Theoretical Analysis on Deflection and Bearing Capacity of Prestressed Bamboo-Steel Composite Beams

A theoretical analysis of upward deflection and midspan deflection of prestressed bamboo-steel composite beams is presented in this study.The deflection analysis considers the influences of interface slippage and shear deformation.Furthermore,the calculation model for flexural capacity is proposed considering the two stages of loading.The theoretical results are verified with 8 specimens considering different prestressed load levels,load schemes,and prestress schemes.The results indicate that the proposed theoretical analysis provides a feasible prediction of the deflection and bearing capacity of bamboo-steel composite beams.For deflection analysis,the method considering the slippage and shear deformation provides better accuracy.The theoretical method for bearing capacity matches well with the test results,and the relative errors in the serviceability limit state and ultimate limit state are 4.95%and 5.85%,respectively,which meet the accuracy requirements of the engineered application.

Vibration attenuation performance of wind turbine tower using a prestressed tuned mass damper under seismic excitation

With the rapid development of large megawatt wind turbines,the operation environment of wind turbine towers(WTTs)has become increasingly complex.In particular,seismic excitation can create a resonance response and cause excessive vibration of the WTT.To investigate the vibration attenuation performance of the WTT under seismic excitations,a novel passive vibration control device,called a prestressed tuned mass damper(PS-TMD),is presented in this study.First,a mathematical model is established based on structural dynamics under seismic excitation.Then,the mathematical analytical expression of the dynamic coefficient is deduced,and the parameter design method is obtained by system tuning optimization.Next,based on a theoretical analysis and parameter design,the numerical results showed that the PS-TMD was able to effectively mitigate the resonance under the harmonic basal acceleration.Finally,the time-history analysis method is used to verify the effectiveness of the traditional pendulum tuned mass damper(PTMD)and the novel PS-TMD device,and the results indicate that the vibration attenuation performance of the PS-TMD is better than the PTMD.In addition,the PS-TMD avoids the nonlinear effect due to the large oscillation angle,and has the potential to dissipate hysteretic energy under seismic excitation.

Investigation of the Effect of the Force Arm on the Bending Capability of Prestressed Glulam Beam

Prestress enables the Glulam beam could make full use of the compression strength,and then increase the span,but it still could not reduce all drawbacks,such as cross-section weakening and small force arm.To avoid slotting and ensure suitable tension and compression couple,one kind of novel anchor has been proposed,which could meet the bearing capacity requirement.And then the bending test of prestressed Glulam beams with a geometric scale ratio of 1:2 was simulated,to investigate the effect of the force arm on bending capacities,failure modes,and deformation performance.Results show that increasing the force arm could improve the ultimate bending per-formance of the beam significantly,and the anchor arm length has a certain effect on the performance,but it is not obvious.Finally,based on Finite element method analysis,the practice design suggestions have been offered.

Laminated Solid Timber Slab with Transverse Prestressing Using the Strategy of Interleaved Vertical Displacement of Lamellae

This article presents a study on the structural behavior of transversely prestressed laminated timber slabs,focusing on an innovative approach:vertically misaligned lamellae.This misalignment,achieved by sliding vertically the wooden lamellae rather than aligning them,enhances the slab’s cross-section moment of inertia,thereby improving load-bearing capacity and stiffness.Testing involved two groups of structural size specimens:one with vertically aligned lamellae(control group)and the other with misaligned lamellae(study group).Results showed the study group exhibited 42%superior stiffness and 10%less load capacity compared to the control.Failures typically occurred individually in the lamellae,particularly in those with defects or lower modulus of elasticity,concentrated in the middle third of the slabs’free span where tensile stresses peak.Despite a higher number of failed lamellae,the study group demonstrated promising performance.Analysis of prestressing bar indicated no damage at all in the thread,suggesting potential for reducing bar diameter.These findings offer crucial insights into applying these slabs in timber construction as well as to any kind of construction.

Discussion on Detection and Evaluation of Simply Supported Prestressed Concrete Small Box Girder Bridge After a Fire

The article takes a simply supported prestressed concrete small box girder bridge project as an example for inspection and evaluation after a fire incident.This includes appearance detection,concrete color hardness detection,concrete strength detection,concrete surface damage layer detection,reinforcement protective layer detection,and concrete carbonation detection.It is hoped that this analysis can be used as a reference for the detection and evaluation of future bridge projects with fire incidents to smoothen its subsequent repair and maintenance.

Study on damage-stress loss coupling model of rock and prestressed anchor cable in dry-wet environment

The loss of anchoring force is one of the problems to be solved urgently.The anchorage loss is a key factor causing the failure of anchoring engineering,so it is crucial to study the time-dependent variation of anchoring force.Alternating dry and wet(D-W)conditions have a significant effect on deformation of rock.The anchoring system is composed of anchoring components and rock mass,and thus rock deformation has a significant impact on the loss of anchoring force.Quantifying rock deformation under the effects of D-W cycles is a prerequisite to understanding the factors that influence loss of anchoring force in anchor bolts.In this study,we designed an anchoring device that enabled real-time monitoring of the variation in strain during D-W periods and rock testing.Nuclear magnetic resonance(NMR)measurements showed that under D-W conditions,the increment in porosity was smaller for prestressed rock than unstressed rock.The trends of prestress loss and strain variation are consistent,which can be divided into three characteristic intervals:rapid attenuation stage,slow attenuation stage and relatively stable stage.At the same stress level,the rate of stress loss and strain for the soaking specimen was the highest,while that of the dried specimen was the lowest.In the same D-W cycling conditions,the greater the prestress,the smaller the strain loss rate of the rock,especially under soaking conditions.The characteristics of pore structure and physical mechanical parameters indicated that prestress could effectively suppress damage caused by erosion related to D-W cycles.The study reveals the fluctuation behavior of rock strain and prestress loss under D-W conditions,providing a reference for effectively controlling anchoring loss and ideas for inventing new anchoring components.

Design on the Prestressed Concrete Frame Beam-column

A bidirectional ribbed concrete beam slab structure was widly adopted for the upper space of industrial buildings.To maintain ample space and minimize the presence of conventional columns,a bidirectional prestressed concrete beam is often employed.The intersection node of the prestressed concrete frame beam column was characterized by a high density of steel reinforcement,significant structural loads,and complex construction requirements.To ensure the quality,safety,and progress of prestressed frame beamcolumn intersection nodes during construction,this article proposed a new technology for constructing such nodes,which includes setting the tensioning and haunching ends of nodes at different positions,using ABAQUS finite element software to optimize the design of cross-sectional dimensions,conducting stress analysis simulations.

考虑锚杆预应力作用下隧道围岩力学分析及参数设计

隧道工程中锚杆设计多依靠经验法和类比法,为研究预应力锚杆支护体系下围岩的力学效应,建立预应力锚杆与围岩力学耦合模型,考虑围岩开挖损伤效应,通过弹塑性力学理论推导出隧道开挖后围岩应力分布及径向位移解析表达式,采用有限差分软件FLAC3D进行算例验证并分析预应力锚杆参数对围岩状态的影响。研究结果表明:理论解析和数值模拟中最大切向应力和围岩塑性区半径分别为4.77 MPa、15 m和4.49 MPa、15.86 m,理论解析与数值模拟所计算隧道围岩应力分布、位移基本一致,在Ⅳ、Ⅴ级围岩地层中验证了理论解析解的合理性;随着预紧力增大,处于塑性区的围岩径向位移及塑性区半径逐渐减小,弹性区基本不受影响;当锚杆自由段长度位于塑性区时,随着锚杆长度增加,围岩塑性区径向位移及塑性区半径逐渐减小。在实际工程中应尽量增大锚杆预紧力,锚杆长度增加对围岩位移以及塑性区的发展控制效果有限,应控制锚杆自由段长度在塑性区内。

预应力在我国大跨度结构中的应用研究综述

为了提高大跨度结构的正常使用性能,通常在混凝土结构中施加预应力.结果表明,预应力混凝土结构具有更好的使用性、耐久性和大跨度适用性,其中预应力混凝土空心板结构在不显著降低承载力和刚度的前提下明显减小结构自重,预应力型钢混凝土梁(板)结构采用较小的截面尺寸即可满足承载力和刚度的需求.开发城市地下空间是解决城市用地紧张的有效手段,我国地下大跨空间常用的结构形式主要包括密排框架(肋梁)结构、折板或拱形结构、变截面(加腋)板结构、预应力混凝土结构、型钢-混凝土组合结构和Y形柱结构6种形式,相比之下,跨度较大时宜采用预应力结构.

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。

基于缩尺模型的高铁桥梁预应力损失试验研究

【目的】为更好的评估在役预应力混凝土桥梁结构预应力损失状况。【方法】选用国内高铁中应用最广的32 m预应力混凝土箱梁作为研究对象,按照1:16的缩尺比例将箱梁转化为T形截面制作了26根C50混凝土试验模型梁。通过对试验梁预应力钢绞线应变、伸长量的瞬时和长期监测得到预应力损失的实际值,并将此实际值与目前国内外常用预应力损失规范计算所得值进行对比分析。【结果】预应力损失主要发生在前期即瞬时损失,约占总损失的70%;84.6%的试验梁锚固损失占瞬时损失总和的70%以上,最高达80.57%;试验梁的长期损失在锚固后的前10 d内变化较快,后期逐渐趋于稳定;将5种规范的计算结果与试验实测值进行对比,对于长期损失,数据显示实测数据与《铁路桥涵设计规范》(TB 10002—2017)计算结果最为吻合。【结论】研究结果可为实际工程中预应力梁的预应力损失计算提供参考。

带锚板预应力螺纹钢筋抗拔性能试验研究

目的为了探讨直径25 mm、强度等级PSB1080的带锚板预应力螺纹钢筋在有效锚固长150,200,250 mm的钢筋混凝土厚板或基础中拔出时的锚固性能,方法以有效锚固长度、套管有无、锚板宽度和构造钢筋数量为试验参数,对7个试件进行抗拔性能试验研究。研究试件的破坏特征,分析荷载-位移曲线、极限抗拔承载力、试件开裂荷载和荷载-应变曲线。结果结果表明:试件抗拔承载力随着锚固长度的增加而增加,当有效锚固长度为250 mm时,预应力螺纹钢筋均能达到屈服;混凝土开裂荷载随着有效锚固长度、锚板宽度和套管的增设而增加,构造钢筋数量对面层混凝土开裂荷载的影响并不明显;采用套管试件的面层混凝土开裂荷载比未采用套管试件提高了2.66倍;根据荷载-位移曲线可知,在锚板上增设构造钢筋可以防止带锚板预应力螺纹钢筋拔出时承载力急剧下降;基于试验结果和相关文献结果,对比锚固区混凝土锥体破坏试件的试验值与计算值可知,Nilforoush建议式和日本JSCE规范式9.2.11分别比试验值低19%和10%。结论增设套管可以有效提高开裂荷载;使用日本JSCE规范式9.2.11计算抗拔承载力更接近试验值。

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。

预应力CFRP布加固混凝土梁受弯试验

目的 研究不同加固方法下预应力碳纤维布加固混凝土梁的受弯性能,解决桥梁加固缺陷的问题。方法 制作了5根试验梁,其中一根为对比梁,不做任何加固处理,其余4根分别采用不同的锚固方式、不同的初始张拉力及不同的加固位置进行加固,通过控制变量,进行加载试验,分析其受弯性能的差异。结果 经加固后的试验梁承载能力与刚度明显增加,与对比梁相比,极限荷载分别提升了25%、22.06%、30.78%及36.76%;各试验梁达到屈服荷载时,经加固的试验梁挠度均小于对比梁产生的挠度,且模腔自锁式锚具锚固的试验梁挠度小于穿孔式自锁锚具锚固的试验梁挠度,相同锚固方法下初始张拉力较大的试验梁挠度要小于初始张拉力较小的试验梁挠度。结论 使用预应力碳纤维布加固混凝土梁能够有效提高混凝土梁的抗弯性能,提升效果与加固位置、锚固方式及初始张拉力大小有关。

预应力CFRP平板式锚具优化设计与应用

针对平板式锚具存在需在混凝土表面开槽、有效行程短、不可重复利用等问题,开展了平板式锚具优化设计与应用研究,提出了一种无须在结构基面设置扣槽,占用空间小、碳纤维增强材料(CFRP)板有效利用长度更长,轻质高强、可重复利用的预应力CFRP平板式锚具。有限元分析表明:在计算荷载作用下,锚具性能满足预应力CFRP加固需要,锚固支座、锚板和锚栓最大应力值分别为133、76、94 MPa,总体应力分布均匀,均小于其屈服强度,最大变形值为0.056、0.024、0.028 mm,保证锚具不先于结构破坏。随着锚栓直径与锚板厚度增大,锚具内部应力与变形均有所改善,其中锚栓直径变化对锚栓与锚板接触部分受力影响较大;锚板厚度对混凝土表面与锚栓接触部分受力影响较大,故建议锚栓直径为18 mm,锚板厚度为20 mm。实际工程应用表明该锚具使用效果良好。

PCCP断丝破坏规律Ⅱ:数值模拟研究

目前预应力钢筒混凝土管(Prestressed Concrete Cylinder Pipe,PCCP)断丝的数值模拟要么整圈删除断丝,要么将断丝的预应力损失范围假设为固定值,无法依据砂浆损伤程度来判断断丝预应力损失范围是否扩展。本文通过抽象分析砂浆、预应力钢丝和管芯混凝土之间的两两相互作用机制,引入弹簧单元、内聚力模型和塑性损伤模型,提出了管芯混凝土预压应力施加、任意位置钢丝割断和断丝预应力损失范围扩展的全过程模拟方法,明确了调控断丝预应力损失范围的初始大小、扩展时机和扩展幅度的关键参数。基于原型试验建立了恒定内压下集中和离散断丝的数值模型,从内压加载到断丝破坏的全过程角度验证了新模拟方法的合理性,揭示了管芯的预应力损失和破坏规律,使实际工程中各种三维断点分布的模拟成为可能,可为更精准地预测和评估断丝PCCP结构性能提供新手段。

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%.

风力发电塔基础预应力锚栓T型法兰连接系统计算方法研究

由于锚固区域基础刚度的影响,风力发电塔基础预应力锚栓组件受力不同于塔筒钢管间锻造法兰连接系统。基于Petersen计算方法的原理,推导出适用于预应力锚栓式风力机基础的计算方法,建立包含锚栓组件在内的单区隔和整体有限元模型研究基础约束刚度的空间效应。通过对单区隔和整体有限元计算所得锚栓拉力的对比发现,基础约束刚度的空间效应可忽略不计;通过对整体有限元模型计算结果和工程算法计算结果的对比,验证了工程算法的精度。

局部受热锈蚀预应力混凝土梁力学性能试验研究

随着我国基础建设的发展,大量混凝土桥梁在恶劣环境影响下发生腐蚀和老化,腐蚀桥梁结构的灾害破坏机理研究对桥梁结构的运营安全具有重要意义。为研究已经锈蚀受损的桥梁在局部受热状态下的高温力学性能,设计10根预应力混凝土梁试件。其中对照组的2根试件在常温下加载,试验变量为预应力筋初始应力,试验组的8根试件在高温下加载,试验变量分别为钢筋锈蚀、预应力筋初始应力、初始荷载。首先,基于电化学原理对4根预应力混凝土梁进行钢筋加速锈蚀处理,然后利用复合高温试验炉对8根预应力混凝土梁(4根锈蚀、4根未锈蚀)在跨中进行三面受火试验。最后,采用数值方法对局部受热预应力混凝土梁进行了仿真分析。研究结果表明:局部受热条件下,预应力混凝土梁的承载能力会发生明显降低,下降幅度约为11.3%~14.9%;钢筋锈蚀导致的混凝土开裂会对预应力混凝土梁的抗火性能产生不利影响,主要表现为2个方面,1)相同试验条件下,锈蚀后的试件预应力增量更大;2)锈蚀试件在局部受热条件下承载能力下降幅度更大,约为19.4%~21.9%;增大预应力筋的初始应力可以减小预应力混凝土梁在局部受热时的高温蠕变变形;局部高温作用下预应力混凝土梁对初始荷载较为敏感,当试件初始荷载值提升20%时,三分点位移量约增大60%。研究成果可以为实际锈蚀桥梁的防火设计和灾后应急提供理论依据。

简支变结构连续小箱梁桥负弯矩区UHPC-NC组合桥面板抗裂性研究

针对当前简支变结构连续小箱梁桥负弯矩区钢束易堵孔、运营中桥面开裂病害等问题,提出一种无负弯矩钢束的UHPC-NC组合桥面板结构。以一座3×30 m简支变结构连续小箱梁桥为研究对象,以正常使用极限状态梁体不开裂为控制准则确定UHPC合理构造尺寸,对所提出的负弯矩组合桥面板结构进行1∶2的缩尺模型试验。试验显示:裂缝首先出现于UHPC-NC交界面处的普通混凝土部分,随后逐渐向UHPC层沿伸,且C50混凝土开裂、梁体破坏对应的截面弯矩分别为3 520,9 152 kN·m(考虑1∶8弯矩缩尺比),大于正常使用极限状态、承载能力极限状态梁体截面弯矩3 300,5 838 kN·m,即该组合桥面板结构满足小箱梁的抗裂与承载能力要求。基于试验结果建立精细化有限元模型,采用参数分析法研究UHPC厚度对梁体开裂荷载、极限承载力等方面的影响。结果表明:梁体开裂弯矩主要由UHPC上覆层厚度决定,相较于普通钢筋混凝土梁,5 cm厚的UHPC上覆层可将梁体开裂弯矩提高28.9%,7.5 cm厚的UHPC上覆层可将梁体开裂弯矩提高41.6%;在配筋率不变的情况下,增大UHPC层厚度对梁体承载力无显著提升。综合考虑梁体受力性能以及施工便利性,建议背景工程UHPC厚度取10 cm。