Experimental study on ductility improvement of reinforced concrete rectangular Columns retrofitted with a new fiber reinforced plastics method

Reinforced concrete （RC） columns lacking adequately detailed transverse reinforcement do not possess the necessary ductility to dissipate seismic energy during a major earthquake without severe strength degradation. In this paper, a new retrofit method, which utilized fiber-reinforced plastics （FRP） confinement mechanism and anchorage of embedded bars, was developed aiming to retrofit non-ductile large RC rectangular columns to prevent the damage of the plastic hinges. Carbon FRP （CFRP） sheets and glass FRP （GFRP） bars were used in this test, and five scaled RC columns were tested to examine the function of this new method for improving the ductility of columns. Responses of columns were examined before and after being retrofitted. Test results indicate that this new composite method can be very effective to improve the anti-seismic behavior of non-ductile RC columns compared with normal CFRP sheets retrofitted column.

Shear capacity of reinforced concrete columns strengthened with CFRP sheet

This paper discusses the results of tests on the shear capacity of reinforced concrete columns strengthened with carbon fiber reinforced plastic (CFRP) sheet. The shear transfer mechanism of the specimens reinforced with CFRP sheet was studied. The factors affecting the shear capacity of reinforced concrete columns strengthened with CFRP sheet were analyzed. Several sug-gestions such as the number of layers, width and tensile strength of the CFRP sheet are proposed for this new strengthening technique. Finally, a simple and practical design method is presented in the paper. The calculated results of the suggested method are shown to be in good agreement with the test results. The suggested design method can be used in evaluating the shear capacity of reinforced concrete columns strengthened with CFRP sheet.

Experimental study on slender reinforced concrete columns wrapped with CFRP

By axial compression tests on 6 reinforced concrete slender columns wrapped with carbon fiber-reinforced plastic (CFRP),with slenderness ratio(SR) from 4.5 to 17.5,the results show that when SR increases the retrofitting effect declines. In the case of same SR,the stability coefficient (SC) for the reinforced concrete(RC) columns with CFRP is much less than that without CFRP. There is 20% increase of stable bearing capacity to the former as compared with the latter when the SR in less than 17.5. The study summarized the simplified formula for SC,which provides a reference for engineering designers.

Square concrete columns strengthened with carbon fiber reinforced plastics sheets at low temperatures

Twenty-one square concrete columns were constructed and tested. The testing results indicate that bonded carbon fiber reinforced plastics(CFRP) sheets can be used to increase the strength and improve the serviceability of damaged concrete columns at low temperatures. The failure of the specimens,in most cases,takes place within the middle half of the columns. And the failure of strengthened columns is sudden and explosive. The CFRP sheets increase both the axial load capacity and the ultimate concrete compressive strain of the columns. The ultimate loads of strengthened columns at-10,0 and 10 ℃ increase averagely by 9.09%,6.63% and 17.83%,respectively,as compared with those of the control specimens. The axial compressive strength of strengthened columns is related to the curing temperatures. The improvement of axial compressive strength decreases with reducing temperature,and when the temperature drops to a certain value,the improvement increases with falling temperature.

Shear-critical reinforced concrete columns under various loading rates

This paper presents an experimental study of shear-governed reinforced concrete columns subjected to different loading rates. Four typical short columns were tested cyclically with loading rate of 0.05, 1, 3, and 5 Hz, simulating seismic load. Test result indicated that the loading rate does not affect the column behavior when the rate is up to 5 Hz. Furthermore, Carbon Nano-Fiber Aggregates （CNFAs） were utilized as internal sensors to detect the damage in the column. The test result shows that the CNFAs work well sensing the structural behavior. The CNFA output was further quantitatively correlated to the structural damage level. Finally, a finite element analytical model was constructed to describe the behavior of short columns with shear failure. The analytical model successfully modeled the cyclic loading test results.

Strength and Deformation of Axially Loaded Fiber-Reinforced Polymer Sheet Confined Concrete Columns

Experimental results of 29 axially loaded fiber-reinforced polymer sheet (FS) confined concrete columns and two reference plain concrete columns are introduced. Twenty four column specimens were confined with carbon fiber sheet (CFS) and five column specimens were hybrid confined with both CFS and glass fiber sheet (GFS). The influence of aspect ratio, FS material, initial axial force ratio, and FS confine-ment degree on the strength and deformation of columns were studied. Based on the experimental results, the equations of complete stress-strain curve of CFS confined concrete are proposed. These equations are suitable for the nonlinear analysis of square and rectangular section columns. Suggestions of applying FS to confine concrete columns are presented.

碳纤维加固钢筋混凝土柱受压分析

碳纤维材料的价格有所下降,且碳纤维材料具有强度高、质量低、施工简单、容易操作等特点,因此碳纤维作为一种新型材料在土木工程领域得到了广泛的应用。为了研究碳纤维布加固钢筋混凝土柱后的受压行为,运用ANSYS对钢筋混凝土进行数值分析,比较了未加固钢筋混凝土圆柱与用碳纤维布加固的钢筋混凝土圆柱的抗压强度变化规律以及粘贴不同碳纤维布层数对构件抗压强度有何影响。结果表明:用碳纤维采用全包裹式环向约束法加固过的钢筋混凝土圆柱要比未加固的钢筋混凝土圆柱抗压能力强。钢筋混凝土圆柱的抗压能力随着碳纤维布层数的增加而提高且钢筋混凝土柱抗压能力提高比例在减小。

爆炸荷载作用下钢筋混凝土柱的动力响应及抗爆加固研究

某些工业厂房对构件抗爆有特殊需求,需对构件进行抗爆设计。淄博某石化企业因增设化工设备,厂房内的局部混凝土柱需承受爆炸冲击荷载,则相关范围内的混凝土柱应进行抗爆加固处理。该文使用有限元软件通过对钢筋混凝土柱采用不同碳纤维布加固方式(封闭缠绕粘贴、侧面粘贴)的破坏模式、动力响应分析发现,当构件受初始冲击作用时,应力较大位置集中于两端,此时构件以剪切变形为主;采用全截面围贴加固钢筋混凝土柱时,碳纤维布作用同于柱内纵向钢筋,并可提供围箍效应,类似于柱内受剪箍筋,故相比于对面粘贴的加固方式可明显改善构件的延性。研究可为同类型混凝土柱的抗爆加固设计提供相关数据支持,并具有一定的借鉴意义。

3种加锚方式下2种碳纤维布加固钢筋砼梁抗剪承载力计算的比较

按照《碳纤维片材加固混凝土结构技术规程》与《混凝土结构加固设计规范》分别对胶锚或钢板锚、环形箍及自锁式、加织物压条一般式3种U形箍加锚方式加固后的梁斜截面承载力进行计算。结果发现,2种计算方式得出胶锚或钢板锚加锚方式的承载力增加值差异最小,加织物压条一般式的差异最大。2个工程抗剪加固应用算例的验证结果与计算结果一致。由此可知,在相同加固要求条件下,采用胶锚或钢板锚加锚方式的加固成本最低。

型钢-钢纤维高强混凝土柱抗震性能试验研究

为改善高强混凝土的脆性,提升型钢高强混凝土柱的抗震性能,采用钢纤维混凝土制备型钢高强混凝土柱试件,开展型钢-钢纤维高强混凝土柱的低周往复加载试验,观察试件的破坏过程和形态,基于荷载-位移滞回曲线、骨架曲线及强度衰减分析钢纤维掺量对试件变形能力、承载力、延性等抗震性能的影响。结果表明:钢纤维体积分数在0~2.0%范围内,不同钢纤维掺量的试件均发生弯曲破坏,但钢纤维的掺入可延缓裂缝发展,有效防止混凝土大面积脱落;加入钢纤维,试件的滞回曲线更饱满,耗能能力显著提升,承载力提高了13%~21%,钢纤维体积分数为1.0%时提高最明显;随钢纤维掺量的增加,试件的延性和变形能力得到改善,钢纤维体积分数为2.0%时延性系数达5.34,强度衰减缓慢,控制位移增大,在变形较大的情况下,试件的强度衰减从28%降为16%。钢纤维的增韧效果能显著提升型钢混凝土组合结构的抗震性能。

锚固碳纤维布加固低强度钢筋混凝土梁有限元分析

为研究不同加固方式下低强度钢筋混凝土梁的受力性能及裂缝开展情况,本文通过有限元软件建立了钢筋混凝土梁的三维有限元模型。通过与试验数据的对比分析,得到的模拟结果和试验结果吻合较好,较准确地反映出混凝土梁的受力特征和受力过程,验证了数值模型的合理性;通过仿真分析进一步验证,相较于碳纤维U形箍锚固梁,钢板U形箍锚固梁可以更好地抑制梁底碳纤维布与混凝土的剥离,从而提高加固效果。

CFRP约束圆中空夹层钢管混凝土短柱轴心受压性能试验研究

对圆中空夹层钢管混凝土(CFDST)短柱和CFRP约束CFDST(CFRP-CFDST)短柱进行了轴压试验,研究混凝土强度和CFRP粘贴层数对CFRP约束CFDST短柱轴压性能的影响,得到了CFDST短柱和CFRP约束CFDST短柱的典型破坏模式、荷载—位移曲线及荷载—应变曲线。试验结果表明:与CFDST试件相比,CFRP约束CFDST试件的极限承载能力显著提高,且贴布层数越多,钢管混凝土短柱的极限承载力越高。给出了避免内钢管先于外钢管屈曲破坏的内钢管最小壁厚计算式,并提出了CFRP约束CFDST短柱的轴压极限承载力计算式,该计算式计算结果与试验结果吻合较好。

方钢管超高强钢纤维混凝土柱轴压性能研究

为研究方钢管超高强钢纤维混凝土柱的受压性能,开展了12个方钢管超高强钢纤维混凝土柱的轴压试验,试验参数包括钢管屈服强度与厚度、混凝土基体强度和钢纤维掺量.结果表明:掺入钢纤维基本不改变试件的破坏形态;对于混凝土棱柱体抗压强度介于80~150 MPa之间、套箍指标介于0.33~1.43之间的方钢管钢纤维混凝土柱,其管内混凝土的抗压强度与对应混凝土棱柱体抗压强度接近;钢纤维对延性的提升作用随着混凝土强度的提高和套箍指标的增大而降低;当混凝土棱柱体抗压强度为130 MPa、套箍指标为0.90时,掺入1.5%的钢纤维对提升方钢管混凝土柱的延性不起作用.

混掺高延性纤维混凝土组合十字形短柱抗震性能研究

为改善钢筋混凝土十字形短柱的抗震性能,将高延性纤维混凝土用于十字形短柱底部。通过对混掺高延性纤维混凝土组合十字形短柱(R/ECC)和普通钢筋混凝土十字形对比柱(RC)进行拟静力试验,分析其裂缝开展模式、破坏形态、滞回性能、延性、耗能能力和刚度退化等,研究混掺高延性纤维混凝土对十字形短柱抗震性能的提升作用。结果表明,在十字形短柱底部采用混掺高延性纤维混凝土,可有效控制裂缝的开展,减小裂缝宽度,改善柱底混凝土的压溃剥落状态;短柱的延性和耗能能力明显提高,刚度退化缓慢,承载力有一定提高。相比RC柱,R/ECC柱位移延性系数、峰值点和极限点时累积滞回耗能分别提高7.3%、225.5%和44.6%,受剪承载力提高9.5%。

碳纤维复材约束椭圆钢管混凝土短柱轴压性能研究

为研究碳纤维复材约束普通强度椭圆钢管混凝土(CFRP-ECFST)短柱轴压性能,开展了8个不同椭圆截面比、不同复材厚度的短柱试件的静力轴压试验,考察了试件的破坏模式及其影响因素。参考已有碳纤维复材-高强钢管约束混凝土应力-应变设计模型,建立了CFRP-ECFST短柱轴压设计模型,并利用试验结果对该模型的准确性进行验证。结果表明:CFRP-ECFST短柱破坏模式均为中部碳纤维断裂;碳纤维断裂应变随椭圆截面比的增大而降低;碳纤维复材的约束效应随复材管用量增加而增强,但随椭圆截面比的增大而降低;由设计模型计算的轴向荷载-应变曲线与试验曲线吻合良好,表明设计模型能较为准确地估计CFRP-ECFST短柱的轴压承载力,可为该类构件的工程设计提供参考。

条带CFRP圆钢管锂渣混凝土短柱轴压性能研究

为实现建筑业的可持续发展,解决工业废料堆积及污染问题,以锂渣取代率、碳纤维增强塑料(carbon fiber reinforced plastics,CFRP)包裹间距和包裹层数为影响因素,将锂渣废料作为胶凝材料部分取代水泥,共设计9根试验柱进行力学试验,探究条带CFRP约束圆钢管锂渣混凝土短柱的轴压性能。通过观察试验现象和破坏形态,采集试验数据绘制力学曲线图,对条带CFRP圆钢管锂渣混凝土柱的极限强度、刚度和延性等多个力学参数进行分析研究。结果表明:锂渣掺量在0~20%时,随着锂渣掺量的提高,试件极限强度和初始刚度均增大,但延性下降约13.9%;将试件的包裹间距从25 mm增至40 mm,试件极限强度、刚度和延性均降低约5.0%,包裹间距为40 mm的条带围压方案在节省物料的同时还有较好的结构性能;将试件CFRP包裹层数从1层提高至3层,试件抗压强度、刚度和延性均提升18.0%~26.0%,可见包裹层数对柱性能影响较大。

冻融环境下碳纤维聚合物加固混凝土施工技术研究

为进一步提高混凝土短柱在冻融环境下的力学性能,使用碳纤维增强聚合物和收缩补偿混凝土加固混凝土受压构件,以研究加固混凝土短柱施工技术。由碳纤维增强聚合物(CFRP)和补偿收缩自密实混凝土(ESCC)组成的加固体系对CFRP外壳施加后张应力,进一步消除应力滞后,并发挥约束作用。实验变量包括冻融循环次数、加固聚合物壳层和加固混凝土类型。试验结果表明,当冻融循环次数达到125次时,混凝土受压构件的动态弹性模量损失率达到24.8%,质量损失率为5.3%。采用收缩补偿自密实混凝土对CFRP施加后张拉应力的方法,可以显著提高混凝土受压构件的承载力,比普通混凝土的承载力分别提高了13.23%和4.22%。且当冻融循环次数增加到75次时,混凝土试件的承载力比对照组降低了5.13%。随着冻融循环次数的不断增加,混凝土试件的损坏程度也逐渐增加,与对照组相比,承载力下降了28.2%。

基于试验与数值模拟的在役PC连续梁桥碳纤维布加固效果分析

为了研究碳纤维布对在役预应力混凝土连续梁桥的加固效果,选取梁体有U形缝的桥跨和无缝的对比跨进行现场试验和数值计算。结果表明,粘贴碳纤维布加固对于开裂结构的刚度提升效果非常有限,不适用于开裂结构在正常使用状态下的刚度提升,也不适用于未开裂结构的预防性加固,但可以通过抑制裂缝开展提高开裂结构的耐久性。

应用碳纤维布增强钢筋混凝土柱抗震能力的研究

本文通过８根钢筋混凝土柱在周期反复荷载作用下受力性能的试验研究，验证了使用碳纤维布 包裹钢筋混凝土柱来提高其延性这种补强加固方法的有效性。本文分析了轴压比、混凝上强度、碳 纤维布强度以及碳纤维布的包裹范围、包裹层数等因素对抗震加固效果的影响。最后，还对碳纤维 布加固钢筋混凝土柱使其延性提高的机理进行了分析。

碳纤维布增强钢筋混凝土柱抗震能力的试验研究

通过 3根钢筋混凝土柱在周期反复荷载作用下受力性能的试验研究 ,验证了用碳纤维布包裹钢筋混凝土柱来提高其延性这种补强加固方法的有效性 ,分析了碳纤维布的包裹范围、包裹方式等因素对补强加固效果的影响 ;同时编制了计算机全过程受力分析程序 ,分析了较高轴压比情况下构件延性的变化情况 ,为进一步研究奠定了基础。