截面尺寸对CC+CFRP共同约束钢筋混凝土方柱受力性能的影响

截面尺寸对于碳纤维增强复合材料(CFRP)约束柱的性能具有重要影响,鉴于CFRP在特殊环境中的耐久性问题,提出了碳纤维布与混凝土帆布(CC)联合加固方式,通过两种加固方案(CFRP加固和CFRP+CC共同加固)的矩形钢筋混凝土方柱轴压试验,研究了不同截面尺寸对混凝土方柱轴向受压承载力的影响,分析了加固后混凝土方柱的破坏形态和延性.结果表明:随着柱截面尺寸的增大,试件的持荷平台变小,截面应力、应变和延性系数均减小;CC+CFRP复合加固柱的承载力和延性较CFRP加固对照组均得到提高,破坏形态也得到明显改善.     

内嵌CFRP筋加固混凝土试件的粘结性能试验研究

在内嵌筋材加固混凝土试件中,良好的粘结质量是保证加固效果的关键。通过对13根内嵌碳纤维复合材料(CFRP)筋的拔出试验,研究了内嵌加固的粘结剪应力、破坏模式、试验现象,分析了混凝土强度、开槽尺寸对粘结性能的影响。结果表明,粘结试件达到破坏荷载时,剪应力的最大值出现在距加载端100~200mm的范围内;当发生结构胶与混凝土界面破坏时,随着混凝土强度的增加,粘结强度增大;开槽尺寸对破坏模式的影响较大。研究结果为实际工程应用提供依据,具有一定的参考价值。     

CFRP加固冻融损伤柱力学试验研究

为了研究碳纤维复合材料(CFRP)加固冻融损伤混凝土柱的力学性能,对CFRP加固混凝土柱进行轴压试验。结果表明:CFRP能有效提高冻融损伤柱的承载力和变形性能;随着冻融损伤程度的加剧,试件破坏逐渐呈45°角剪切破坏,裂缝多且分散;试件冻融损伤程度越严重,CFRP加固效果越好,特别是全包方式。     

CFRP加固组合梁承载力性能实验研究

对碳纤维复合增强材料(CFRP)条带加固的混凝土-钢组合梁抗弯性能进行实验研究。在考虑CFRP条带加固长度和宽度两个变量的基础上,采用四点加载的方式,研究加固和未加固组合梁在加载过程中的承载力性能。通过分析试件的荷载-位移曲线和其破坏模态,揭示在加固前后混凝土试件的初裂荷载和极限承载力的变化规律,并分析组合梁各类破坏模态的产生机理。实验研究结果表明:采用CFRP条带加固的组合梁承载能力会提高,当CFRP加固长度为试件总长的60%时,承载力的提高效率最高。同时提出一桁架模型,用以分析加固前后组合梁中混凝土板、钢梁腹板以及FRP条带的内力,为该类加固梁的极限荷载预测提供了依据。     

纤维布加固混凝土的轴压力学性能研究

为了提升混凝土柱的轴压力学性能,共设计了5组纤维布加固混凝土柱,分别对5组混凝土柱进行了轴压性能测试。结果表明,JFRP和NFRP试件相较未采用纤维布加固的混凝土柱的承载力分别提升了34%和43%,最大压应变分别提升了196%和178%,纵向钢筋的最大应变分别提升652%和552%;相较于CFRP试件,JFRP和NFRP试件的最大承载力也提升了约85%左右,表明组合方式更加有利于提升纤维布加固混凝土的承载力和延性。相较于CFRP试件的脆性破坏,JFRP和NFRP试件的破坏形式则呈现出弹塑性破坏形态。     

碳纤维加固钢筋砼柱承载力的影响因素研究

利用试验数据验证,建立一个有效、精确的有限元模型,使用ANSYS软件计算CFRP加固间距、层数、柱的截面尺寸及长细比的变化对碳纤维加固钢筋砼柱极限承载力的影响.结果表明,在加固层数相同时,柱的承载力随加固间距的增大而减小;应力随着CFRP布层数的增多而提高,CFRP加固层数较少时应力提高幅度相对较大,其极限加固层数为5层,超过此层数则CFRP利用率将变小;在短柱的范围内,CFRP加固后混凝土柱的最大轴向应力的计算结果十分相近,并不随着柱长细比的增加而变化较大;柱尺寸的变化对CFRP约束效果的影响较明显,约束后混凝土柱的承载力提高幅度随着尺寸的增大而减小.     

钢筋直径对混凝土试件早期应力应变影响的试验研究

使用混凝土温度应力试验方法,利用华南地区某码头工程胸墙混凝土结构施工阶段温度发展历程作为养护条件,在100%约束度条件下进行素混凝土及配筋直径为12 mm、16 mm、20 mm、25 mm单根配筋混凝土试件的温度应力试验,测试各混凝土试件的应力及应变发展过程,探究在高约束度下配筋直径对混凝土试件温度应力、应变的影响,为配筋混凝土结构早期温度与收缩裂缝的控制提供试验参考。     

FRP环向加固木柱轴心受压性能试验研究

提供了15根FRP环向加固木柱的轴心抗压性能试验数据,详细探讨了受载后试件的工作机理和破坏模式,试件的设计参数为FRP的层数和FRP的类型,分析了各设计参数对加固木柱承载力和峰值应变的影响。试验结果表明,FRP环向加固木柱可提高木柱的抗压承载力,改善木柱的延性。在极限荷载以前,加固木柱的荷载-应变关系曲线基本保持线性变化,在极限荷载以后曲线为近似理想塑性。加固木柱的承载力和峰值应变随加固层数的增加而增加。3层GFRP可提高木柱承载力和峰值应变分别达21.82%和94.95%。试件的极限荷载和轴向应变随环向FRP的弹性模量的增加而增加,但增幅逐渐变缓。加固木柱达到极限荷载时,环向加固层没有出现拉断现象,其环向应变并未达到环向加固层的极限应变,仅为FRP极限拉应变的10%左右。木柱的破坏始于木纤维的弯曲变形,环向FRP可有效约束这种变形的发展,这是改善木柱轴心受压性能的主要原因。所有试件的破坏模式都表现为木柱产生错动变形,被完全压皱破坏。     

碳纤维再生混凝土循环受压性能及本构关系研究

为了研究循环荷载下碳纤维再生混凝土(CFRAC)的受压性能,以再生粗骨料取代率、碳纤维体积掺量和加载速率作为变化参数,设计并制作了40个圆柱体试件进行循环受压加载试验。试验观察了试件的破坏形态,获取了应力-应变曲线,分析了不同变化参数对峰值应力、峰值应变、塑性应变、刚度退化和应力退化等性能的影响规律。结果表明：碳纤维再生混凝土试件在循环荷载作用下主要发生脆性破坏;碳纤维改善了再生混凝土的循环受压性能,与未掺碳纤维混凝土相比,当碳纤维体积掺量为0.3%时,峰值应力和峰值应变分别提高了11.33%和12.22%;刚度退化与应力退化程度得到降低;当再生粗骨料取代率为100%时,峰值应力和峰值应变分别提高了10.16%和14.29%;最后,提出了碳纤维再生混凝土在循环受压下应力-应变本构方程。     

CFRP修复混凝土粘结应力分析

为了研究碳纤维增强复合材料(CFRP)修复混凝土层间的粘结力学性能,本文通过对42根CFRP加固混凝土试件进行弯剪试验和理论分析,结果表明:粘结力与CFRP的粘贴长度、层数、梁几何尺寸以及加载方式有关,粘结力随CFRP层数、长度增加而增加,其中,最优层数、长度分别为2层和250mm。     

端部增强方式对CFRP管轴压力学性能的影响

端部局部破坏严重制约CFRP(Carbon Fiber Reinforced Polymer)管轴压承载力的发挥,对采用金属加强箍-金属端帽增强与碳纤维-金属内衬增强两种端部增强方式的CFRP层合管进行了轴压试验,得到了试件受力过程和破坏形式。基于Hashin失效准则,利用有限元模型分析两种端部增强方式下CFRP管首层失效模式和承载力,并解释了增强机理。研究表明:与未施加端部增强的试件相比,端部增强可改变试件失效模式并提高承载力;端部增强时,外部增强约束刚度不宜过大,增强件与试件较大的刚度差会导致变形不一致,易在增强端边缘处发生剪切破坏;采用碳纤维-金属内衬的端部增强方式可有效防止端部发生"开花式"破坏和剪切破坏,可使层合管发生整体破坏,轴压承载力提高了46.37%。     

Experimental study on bond behavior between corrosion-cracked reinforced concrete and CFRP sheets

Bond behavior between corrosion damaged reinforced concrete and carbon fiber reinforced concrete polymer (CFRP) sheets was experimentally investigated. Forty ordinary strength concrete blocks (150 × 150 × 200 mm) were reinforced at one side across the 200-mm-dimension using three conventional ?12 mm steel bars at a spacing of (30, 40, and 50 mm) at a concrete clear cover of 15 mm. Thirty blocks were subjected to a cyclic treatment in 3% chloride solution until corrosion initiated and resulted in three different global cracking widths of up to 0.90 mm. Both control and corrosion damaged blocks were attached to CFRP sheets over their steel reinforced zone at bond lengths and widths ranging from (90 to 150 mm) and (50 to 150 mm), respectively, with CFRP bond length-to-bar spacing ratio kept constant at 1/3. Near-end pull-off tests were carried out using a special setup, mounted on a Universal Testing machine. Corrosion cracking caused significant reductions in bond strength, and slippage at ultimate stress at (41 and 68%), respectively. Other bond characteristics such as stress at first slippage, and bond stiffness and toughness were reduced, as well, by as high as (83, 44 and 67%) of those of control specimens, respectively. Corrosion cracks were more detrimental for smaller bond length and width values; especially after first and second corrosion stages, where bond failure was categorized by concrete skin peeling-off.     

CFRP布约束H型钢部分外包混凝土柱的试验与设计方法研究

提出H型钢部分外包混凝土柱(PEC柱)结构,通过对18根PEC柱试件的轴心和偏心受压试验,研究了不同的碳纤维布粘贴层数、不同的碳纤维布粘贴间距、不同的偏心距分别对PEC柱的承载能力和破坏模式的影响。研究发现:粘贴碳纤维布的PEC柱承载力大于不粘贴碳纤维布的PEC柱;相同碳纤维布粘贴间距时,粘贴两层布比单层布的PEC柱承载力有所提高;碳纤维布粘贴间距越小,PEC柱的极限承载力越大;所有试件柱的极限承载力随偏心距的增大而降低。基于试验数据,提出承载力计算公式。     

Strain rate-dependent deformation behaviors of multi-layer carbon fiber reinforced polymer laminates

This paper focuses on the contributions of diversities of strain rate and orientations for aggravating the diversities of micro failure behaviors on carbon fiber reinforced polymer (CFRP) laminates. A miniature horizontal type tensile tester is employed to conduct experiments with strain rate ranging from 2.6 × 10⁻⁶ s⁻¹ to 2.6 × 10⁻³ s⁻¹. The CFRP laminates are obtained based upon a thermoset toughened epoxy matrix (termed CF/Epoxy) with ply orientations of (0°/0°) and (0°/90°). Significant differences in deformation behaviors of CFRP laminates are determined through tests. The study clearly reveals the strain rate-dependent deformation modes of CFRP laminates, involving pure fiber fracture, epoxy crack with stepped surface and interface failure with residual voids, determines the “low-high-low” variation tendency of Young's modulus and strength as a function of strain rate. Ply orientation-dependent differences in deformation behaviors are also investigated via severe interfacial shearing effect. A unified model consisted of four deformation modes to is clarified to analyze the complexity of CFRP laminates failure mechanism.     

Comparative behavior under compression of concrete columns repaired by fiber reinforced polymer (FRP) jacketing and ultra high-performance fiber reinforced concrete (UHPFRC)

This paper summarizes the experimental results from a comprehensive research program to study the fundamental stress–strain behavior of damaged concrete repaired by two techniques: increased concrete section and bonding fiber reinforced polymer (FRP). In this work, two types of FRP composite jackets were used, carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer, and two types of concretes were used to repair the damaged concrete by increased concrete section: ordinary concrete and ultra high-performance fiber reinforced concrete (UHPFRC). Fifteen circular columns of concrete (110 × 220) cm³ were initially pre-damaged up to intense cracking, repaired by increased concrete section and by bonding FRP, and tested under uni-axial compression by loading up the damage. The impact of different design parameters, including plain concrete strength, types of composites, and type of concrete used for increasing section, was considered in this study. The strength enhancement and ductility improvement of specimens are discussed. A simple model is presented to predict the compressive strength of repaired damaged concrete columns. A significant strength and an increase in ductility were achieved, particularly when the columns were repaired by increasing section with UHPFRC and by bonding CFRP. These preliminary tests indicate that the use of UHPFRC is an effective technique for rehabilitating damaged concrete columns, highly competitive with the repaired concrete by wrapping specimens with FRP composite jackets.     

Experimental investigation into strengthened short reinforced concrete corbels by bonding carbon fiber fabrics

This paper presents the mechanical behavior of strengthened short reinforced concrete corbel bonded by composite carbon fiber fabrics. Often, short reinforced concrete corbel is used in Civil Engineering and in building constructions. In fact, this paper investigated the influence of some parameters on the mechanical behavior of corbel specimens. The parameters are the carbon fiber fabric layers, type of strengthening by gluing directly fabrics on the front and rear of specimen faces or by wrapping. The composite materials used in this study are unidirectional and bidirectional carbon fiber fabrics. The ultimate load is obtained from monotone static test. The extensometer technique based on gauge strain is used to study the local behavior of structures. This technique allows one to measure strains of electric gauges glued to the surface of carbon fiber fabrics, concrete and steel bar. Finally, the cracking and failure modes of specimen are presented.     

Dynamic mechanical properties of carbon fiber reinforced geopolymer concrete at different ages

In order to improve the strength and toughness of geopolymer concrete (GC) at different ages under impact load, using slag and fly ash as cementitious materials, NaOH and sodium silicate as alkaline activators, carbon fiber as reinforcement, carbon fiber reinforced geopolymer concrete (CFRGC) was prepared. The dynamic compression test of CFRGC was carried out by Φ 100 mm SHPB test system. The effects of age (3 d, 7 d, 28 d) and fiber content on the dynamic mechanical properties of CFRGC were studied, and the strengthening and toughening effects of carbon fiber on GC were analyzed. In addition, the strengthening and toughening effects of carbon fiber on GC and ordinary Portland cement based concrete (PC) were compared and analyzed. The results show that the performance indicators of CFRGC at different ages have strain rate effect under impact load, and the dynamic compressive strength and specific energy absorption of CFRGC increase approximately linearly with the strain rate. With the increase of age, the dynamic compressive strength and specific energy absorption of CFRGC increase, and the strain rate sensitivity of dynamic compressive strength and specific energy absorption also increases. With the increase of carbon fiber content, the dynamic compressive strength and specific energy absorption of CFRGC increase first and then decrease, and the strain rate sensitivity of dynamic compressive strength and specific energy absorption also increase first and then decrease. When the carbon fiber content is 0.2%, the dynamic mechanical properties of CFRGC are the best, and the strain rate sensitivity of performance indicators is the strongest. Carbon fiber has strengthening and toughening effects on GC and PC. When the fiber content is 0.2%, carbon fiber has the best strengthening and toughening effects on GC and PC. The strengthening and toughening effects of carbon fiber on GC is better than that of PC. Compared with 28 d, carbon fiber has better strengthening and toughening effects on GC at the ages of 3 d and 7 d.     

绿色再生轻骨料混凝土短肢剪力墙抗震性能的研究

分析绿色再生轻骨料混凝土不同取代率"L"形截面短肢剪力墙力学性能,研究普通混凝土和最优配合比剪力墙试件抗震性能。试验结果表明:最优配合比试件比废砖掺量为0和100%的试件墙体达到屈服的时间较晚;竖向钢筋配置较多的会使钢筋较晚的进入屈服状态,能承受水平往复荷载的能力更强;较高的竖向钢筋配筋率能提高试件的耗能能力。最优配合比能提高试件耗能能力、承载能力、延性系数、结构耗能能力。研究的成果可为绿色再生轻骨料混凝土短肢剪力墙构件的设计和实际工程应用提供参考,同时为该类构件的深入研究打下基础。     

Specimen design,manufacturing and testing procedures for flat carbon fiber reinforced plastic laminates under biaxial loading

The optimization of a specimen design allowing the investigation of the biaxial strength of composite laminates over the full range of failure strain was the primary objective of this work. Multiaxial strength criteria are often found unreliable mainly as a result of the inherent complexity of biaxial tests and, in many cases, as a result of inefficient specimen designs. As a result of a development program combining numerical simulations and experimental measurements, a flat cruciform-shaped specimen has been developed for carbon fiber reinforced plastic (CFRP) laminates. The design fulfills the basic criteria for such a specimen, namely allowing for a uniform biaxial stress/strain state to exist in the gauge area and for testing the virgin material up to failure in both the tension-tension and tension-compression quadrants of the strain/stress space. The fabrication of the specimen is described and a three-step testing procedure for generating biaxial strength data is proposed. Typical results obtained from specimens of the proposed configuration tested in accordance with this procedure are presented. Results compare well with those obtained from tubular specimens, thus confirming the effectiveness of the proposed design. Experimental data obtained for the AS4/3501-6 carbon/epoxy composite system are finally compared against strength predictions of recognized failure theories.