Analysis and calculation of factors on curvature ductility of unbonded prestressed concrete beams

In consideration that behavior of curvature ductility of interior support directly influences the degree of moment modification of unbonded prestressed concrete (UPC) continuous structures, constitutive relationships of concrete, non-prestressed reinforcement and prestressed reinforcement used for nonlinear analysis are given. Through simulation analysis on simple beams subjected to single loading at the middle of the span, the law of factors influencing curvature ductility, such as global reinforcing index, prestressing degree, effective prestress, strength of concrete and grade of non-prestressed reinforcement are explored. Based on these researches, calculating formula of curvature ductility coefficient of UPC beams is established, which provides basic data for further research on plastic design of UPC indeterminate structures.

Fatigue Behavior of Unbonded Partially Prestressed Concrete Beams with Flexure

A study on fatigue behavior of unbonded partially prestressed concrete beams is presented. Model tests have been carried out in static loading and cyclic compressive loading on 15 beams with flexure. The ratios of the lower limit to the upper limit of fatigue load are 0.5 and 0.3 respectively, and the frequencies of cyclic loading are 8 Hz and 4.5 Hz respectively. The experimental results of the strains of the concrete and steel bars, the deflection of test beams, and the crack width of normal section are analyzed. According to statistics and analysis of test results, the corresponding calculation models are developed and presented.

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.

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.

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。

无粘结环锚预应力衬砌张拉工艺足尺模型试验研究

针对预应力衬砌张拉过程中易出现应力集中而导致张拉裂缝的现象,通过开展洞外地面足尺模型试验,提出了分级分步张拉顺序和质量控制指标。首先根据钢绞线摩阻测试计算出摩擦系数,随后应用上述张拉顺序和质量控制方法进行自动张拉,并采用磁通量传感器和混凝土应变计分别对钢绞线和内衬混凝土的应力变化开展实测。现场张拉试验结果表明:①钢绞线沿程预应力损失约16.3%,采用的双层钢绞线在实践中可保证较高的有效预应力;②对锚具槽进行分级分步张拉,可使内衬混凝土获得较均匀的封闭环向压应力环,平均压应力达-10.9 MPa;③提出的3项控制指标可进行量化管理,结合自动张拉技术可有效地保证张拉质量。

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.

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。

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.

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。

无粘结预应力混凝土结构抗震性能研究分析

无粘结预应力混凝土(unbonded prestressed concrete,简称UPC)结构具有结构恢复性能好、摩擦系数小、施工方便等特点,故其被广泛应用在高层建筑、大跨度工程中。研究从UPC结构中柱节点的特性、节点研究的重要性、其国内外研究发展状况和目前抗震性能的分析方法等角度,对UPC结构中柱节点抗震性能的相关研究进行了分析和归纳。结论总结如下:目前UPC结构的研究主要是针对无框架边节点以及梁的试验研究,而对UPC结构中柱节点的试验研究甚少。

自复位混凝土剪力墙研究进展

自复位剪力墙在遭受地震时能够实现大位移而不会有明显的残余变形或大量损伤,适用于地震后的快速恢复结构。为研究自复位混凝土剪力墙的发展趋势,文中介绍了国内外自复位混凝土剪力墙结构的相关研究进展,对相关研究进行展望和总结,表明在自复位混凝土剪力墙中加入耗能部件或选择合适的配筋方式,可以改善墙体的力学性能并控制损伤。

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。

自复位预制节段桥墩抗震性能试验研究

为提高装配式预制桥墩的抗震性能以及解决震后可修复的问题,本文基于后张无黏结预应力筋的连接技术,提出了一种新型自复位预制节段桥墩(self-centering precast segmental bridge pier,SPSBP)。该新型自复位预制节段桥墩由预制构件(盖梁、节段、基础)、可更换耗能角钢和连接钢板组成。本文设计并完成了三组SPSBP试件的拟静力试验,研究初始预应力、耗能角钢厚度以及长度三个参数对SPSBP试件抗震性能的影响。试验结果表明:该新型结构形式具有较好的自复位以及耗能能力;当加载到最大位移比时,试件变形主要集中于耗能角钢,主体预制结构并未发生明显破坏,表明了结构的完整性;提高初始预应力能有效提高结构的承载力等抗震性能并减小残余变形;增加耗能角钢厚度,可以提高SPSBP耗能能力以及承载力;耗能角钢长度对SPSBP性能影响不明显。

无粘结预应力UHPC梁剪切性能试验研究

为研究无粘结预应力无腹筋UHPC梁的剪切力学行为,设计了1片矩形截面UHPC梁并进行了剪切试验。试验采用1000 t电液伺服长柱压力试验机对试验梁进行了单点加载,测试了UHPC梁的挠度、梁腹位置主应变、加载点截面正应变和钢绞线应力增量等数据,并将抗剪承载力试验结果与法国标准和瑞士标准UHPC梁抗剪承载力计算结果进行对比。结果表明:在剪跨比λ适中时(λ=1.86),无粘结预应力无腹筋UHPC梁发生剪压破坏;由于UHPC中钢纤维的桥接作用,试验梁在斜裂缝出现以后并未立即失去承载能力,仍然可以承受继续增大的荷载;试验梁在发生破坏时加载点下方截面底缘混凝土拉应变达到2700με,表明UHPC材料具有较好的抗变形能力;现有法国标准和瑞士标准对于UHPC梁抗剪承载力的计算方法均偏保守,未能考虑剪跨比和纵向钢筋消栓作用对抗剪承载力的影响。

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。