FRP加固混凝土梁的有限元分析

碳纤维复合材料(CFRP)加固混凝土结构是一种新型结构加固方法。在大比例模型试验的基础上,应用有限元程序对 T 型梁进行了加固分析,以研究 CFRP 布加固对混凝土梁抗弯能力及刚度的提高程度。分析结果表明,CFRP 布加固可应用于大型钢筋混凝土桥梁。     

Truss-arch model for shear strength of seismic-damaged SRC frame columns strengthened with CFRP sheets

Carbon fiber reinforced polymer (CFRP) materials are important reinforcing substances which are widely used in the shear strengthening of seismic-damage steel reinforced concrete (SRC) frame structures. To investigate the shear strength of SRC frame columns strengthened with CFRP sheets, experimental observations on eight seismic-damaged SRC frame columns strengthened with CFRP sheets were conducted at Yangtze University and existing experimental data of 49 SRC columns are presented. Based on the existing experiments, the theories of damage degree, zoning analysis of concrete, and strengthening material of the column are adopted. To present the expression formula of the shear strength of SRC frame columns strengthened with CFRP sheets, the contributions of strengthening material and transverse reinforcement to shear strength in the truss model are considered, based on the truss-arch model. The contribution of arch action is also considered through the analysis of the whole concrete and that of the three zones of the concrete are also considered. The formula is verified, and the calculated results are found to match well with the experimental results. Results indicate that the proposed whole analysis model can improve the accuracy of shear strength predictions of shear seismic-damaged SRC frame columns reinforced with CFRP sheets.     

持载混凝土梁端锚无黏结预应力U形碳纤维带受剪加固试验研究

利用已研发的适用于U形纤维增强复材(FRP)的端锚无黏结预应力系统,对1根未加固梁及6根预应力碳纤维(CFRP)条带加固的不同持载水平钢筋混凝土梁进行受剪性能试验,探究端锚无黏结预应力加固法的有效性。研究结果表明：该方法能够对不同持载水平混凝土梁进行有效加固,可避免条带的端部剥离破坏并实现拉断破坏,提高纤维强度利用率,延缓箍筋屈服,抑制梁刚度的退化和斜裂缝的开展,提升构件受剪承载力,最大提升率约75%;预应力加固效果易受持载水平和配纤率影响,其他加固参数相同时,较高持载水平和配纤率的加固梁受剪性能更好,受剪承载力提高幅度更大。端锚无黏结预应力U形CFRP条带加固梁受剪承载力计算结果与实测结果吻合较好,可为加固设计提供参考。     

Assessing the effectiveness of embedding CFRP laminates in the near surface for structural strengthening

Near surface mounted (NSM) is a recent strengthening technique based on bonding carbon fiber reinforced polymer (CFRP) bars (rods or laminate strips) into pre-cut grooves on the concrete cover of the elements to strength. To assess the effectiveness of the NSM technique, an experimental program is carried out involving reinforced concrete (RC) columns, RC beams and masonry panels. In columns failing in bending the present work shows that the failure strain of the (CFRP) laminates can be attained using the NSM technique. Beams failing in bending are also strengthened with CFRP laminates in order to double their load carrying capacity. This goal was attained and maximum strain levels of about 90% of the CFRP failure strain were recorded in this composite material, revealing that the NSM technique is also very effective to increase the flexural resistance of RC beams.The effectiveness of externally bonded reinforcing (EBR) and NSM techniques to increase the flexural resistance of masonry panels is also assessed. In the EBR technique the CFRP laminates are externally bonded to the concrete joints of the panel, while in the NSM technique the CFRP laminates are fixed into precut slits on the panel concrete joints. The NSM technique provided a higher increase on the panel load carrying capacity as well as a larger deflection at the failure of the panel.The performance of EBR and NSM techniques for the strengthening of RC beams failing in shear is also analyzed. The NSM technique was much more effective in terms of increasing the beam load carrying capacity as well as the beam deformability at its failure. The NSM technique was easier and faster to apply than the EBR technique.     

预应力碳纤维布加固钢筋混凝土梁力学性能试验

基于预应力碳纤维布加固钢筋混凝土梁能够提高其承载能力的理论,进行了6根外贴预应力碳纤维布(CFRP)加固钢筋混凝土梁的力学性能试验。研究了在不同预应力和不同端部锚固方式下加固后的钢筋混凝土梁的预应力损失、开裂荷载、跨中挠度、极限荷载及抗弯抗剪性能。结果表明:碳纤维布预应力在一定范围内能够决定钢筋混凝土梁的加固效果,同时在梁端部采取锚固方式能有效阻止预应力碳纤维布在放张过程中的预应力损失;预应力碳纤维布加固后梁的开裂荷载随着预应力的增大而增大,最大增大幅度达到81.8%;极限荷载在一定范围内随预应力的增大先增大后减小,极限荷载最大增大幅度为41.07%。     

外包角钢与碳纤维布复合加固钢筋混凝土柱抗剪性能试验研究

外包角钢与碳纤维布(CFRP)复合加固钢筋混凝土柱是一种新型加固方式。对6根复合加固柱及1根未加固对比柱进行低周反复受剪性能试验研究,探讨影响复合加固柱抗剪性能的因素,并分析不同条件下CFRP与外包钢缀板的应变情况。试验结果表明,复合加固方法能显著提高钢筋混凝土柱的抗剪承载力,试验中最大提高47%,且复合加固柱在破坏时延性得到较大程度的改善。在轴压比较低的范围内,复合加固柱的抗剪承载力随轴压比的增大而增大,但其延性下降。随着钢缀板加固量的增大,复合加固柱的抗剪承载力随之增大。随着复合加固柱剪跨比的增大,其抗剪承载力随之降低,但外加片材应变增大。CFRP与角钢复合加固体系能很好的约束混凝土的横向变形,两种材料能良好地共同工作,但约束材料强度的发挥是有限的,在达到极限承载力时,两种加固材料都不能被充分利用。     

无机胶凝材料粘贴碳纤维布加固混凝土结构研究进展

总结了近年来用无机胶凝材料粘贴碳纤维布加固混凝土结构的研究进展，包括各种无机胶凝材料（碱激发胶凝材料、氯氧镁水泥和水泥基复合材料）的分类与起源，碳纤维布常温与高温力学性能，以及无机胶凝材料加固混凝土结构常温与抗火性能等，指出了无机胶凝材料在加固技术中尚存在的一些问题，如各种无机胶凝材料的极限变形能力尚显不足等。分析结果表明：碱激发胶凝材料可耐600℃高温，氯氧镁水泥可耐300℃高温，且二者黏结加固效果均优于水泥基复合材料；常温下无机胶凝材料的粘贴加固效果与环氧类有机胶大体相当，高温下其加固效果明显优于环氧类有机胶，因此，用无机胶凝材料粘贴碳纤维布加固混凝土结构并以此提高结构的承载力是可行的；用无机胶凝材料粘贴碳纤维布加固混凝土结构的耐久性及其抗火设计方法等，应是今后一段时间建筑结构加固领域值得关注的课题。     

碳纤维加固与软件设计——碳纤维受剪加固

结合《混凝土结构设计规范》(GB 5 0 0 10 - 2 0 0 2 )及《碳纤维片材加固混凝土结构技术规程》(CECS14 6 :2 0 0 3) ,对钢筋混凝土梁、柱碳纤维受剪加固的计算理论进行探讨 ,并给出设计计算流程 ,应用VB语言实现了软件设计 ;还重点介绍了东大迪普加固软件系统的梁、柱碳纤维受剪加固模块和计算方法 ,并应用实例进行详细说明     

A way for preventing tension delamination of concrete cover in midspan of FRP strengthened beams

In order to prevent tension delamination of concrete cover in midspan more efficiently, an attempt to strengthen reinforced concrete beams by combining unidirectional carbon fibre reinforced polymer (CFRP) sheet (to bond to the tension faces of the beams) and bi-directional glass fibre reinforced polymer (GFRP) sheet (to wrap 3 sides of the beams continuously) was proposed. The feasibility and potential advantages of the attempt were discussed. A comparative test program including ten beams was carried out. The test results showed that the hybrid CF/GF reinforced polymer (H-CF/GF-RP) strengthening could not only prevent the tension delamination of the bottom concrete cover, but also lead to a significant increase of deformation capacity of the strengthened beams at a very low cost compared to CFRP strengthening.     

预应力碳纤维板加固钢筋混凝土梁施工工艺及试验研究

在研究已有的预应力CFRP片材加固施工工艺的基础上,利用自主研发的一套预应力CFRP板张拉设备,对6根预应力CFRP板加固混凝土梁进行抗弯试验,介绍预应力CFRP板加固混凝土梁的施工方法和端锚预应力加固技术的关键工艺,可为实际工程应用提供参考。     

碳纤维增强复合网格-聚合物水泥砂浆加固RC梁抗剪性能试验研究

为研究碳纤维增强复合(CFRP)网格和聚合物水泥砂浆(PCM)复合加固工字形截面钢筋混凝土(RC)梁的抗剪性能,对3个试件进行抗剪性能试验和有限元模拟,分析了CFRP网格-PCM加固RC梁的抗剪破坏机理,研究了不同加固方式对试件抗剪性能的影响。研究结果表明：采用CFRP网格-PCM对RC梁进行抗剪加固可有效抑制斜裂缝的发展,能够较大幅度提高RC梁的抗剪承载力;相比仅腹部加固的试件,腹部和腋部都加固的试件的二次刚度、极限荷载均有所提高,且CFRP网格变形减小,与混凝土界面的黏结能力增强;在有限元分析中,采用混凝土的CDP模型和Spring2弹簧单元来预测CFRP网格加固混凝土的抗剪承载力是可行的;建立了基于杆状材料有效应变的抗剪计算方法,该方法可有效预测加固RC梁的抗剪承载力,为结构加固设计提供参考。     

Compressive and flexural behaviour of CFRP-repaired concrete-filled steel tubes after exposure to fire

This paper presents the results of axial compression and bending tests of fire-damaged concrete-filled steel tubes (CFST) repaired using unidirectional carbon fibre reinforced polymer (CFRP) composites. Both circular and square specimens were tested to investigate the repair effects of CFRP composites on them. The test results showed that the CFRP jackets enhanced the load-bearing capacity of the stub columns effectively. Enhancement of the columns’ stiffness due to the CFRP jackets was also observed. However, for beams, the test results demonstrated that the repair effect was not as good when compared with that for stub columns. From the test results, it is recommended that other appropriate repair measures should be taken in repairing severely fire-damaged CFST beams, or those members subjected to comparatively large bending moments.     

预应力高强钢丝绳抗弯加固钢筋混凝土梁的试验研究

提出一种预应力高强钢丝绳抗弯加固混凝土结构的新方法(简称P-SWR加固技术)。介绍这种新技术的提出思想及实现工艺,对预应力高强钢丝绳抗弯加固混凝土梁进行试验研究,重点讨论直接加载、先损伤后加载、钢丝绳层数、钢丝绳与混凝土黏结性能、锚固方式等参数对加固性能的影响,并与粘贴CFRP和钢板加固混凝土梁性能作了比较。试验结果表明,预应力高强钢丝绳加固能同时显著提高混凝土梁的开裂荷载、截面刚度、屈服荷载、最大承载力,加固后的梁发生钢筋屈服、受压区混凝土压坏、钢丝绳断裂的延性破坏,能有效限制混凝土裂缝宽度,钢丝绳能达到极限拉伸应变而充分发挥作用。P-SWR加固技术可较好地解决现有加固方法中的诸多缺点,是一种高效主动式的加固技术。另外,该技术还具有易施工、耐火、耐老化、成本低等优点,值得在实际工程中大力推广应用。     

CFRP网格-聚合物水泥砂浆加固RC梁的#br# 抗剪性能与计算公式

为揭示不同网格单位加固量对碳纤维增强复合网格(carbon fiber reinforced polymer grid,简称CFRP grid) 聚合物水泥砂浆(polymer cement mortar,简称PCM)复合加固钢筋混凝土(reinforced concrete,简称RC)梁抗剪性能的影响,构建CFRP网格-PCM加固RC梁的承载力计算方法,文章首先对7根采用CFRP网格 PCM复合加固RC梁进行四点弯曲静力加载试验,并在试验研究的基础上,提出基于横竖双向网格实际抗剪贡献的CFRP网格-PCM加固RC梁的承载力计算公式。研究结果表明：采用CFRP网格-PCM复合加固RC梁能显著提高其抗剪承载力,其中CFRP网格对于抗剪承载力的提高发挥主要作用,而PCM仅起到黏结剂的作用;加固梁的抗剪承载力与CFRP网格单位加固量呈正相关,但CFRP网格的协同变形性与CFRP网格单位加固量呈负相关;所提出的抗剪承载力计算公式与试验结果吻合良好。     

玄武岩纤维布加固钢筋混凝土梁受弯受剪承载力计算分析

基于现行混凝土结构加固设计规范关于粘贴纤维增强复合材料加固法的计算理论,分别对玄武岩纤维布和碳纤维布加固钢筋混凝土梁的正截面受弯承载力、斜截面受剪承载力进行计算分析,以探讨玄武岩纤维布对钢筋混凝土梁的加固效果。计算结果表明,设计人员可以方便地按现行加固设计规范对玄武岩纤维受弯、受剪加固进行计算。     

CFRP加固锈蚀钢筋混凝土短柱的抗震性能

为评估CFRP加固锈蚀钢筋混凝土短柱抗震性能的效果,选取1根未锈蚀钢筋混凝土短柱、2根锈蚀钢筋混凝土短柱和4根CFRP加固锈蚀钢筋混凝土短柱进行抗震性能试验研究,考察了CFRP加固量、细骨料类型对抗震加固效果的影响情况,建议了CFRP加固锈蚀钢筋混凝土短柱受剪承载力的实用计算公式。结果表明:钢筋锈蚀会降低短柱的抗震性能,锈蚀钢筋试件的受剪承载力、极限变形能力和累积滞回耗能较未锈蚀钢筋试件分别降低了7.8%、35.5%和42.2%;外包CFRP加固能将锈蚀钢筋试件的受剪承载力提高至未锈蚀钢筋试件的107.1%～109.1%,并显著改善短柱的延性和耗能能力;外包CFRP的层数由1层增至2层时,加固试件的受剪承载力提高较少,且试件达到峰值荷载时,CFRP的最大应变减少;在钢筋锈蚀前后和CFRP加固前后,混凝土短柱无量纲近极限滞回环的滞回规则大体相同。     

Strengthening and Rehabilitation of Reinforced Concrete Slabs with Carbon‐Fiber Reinforced Polymers Using a Refined Bond Model

Abstract: Slabs are one of the main load‐bearing elements in nearly every structure. Because of additional live loads or modifications of the building structure these slabs often have to be strengthened. Using externally bonded carbon‐fiber reinforced polymer (CFRP) strips to strengthen existing concrete structures has become common practice. One of the main failure modes is the loss of the composite action between the concrete and the CFRP strip making the bond force transfer very important. This bond force transfer depends on many parameters including the concrete strength, the ratio between shear force, and bending moment. A new parameter recently discovered by the Technische Universität München (TUM) is the deflection of the structural elements themselves. Because of this deflection self‐inducted contact pressure occurs. This contact pressure affects a higher bond transfer. The lower effective depth of slabs compared to beams causes higher deflections. In this article, first a few principles on the strengthening with adhesive‐bonded CFRP strips and the characteristics of the bond are explained. Then, the basics of the bond force transfer, at the end anchorage and in the rest of the element, are summarized. Based on these essentials, as well as numerous experiments, the change in the bond force transfer at the structural element caused by the curvature is then derived. With these findings, a complete verification concept is presented, which is ideal for computerized calculations. This verification concept is finally compared to several full‐scale test results presented in pertinent literature.     

预应力CFRP片材抗剪加固钢筋混凝土T梁试验研究

针对外贴FRP片材抗剪加固钢筋混凝土梁存在材料利用率低、易发生剥离破坏等问题,开发了用于抗剪加固的CFRP片材预应力张拉和锚固系统,给出了相应的施工工艺和方法。为验证提出系统的有效性,进行了预应力CFRP片材抗剪加固钢筋混凝土T型截面梁试验。基于CFRP片材断裂的破坏模式,提出了预应力CFRP片材加固钢筋混凝土梁的抗剪承载力计算公式。结果表明,该文开发的预应力张拉和锚固系统能有效地对CFRP片材施加预应力,减少预应力损失。预应力CFRP片材抗剪加固梁均发生以受压区混凝土压碎为标志的受弯破坏模式,锚固装置能够确保CFRP片材在断裂之前不发生剥离破坏。预应力CFRP片材对混凝土梁斜裂缝的产生和发展有明显的抑制作用,加固后钢筋混凝土梁的抗剪承载力得到大幅提升。计算结果与试验值吻合较好,验证了加固梁抗剪承载力模型的有效性。     

钢筋混凝土柱修复后受剪性能研究

以重度受损钢筋混凝土柱为研究对象,研究其经加固修复后斜截面的抗剪性能。将重度受损钢筋混凝土柱根部塑性铰区范围内的混凝土用高强度灌浆料置换,并环向粘贴单向碳纤维布对试件进行斜截面抗剪加固,通过对其施加低周期反复荷载,观察其斜裂缝开展情况及裂缝宽度,分析其斜截面受剪承载力,与未做加固修复的试件进行对比,研究加固后试件的抗剪性能。其加固后试件受剪承载力有明显提高。     

The problem of shear in RC beams strengthened with CFRP laminates

The effectiveness of externally bonded reinforcement of a strengthened Reinforced Concrete (RC) beam subjected to a shear-dominant loading regime is not well-established. The aim of this paper is to clarify the structural performance of RC beams without any internal shear reinforcement but strengthened with Carbon Fibre Reinforced Polymer (CFRP) laminates when the primary mode of failure of the un-strengthened beam is in shear. Four RC beams were specifically designed without and with an externally anchorage system, which was carefully detailed to enhance the benefits of the strengthening lamina and counteract the destructive effects of shear forces. All the four beams were identical in terms of their geometry, internal reinforcement and concrete strength but varied in their test loading regime to highlight the role of shear. All the beams were tested under four point bending and extensively instrumented to monitor strains, cracking, load capacity and failure modes. The structural response of the four beams is then critically analysed in terms of deformability, strength and failure processes under a shear loading regime. It is shown that with a carefully designed anchorage system, a predominantly brittle shear failure of a strengthened beam can be transformed to an almost ductile failure with well-defined enhancement of structural performance in terms of both deformation and strength. The results presented in this paper should enable engineers to totally avoid shear failure in strengthening beams with little or even no internal shear reinforcement.