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Research on Axial Compressive Properties of Preloaded Concrete Columns Strengthened with Prestressed CFRP Sheets

- , 2017,
Abstract: 为开展轴心压力作用下预应力碳纤维增强复合材料(CFRP)布加固负载圆形截面混凝土短柱力学性能研究,设计制作了11根圆形截面混凝土短柱,其中1根普通混凝土柱为对比柱,其余10根混凝土柱在负载与非负载2种情况下分别利用预应力CFRP布或非预应力CFRP布进行加固。通过轴心加载试验,获得了各试件极限荷载、轴向变形、材料应力变化等试验数据。基于试验数据分析了试件轴心压力作用下的力学性能。结果表明:与普通混凝土柱相比,利用预应力CFRP布加固的负载混凝土柱在二次受力过程中其屈服荷载有显著提高,且提高幅度与CFRP布预应力水平成正比,但极限承载力与CFRP布的预应力水平无关;利用预应力CFRP布加固的负载混凝土柱延性性能有显著提高。
In order to study the mechanical properties of preloaded circular short concrete columns strengthened with prestressed carbon fiber reinforced polymer (CFRP) sheets under axial compression, 11 circular short concrete columns were designed, including an ordinary concrete column served as reference column and 10 columns strengthened with prestressed and non??prestressed CFRP sheets at preloaded and non??preloaded states, respectively. The ultimate loads, axial deformations and stress variations of materials were obtained by the axial load test. The mechanical properties of the test columns under axial compression were analyzed based on the test data. The results show that the yield loads of the preloaded concrete columns strengthened with prestressed CFRP sheets compared with the ordinary column are significantly improved in the second load, and the increased range is proportional to the prestress level of CFRP sheets. However, the ultimate bearing capacities of the test columns have no obvious relationship with the prestress level of CFRP sheets. The ductility of the preloaded concrete columns strengthened with prestressed CFRP sheets is improved significantly
碳纤维布加固震损砖柱受压性能研究 Research on mechanical behavior of earthquake-damaged brick columns strengthened by CFRP  [PDF]
- , 2015,
Abstract: 针对震损砌体结构的加固需求,提出采用碳纤维布(CFRP)加固震损砖柱的方法.通过轴心、偏心受压试验,对碳纤维布(CFRP)条带满包加固震损砖柱的受压性能展开研究,对加固前后砖柱的承载能力、变形能力及碳纤维布(CFRP)条带的应变等进行对比分析,讨论了碳纤维布(CFRP)在砖柱受力过程中发挥的作用,在此基础上提出碳纤维布(CFRP)加固砖柱承载力计算公式.研究表明,碳纤维布(CFRP)加固震损砖柱效果良好,提出的计算公式与试验结果吻合良好
Experimental and Analytical Investigations on the Structural Behaviour of Steel Plate and CFRP Laminate Flexurally Strengthened Reinforced Concrete Beams  [PDF]
M.Z. Jumaat,A. Alam
Journal of Applied Sciences , 2008,
Abstract: This study presents an experimental and analytical investigation to compare the structural behaviour of externally bonded steel plates and Carbon Fiber Reinforceed Polymer (CFRP) laminates flexurally strengthened r.c. beams. For the experimental investigation, three r.c. beams were cast. One beam was tested in the un-strengthened condition to act as the control beam. The second beam was strengthened using steel plate while the third beam was strengthened using CFRP laminate. The strengthened beams were designed to have the same strength with the assumption that they would fail in a ductile manner. The test results indicated that although both beams were designed for the same strength, the CFRP laminate strengthened beam recorded a slightly higher failure load compared to the steel plate strengthened beam. The steel plate strengthened beam recorded a higher cracking load and less deflections, reinforcement bar strains, concrete strains and crack widths compared to the CFRP laminate strengthened beam. Results also showed that the CFRP laminate strengthened beam failed by premature concrete cover separation failure, whereas the steel plate strengthened beam failed by premature plate end interfacial debonding followed by concrete cover separation. The beams were also modelled using a Finite Element Method (FEM) package. The numerical results seemed to agree well with the experimental results.
Behavior of RC two-way slabs strengthened with CFRP-steelgrid under concentrated loading  [PDF]
Lu Yiyan, Zhu Tao, Li Shan, Zhang Haojun
- , 2018, DOI: 10.3969/j.issn.1003-7985.2018.03.008
Abstract: A novel composite technique of orthogonally bonding carbon fiber-reinforced polymer(CFRP)strips and steel strips is proposed to improve the performance of reinforced concrete(RC)structures based on co-working of CFRP strips and steel strips. To verify the effectiveness of the method for strengthening RC two-way slabs, seven flat slabs with the dimensions of 1 500 mm × 1 500 mm × 70 mm and an internal reinforcement ratio of 0.22% were prepared and tested until failure under concentrated loading, of which one was unstrengthened, one was strengthened with CFRP strips bonded to its soffit making a grid pattern(termed the CFRP grid), and five were strengthened with a hybrid grid of CFRP strips and steel strips in two orthogonal directions(termed the CFRP-steel grid)to the bottom with steel bolt anchorage. The investigation parameters are the strengthening method, the strip spacing(150, 200, and 250 mm)and the layers of CFRP strips(one layer, two layers, and three layers of CFRP strips are applied for CFRP-steel grid). The experimental results show that the strengthening RC two-way slabs with CFRP-steel grid are effective in delaying concrete cracking and enhancing the load-carrying capacity and deformability in comparison to the CFRP grid strengthening. The yield-line analysis model is proposed to predict the load-carrying capacity of the strengthened slabs. The prediction results are in good agreement with the experimental results.
Experiment on Fatigue Behaviors of Flexural Concrete Interface Strengthened with BFRP and CFRP

- , 2015,
Abstract: 以纤维增强复合材料(FRP)片材外贴混凝土受弯构件为研究对象,探讨玄武岩纤维(BFRP)和碳纤维增强复合材料(CFRP)加固混凝土界面疲劳性能。通过实施四点弯曲加载试验,研究了BFRP和CFRP加固混凝土界面疲劳破坏模式、界面疲劳裂缝扩展规律以及构件跨中挠度和FRP应变随加载循环次数的变化规律,并对BFRP和CFRP加固混凝土界面的静载剥离承载力和疲劳寿命进行了分析,给出了BFRP和CFRP加固混凝土界面的疲劳强度。研究结果表明:与BFRP?不炷?土界面相比,CFRP?不炷?土界面的静载剥离承载力提高了约50%,其疲劳寿命也明显提高;既有疲劳历程对BFRP和CFRP加固混凝土界面的静载剥离承载力影响不大。
Taking the flexurally strengthened concrete members with fiber reinforced polymer (FRP) as the research object, the fatigue behaviors of the concrete interface strengthened with basalt fiber reinforced polymer (BFRP) and carbon fiber reinforced polymer (CFRP) were investigated. Based on a series of four??point bending loading tests, the fatigue failure modes and the propagation law of interface crack strengthened with BFRP and CFRP, as well as the evolution of mid??span deflection and FRP strain change rule with loading cycle numbers were studied. Moreover, the debonding load??carrying capacity and the fatigue life of the BFRP??concrete and CFRP??concrete interface were analyzed, and the fatigue strength of the concrete interface flexurally strengthened with BFRP and CFRP was proposed. The study results show that compared with the concrete members strengthened with BFRP, the debonding load??carrying capacity of those with CFRP increases about 50%, and the fatigue life of those with CFRP is significantly longer. The effects of pre??fatigue damage are slight on the debonding load-carrying capacity of BFRP??concrete and CFRP??concrete interface
Hysteretic Behavior of Steel Column Strengthened With CFRP in Thermal Environment
Zhen-Guo Li
TELKOMNIKA : Indonesian Journal of Electrical Engineering , 2012, DOI: 10.11591/telkomnika.v10i5.1278
Abstract: This paper is concerned with analysis for the strengthening effect of carbon fiber-reinforced polymer (CFRP) on steel columns under cyclic lateral loading in thermal environment. Based on the finite element theory of thermo-elastic problem and steel structure stability theory, the hysteretic behavior of axial compression steel columns was studied by using Ansys software. The main variables investigated are: cyclic lateral loading, temperature, axial compression ratio and ductility. The results show that the CFRP wraps can improve the ultimate cyclic lateral loading and ductility of steel columns prominently in thermal environment which benefit to the anti-seismic capacity of steel structure. The effect of axial compression ratio on ultimate cyclic lateral loading is very obvious, more enhancements achieved with the axial compression ratio increased. While effect of temperature on ultimate cyclic lateral loading is not very obvious below 300℃.
Durability of High Strength Concrete Strengthened with Prestressed CFRP Under Wet-thermal Environments

- , 2017,
Abstract: 通过试验研究了湿度为98%,温度分别为20 ℃,40 ℃,60 ℃的湿热环境下预应力碳纤维增强复合塑料(CFRP)加固高强混凝土的破坏形态和承载性能,分析了预应力等级、温度、环境作用时间等因素对加固试件耐久性的影响。结果表明:经过湿热环境作用后,施加预应力等级为CFRP极限抗拉强度30%的预应力加固试件的开裂荷载和极限荷载均有不同程度的下降;随着环境温度的提高,加固试件的破坏形态逐渐由弯剪破坏转变为弯曲破坏;湿热环境作用对预应力CFRP加固试件的整体不利影响大于非预应力试件,并且随着预应力增加,不利影响会进一步加剧。
The failure patterns and bearing performances of high strength concrete specimens strengthened with prestressed carbon fiber reinforced polymer(CFRP)were studied by experiments under wet??thermal environment where the humidity was 98% and the temperatures were 20 ℃, 40 ℃, 60 ℃. The influences of different factors including prestressed degree, temperature and environment action time on durability of strengthened specimens were analyzed. The results show that the cracking loads and ultimate loads of specimens strengthened with prestress being 30% of tensile strength for prestressed CFRP decline in varying degrees after being subjected to wet-thermal environments. With rising of the environment temperature, the failure patterns change from bending shear failure to flexural failure. In addition, the overall adverse effects of wet??thermal environments on specimens strengthened with prestressed CFRP are greater than those on specimens strengthened without prestressed CFRP, and the adverse effect will be aggravated when prestress rises
Experiment on Shear Transfer Capacity of Reinforced Concrete Strengthened with CFRP

- , 2015,
Abstract: 设计15个外贴碳纤维增强复合材料(CFRP)的Z型试件进行直剪加载试验,试验参数包括直剪面钢筋配筋率(0.46%~1.2%)和CFRP加固率(0%~0.3%)。依据试验结果提出加固后钢筋混凝土直剪承载力预测表达式,并基于分量模型分析其加固机理。研究结果表明:直剪承载力随CFRP加固率增大而提高,提高幅度为6%~50%;相同CFRP加固率时,直剪承载力提高幅度随配筋率的增加而降低,承载力提高源于CFRP提供了附加的侧向夹紧力;当外贴CFRP和内埋直剪钢筋提供相等的侧向夹紧力时,两者对直剪承载力的贡献作用相近;所提出的承载力预测表达式具有较好的适用性。
Total fifteen typical Z-type specimens strengthened with external carbon fiber reinforced polymer (CFRP) strips were tested to investigate their shear transfer capacities. Test parameters included reinforcing steel bar ratios(0.46%-1.2%) and CFRP reinforcement ratios (0%-0.3%). Expressions were proposed to predict the shear transfer capacities of CFRP streng??thened concrete. The reinforcement mechanism of shear transfer was analyzed based on component model. The study results show that the shear transfer capacities improve in a range of 6%-50%with the increasing of CFRP reinforcement ratios. Moreover, for a given CFRP reinforcement ratio, the percentage of improvement decreases with the increasing of reinforcing steel bar ratios. The capacity improvement is believed due to the clapping force from CFRP.An approximate strengthening effect is realized when the external CFRP and the internal reinforcements provide identical clapping force in lateral direction. The proposed expressions to predict the shear transfer capacities have good applicability
Durability of high strength concrete strengthened with prestressed CFRP under freeze-thaw cycles

, JIANG Haixin, WANG Suyan

- , 2017,
Abstract: 通过4点弯曲试验研究冻融循环作用下预应力CFRP(碳纤维增强聚合物)加固高强混凝土的耐久性。在非预应力试件为对比的基础上设置2种预应力等级,预应力分别为CFRP抗拉强度标准值的15%和30%。分析冻融循环和预应力对加固试件荷载-挠度曲线及破坏形态的影响,结果表明:冻融循环后加固试件的承载力均有不同程度的下降,预应力等级越高,承载力降低越显著;最大预应力等级试件的破坏形态由弯剪裂缝引起的剥离破坏发展为剪切剥离破坏。
The four-point bending test was conducted to investigate the effects of freeze-thaw cycles on the durability of high strength concrete strengthened with prestressed CFRP (carbon fiber reinforced polymer). Two group of prestressed specimens were setup, and the tension control stress were equal to 15% and 30% of the standard value tensile strength of the CFRP. Another group of specimens strengthened with non-prestressed CFRP. The effects of freeze-thaw cycles and prestress were elaborated on the load-deflection curves and failure model. The results reveal that freeze-thaw cycles will lead to the decrease of the carrying capacity of all specimens. And the effect is gradually increasing with the increase of tension strength. The failure modes of specimens with the maximum level of prestress transformed from debonding of interface between CFRP and concrete were caused by flexural-shear crack to shear modes
Numerical Simulation Analysis of RC Beams Strengthened with CFRP Using Viscoelasticity Constitutive

徐佰顺, 马明, 钱永久, 唐继舜, 张方
XU Baishun
, MA Ming, QIAN Yongjiu, TANG Jishun, ZHANG Fang

- , 2017, DOI: 10.3969/j.issn.0258-2724.2017.05.021
Abstract: 为探讨胶黏剂粘弹性对碳纤维增强复合材料(CFRP)加固钢筋混凝土(RC)梁力学行为的影响,以Burger模型表征胶黏剂的应力-应变-时间关系,利用Laplace变换和逆变换推导了Burger模型Prony级数形式的松弛剪切模量;采用ABAQUS对粘贴CFRP加固RC梁进行数值模拟,分析了胶黏剂粘弹性对界面应力、CFRP轴力、RC梁弯矩和加固梁挠度的影响.研究结果表明:胶黏剂的粘弹性对加固梁的力学行为有一定的影响,随着持载时间的增加,界面峰值剪应力和峰值正应力均减小,CFRP轴力减小,RC梁弯矩增大,加固梁挠度增大;当胶层厚度为0.2 mm时,加载30 d后,界面峰值剪应力减小了40.1%,界面峰值正应力减小了33.0%,加固梁挠度增加了3.7‰,距离CFRP端部20 mm处截面上CFRP轴力减小了15.8%,RC梁弯矩增加了17.4%.
:In order to investigate the mechanical behavior influence of the adhesive viscoelastic on reiforced concrete beams strengthened with the carbon fiber reinforced polymer, the Burger model was used to describe the stress-strain-time relation for the adhesive. The relaxation shear modulus with Prony series forms of Burger model was derived by the mathematical method of Laplace transform and inverse Laplace transform. The finite element software ABAQUS was used to simulate RC beams strengthened with the CFRP. The influence of the adhesive viscoelastic on the stresses of the adhesive, the axial force of the CFRP, the moment of RC beams and the deflection of the reinforced beam were analyzed. The results show that the adhesive viscoelastic affect the mechanical behavior of the reinforced beam to a certain degree. With the increasing of the loading time, the shear stresses and normal stresses peak value of the adhesive decrease, the axial force of the CFRP decrease, the bending moment of the RC beam increase and the deflection of the reinforced beam increase. When the adhesive layer thickness is 0.2 mm, and the reinforced beam has been loaded for 30 d. The peak shear stress decreases by 40.1%, the normal peak stress decreases by 33.0%, the deflection of the reinforced beam increase by 3.7 ‰. On the cross section 20 mm away from the end of the CFRP, the CFRP axial force decreases by 15.8% and the bending moment of the RC beam increases by 17.4%
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