Strut-and-Tie Method as a Basis for Optimization of Hoop Prestressed Tendons in Abnormally Shaped Anchorage Zone of Cable-Stayed Bridge Pylon

Based on full-scale segment model tests of the abnormally shaped anchorage zone of the Maling River cable-stayed bridge pylon and FEM analysis, its mechanical and deformation properties were obtained, and the validity of FEM analysis was verified. An optimal layout of prestressed tendons in the anchorage zone was obtained by using the strut-and-tie method （STM）. The comparison FEM analysis between the full-scale segment model and the optimal prestressed tendons model show that： the optimal model not only saves prestressed tendons, but also achieves the same cracking resistance; STM method is reliable and accurate in the analysis of the abnormally shaped anchorage zone of cable-stayed bridge pylon.

Finite element failure analysis of continuous prestressed concrete box girders

In order to analyze the load carrying capacity of prestressed concrete box girders, failure behaviors of in-situ deteriorated continuous prestressed concrete box girders under loading are experimentally observed and a finite failure analysis method for predicting behaviors of box girders is developed. A degenerated solid shell element is used to simulate box girders and material nonlinearity is considered. Since pre-stressed concrete box girders usually have a large number of curve prestressed tendons, a type of combined element is presented to simulate the prestressed tendons of box girders, and then the number of elements can be significantly reduced. The analytical results are compared with full-scale failure test results. The comparison shows that the presented method can be effectively applied to the failure analysis of in-situ continuous prestressed concrete box girders, and it also shows that the studied old bridge still has enough load carrying capacity.

Experimental research on mechanical properties of prestressed truss concrete composite beam encased with circular steel tube

Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of the tensile steel tube is 0.252 during the using stage,and the average crack space of beams depends on the ratio of the sum of the bottom chord steel tube's outside diameter and the secondary bottom chord steel tube's section area to the effective tensile concrete area. The coefficient of uneven crack distribution is 1.68 and the formula for the calculation of crack width is established. Test results indicate that the ultimate stress increment of unbonded tendon in the beams decreases in linearity with the increase of the composite reinforcement index β0. The pure bending region of beams accords with the plane section assumption from loading to failure. The calculation formula of ultimate stress increment of the unbonded tendon and the method to calculate the bearing capacity of normal section of beams have been presented. Besides,the method to calculate the stiffness of this sort of beams is brought forward as well.

光纤光栅传感器研发及其在土木工程中的应用进展

从传感器类型出发介绍了表贴式、纤维增强聚合物式、管式和内嵌式封装光纤布拉格光栅传感器的结构型式、实施方式和关键技术,简述了各种封装方式传感器的工作原理、技术研发及工程应用进展,总结了不同封装方式传感器的优势和不足。然后,简要介绍了光纤布拉格光栅传感器在桥梁结构状态监测或检测中的典型工程应用案例。最后,指出了光纤布拉格光栅传感器在土木工程领域中的工艺工法、耐久性和分布式测量以及未来推广应用有待解决的关键问题等,为光纤布拉格光栅传感器技术优化及其在土木工程中的推广应用提供参考。

某全民健身中心大跨度预应力钢筋混凝土跨层桁架结构分析与设计

为了实现某全民健身中心局部多层的无柱大空间,结构设计采用了在二层设置大跨度预应力梁和在三层、四层设置大跨度预应力钢筋混凝土跨层桁架的方案。采用SAP2000软件对比了跨层桁架中预应力筋一次性全部张拉施工和分层浇筑、分批张拉施工下杆件的内力情况,结果表明后者的桁架下弦杆件的最终拉力较小,符合设计要求。通过各施工阶段下桁架杆件的内力变化情况,确定了预应力筋的布置及数量。最后,介绍了本工程预应力杆件的设计和采取的针对性设计措施,说明了施工阶段的监测情况。通过以上分析及设计,验证了预应力钢筋混凝土跨层桁架结构的可行性,较好地实现了建筑功能。

基于实际损伤的桥梁体外预应力加固锚固区应力分析与配筋设计

为准确计算桥梁体外预应力加固锚固区应力,指导锚固区配筋设计,以一座4跨预应力混凝土连续刚构桥为背景,提出一种基于实际损伤的体外预应力加固锚固区应力分析与配筋设计方法。首先根据连续刚构桥下挠计算参数敏感性分析结果,确定计算参数组合,建立锚固区局部分析有限元模型;然后基于容许应力法对锚固区进行应力分析;最后对锚固区三向应力较大区域进行配筋设计。以3座桥梁为算例计算锚固区配筋量,并与基于全桥有限元法的实桥配筋结果进行对比,结果表明:采用该方法计算的锚固区横桥向、竖向和单锚局部承压区配筋量与采用全桥有限元法计算的配筋结果基本接近。该方法考虑了加固前原结构的损伤,对于非规则、异形锚固构造也具有适用性,同时避免了冗繁的全桥有限元建模与计算过程。

高速公路30 m UHPC无腹筋预应力U型节段组合梁抗弯承载能力足尺试验研究

中开高速公路改扩建工程中首次在高速公路中大规模采用30 m跨度的UHPC无腹筋预应力U型节段组合梁,充分利用了新型桥梁质量轻、整体性好、耐久性优异的特点。成果是世界首次针对这种梁型开展足尺寸抗弯承载能力试验。详细介绍了新型结构的力学特点和试验结果。研究结果表明:UHPC无腹筋预应力U型节段组合梁具有承载能力高、结构延性优异的特点。

斜拉桥索塔锚固区环向预应力筋优化方法研究

为防止斜拉桥索塔锚固区开裂、改善锚固区应力分布,基于遗传算法结合三维数值仿真提出一种索塔锚固区环向预应力筋优化方法,该方法利用数值仿真模型识别混凝土待优化区域,将张拉系数作为设计变量,建立数学优化模型,再结合遗传算法不断迭代优化设计变量,使索塔锚固区达到最优应力状态。以溧宁高速公路景宁高架段斜拉桥为背景,通过数值仿真和足尺模型试验,建立优化模型并采用遗传算法以锚固区应力水平为优化目标对索塔锚固区环向预应力筋进行优化迭代,并依据实测预应力损失修正优化方案。结果表明:环向预应力筋能为锚固区塔壁提供6~8 MPa的预压应力,可有效增强锚固区塔壁的抗拉能力;足尺模型试验实测预应力损失约为10%,且通过试验测得的应力值与理论计算值相吻合,数值仿真结果准确;采用最终得到的预应力方案可使索塔锚固区最大拉应力降低27.1%,有效改善锚固区应力分布状况。

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。

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.

先张空心板支座附近底板开裂原因及防治措施

为探讨先张空心板支座附近底板常出现横向开裂原因及其控制措施,根据实际先张空心板支座底板裂缝特点,基于精细化的空间实体模型,分析了荷载作用下先张空心板预应力筋失效孔的存在、数目及布置方式对其底板的影响,明晰了该类空心板底部裂缝的主要原因,并针对性地提出了防治措施。研究表明:预应力筋失效孔引起的底板应力过大是先张空心板支座附近底板开裂的主要原因,建议在进行先张法空心板设计时应计入预应力筋失效孔的影响,同时对钢束端部失效段的孔洞应采取填充等必要措施。

既有砌体结构外套门式刚架-内置预应力拉杆成套加固技术研究

针对老旧小区入户加固困难的问题,基于悬索桥荷载悬吊理论和拉杆拱理论,提出外套门式刚架-拉杆加固方法,通过在砌体结构外部增设钢筋混凝土门式刚架和预应力拉杆,提高既有砌体结构的竖向承载力和水平抗震性能。研发了墙内长距离钻孔设备和成套工艺,为本加固方法的实现提供了技术支撑。在此基础上,本文进行了外套钢筋混凝土门式刚架加固砖墙的拟静力试验及竖向承压试验,并进行有限元数值模拟,建立了外套门式刚架加固计算方法。研究表明,外套门式刚架-拉杆加固技术可以大幅提升既有砌体结构的抗震承载力,显著提高墙体竖向承载力。

65 m+110 m+65 m连续刚构计算分析

某特大桥中65 m+110 m+65 m连续刚构采用预应力变截面混凝土箱梁,文章阐述了该桥的箱梁构造、预应力钢束的布置,并结合相应的施工工艺,采用桥梁结构有限元软件Midas Civil对该桥进行建模分析,以保证其设计安全、合理。

大跨径预应力混凝土盖梁在高速公路桥梁跨越管线中的应用

在高速公路建设过程中,地下管线工程往往会影响设计方案,制约施工工期。采用大跨径预应力盖梁直接跨越桥下管线具有明显的社会和经济效益。介绍了沾临高速一座分离立交桥采用大跨径预应力盖梁跨越济青二线燃气管线的设计方案,并分析预应力盖梁的受力特性。根据盖梁不同结构类型,合理选用钢束张拉方案,减小施工阶段墩身过大的弯矩效应,为类似工程提供参考。

Ultimate stress increase in unbonded tendons in prestressed concrete beams

Since the assumption of plane sections cannot be applied to the strain of unbonded tendons in prestressed concrete beams subjected to loadings,a moment-curvature nonlinear analysis method is used to develop analytical programs from stress increases in unbonded tendons at the ultimate limit state.Based on the results of model testing and simulation analysis,equations are proposed to predict the stress increase in tendons at the ultimate state in simple or continuous beams of partially prestressed concrete,considering the loading type,non-prestressed reinforcement index βp,prestressing reinforcement index βs,and span-depth ratio L/h as the basic parameters.Results of 380 beams studied here and test results for 35 simple beams obtained by the China Academy of Building Research were compared with those from prediction equations given in codes and other previous studies.The comparison reveals that the values predicted by the proposed equations agree well with experimental results.

Behavior Characteristics of Bonded Type Anchorage for CFRP Tendon

This paper examines the shear stress and displacement occurring in CFRP tendons through finite element analysis on the parameters influencing the anchoring performance to evaluate the behavioral characteristics of the bonded type anchorage for CFRP tendon. The selected parameters are the inner angle of the anchorage barrel, the friction between the barrel and filling material, and the elastic modulus of the filling material. The difference in the behavioral characteristics is examined for each parameter. In view of the analytic results, the shear stress developed in the CFRP tendon reduces with larger inner angle of the barrel and lower elastic modulus of the filling material. However, such combination provokes also the increase of the relative displacement of the CFRP tendon. Especially, slip failure may occur due to the lack of the confining force necessary for the anchorage due to the sudden loss of vertical force brought by the wedge force. The experimental results relative to barrel inner angles of 2° and 4° showed that the specimen with an angle of 2° preserved its anchoring performance up to tensile failure whereas the specimen with an angle of 4°?failed in developing its maximum anchoring performance due to slip failure.

Parametric Analysis on the Optimal Dimensions of Steel Sleeve in Swaging Type Anchorage for CFRP Tendon

This paper presents the parametric analysis conducted to derive the optimal dimensions of the steel sleeve necessary to secure the bond performance of the swaging type anchorage for CFRP tendon with diameter of 5 mm. To that goal, finite element analysis is performed on the parameters determining the dimensions of the sleeve like the thickness and inner diameters of the sleeve. The results show that a constant swaging pressure of about 450 MPa on the mean is distributed in the sleeve when the thickness ratio of the stress relief zone to the effective swaging zone of the sleeve is larger than 1.1 and that the swaging pressure tends to reduce linearly as much as this thickness ratio becomes smaller than 1.1. The pressure varies within a range of about 30% according to the change in the inner diameter of the sleeve whereas varies within a range less than 10% according to the change in the inner diameter when the thickness ratio is larger than 1.1. Finally, the optimal dimensions of the steel tube sleeve enabling to secure an anchor force larger than the rupture strength of the CFRP tendon with diameter of 5 mm are determined based upon the results of the parametric analysis.

轨道交通大跨度预应力混凝土连续梁桥加固设计

针对轨道交通大跨度预应力混凝土连续梁桥跨中下挠及开裂等病害,以某轨道交通(65+120+65)m预应力混凝土连续梁桥为背景,研究该类病害桥梁加固方法。根据资料调研及有限元计算,对受损主梁进行病害成因分析及状态模拟。经过方案比选,确定加固方案为:补充张拉2束15-∅15.2 mm备用体内预应力束;增设12束19-∅15.2 mm体外预应力束;预应力管道补充注浆、裂缝封闭。施工监测结果显示:加固后主梁中跨跨中截面增加了5.73 MPa压应力、上拱22.3 mm。加固后轨道交通恢复正常速度通行,监测结果表明桥梁轨道平顺、行车舒适度良好,证明了加固方案安全适用、效果显著。

纵筋锈蚀对后张混凝土梁预应力筋应力的影响规律

为探究非预应力筋锈蚀对预应力筋应力的影响,记录了试验梁在不同锈蚀环境下180 d的应力值.通过通电-氯盐溶液干湿循环方式,加速预应力混凝土试验梁内非预应力纵筋锈蚀,并采用振弦式锚索测力计测试梁内预应力筋应力.试验结果发现:预应力筋应力变化值与环境温度密切相关;与大气环境中静置的试验梁相比,干湿循环会增大预应力筋应力,并且在研究期限内,预应力筋应力持续增长,变化值最大为42.6 MPa,这与混凝土湿胀和盐胀的特性相关;纵筋锈蚀及其引起的混凝土截面损伤会使混凝土轴心放置的预应力筋应力下降31.5%;所建立纵筋锈蚀率与预应力筋应力变化值之间的关系模型与试验测试结果较为吻合.因此,纵筋锈蚀对预应力混凝土梁内预应力筋应力产生显著影响,需要在设计和维护中予以考虑.

某单层砖木结构后张预应力加固与常规加固技术的综合应用

某单层砖木结构房屋,建于1990年。由于改变使用功能需要,现对房屋结构进行了综合安全性鉴定,结果表明其不满足现行抗震鉴定标准的要求,需采取相应的加固措施。综合考虑改造中经济成本及使用要求,为尽量不减少房间使用率。特提出了建筑纵墙采用新型后张预应力技术加固结合水泥砂浆抹面加固,利用附属功能房间增设内横墙加固,木屋架之间增设型钢剪刀撑加固的综合方案。以上综合加固方案在提高房屋抗震能力的同时,房间使用面积充分合理利用,全面满足了加固改造需求。