多丝碳纤维拉索研制及静载试验研究

为了解决拉索锈蚀和疲劳问题,提高其耐久性,采用轻质、高强、耐腐蚀和耐疲劳的碳纤维(CFRP)筋制作拉索.以环氧树脂砂浆为粘结剂,研制CFRP筋粘结式锚具及成套拉索,并进行了静载试验.分析了影响CFRP拉索锚固性能的各种因素,并进行了相关试验.研究结果表明,筋表面粗糙程度、锚具内锥度、粘结胶的性能和灌浆压力等直接影响锚具的锚固性能.所研制的多丝CFRP拉索的性能稳定,锚固效率系数达95%以上,可直接应用于实际工程.     

CFRP筋在RPC中锚固性能的理论分析及试验研究

静载试验详细研究了碳纤维增强塑料CFRP筋在活性粉末混凝土RPC的锚固性能。试验结果表明:对于抗拉强度不大于3000MPa的表面压纹CFRP筋在抗压强度130MPa的RPC中的临界锚固长度为20倍CFRP筋直径;多根压纹CFRP筋的合理筋间距为1倍CFRP筋直径。平均粘结强度及其对应滑移量的公式具有较好的适用性。平均粘结应力与滑移之间的预测曲线与试验曲线吻合较好,验证了提出的粘结滑移本构关系。理论推导了锚固变量沿锚固长度分布的表达式,算例验证了有效性。分析表明:距离自由端约为0.6倍锚固长度位置处的粘结应力等于平均粘结应力。对于压纹CFRP筋,当锚长≤12.5倍筋材直径时,粘结应力沿埋长分布较为均匀,其不均匀性系数在1.02―1.05之间;当埋长>12.5倍且≤20倍筋材直径时,粘结应力沿埋长分布较为不均匀,其不均匀性系数在1.05―1.14之间。     

CFRP加固青白石梁受弯性能试验研究

对4个未加固石梁及4个碳纤维布(CFRP)加固石梁进行了受弯性能试验研究,主要分析了未加固石梁与加固石梁在破坏形态、承载能力及变形能力方面的差异。试验结果表明:未加固石梁为典型的脆性破坏,加固石梁则表现出了非完全脆性破坏特征;加固后石梁的极限承载力有所提高,变形能力有所改善。对加固石梁的受弯承载力进行了理论分析,提出了极限受弯承载力的简化计算公式;达到极限荷载后,由于CFRP的作用,石梁仍有一定的承载能力,即承载力裕量,可避免石梁发生突然塌落的严重后果。     

混凝土结构用CFRP筋的感知性能试验研究

对混凝土结构用CFRP筋及其加筋混凝土梁的力学性能和感知性能进行试验研究。自行研制开发了不同直径和表面处理形式的CFRP筋。在此基础上,制作了三组各6个标准受拉试件,分别测试了CFRP筋的弹性模量、极限抗拉强度和电阻变化率,得到了相应的变化曲线;其次制作了两组各3根CFRP加筋混凝土梁,测试了梁中CFRP筋电阻随载荷增加的变化曲线。研究表明,CFRP筋具有很好的力学性能和感知性能,对于混凝土结构加强筋和结构受力状态监测具有广泛的应用前景。     

循环荷载作用对CFRP筋力学性能的影响

应用于桥梁工程的碳纤维增强复合材料（CFRP）筋通常受循环荷载作用,导致其力学性能的退化,这将影响桥梁结构的受力。为了考察循环荷载作用对CFRP筋力学性能的影响,首先利用静载试验对CFRP筋的初始力学性能进行了检测,然后结合静载试验结果并利用疲劳试验考察了各阶段循环荷载作用对CFRP筋弹性模量、松弛及抗拉强度的影响。研究结果表明,极限拉力作用下CFRP筋的弹性模量较初始状态高约5%,对于CFRP筋构件的变形对结构内力有较大影响的结构,在设计阶段建议适当地考虑CFRP材料的非线性问题;桥梁工程中,经200万次正常使用设计循环荷载作用的CFRP筋,其弹性模量和松弛性能较初始状态未发生明显退化,经应力幅为4.3%的极限抗拉强度的循环荷载作用后,CFRP筋的抗拉强度提高了1.2%,但应力幅提高至7%的极限抗拉强度时,其抗拉强度与初始状态相比无明显变化。     

预应力CFRP筋混凝土梁疲劳全过程分析

CFRP筋具有耐腐蚀、抗拉强度高、弹性模量低和重量轻等优点,是暴露及恶劣环境下预应力钢筋的理想替代品.目前国内外关于预应力CFRP筋混凝土结构静力性能的研究已开展较多,而关于其疲劳性能的研究则刚刚起步.为此,对混凝土、钢筋以及CFRP筋的疲劳性能进行了总结,在考虑了疲劳刚度退化、疲劳强度退化以及疲劳残余变形等因素的基础上,提出了预应力CFRP筋混凝土梁疲劳全过程的简化分析方法,并基于ANSYS二次开发实现了疲劳全过程分析.为验证提出的疲劳全过程简化分析方法,进行了预应力CFRP筋混凝土梁的300万次疲劳试验,计算值与试验结果吻合良好.     

CFRP筋增强ECC梁弯曲性能试验研究

为研究碳纤维增强树脂复合材料(Carbon fiber reinforced polymer,CFRP)筋/超高韧性纤维增强水泥基复合材料(Engineered cementitious composite,ECC)梁的抗弯性能,对3根CFRP筋/ECC梁、1根玻璃纤维增强树脂复合材料(Glass fiber reinforced polymer,GFRP)筋/梁和1根CFRP筋混凝土梁进行了四点弯曲试验,分析了配筋率、纤维增强树脂复合材料(Fiber reinforced polymer,FRP)筋类型和基体类型对梁抗弯性能的影响。试验结果表明:CFRP筋/ECC梁与GFRP筋/ECC梁和CFRP筋混凝土梁类似,均经历了弹性阶段、带裂缝工作阶段和破坏阶段;配筋率对CFRP筋/ECC梁的受弯性能影响较大。随着配筋率的增加,CFRP筋/ECC梁的承载能力不断提高,延性性能逐渐减弱;ECC材料优异的应变硬化能力和受压延性,使得CFRP筋/ECC梁的极限承载能力和变形能力均优于CFRP筋混凝土梁;由于ECC材料多裂缝开裂能力,CFRP筋/ECC梁开裂后,纵筋表面应变分布比CFRP筋混凝土梁更均匀; 由于聚乙烯醇(Polyvinyl alcohol,PVA)纤维的桥联作用,CFRP筋/ECC梁破坏时,其表面出现了大量的细密裂缝,且能保持较好的完整性和自复位能力;正常使用阶段,CFRP筋/ECC梁的最大弯曲裂缝宽度均小于CFRP筋混凝土梁。最后,根据试验结果,建立了基于等效应力图的CFRP筋/ECC梁弯曲承载力简化计算模型,确定模型中的相关系数。由简化模型计算的极限承载力与试验结果具有较好的相关性。      

碳纤维增强复合材料筋混凝土梁非线性力学性能

为了研究碳纤维增强复合材料(CFRP)筋混凝土梁的非线性力学性能,基于非线性理论推导了CFRP筋梁的有限元分析模型：对4个预应力CFRP筋混凝土梁进行了非线性全过程分析,考察了预应力CFRP筋、GFRP筋和普通钢筋的应力发展规律。与试验资料对比可知,计算结果与试验数据吻合良好,说明采用弥散裂缝模式、Owen屈服准则和Hinton压碎准则能较好地描述混凝土开裂、屈服和压碎特性,同时也说明了CFRP筋及其力学效应用组合单元模拟的有效性以及本文中研制程序的正确性。CFRP筋具有高强度性能,梁试件破坏时CFRP筋均未失效;与受拉区配筋为钢筋相比,GFRP筋在全过程中处于弹性阶段。     

基于ABAQUS的表面内嵌CFRP筋粘结滑移性能数值模拟分析

利用ABAQUS有限元软件,对混凝土、CFRP筋或板条以及粘结剂分别采用不同的单元类型,特别是运用Spring2非线性弹簧单元来模拟表面内嵌CFRP筋或板条混凝土的粘结作用,同时考虑材料各自的本构关系,对表面内嵌CFRP筋混凝土拉拔试件和内嵌CFRP板条加固混凝土梁试件进行有限元模拟,将模拟结果与已有试验结果进行对比验证。结果表明,利用数值模拟的方法可以得到较为准确的拉拔试件的极限值,也可以较为正确地模拟加固梁的受力过程。在验证模拟结果正确的基础上,进一步分析了拉拔试件CFRP筋应力、滑移、粘结应力随不同位置的变化规律以及加固梁CFRP板条粘结区域内应变和粘结应力的分布情况。研究结果表明,对于拉拔试件,不同荷载等级作用下,CFRP筋在粘结区域内不同位置处的应力呈非线性变化,而粘结应力峰值出现在距加载点20mm~40mm位置处,其随位置的变化曲线呈偏态曲线特点。对于表面内嵌CFRP板条加固梁,粘结区域内CFRP应变和粘结应力在梁屈服后激增,且呈非线性变化。     

CFRP筋夹板式锚具锚固性能试验研究

设计了一种CFRP 筋夹板式锚具,通过对40 个CFRP 筋-锚具组装件的拉拔试验,研究了锚固长度、螺栓预紧力、螺栓数量和CFRP 筋表面处理等对锚具锚固性能的影响.试验结果表明:试件的破坏形态包括CFRP筋的滑移、断裂和拉脱三种,试件达到极限荷载时的滑移量较小.增加锚固长度、螺栓总预紧力、螺栓数量以及对CFRP 筋表面打磨处理均可在一定范围内提高锚具试件的极限荷载.通过合理控制上述参数,可以使锚具发挥良好的锚固性能,满足实际使用要求.该文给出了CFRP 筋夹板式锚具合理的构造和螺栓预紧力值.在试验研究基础上,分析了CFRP 筋夹板式锚具的锚固作用机理,建立考虑锚固长度、螺栓预紧力和螺栓数量的CFRP 筋-锚具界面平均摩擦系数模型,并提出夹板式锚具的极限荷载计算公式,与试验结果吻合良好,具有较好的适用性.     

Fatigue behavior of RC beams strengthened with prestressed NSM CFRP rods

The fatigue performance of Reinforced Concrete (RC) beams strengthened using NSM CFRP rods was examined in this study. The testing matrix consisted of one un-strengthened beam and four beams strengthened using NSM CFRP rods prestressed to effective strain values of 0, 3260, 6899, and 9177 μ representing 0%, 20.4%, 43.1%, and 57.4% of the CFRP rod ultimate tensile strain, 1.6%. All beams were tested in four-point bending under fatigue conditions representing in-service loading for 3 million cycles at a frequency of 2 Hz. Upper and lower load limits were chosen to induce a stress range of 125 MPa in the tension steel during the first cycle. The fatigue results were compared with experimental test results of identical beams strengthened using prestressed NSM CFRP strips tested under identical fatigue conditions found elsewhere in literature. Test results showed that all strengthened beams experienced deflection increase lower than that of the un-strengthened beam which indicates the efficiency of the strengthening process in reducing the damage accumulation. Also, the percentage deflection increase as well as the stiffness degradation after 3 million cycles are almost the same for all the strengthened beams which indicates that damage accumulation is independent from the prestress level. The groove dimensionality, rather than the CFRP geometry, has a detrimental effect on the bond behavior.     

CFRP 主缆在鞍座及索夹处的抗弯折性能研究

为研究CFRP 主缆在鞍座及索夹处的抗弯折性能,首先理论分析CFRP 主缆的抗弯折性能取决于所用材料即CFRP 丝,然后分析CFRP 丝在鞍座及索夹处两种不同的弯折变形状态及内力分布,推导抗弯折效率的计算公式,并对各影响因素进行参数分析,最后针对不同工况,对CFRP 丝在鞍座和索夹处的抗弯折性能分别进行试验研究。理论与试验分析结果表明:CFRP 丝半径与弯折半径的比值与抗弯折效率呈线性关系,比值越小,抗弯折效率越高;抗弯折效率还受弯折包角、CFRP 丝的极限应变的影响,尤其当CFRP 丝半径与弯折半径的比值较大时抗弯折效率对这些因素的敏感度较高;鞍座与索夹处CFRP 主缆均能达到90%以上的抗弯折效率;理论分析与试验结果能够较好吻合。     

Mechanical behaviour of corroded RC beams strengthened by NSM CFRP rods

Corrosion of steel in reinforced concrete leads to several major defects. Firstly, a reduction in the cross-sectional area of the reinforcement and in its ductility results in premature bar failure. Secondly, the expansion of the corrosion products causes concrete cracking and steel–concrete bond deterioration and also affects the bending stiffness of the reinforced concrete members, causing a reduction in the overall load-bearing capacity of the reinforced concrete beams. This paper investigates the validity of a repair technique using Near Surface Mounted (NSM) carbon-fibre-reinforced polymer (CFRP) rods to restore the mechanical performance of corrosion-damaged RC beams. In the NSM technique, the CFRP rods are placed inside pre-cut grooves and are bonded to the concrete with epoxy adhesive.Experimental results were obtained on two beams: a corroded beam that had been exposed to natural corrosion for 25 years and a control beam, (both are 3 m long) repaired in bending only. Each beam was repaired with one 6-mm-diameter NSM CFRP rod. The beams were tested in a three-point bending test up to failure. Overall stiffness and crack maps were studied before and after the repair. Ultimate capacity, ductility and failure mode were also reviewed. Finally some comparisons were made between repaired and non-repaired beams in order to assess the effectiveness of the NSM technique. The experimental results showed that the NSM technique improved the overall characteristics (ultimate load capacity and stiffness) of the control and corroded beams and allowed sufficient ductility to be restored to the repaired corroded elements, thus restoring the safety margin, despite the non-classical mode of failure that occurred in the corroded beam, with the separation of the concrete cover due to corrosion products.     

Development and Assessment of a New CFRP Rod–Anchor System for Prestressed Concrete

Design concepts and experimental assessment of a new wedge anchor system for prestressing CFRP rods are presented. This compact and reusable anchor consists of an outer cylinder (barrel), a number of wedges, and a soft metal sleeve. The contacting surfaces of the wedges and barrel have a circular profile along the length of the anchor. Tensile testing using different presetting loads, geometric configurations, and rod sizes was carried out. The relationship of the tensile load and displacement of the rod was established. Presetting was found unnecessary since the anchor system was found to be capable of carrying the full design strength of the rods.     

基于可靠度的FRP筋材料分项系数的确定

基于中国混凝土结构设计资料以及构件几何尺寸与材料力学性能的概率统计参数,建立了FRP筋混凝土梁受弯正截面承载力的计算公式,并采用验算点法计算了在六种荷载效应比情况下的受弯承载力可靠指标平均值,最后在考察FRP筋材料分项系数对可靠指标平均值影响的基础上,建议GFRP筋和CFRP筋的材料分项系数统一取为1.25。可靠度分析表明:过于保守的FRP筋材料分项系数只能使得截面发生混凝土破坏模式的概率增大,而这种破坏模式对应的可靠度水平基本与FRP筋材料分项系数无关,因此只能造成巨大的材料浪费。截面的设计破坏模式与实际破坏模式不完全一致,这种不一致现象存在的范围随着FRP筋材料分项系数的增大而扩大。     

Strengthening R/C beams with opening by externally installed FRP rods: Behavior and analysis

This paper discusses the strengthening of opening in R/C beams by FRP rods. A total number of thirteen beams with circular and square opening have been tested. The opening is shown to significantly reduce the shear capacity of beam. Two patterns of strengthening by FRP rod are investigated: one is to place FRP rods enclosing the opening and the other is to place FRP rods diagonally throughout the entire depth of the beam. It is found that simply placing FRP rods around the opening is not fully effective because a diagonal crack can propagate through the beam with the crack path diverted to avoid intersecting with the FRP rod. When FRP rods are placed throughout the entire beam’s depth, a significant improvement in loading capacity and ductility is achieved, similar to strengthening by pre-fabricated internal steel bars. The flexural failure mode is restored. A nonlinear finite element analysis, based on smeared crack approach, is conducted for numerical verification and examining the effect of length, position and inclination of FRP rods. The plot of analytical principal compressive stress illustrates two strut mechanisms associated with FRP rod. The inclined rods are found to be more effective than vertical ones.     

Strain Measurement Using Embedded Fiber Bragg Grating Sensors Inside an Anchored Carbon Fiber Polymer Reinforcement Prestressing Rod for Structural Monitoring

Results are reported from a study carried out using a series of Bragg grating-based optical fiber sensors written into a very short length (60 mm) optical fiber network and integrated into carbon fiber polymer reinforcement (CFPR) rod. Such rods are used as reinforcements in concrete structures and in tests were subjected to strain through a series of cycles of pulling tests, with applied forces of up to 30 kN. The results show that effective strain measurements can be obtained from the different sensors mounted along the rod. Additionally, the tests show that close agreement with the results obtained from the calibrated force applied by the pulling machine and from a conventional resistive strain gauge mounted on the rod itself is obtained. Calculations from strain to shear stress show a relatively uniform stress distribution along the bar anchor used. The results give confidence to results from various methods of in situ monitoring of strains on such CFRP rods when used in different engineering structures.     

Effect of surface pre-conditioning on bond of carbon fibre reinforced polymer rods to concrete

The experimental program developed in this work aims at investigating the possibility of using carbon fibre reinforced polymer rods to strengthen concrete structural members. Firstly, physical, chemical and mechanical tests were performed on carbon fibre reinforced polymer. Secondly, the bond between carbon fibre reinforced polymer rod and concrete was studied by using the pull-out test. Different types of surface treatment were applied to the smooth rods in order to enhance the bond with concrete. Firstly, the rods were machined using a lathe and a grinding stone to create lugs with different configurations. Secondly, the rods were coated with sand of various grain sizes. The sand was fixed on the rods with a thin layer of epoxy resin.The experimental results indicate that carbon fibre reinforced polymer rod seems to be a good option for strengthening concrete structural members. Results showed a very good physical, chemical and mechanical compatibility between the rods and the concrete. Depending on the surface treatment process, the ultimate bond strength can reach twice that of ribbed steel bars. Moreover, the residual friction between the carbon fibre reinforced polymer rods and the concrete (softening branch) remained equivalent to or greater than that of ribbed steel bar.     

CFRP布端绕双杆自锁加固混凝土窄梁抗弯试验

为了抵抗粘贴碳纤维增强聚合物基复合材料（CFRP）加固钢筋混凝土结构中常见的剥离破坏,发明了将CFRP布端部以特定方式绕平行双杆实现自锁的方法。鉴于窄梁截面宽度有限,提出将CFRP布贴梁受拉底面布置后,用安装在梁侧面的双L形端锚装置固定双杆,形成侧锚底贴加固方案。完成了5根混凝土强度较低的矩形截面梁四点弯曲试验,其中4根采用上述锚固方式抗弯加固,检验了锚固效果,考察了CFRP布宽度及其沿全长与梁底面是否粘结对加固效果的影响。试验结果表明,采用本文方法进行加固后,端部剥离得以避免,中部剥离即使发生,或在无粘结加固梁受力后期,CFRP布仍能承担较大拉力,因此,极限荷载较对比梁有明显提高。比较而言,CFRP布与梁底有粘结时加固效果更好,CFRP布宽度加大也对提高承载力有益。