High-temperature Resistance Performance of An Inorganic Adhesive for Concrete Structures Strengthened with CFRP Sheets

Organic epoxy matrices have been widely used in the FRP reinforcing technique, but they have serious disadvantages of poor high-temperature resistance. An inorganic adhesive is invented to replace the organic adhesive. For the inorganic adhesive at normal temperature and different high temperatures, the microstructure and phase composition are investigated by means of X-ray diffraction （XRD） and SEM respectively. Results show that inorganic adhesive can resist at least 600 ℃ high temperature. Fire-resistance performance of inorganic adhesive can meet the requirements of fiber reinforced polymer （FRP） strengthened RC structures.

Experimental research on refractory performance of reinforced concrete beams strengthened with CFRP sheets bonded with an inorganic adhesive

To meet the requirement of fire endurance for concrete structures strengthened with CFRP sheets, this study develops an inorganic adhesive whose strength at 600 ℃ is not lower than that at normal room temperature. The inorganic adhesive is then used to bond CFRP sheets on reinforced concrete beams in order to strengthen them. The fire protection of the CFRP sheets is done using the thick-type fireproofing coatings for tunnel ( TFCT) and steel structure ( TFCSS) respectively. Four specimens are tested in the furnace together. Specimens are exposed to fire for 1. 5 h in according to the ISO834 standard fire curve,and then naturally cooled for 1 h. In the tests,the largest displacements at the mid-span positions of specimens are only from 1 /1400 to 1 /318 of actual span corresponding to the highest temperatures from 300 ℃ to 470 ℃. After the specimens are naturally cooled to the normal temperature and the fireproofing coatings are then removed,it can be seen that the CFRP sheets keep in a good state,which indicates that CFRP sheets can be tightly bonded on the concrete and work well together with the concrete beams during and after fire. Besides,the tests also verify that the fire performance of TFCT is superior to TFCSS for the strengthened beams.

Flexural behavior of composite beams after the ultimate limit state externally strengthened with CFRP sheets bonded with high-temperature resistant matrix

In this paper the alkali-activated slag cementitious materials(AASCM)which strength at 600 ℃ is larger than that of AASCM at room temperature,were prepared to paste CFRP sheets to strengthen four simply supported unbonded prestressed composite beams encased circular steel tube truss after ultimate limit state.Test on flexural behavior of these four beams was performed.Moreover,normal section load-bearing capacity of these beams and the curve load-deflection at mid-span were obtained.Experimental results show that it is feasible to strengthen concrete members with CFRP sheets bonded with AASCM.Based on the experimental results and theoretical study,computational method of stiffness is proposed for calculating bending rigidity and normal section load-bearing capacity of concrete simply supported beams strengthened with CFRP sheets bonded with AASCM.Formula of bending rigidity calculation was founded which results are in good agreement with testing data.

Numerical Determination of Shear Strength of Steel Reinforced Concrete Column Strengthened by CFRP Sheets

The earthquake resistant property of reinforced concrete members depends on the interaction between reinforcing bars and surrounding concrete through bond to a large degree. In this paper a general system aimed at dealing with the failure analysis of reinforced concrete columns strengthened with carbon fiber reinforced plastic (CFRP) sheets including bond slip of the anchored reinforcing bars at the foot of the columns is presented. It is based on the yield design theory with a mixed modeling of the structure, according to which the concrete material is treated as a classical two dimensional continuum, whereas the longitudinal reinforcing bars are regarded as one dimensional rods including bond slip at the foot of the columns. In shear reinforced zones both the shear CFRP sheets and transverse reinforcing bars are incorporated in the analysis through a homogenization procedure and they are only in tension. The approach is then implemented numerically by means of the finite element formulation. The numerical procedure produces accurate estimates for the loading carrying capacity of the shear members taken as an illustrative application by correlation with the experimental results, so the proposed approach is valid.

弯-剪-扭复合受力CFRP布加固RC梁抗扭性能细观数值分析

为了研究弯-剪-扭复合受力条件下碳纤维增强复合材料(carbon fiber reinforced polymer, CFRP)布加固钢筋混凝土(reinforced concrete, RC)梁的抗扭性能,建立体现混凝土材料非均质性、钢筋-混凝土黏结滑移关系和CFRP布-混凝土相互作用关系的细观数值分析模型。由于缺乏CFRP布加固RC梁在弯-剪-扭复合受力作用下失效破坏的典型物理试验,采用复合对比验证法对数值模型的合理性进行验证,即分别与单独受剪、单独受扭以及受弯-扭复合作用下RC梁和CFRP布加固RC梁的试验结果进行对比验证。进而,基于建立的细观数值分析模型探究了配纤率和扭弯比对CFRP布加固RC梁在弯-剪-扭复合受力作用下抗扭力学性能的影响。结果表明:1)采用CFRP布加固能够显著提高RC梁的峰值扭矩;2)随配纤率增加,RC梁损伤分布范围逐渐变大,CFRP布应变逐渐减小,梁整体峰值扭矩增大,但其增大幅度减小;3)随扭弯比增加,RC梁裂缝分布愈加集中,裂缝与水平方向夹角逐渐减小,梁整体峰值扭矩增大,CFRP布应变减小。建立的考虑弯-剪-扭复合受力作用的数值模拟方法可为后续研究复杂应力状态下CFRP布加固RC梁尺寸效应行为等奠定基础。

CFRP布抗剪加固预加载RC梁的力学性能研究

【目的】为了研究端部锚固方法和预加载对碳纤维复材(CFRP)加固钢筋混凝土(RC)梁抗剪性能的影响,【方法】进行了4根矩形RC梁的剪切试验,分析了失效模式、荷载-挠度曲线、特征荷载、箍筋和CFRP应变的发展,最后,采用既有的CFRP加固RC梁抗剪承载力计算方法对文章试件的抗剪承载力进行了预测。【结果】试验结果表明,在可靠的端部锚固下,采用U形CFRP条带加固可以显著提升RC梁的抗剪性能;抗剪加固效果受CFRP条带的端部锚固方法影响很大,机械锚固显著优于CFRP布压条锚固,相比于未加固梁,采用机械锚固的加固梁抗剪承载力提高了约60%,而CFRP布压条锚固的抗剪承载力仅提高了9.8%;预加载虽然明显降低了加固梁的开裂荷载,但对抗剪承载力几乎没有影响。【结论】研究结果可为CFRP布抗剪加固RC梁的工程应用提供参考。

Seismic retrofitting of severely damaged RC connections made with recycled concrete using CFRP sheets

An experimental and numerical program is carried out in this research to investigate the influence of CFRP sheets on the cyclic behavior of unconfined connections made with recycled concrete.Cement is partially replaced by silica fume,iron flling and pulverised fuel ash using two different percentages:15%and 20%.Each specimen is partially loaded at the first stage and then specimens are repaired using CFRP sheets.The repaired specimens are then laterally loaded until failure.In addition,a finite element model is built in ABAQUS and verfed using the experimental results.The experimental results have shown that the repaired specimens have regained almost double the capacity of the un-repaired specimens and hence the adopted repair configuration is recommended for retroftting seismically vulnerable RC connections.Increasing cement replacement percentage by silica fume,fuel ash or iron flling from 15%to 20%has reduced joint carrying capacity and weakened the joint.It is recommended using 15%pulverised fuel ash or silica fume as cement partial replacement to enhance the strength and ultimate drift of beam-column joints under cyclic loading.Iron filling concrete is also recommended but the enhancement is relatively less than that found with pulverised fuel ash concrete and silica fume concrete.

冻融环境下CFRP布加固混凝土梁抗弯承载力有限元分析

为进一步研究冻融环境下碳纤维布(carbon fiber reinforced polymer, CFRP)加固混凝土梁的抗弯承载力,利用ABAQUS有限元分析软件分别对混凝土梁和CFRP布等构件进行建模,用冻融循环后混凝土的塑性损伤模型代替普通混凝土的塑性损伤模型。对冻融循环后的混凝土梁进行静态模拟,得到基本受力性能模拟值,再采用CFRP布加固混凝土梁进行相同环境的静态模拟,得到加固后的基本性能模拟值。将CFRP布加固混凝土梁与未加固混凝土梁进行力学性能对比分析。结果表明,随着冻融循环次数的增加,相比于未加固的混凝土梁,CFRP布加固的混凝土梁的极限承载力下降幅度更小。

CFRP布加固损伤RC短梁受弯性能试验研究

通过对3根钢筋混凝土短梁进行抗弯性能试验,研究了普通RC短梁、CFRP布加固未损伤及损伤RC短梁的破坏形态、混凝土应变、抗弯承载力、挠度变形、曲率和抗弯刚度的变化规律。试验研究结果表明:(1)CFRP布加固未损伤及损伤RC短梁的极限破坏特征一致,都是CFRP布部分拉断破坏;(2)CFRP布加固未损伤及损伤RC短梁的跨中截面混凝土应变均近似符合平截面假定;(3)CFRP布加固未损伤及损伤RC短梁的荷载-挠度曲线分别为三阶段和两阶段特征,加固损伤RC短梁没有开裂阶段曲线;(4)采用CFRP布加固损伤RC短梁比加固未损伤RC短梁更能提高原试件的极限承载力;(5)CFRP布加固损伤RC短梁比加固未损伤RC短梁的延性更好。

CFRP加固钢筋混凝土构件受弯承载力的计算表格及其应用

本文阐述了钢筋混凝土构件使用CFRP进行受弯承载力加固的配筋增量设计法的原理,并以现行结构设计规范中的有关条文为基础推导了相应的计算公式,同时编制了对应的计算表格,得到的结果经验证具有很高的精确度。把构件受弯加固的承载力计算问题转变成查表求解简化了设计过程,并且适合构件进行批量加固的情况。本文还利用计算表格输出的数据分析了构件配筋率以及滞后应变的变化对碳纤维复合材强度利用系数的影响,并根据分析结果提出了一个简明实用的估算方法。

混凝土梁侧面粘贴CFRP布的结构加固性能的试验研究

研究采用在混凝土构件侧面粘贴碳纤维布这种新形式加固受弯构件的受力性能 .试验研究共设计了 4根少筋梁 ,试验时 ,先通过 2个对称的集中荷载将梁预加载至纯弯段出现一道主裂缝并失效 ,然后 ,卸载并用碳纤维布粘贴于梁侧面受拉区予以加强 ,待粘贴树脂固化后 ,再重新加载至梁的极限荷载 .试验重点研究了该种加固梁的极限荷载、变形、开裂和碳纤维布粘贴形式对加固效果的影响 .试验结果表明 ,该种加固梁不但承载力提高显著 ,而且具有很好的延性 ,消除了原来在梁底粘贴碳纤维加固梁在极限状态时因碳纤维布突然断裂而出现的脆性破坏现象 .基于试验研究结果 ,导出了这种加固梁承载力的实用计算方法 ,该方法计算精度较好且偏于安全 ,可直接应用于实际加固工程 ,特别是当构件底面有管道等障碍物时 .

CFRP布加固木梁界面粘结应力的试验研究和理论分析

为了研究CFRP布加固木梁的界面粘结应力,对6根CFRP布加固的木梁进行了静力试验,得到了碳纤维布端部的应变分布。由相邻两测点的应变计算出了CFRP布与木材的平均界面粘结剪应力。忽略碳纤维布和木梁的剪切变形,推导了在任意荷载作用下两者之间的界面粘结剪应力和粘结正应力的计算公式,并根据边界条件给出了在两点对称集中荷载作用下公式中的系数,应用该公式计算了试验梁碳纤维布端部的界面粘结剪应力和正应力,结果表明粘结剪应力的计算值与试验值吻合较好,说明该公式是可行的。

考虑预应力损失的CFRP布加固钢筋混凝土梁正常使用极限状态可靠度研究

在考虑预应力损失和二次受力的情况下,对预应力CFRP布加固钢筋混凝土梁,推导了挠度和裂缝宽度的计算公式,并基于改进的蒙特卡罗法和等效线性化方法进行了挠度和裂缝宽度的可靠度计算。可靠度计算结果表明,当预应力损失从500με增加到4000με时,裂缝宽度的可靠指标从7.78减小到0.97;挠度的可靠指标从4.09减小到3.96;预应力损失对裂缝宽度可靠指标的影响更加显著。在未充分卸荷、CFRP布截面面积较小或CFRP布弹性模量较低时,更易加剧裂缝宽度的可靠指标随预应力损失增加而降低的趋势。为防止因预应力损失而影响梁的正常使用,建议采用预应力CFRP布加固钢筋混凝土梁时,尽可能卸荷;选用CFRP布截面面积时,尚应考虑正常使用阶段的功能要求,可适当增加CFRP布的截面面积;同时为了在正常使用阶段充分发挥CFRP布的高强特性,可选择较高弹性模量的CFRP布。

CFRP布包镶加固底部糟朽木柱轴压试验

为探讨适用于糟朽柱根的有效加固方法,提出了采取CFRP布代替铁箍来包镶加固古建木柱柱根的方法.制作了6个模型,其中部分模型考虑柱根糟朽,并采用CFRP布进行包镶加固.采取静力加载试验方法,研究了CFRP布包镶加固前后木柱的轴压受力性能.基于试验结果,获得了木柱的力-变形曲线、力-应变曲线、极限承载力及延性性能,讨论了CFRP布包镶层数对加固效果的影响.结果表明,采用CFRP布包镶加固柱根后,木柱极限承载力可恢复81.4%~92.4%左右,延性性能恢复87.3%~95.8%左右,水平及竖向峰值压应变均有不同程度提高.当CFRP布包镶层数为3层时,木柱柱根加固效果最明显,但加固后的木柱承载性能略低于完好木柱.

预应力CFRP布加固负载混凝土梁受剪性能试验

为研究负载状态下利用预应力碳纤维布加固混凝土梁斜截面受剪性能,根据配箍率的不同制作3组共计12根钢筋混凝土梁,每组选择1根混凝土梁进行单点加载受剪试验,获取极限受剪承载力及裂缝分布等试验数据.对另9根梁预加载至极限受剪承载力的0.4倍,在持荷状态下对试验梁弯剪区段利用预应力碳纤维布加固.完成这9根梁负载加固后的斜截面二次受力受剪承载力试验,在试验数据基础上分析负载加固梁斜截面受剪破坏机理和影响因素.结果表明:采用预应力碳纤维布加固负载混凝土梁斜截面能够抑制斜截面裂缝的产生和发展,增大混凝土受压区高度,提高斜截面受剪承载力.

用无机胶粘贴CFRP布加固混凝土梁受弯试验研究

目前粘贴碳纤维布加固混凝土结构多采用环氧类有机胶,但其软化点过低,多为60℃～80℃。夏季由于气温高,一些地区混凝土桥梁的结构表面温度常超过环氧类有机胶的软化点,火灾下环境温度更高,用环氧类有机胶粘贴碳纤维布加固的混凝土结构难以满足耐高温要求。为此,选用600℃时强度不低于常温强度的碱矿渣胶凝材料粘贴碳纤维布,对6根混凝土简支梁进行加固,并完成了这6根梁的受力性能试验。获得了加固梁的正截面承载力、裂缝分布与开展的试验值和荷载-实测跨中挠度曲线。试验梁呈现继纵向受拉钢筋屈服后碳纤维布被拉断和纵向受拉钢筋屈服后混凝土被压碎的两种破坏模式,并且均满足平截面假定,表明用碱矿渣胶凝材料粘贴碳纤维布加固混凝土结构构件是可行的。在试验研究和理论分析的基础上,提出了用碱矿渣胶凝材料粘贴碳纤维布加固混凝土简支梁的刚度、最大裂缝宽度、正截面承载力的计算方法,基于所提方法的计算值与实测值吻合良好。

CFRP布加固钢筋混凝土梁的新型复合粘结技术

针对外贴碳纤维增强复合材料(CFRP)布加固钢筋混凝土构件通常发生CFRP布与混凝土之间的剥离破坏,使得CFRP布的抗拉强度得不到充分利用的问题,提出了一种将外贴法与机械锚固法相结合的新型复合粘结技术,由1个钢片和2个螺栓组成的锚固件对外贴在钢筋混凝土构件上的CFRP布进行锚固,并进行了7根钢筋混凝土梁的试验,主要研究CFRP布的粘贴层数及锚固件间距对加固效果的影响。分析结果表明:新型复合粘结技术可以有效地阻止剥离破坏的发生,使梁的极限承载力得到显著提高,提高程度随CFRP布粘贴层数的增加而增加。

CFRP布加固破坏混凝土框架的拟静力试验研究

按1∶3比例缩尺模型设计了1榀混凝土框架模型,进行了拟静力试验,分析比较了混凝土框架结构及该框架破坏后经碳纤维布加固后的框架结构受力性能、裂缝发展、破坏形态、滞回曲线、骨架曲线及位移延性,研究碳纤维加固已严重损伤的混凝土框架结构的抗震性能.试验结果表明,碳纤维加固震后严重损伤框架结构后,其极限承载能力、耗能能力及延性等抗震性能有明显提高.

CFRP在土木工程中的应用研究

碳纤维增强复合材料(CFRP)由于具有自重轻、耐腐蚀、抗拉强度高等优点,在土木工程中的应用日益增多。从CFRP片材、CFRP棒材、CFRP索材以及CFRP锚固系统四方面综述了CFRP在土木工程领域中的研究情况,总结了其在理论研究、数值分析、试验研究及设计应用等方面的最新研究成果;结合当前土木工程的发展趋势,指出CFRP在土木工程中应用研究的不足之处,进而提出研究中亟待解决的关键问题。