Prestressed tensioning method and its application to testing anchor stress of anchor cables for side-slope stabilization

The anchor stress extent of a prestress anchor cable project has a direct relation with the project safety and performance. Prestressed tensioning method is a kind of nondestructive testing method, by which a reverse stretching load is applied on the external exposure section of anchor cable under construction or in service, and then the elongation variation of stress bars is measured to determine the anchor stress. We elaborated the theory and testing mechanism of prestressed tensioning method, and systematically studied key issues during the prestressed tensioning process of anchor cable by using physical model test, including the composition of tension stress-elongation curve, the variation of anchor stress, the compensation of locked anchor stress, and the judgment of anchor stress, and verified the theory feasibility of prestressed tensioning method. A case study on slope anchor cable of one highway project was conducted to further discuss on the test method, operation procedures and judgment of prestressed tensioning method on obtaining anchor stress, and then the test data of three situations were analyzed. The result provides a theoretical basis and technical base for the application of prestressed tensioning method to the evaluation of construction quality and operation conditions of anchor cable project.

ANALYSIS ON INCREMENTAL COHESION OF SURROUNDING ROCK DUE TO PRESTRESSED CABLE ANCHOR

A new method for determining the incremental cohesion △Cm of surrounding rock due to prestressed cable anchor is presented, and the formulas for △Cm are deduced and △Cm distributions also are discussed, based on the two anchorage effects, one is the effect with the prestressed vaIue △σ3 of cable anchor improving the stress state of surrounding rock and increasing the surrounding rock strength, the other is the fully encapsulated effect. The determined incremental cohesion △Cm is subiected to the model test and field measurement in the references, and coincides well with those tested results. The formulas for △Cm can be used in designing supoport parameters and related numerical analyses of prestressed cable anchor.

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.

Exploring the feasibility of prestressed anchor cables as an alternative to temporary support in the excavation of super-large-span tunnel

Excavating super-large-span tunnels in soft rock masses presents significant challenges.To ensure safety,the sequential excavation method is commonly adopted.It utilizes internal temporary supports to spatially partition the tunnel face and divide the excavation into multiple stages.However,these internal supports generally impose spatial constraints,limiting the use of large-scale excavation equipment and reducing construction efficiency.To address this constraint,this study adopts the“Shed-frame”principle to explore the feasibility of an innovative support system,which aims to replace internal supports with prestressed anchor cables and thus provide a more spacious working space with fewer internal obstructions.To evaluate its effectiveness,a field case involving the excavation of a 24-m span tunnel in soft rock is presented,and an analysis of extensive field data is conducted to study the deformation characteristics of the surrounding rock and the mechanical behavior of the support system.The results revealed that prestressed anchor cables integrated the initial support with the shed,creating an effective“shed-frame”system,which successively maintained tunnel deformation and frame stress levels within safe regulatory bounds.Moreover,the prestressed anchor cables bolstered the surrounding rock effectively and reduced the excavation-induced disturbance zone significantly.In summary,the proposed support system balances construction efficiency and safety.These field experiences may offer valuable insights into the popularization and further development of prestressed anchor cable support systems.

Reliability analysis of prestressed anchors in rock slopes of open-pit mines

Prestressed anchor cables are widely used for slope reinforcement,but the loss of prestress makes it difficult to guarantee the reinforcement effect.Anchor cable prestress degradation was considered as a stochastic process,and the probability density function of this process was established using gamma theory and impact theory respectively.Combined with the failure threshold,the probability density was integrated to find the time-dependent reliability of the anchor cable.Based on the monitoring data of the prestress degradation of the anchor cable,parameters in the probability density function were solved by the maximum likelihood method,and the time-varying reliability and service life of the anchor cable were obtained analytically.The applicability of two degradation theories,gamma stochastic process and impact theory,was compared.The results showed that the probability density curves of both degradation models were normally distributed and the error of reliability results did not exceed 0.06.The life prediction results of the gamma stochastic process were closer to the actual life of 400 h than the 500 h of the impact theory,and the probability curves of the anchor cable life also indicated that the impact theory overestimated the service life probability of the anchor cable.Taking the anchor cable reinforcement within the slope of the Dagushan open-pit mine as an example,and the results verify the feasibility of using gamma theory to predict the degradation of anchor cables and provides theoretical support for prevention of the degradation of anchor cables in the slope of an open-pit mine under the action of external forces.

Parametric Study on Cable-Stayed and Knee-Braced Steel Portal Frames

To improve wind resistance capacity of cable-braced steel portal frames,a double-braced portal frame was proposed by adding two pre-stressed knee braces to a cable-braced portal frame. To study the reasonable range of application and method of cable parameter determination for this novel structure,the influences of load condition, span, base constraint, and cable parameters on structural performance were investigated by using the finite element code SAP2000. The results show that pre-stressed knee braces can effectively resist both uplifted and lateral wind loads,so this cablestayed and knee-braced steel portal frame is suitable for large wind.When the vertical load is comparable with the wind load,this novel type of portal frames is suitable for a medium span( 21-48 m). The cables in the cable brace can be determined by structural vertical stiffness,and the cables in the knee brace can be designed as the same as those in the cable-stayed part for the reason that their cross sectional area has only a weak effect on the structure. If no cable fails,the pretension variation of the cable does not affect the stiffness of the portal frame. The cable in the cable brace,working together with the cables in the knee braces,can ease uneven distribution of internal force,and their pretensions can be determined according to actual engineering projects.

PPC斜拉桥主梁多状态疲劳及疲劳后静力性能试验研究

为研究大跨径部分预应力混凝土(PPC)斜拉桥主梁的抗疲劳性能,进一步探究混凝土斜拉桥主梁采用部分预应力设计的可行性及合理性,制作了斜拉桥缩尺节段模型,并对主梁采用部分预应力设计,开展4轮共4×250万次主梁具有不同初始损伤及带裂缝工作状态下的疲劳试验;疲劳试验结束后,以4种不同主梁裂缝宽度(0.1mm、0.2mm、0.3mm和0.5mm)为控制工序,反复加载一定倍数的等效活载至主梁裂缝宽度逐步达到0.5mm,以全面研究PPC斜拉桥主梁多状态疲劳后的受力性能。试验结果表明:在等效设计疲劳荷载作用下,主梁无初始损伤时,体系刚度基本无退化,主梁最大裂缝宽度预损伤分别为0.1mm、0.2mm时,跨中截面体系刚度下降量仅为3.35%、4.44%,且未发现裂缝张开;主梁带裂缝工作状态下,跨中截面体系刚度平缓下降7.46%,上峰值静载下,裂缝数量及高度略有增加,但卸载后裂缝均闭合,说明PPC斜拉桥具有良好的抗疲劳性能;疲劳后主梁大损伤静载试验中,主梁裂缝平稳发展,各工序反复加载过程中,主梁挠度、裂缝状态及斜拉索索力均具有较好的恢复能力,当主梁最大裂缝宽度为0.5mm时,荷载达到了7.49倍活载,斜拉桥体系仍然具有较大的剩余承载力。该文试验研究结果表明混凝土斜拉桥主梁采用部分预应力设计具有工程应用的可行性。

斜拉桥非对称V形钢塔-混凝土基座结合部构造设计优化

某空间异型斜拉桥主塔钢柱与斜撑在底部形成非对称V形结构,钢构件轴线严重偏离下部混凝土基座顶面垂线,给结合部构造设计带来困难。目的 为了确定所采用构造方案中的众多参数,缓解塔柱到基座的刚度陡变,降低结合部各部件的应力最大值,方法 基于精细化非线性有限元模拟,通过改变参数取值,对多种典型工况下各部件的应力进行分析、对比、验算,对于锚杆设置这一参数的影响,还研究了承压板与混凝土基座之间的界面应力。结果 研究结果表明:张拉1~4号索的施工极端工况和平面内外弯矩绝对值相加最大的使用工况最为关键,基座混凝土主拉应力常起控制作用,塔根应力比较接近规范限值;加厚承压板、适当提高混凝土强度有利于控制锚箱钢板和基座混凝土应力;原方案锚箱中部纵横向钢板作用很小;锚杆布置位置合理远比数量重要,弯矩作用下受拉侧施加预应力能够起到有益作用。结论 最终优化方案大量减少了锚箱钢板块数和锚杆根数,预应力分布也更合理。研究结果兼顾安全、适用和经济,对相关工程具有借鉴意义。

钢绞线热铸锚节点高温下抗拉性能试验研究

针对锌铜合金熔点较低(约460℃±10℃)、高温下热铸锚节点容易失效的问题,对预应力钢绞线热铸锚节点进行了高温抗拉性能试验,获得了高温下试件的破坏模式和抗拉承载力,提出了钢绞线热铸锚节点在高温下极限抗拉承载力计算公式,以及在各荷载比下的临界温度,可用于钢绞线热铸锚节点的抗火承载力验算与防火保护层厚度设计.试验研究表明,温度低于200℃时,破坏模式为钢绞线断裂;温度高于200℃时,破坏模式通常为钢绞线滑脱.温度为150~440℃时,钢绞线热铸锚节点的极限抗拉承载力随温度升高而降低,287℃、340℃、392℃和425℃时的极限承载力分别为常温时的77.3%、39%、35.2%和10.5%.

初始张拉力对预应力-CLT组合结构受力影响研究

正交胶合木(CLT)是一种适合于建筑工业化的人工绿色材料,具有可预制、可再生、自重轻但强度和刚度较高等特点,有较好的环境效应。如果能够在正交胶合木基础上加上预应力,则该组合结构受力性能将会得到进一步提升。主要对不同初始张拉力下预应力-正交胶合木组合结构进行试验研究:考虑预应力钢绞线的2种不同初始张拉力,设计了2个CLT剪力墙构件进行拟静力往复加载试验,得到了2个构件的骨架曲线、刚度退化曲线、等效粘滞阻尼系数、变形模式等内容;同时,通过将试验结果与国内相关研究成果进行对比分析,发现施加预应力对CLT结构整体刚度、耗能能力等有较大提升;相比于预应力-木组合结构组装于钢底梁上,预应力-木组合结构组装在混凝土底梁上在一定程度上减少了钢节点的使用,缩小了两者之间的刚度差,使得混凝土底梁情况下构件屈服荷载、屈服位移以及最大承载力方面有一定的提升。

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。

受损PPC斜拉桥主梁灌缝加固后疲劳性能试验研究

为进一步研究受损部分预应力混凝土(PPC)斜拉桥主梁裂缝灌浆加固后的疲劳性能,对受较大疲劳及静力损伤的PPC斜拉桥节段缩尺模型主梁进行裂缝灌浆加固,并开展疲劳及疲劳后静载试验研究。研究结果表明:在疲劳荷载作用下,灌浆裂缝未重新开裂,在疲劳加载初期(约20万次),结构体系刚度下降较快,后期下降较平缓;250万次疲劳加载后,主梁L/4、L/2和3L/4截面处的结构体系刚度分别降低12.83%、9.48%、13.62%,较原主梁第4轮疲劳加载下结构体系刚度下降幅度大,但疲劳结束时结构体系刚度仍然比原主梁第4轮疲劳加载初始结构体系刚度大;对裂缝进行灌浆处置能有效恢复PPC斜拉桥主梁的抗裂强度及结构体系刚度;随着荷载增大,灌浆裂缝逐步张开,但最大裂缝宽度对应位置发生转移,同时不断有新裂缝产生,且裂缝分布区域范围增大,环氧树脂胶的作用极大地延缓了裂缝宽度的增大,提高了主梁的抗裂性能;环氧树脂胶不仅能修复混凝土裂缝界面,同时能有效恢复钢筋与混凝土间的黏结滑移损伤;对受严重损伤的PPC斜拉桥主梁仅进行裂缝灌浆处置后,主梁仍然具有良好的抗疲劳性能,同时,其疲劳后的抗裂性能及刚度也得到较大恢复。

地震荷载下预应力锚固边坡离心振动模型试验研究

预应力锚索作为边坡支护的重要技术,已经在边坡加固中得到了广泛应用,但锚固岩质边坡在地震荷载作用下的响应机制以及锚索受力变形规律还不明确。为此,开展了预应力锚固边坡离心振动模型试验,系统介绍了模型相似设计、模型设计与制作、地震荷载施加等试验关键技术,并以紫坪铺水库泄洪洞进口岩质边坡为原型,开展了简谐地震波作用下的锚固边坡离心模型试验。对试验结果进行了分析,并对该离心振动试验的主要影响因素进行了探讨。研究结果表明:地震作用下预应力锚索发挥了较强的被动支护作用,且越靠近滑面处应力应变响应越明显;边坡竖向位移与应力应变值的响应情况随地震烈度的改变产生明显变化。研究成果可为今后离心振动模型试验的开展提供参考与借鉴。

渐进式滑坡锚索抗滑桩预应力张拉值计算

依据渐进式滑坡蠕变特点,现有锚索抗滑桩计算模型针对渐进式滑坡桩–锚–土三者相互作用过程考虑较少。针对这一问题,将渐进式滑坡缓慢失稳的变形特征和预应力锚索抗滑桩从空载到满载动态工作过程相结合,利用Winkler弹性地基梁理论,优化了锚索抗滑桩桩–锚变形协调条件,考虑桩后土压力渐进变化过程,构建不同工况桩–锚–土协同工作的计算模型,推导了预应力锚索抗滑桩施工阶段初张拉值的计算方法。结合工程算例和有限元软件数值模拟结果,为获取较高精度的计算数值,采用MATLAB软件编译程序进行计算分析。结果表明:1)渐进式滑坡“稳定–蠕动–失稳”阶段性变形特点决定了预应力锚索抗滑桩“空载–加载–满载”三阶段桩–锚动态内力变形过程,明确了各阶段桩后可能存在的土压力模型,单纯进行满载阶段锚索拉力设计不符合渐进式滑坡实际作用机理,进一步证明施工阶段锚索预应力张拉值设计的重要性;2)渐进式滑坡推力由尚未产生的初始空载阶段至完全作用的满载阶段,两阶段并非互相独立存在,二者通过桩–锚变形协调条件相互作用,表明了施工阶段抗滑桩预应力张拉力值大小受满载阶段桩锚内力及变形大小的影响;3)依据渐进式滑坡锚索抗滑桩动态内力变形过程,保证抗滑桩受荷段和锚固段内力大小均衡相等,优化了满载阶段全桩弯矩平衡设计原则,确立了以静止土压力作为施工阶段预应力张拉值设计标准,对比表明,此计算方法优于其余4种现有算法,同时有限元数值模拟结果与本文算法贴合度较高,进一步验证了此计算方法的合理性和可靠性。研究成果可为渐进式滑坡中预应力锚索抗滑桩的设计计算和施工提供技术指导。

高速公路边坡预应力锚索桩板墙结构参数优化与受力特征分析

桩板墙是高速公路滑坡治理中常用的一种支护措施,其结构参数的优化设计是工程施工的研究重点。以云南省红河州建水(个旧)至元阳高速公路工程AK0+560~AK0+660段桩板墙工程为背景,采用数值模拟与灰色关联分析、正交试验设计相结合的方法,研究桩体嵌固长度、桩间距、桩宽3种结构参数的影响与优化,最终验证优化后的结构参数在地震工况下的稳定性。结果表明:桩间距为主要影响因素,桩体嵌固长度和桩宽的关联度相近,为次要影响因素;桩板墙结构参数最优组合为桩体嵌固长度15.0 m、桩间距5.0 m、桩宽3.0 m;地震工况下,抗滑桩悬臂段土压力以及桩身偏移量和沉降差满足规范要求,边坡稳定性较好。

超高层大悬挑钢结构平台钢拉索施工技术

以某超高层悬挑钢结构平台预应力拉索为研究对象,在确保结构受力安全的前提下,对新型空间钢拉索结构的安装及张拉进行深入研究,通过有限元软件对各阶段进行分析模拟计算,了解结构受力特点,模拟各工况下施工受力,在工期紧张环境下能够及时调整施工方法,通过过程施工监测,确保拉索施工顺利进行,经过分析、深化设计、测试、施工全过程模拟,最终实现大悬挑钢结构平台钢拉索固定,实现其使用功能。

基于理论承载性能与应力扩散计算的高强预应力锚索适配垫板设计方法

垫板是高强预应力锚索系统的核心组成构件,当其与锚索间适配性不足时,会出现结构可靠性低以及围岩支护效果差等问题。基于垫板的承载力学特性及其应力扩散作用,提出适配高强预应力锚索的垫板设计方法。为此,首先分析垫板的应力扩散作用与锚索的支护效应间的关联性。其次,基于不同形式垫板的结构受力特征,提出碗形垫板和平板形垫板的理论承载力计算公式,并由此计算得到满足高强预应力锚索承载性能需求的垫板型式及其结构参数。接着,通过建立“垫板(碗形、平板形)-围岩”三维数值仿真模型,分析不同型式及结构参数垫板的围岩应力扩散效果,并由此优选得到适配高强预应力锚索的垫板型式及其结构参数。最后,通过现场应用案例,分析适配垫板下高强预应力锚索系统支护效果。研究结果表明:提出的垫板设计方法实现了对高强预应力锚索系统中垫板的有效选用,适配加载300 kN的高强预应力锚索系统垫板为25 cm×25 cm×16 mm的碗形垫板,其拱高35 mm、孔口半径32 mm、碗底半径75 mm;同时,适配垫板下高强预应力锚索系统的围岩变形控制效果提升了11.9%~15.2%。研究结果有助于提升高强预应力锚索系统的可靠性与支护效果,并为预应力锚固系统中垫板的设计提供了一种可行且有效的方法。

土钉墙+桩锚式组合的深基坑支护技术研究

以石家庄市某深基坑项目为案例背景,通过研究土钉墙+预应力锚索组合的支护形式,将理论与施工现场实际相结合,同时对常见的施工质量问题进行分析并提出相应的解决措施,以期为相关工程提供参考经验。

桩锚结构体系在深基坑支护中应用研究

桩锚支护结构具有合理的受力形式,较大的支护刚度,节约施工空间等优点,在深基坑支护中被广泛应用,文中以定西市某基坑桩锚支护结构为依托,通过计算分析不同预应力锚索组合下,桩身最大内力与位移的影响,合理选取桩身及锚索参数,能有效降低桩身内力及桩顶位移,使护坡桩结构受力更合理,可取得更可靠经济的支护方案。