术难以应用于截面横纵比大的薄壁墙式墩的问题,提出了一种节段水平并联的新型装配式桥墩结构方案,预制节段采用双向无黏结预应力筋、灌浆套筒及混凝土剪力榫混合连接.依托某国际机场飞机荷载宽幅桥梁工程实例,基于ABAQUS平台分别建立了新型装配式桥墩和现浇桥墩的精细化有限元模型,通过拟静力分析对比研究了2种桥墩抗震性能的差异,并讨论了预应力筋配筋率以及剪力榫埋深对新型装配式桥墩抗震性能的影响规律.结果表明:新型装配式桥墩与现浇桥墩在纵向水平荷载作用下呈现墩底塑性铰充分发展的弯曲破坏形态,而在横向水平荷载作用下则呈现弯剪破坏形态;相较于现浇桥墩,装配式桥墩纵桥向与横桥向水平承载力分别提高68.5%和43.0%,但残余位移分别降低49.2%和67.8%;增大竖向预应力筋配筋率可显著提升装配式桥墩的水平承载力,而增加水平向预应力筋配筋率和剪力榫埋深则对限制节段接缝处的相对变形作用明显.