震损RC柱FRP加固后抗震性能数值模拟分析

使用有限元软件ABAQUS,基于箍筋约束混凝土、钢筋以及FRP材料的材料本构模型,完成了未震损未加固、未震损FRP加固和震损后FRP加固的RC柱抗震数值模拟分析。对震损后FRP加固的RC柱,完成不同程度震损模拟;使用生死单元法实现严重震损混凝土的剔除与替换以及FRP的加固;再模拟修复加固后RC柱的加载,模拟结果与试验结果基本吻合。对比了3种RC柱抗震性能的数值模拟结果,发现严重震损后用FRP加固的RC柱其抗侧刚度与承载力不能完全恢复,需要考虑不同损伤程度与不同FRP加固措施等对加固效果的影响。研究了不同损伤程度和加固方法下的RC柱,结果表明：对于中等震损的试件,纵横向FRP组合加固可以完全恢复并超越原有抗震性能;对严重损伤RC柱,外围损伤严重混凝土的修复与替换是影响震损RC柱加固后性能的关键;相较于仅有横向GFRP环向加固,纵横向FRP组合加固的效果更好。     

FRP加固钢筋混凝土柱抗震性能的探讨与研究进展

介绍了地震作用下钢筋混凝土柱的三种破坏模式,并指出FRP在其中的影响和作用机理。通过收集国内外有关资料,阐述了FRP加固钢筋混凝土柱抗震性能的研究进展,并归纳出FRP加固钢筋混凝土抗震性能研究中的三个关键问题。     

组合FRP技术加固混凝土矩形柱的抗震性能试验研究

研究了一种利用植筋及纤维增强复合材料(FRP)布横向包裹钢筋混凝土柱来改善其抗震性能的新型加固技术.通过5个钢筋混凝土方柱的模型试验,分别研究了植玻璃纤维(GFRP)筋、横向包裹碳纤维(CFRP)布及两者组合的加固技术对提高混凝土柱抗震性能的作用,分析讨论了不同加固方法对混凝土柱位移延性系数的提高、刚度退化及能量耗散能力的影响.试验结果表明,采用植GFRP筋和包裹CFRP布的组合加固技术较前两种加固方法能更加有效地改善钢筋混凝土柱的抗震性能.     

喷射FRP加固震损钢筋混凝土柱抗震性能试验

通过12组72件喷射纤维/树脂复合材料(FRP)试样的拉伸强度试验,研究了纤维种类、树脂基体材料、纤维体积分数、纤维混杂比及纤维长度等因素对喷射FRP拉伸强度、弹性模量和断裂伸长率等性能的影响。通过8根钢筋混凝土(RC)柱试件的拟静力试验,研究了喷射玄武岩纤维/树脂复合材料(BFRP)和混杂玄武岩-碳纤维/树脂复合材料(BF-CFRP)加固震损RC柱的抗震性能,分析了喷射FRP层厚度、纤维混杂比、柱预损程度和柱轴压比等对加固试件的极限承载力、抗侧变形能力、刚度退化特征和滞回特性的影响。结果表明:玻璃纤维与乙烯基酯树脂基体的协同工作性能最优,而玄武岩纤维具有耐久性高、延性好、与乙烯基酯树脂基体协同工作性能好等优良性能,可以作为玻璃纤维的良好替代品;玄武岩纤维混杂少量比例的碳纤维作为树脂基体增强材料,可以有效提高喷射FRP的拉伸强度和变形性能;震损RC柱经喷射FRP加固后,可以基本恢复其震损前设计极限承载力,并有效提高其延性和耗能能力。该加固方法可以对地震区已震损RC柱进行快速加固,有效防止整体结构在余震中发生倒塌等严重破坏。      

外包型钢加固箍筋锈蚀混凝土柱恢复力模型研究

为研究外包型钢加固后箍筋锈蚀混凝土柱的恢复力模型，对9根不同箍筋锈蚀率、体积配箍率的各混凝土柱进行通电锈蚀，锈蚀完成后加固，进而进行低周往复荷载试验。对各试验试件的骨架曲线及滞回曲线进行分析。在完好试件恢复力模型特征参数计算的基础上，对数据进行拟合回归，给出了外包型钢加固后箍筋锈蚀混凝土柱的退化三线型恢复力模型，并提出了不同因素作用下特征参数的计算公式。结果表明：箍筋锈蚀柱经外包型钢加固后各抗震性能指标有显著提升，破坏特征点明显滞后于完好试件，且以剪切破坏为主。通过对比分析，所得模型与试验结果吻合较好，能很好地反映外包型钢加固柱的滞回特性，为此类柱恢复力模型的计算提供参考。     

钢筋钢丝网砂浆加固混凝土圆柱的抗轴压性能

为大幅度提高加固效率,提出用钢筋钢丝网砂浆加固混凝土圆柱的思路。分别用钢筋钢丝网(SW)、钢筋网(S)、单一纤维复合材料(FRP)和混杂纤维复合材料(HFRP)加固混凝土圆柱共36根,进行轴压对比试验,探讨不同加固方法对试件承载能力和延性的影响。结果显示:SW加固柱保护层砂浆剥落与内部核心混凝土破坏几乎同时发生;且保护层砂浆裂缝间距基本与钢丝网格间距相等(11mm左右),因而裂缝又多又密;故SW加固柱与S加固柱相比,在承载力提高30%的前提下,延性仍达S加固柱的2倍左右。FRP或HFRP加固柱的承载力提高幅度最大,但两种加固柱的延性和变形能力明显低于SW加固柱。该文给出了SW加固混凝土圆柱的极限承载力计算公式。     

FRP加固非延性RC框架结构的地震易损性分析

对FRP加固非延性RC框架结构的地震易损性进行分析。以3层、6层和9层非延性RC框架结构为研究对象,针对三种不同的FRP加固方案,分别采用云图法和Pushover方法对结构的地震需求和抗震能力进行分析。通过对比FRP加固前后非延性RC框架结构的地震易损性,评估FRP加固方法对非延性RC框架结构抗震性能的影响。研究结果表明:FRP加固方法可以有效提高非延性RC框架结构抗震性能。在所采用的FRP加固方案中,底层关键楼层加固方案对非延性RC框架结构的抗震性能改善作用最为明显。此外,FRP加固方法对非延性RC框架结构的性能改善作用与结构高度相关,结构越高,FRP加固效果越差。     

地震荷载作用下FRP加固钢筋混凝土圆柱变形能力计算方法研究

基于性能的抗震设计要求对结构的变形能力能够进行计算,以确保不同的性能目标要求得以满足。该文研究地震荷载作用下纤维增强复合材料(FRP)加固钢筋混凝土(RC)圆柱截面曲率延性和柱顶侧向位移角计算方法。根据数值计算结果,得到了截面屈服曲率计算方法,由试验结果得到了FRP加固RC圆柱截面极限曲率计算方法。试验结果表明加固柱塑性铰长度和FRP用量密切相关,通过对29个大比例柱试验结果进行回归,得到了加固柱塑性铰长度计算方法,并分析了高FRP用量导致加固柱塑性铰长度减小的原因。经参数分析,探讨了FRP用量、轴压比与加固柱顶侧向变形能力的关系,提出了具有理想加固效率的FRP用量上限范围。     

FRP布加固混凝土框架子结构抗连续倒塌的精细有限元分析EI北大核心CSCD

外贴FRP布加固是一种有效提高既有建筑抗连续倒塌性能的手段,但现有FRP布加固方式存在降低结构抗震性能、加固施工不便等缺点。该文采用数值模拟方法分析了FRP布加固方式对现浇和装配式混凝土框架子结构抗连续倒塌与抗震性能的影响,并开展了优化方案研究。基于通用有限元软件LS-DYNA建立了FRP布加固混凝土框架子结构的连续倒塌精细数值模型,其中混凝土、钢筋与FRP布分别采用实体、梁与壳单元进行模拟,考虑了FRP布和钢筋的滑移、新旧混凝土界面的粘结失效和机械套筒处的钢筋截面损失。试验验证表明该方法可准确模拟试验试件的破坏模式和承载力发展。分析试验试件的不同粘贴方案结果发现:对现浇混凝土子结构,梁底与梁侧中性轴粘贴纵向FRP布并在梁端塑性铰区粘贴U形横向FRP布后,小变形下的结构倒塌抗力提升有限(最大仅2.6%)、基本不影响结构抗震性能,而对大变形下的结构倒塌抗力提升幅度可达49.5%;对于装配式混凝土子结构,在梁底、梁顶与梁侧底部外贴纵向布并在梁端塑性铰区粘贴U形横向FRP布可将小变形和大变形下的结构抗力最大提升24.2%和48.1%,使得装配式子结构在小变形下受力等同现浇结构,提升了原装配式子结构的抗震性能。对上述最优方案进一步的分析表明:保持FRP布用量不变而将塑性铰区内U形横向FRP布的分布范围和条数增加可提高大变形下的结构倒塌抗力,而不影响小变形下的加固效果。     

型钢混凝土柱火灾后恢复力计算模型

根据8根大比例型钢混凝土柱试件温度场和火灾后抗震性能试验结果,考虑受火时间、轴压比的影响,通过理论推导和回归分析,提出了开裂点、屈服点、峰值点和极限点为特征点的型钢混凝土柱恢复力-位移骨架曲线,并给出了这些特征点的计算公式。同时,通过试验数据的回归,得出卸载刚度与弹性刚度之间的关系。在上述工作的基础上提出了火灾后型钢混凝土柱的四线型荷载-位移恢复力模型。研究表明:建议的四线型恢复力模型与试验结果吻合较好,可用于火灾后型钢混凝土柱抗震性能的评估以及非线性地震反应分析。     

预应力钢绞线网加固钢筋混凝土柱恢复力模型研究

基于16根采用新型预应力钢绞线网张拉锚固技术加固的钢筋混凝土柱和2根对比柱在反复荷载作用下的试验结果, 进行了恢复力模型研究。结合之前相关试验研究, 确定出材料的本构关系, 建立了预应力高强钢绞线网约束加固钢筋混凝土的应力-应变关系方程;考虑构件轴力的二次矩效应, 提出了在反复荷载下预应力加固钢筋混凝土柱骨架曲线的计算方法, 建立了相应理论模型;结合Clough滞回规则, 建立了相应的恢复力模型。研究表明:对试验的材料本构关系适当简化, 通过合理的假定, 由基本的内外力平衡方程和简单的滞回规则, 可得到构件从加载到破坏全过程与试验吻合良好的骨架曲线和滞回曲线, 由此建立的恢复力模型简单、适用, 可为预应力高强钢绞线网加固钢筋混凝土柱设计和施工提供参考。     

Development of P-I diagrams for FRP strengthened RC columns

In this study, numerical simulations are performed to construct the Pressure-Impulse (P-I) diagrams for FRP strengthened RC columns to provide correlations between the damage levels of FRP strengthened RC columns and blast loadings. Numerical model of RC columns without or with FRP strengthening is developed using LS-DYNA. The accuracy of the model to simulate RC column responses to blast loads is verified by comparing the numerical simulation results with the tests results available in the literature. Dynamic response and damage of RC columns with different FRP strengthening measures are then calculated using the developed numerical model. The residual axial-load carrying capacity is utilized to quantify the damage level since the columns are primarily designed to carry the axial loads. Parametric studies are performed to examine the influence of column dimension, concrete strength, steel reinforcement ratios, FRP thickness and FRP strength on the P-I diagrams. The empirical formulae are derived based on numerical results to predict the impulse and pressure asymptote of P-I diagrams. These empirical formulae can be straightforwardly used to construct P-I diagrams for assessment of blast loading resistance capacities of RC columns with different FRP strengthening measures.     

Optimal performance-based design of FRP jackets for seismic retrofit of reinforced concrete frames

External bonding of fiber-reinforced polymer (FRP) composites is now a well-established technique for the strengthening/retrofit of reinforced concrete (RC) structures. In particular, confinement of RC columns with FRP jackets has proven to be very effective in enhancing the strength and ductility of columns, and has become a key technique for the seismic retrofit of RC structures. Despite the large amount of research on the behavior of RC columns confined with FRP, little research has been conducted on the behavior of RC frames with FRP-confined columns. For the seismic retrofit of RC frames with FRP, apart from the structural response of a retrofitted frame, an important issue is how to deploy the least amount of the FRP material to achieve the required upgrade in seismic performance. With these two issues in mind, this paper presents an optimization technique for the performance-based seismic FRP retrofit design of RC building frames. The thicknesses of FRP jackets used for the confinement of columns are taken as the design variables, and minimizing the volume and hence the material cost of the FRP jackets is the design objective in the optimization procedure. The pushover drift is expressed explicitly in terms of the FRP sizing variables using the principle of virtual work and the Taylor series approximation. The optimality criteria (OC) approach is employed for finding the solution of the nonlinear seismic drift design problem. A numerical example is presented and discussed to demonstrate the effectiveness of the proposed procedure.     

近海大气环境下锈蚀RC框架梁恢复力模型研究

为了研究近海大气环境下锈蚀RC框架梁的抗震性能,对8榀经受不同盐雾腐蚀循环作用的RC框架梁进行了低周反复加载试验,分析RC框架梁的滞回特性。基于试验结果,得到了带有负刚度段的三折线骨架曲线,并根据完好构件恢复力模型特征参数,得到了考虑钢筋锈蚀率和配箍率的锈蚀RC框架梁骨架曲线特征点计算公式。采用回归分析法,得到基于滞回耗能的循环退化指数,通过循环退化指数建立可综合考虑构件的捏拢效应、强度退化、卸载刚度退化、硬化刚度退化和再加载刚度加速退化的锈蚀RC框架梁恢复力模型。研究表明:随着钢筋锈蚀程度的增加,锈蚀RC框架梁的抗震性能劣化较明显,滞回耗能逐渐降低;配箍率对锈蚀RC框架梁恢复力特性的影响与未锈蚀RC框架梁相似;所建立的恢复力模型能够较好的描述锈蚀RC框架梁的滞回特性,可为该类结构的弹塑性时程分析提供理论参考。     

Comparative behaviour of hollow columns confined with FRP composites

Confining columns with fibre reinforced polymer (FRP) composites have been investigated in the last few decades to address the problem of upgrading and retrofitting reinforced concrete (RC) columns; however, most studies have concentrated on solid columns. This paper investigates the comparative behaviour of FRP confined hollow RC columns subjected to concentric loading. A total of twelve RC columns made from high strength concrete (HSC) were cast and tested. Six of the columns had a circular cross section (two solid columns, two hollow columns each having a circular hole, and two hollow columns each having a square hole) and the remainder columns had a square cross section (two solid columns, two hollow columns each having a circular hole, and two hollow columns each having a square hole). Six columns in total, three from each configuration were left unconfined as control specimens, while the others were confined with FRP. It was found that FRP confinement increased hollow RC columns’ axial load and ductility capacities; and hollow columns having circular holes had better performance compared to hollow columns having square holes.     

酸雨环境下锈蚀RC剪力墙恢复力模型研究

出于酸雨环境下锈蚀RC剪力墙结构抗震性能评估的需要,该文提出了酸雨环境下RC剪力墙宏观恢复力模型,通过对6榀锈蚀RC剪力墙拟静力试验结果进行回归分析,得到了考虑轴压比与钢筋锈蚀率影响的锈蚀RC剪力墙骨架曲线特征点荷载与位移修正系数计算公式,以循环退化速率来表征构件强度和刚度的退化,确定了基于循环耗能的循环退化指数β_i,并进一步建立了可考虑捏缩效应、屈服强度退化、峰值强度退化、卸载刚度退化及再加载刚度退化的锈蚀RC剪力墙滞回模型。与试验结果对比发现:采用该模拟方法得到的各试件的骨架曲线、滞回曲线以及试件破坏时的累积耗能均与试验结果吻合较好,表明所建立的锈蚀RC剪力墙宏观恢复力模型能较为准确的反应酸雨环境下RC剪力墙结构的力学性能及抗震性能,可为该类结构的抗震性能评估提供理论参考。     

轴向往复荷载作用下圆钢管混凝土柱恢复力模型研究

为研究钢管混凝土柱的轴向恢复力模型,设计制作了8个钢管混凝土柱试件并对其进行轴向往复加载,分析其受力机理和恢复力特性。基于试验结果,选用退化三线型模型,建立了钢管混凝土柱无量纲骨架曲线模型,并提出其轴拉与轴压方向的峰值承载力和位移的计算方法。鉴于钢管混凝土试件在轴拉与轴压方向受力机理的差异,对滞回曲线的正负向选用不同的滞回规则,建立了相应的卸载刚度函数。据此提出了钢管混凝土柱的轴向恢复力模型,并与试验滞回曲线进行对比,验证了恢复力模型的合理性,所建立的恢复力模型可为斜交网格结构体系的弹塑性分析提供依据。     

FRP约束RC矩形空心截面桥墩分析模型及试验验证

针对纤维复合材料(FiberReinforcedPolymer,FRP)约束钢筋混凝土(RC)矩形空心截面墩的抗震性能分析问题,该文提出了一种考虑有效强度系数和面积配箍率的FRP有效侧向约束力的简化计算方法。并通过与试验体桥墩的墩顶水平位移-承载力、墩底截面转动变形-弯矩曲线的对比分析,验证了该文提出简化计算模型的正确性。最后,基于该文提出的简化计算方法,对不同种类FRP约束RC矩形空心截面墩截面的抗弯承载力、曲率、塑性转动能力等抗震性能参数进行了研究,结果表明环包FRP布对空心墩的延性贡献较大,对提高其承载力影响较小。     

Compressive behavior of large-scale square reinforced concrete columns confined with carbon fiber reinforced polymer jackets

Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. The data available for square/rectangular columns are still limited. This paper reports the results of an experimental research program on the performance of large-scale square RC columns wrapped with carbon fiber reinforced polymer (CFRP) sheets. Attention is focused on the investigation of the total effect of longitudinal and transverse reinforcement and FRP jackets on the behavior of concentrically loaded columns. A total of 20 large-scale RC columns were fabricated and tested to failure under axial loading in the structural laboratory. Three types of columns were primarily considered: unwrapped; fully wrapped; and partially wrapped. Based on the test results of RC columns, existing experimental data and procedures in the literature are also evaluated. Furthermore, stress–strain curves of the columns are successfully predicted by the analytical approach previously proposed for FRP-confined concrete.     

Seismic performance of post-mainshock FRP/steel repaired RC bridge columns subjected to aftershocks

This study compares the performances of three types of repair jackets on mainshock (MS) earthquake-damaged RC bridge columns subjected to aftershock (AS) attacks. These repair jackets include fiber reinforced polymers (FRP), thick steel, and thin steel wrapped with prestressing strands. Results obtained from incremental dynamic time history analyses on refined numerical finite element bridge models were utilized to evaluate the efficacy of different repair jackets application on the post-MS collapse safety of RC bridges subjected to AS attacks of various intensities. Numerical results indicated that the three repair jackets can effectively improve the bridge collapse capacity by approximately 20% under severe MS-severe AS even though they cannot restore the initial stiffness of damaged columns. Repair jackets for the severe MS-damaged columns were ineffective under moderate AS events and thus not required. Steel repair jackets exhibited higher energy dissipation under MS–AS sequences than FRP jackets. In the case of FRP jackets, bidirectional fiber wraps are recommended for plastic hinge confinement of MS-damaged bridge columns subjected to aftershocks.