碱环境下不同应力水平GFRP筋抗拉性能试验

基于ACI 440.3R-04规定的试验方法,对60 ℃碱环境下应力水平分别为0、25%和45%的玻璃纤维塑料（GFRP）筋的抗拉性能进行了试验研究。试件数量共90根,侵蚀时间分别为3.65、18、36.5、92、183天。采用SEM对腐蚀前后GFRP筋的微观形貌进行了观测,发现碱溶液造成了GFRP筋内部结构致密性的降低,且随着应力水平的增加,其降低愈发明显。在60 ℃碱溶液中侵蚀183天后,应力水平为0和25%的GFRP筋的抗拉强度分别下降了48.81%和55.56%,而弹性模量仅分别下降了5.47%和5.73%,应力水平为45%的GFRP筋则出现了断裂现象。GFRP筋的吸湿试验表明,OH^-离子在GFRP筋中的扩散过程符合Fick定律。在分析了应力水平、侵蚀时间等参数对GFRP筋抗拉性能影响的基础上,基于Fick定律提出了碱环境下带应力GFRP筋抗拉强度的退化模型。     

人工海水环境下GFRP筋受压性能试验研究

该文开展了人工海水环境下GFRP(玻璃纤维增强塑料)筋(玻璃纤维增强塑料筋)持续浸泡及干湿循环腐蚀试验,探讨研究了两种腐蚀方式对GFRP筋受压力学性能的劣化机理。研究结果表明:试件抗压强度随浸泡时间和干湿循环次数的增长基本呈线性下降;干湿交替循环腐蚀作用对GFRP筋受压性能的影响大于单纯氯盐溶液浸泡腐蚀;与碱溶液浸泡腐蚀数据对比可知,相同腐蚀条件下,碱溶液环境对GFRP筋抗压性能的劣化较氯盐溶液更为严重。     

恶劣环境下纤维增强聚合物片材拉伸性能

通过拉伸试验,研究了恶劣环境作用后纤维增强聚合物(FRP)片材的拉伸性能。试验参数包括恶劣环境类别和作用方式、FRP片材种类和层数。试验结果表明,常温环境下、冻融和干湿循环作用后,碳纤维增强聚合物(CFRP)片材和玻璃纤维增强聚合物(GFRP)片材的拉伸应力-应变关系近似为直线;常温环境下,CFRP片材和GFRP片材的拉伸强度和延伸率几乎不受片材层数的影响;冻融循环对GFRP片材的影响大于CFRP片材,冻融循环75次时,CFRP片材和GFRP片材的拉伸强度分别是未冻融的0.978倍和0.898倍,并且随着循环次数的增加,CFRP片材和GFRP片材拉伸强度逐渐下降;干湿循环作用对GFRP片材拉伸性能没有明显的影响。基于对有关文献及本文试验结果的分析,提出了恶劣环境下FRP片材拉伸强度的计算方法。     

海水浸泡对FRP筋-珊瑚混凝土粘结性能的影响

开展了30℃海水浸泡条件下玻璃纤维增强树脂基复合材料（GFRP）筋、碳纤维增强树脂基复合材料（CFRP）筋与珊瑚混凝土粘结性能的试验研究,分析了纤维增强树脂基复合材料（FRP）筋-珊瑚混凝土粘结滑移曲线特征、破坏形态及粘结强度变化。试验结果表明,海水浸泡后FRP筋力学性能和粘结性能均表现为不同程度的降低。随浸泡时间增加,GFRP筋表层树脂与纤维间的孔隙率明显增大,并逐渐出现脱粘现象,纤维本身遭受到侵蚀,而CFRP筋仅表面基体有少许损伤,其耐久性明显优于GFRP筋;FRP筋-珊瑚混凝土粘结强度呈现出先增加后减小的趋势,且后期下降速率逐渐变小,部分GFRP筋-珊瑚混凝土试件的破坏模式逐渐由筋被拔出转变为筋材断裂;增加保护层厚度能有效地减缓海水对GFRP筋的侵蚀,有利于保持GFRP筋-珊瑚混凝土间的粘结性能。     

温度老化对GFRP/BFRP筋残余弯曲性能的影响

对玻璃/玄武岩纤维增强复合材料(GFRP/BFRP)筋材在温度老化作用后的弯曲性能进行了试验研究,重点探讨了不同作用温度及恒温时间对不同直径的两类FRP筋材的弯曲性能影响特性,同时采用扫描电子显微镜(SEM)对温度老化作用后部分GFRP/BFRP筋的微观结构变化及损伤机理进行了分析.试验与分析结果表明:(1)温度老化作用后GFRP/BFRP筋材弯曲强度与最大应变随作用温度升高均呈阶段性下降的趋势,而弯曲弹性模量无明显退化,其保留率均在90％以上;(2)温度老化作用后直径较大的GFRP筋材的弯曲性能退化更为明显;且G12筋的弯曲性能保留率退化曲线均高于B12筋,说明BFRP筋的弯曲性能对温度作用更为敏感;(3)在270℃高温环境下,GFRP/BFRP筋弯曲性能随着恒温时间的延长均呈现线性下降趋势;(4)结合试验结果和SEM微观结构分析,可认为造成温度老化作用后两类FRP筋弯曲强度退化的主要原因是纤维与树脂基体间协同工作效果和纤维-树脂基体界面性能的显著降低.最后,结合本试验结果,给出了500℃以内温度老化作用后GFRP/BFRP筋材弯曲强度退化的计算模型以及线性插值预测方法,便于实际工程应用.     

几何非线性高性能复合材料筋混凝土梁Heterosis组合壳单元

对于高性能碳纤维增强聚合物复合材料(CFRP)筋混凝土梁,研究几何非线性组合壳单元模型,对预应力CFRP筋混凝土梁进行了全过程分析。引入Von Karman理论,推导了局部坐标系下Piola2Kirchhoff 应力矩阵和几何刚度矩阵;分别采用组合壳单元和分层壳单元模拟预应力CFRP 筋和玻璃纤维增强聚合物复合材料(GFRP)筋,并推导了CFRP筋对组合壳单元刚度矩阵的贡献,同时采用Heterosis选择积分技术以避免剪切锁定和零能量模式,研制了相应的非线性计算程序。计算结果与试验数据对比可知,挠度发展规律和预应力CFRP筋应变发展规律均吻合良好,说明了研究单元的有效性及研制程序的正确性;CFRP筋具有高强度性能,梁试件破坏时CFRP筋均未失效;利用预应力CFRP筋应变重分布系数研究了梁的刚度退化规律,表明采用GFRP筋代替普通钢筋在加载后期会使梁的刚度退化减小。      

侵蚀环境下FRP条带加固锈蚀钢筋混凝土圆柱轴心受压试验

通过侵蚀环境下碳纤维增强聚合物(CFRP)复合材料条带和玻璃纤维增强聚合物(GFRP)复合材料条带加固锈蚀钢筋混凝土圆柱试验,分析了侵蚀环境对混凝土强度、纤维增强聚合物基复合材料加固锈蚀柱的极限荷载和荷载-轴向位移曲线的影响。结果表明,混凝土强度受冻融环境影响较大,受干湿环境影响较小;纤维增强聚合物(FRP)复合材料加固锈蚀柱的轴向极限荷载与冻融循环次数、钢筋锈蚀率及FRP复合材料种类有关,随冻融循环次数分别增加到25次、50次、75次,GFRP复合材料条带和CFRP复合材料条带加固锈蚀钢筋混凝土圆柱的轴向极限荷载分别降低了10.97%、13.37%、16.04%和5.95%、4.66%、4.33%;FRP复合材料加固锈蚀柱的刚度和耗能受侵蚀环境种类、侵蚀环境作用次数、锈蚀率及FRP复合材料种类的影响。在试验研究的基础上,通过理论分析侵蚀环境下混凝土强度损伤系数和锈蚀钢筋强度退化方程,提出了侵蚀环境下FRP复合材料条带加固锈蚀钢筋混凝土圆柱轴心受压承载力计算方法。      

FRP加固混凝土框架梁柱节点研究进展

简要阐述了纤维增强复合材料(FRP)在混凝土框架节点加固领域中应用的重要意义,详细介绍了CFRP、GFRP、BFRP及AFRP等FRP复合材料加固框架节点抗震性能方面的研究进展,期望为FRP材料的应用以及框架节点加固的设计、施工和实际加固改造提供应用参考。     

纤维增强聚合物基复合材料加固锈蚀钢筋混凝土圆柱轴心受压性能

为了给纤维增强聚合物基复合材料（FRP）加固腐蚀环境下钢筋混凝土圆柱的设计和施工提供参考,促进FRP加固钢筋混凝土圆柱的应用,本文通过加速腐蚀得到类似实际环境中已锈损钢筋混凝土圆柱,采用碳纤维增强聚合物基复合材料（CFRP）条带和玻璃纤维增强聚合物基复合材料（GFRP）条带分别对锈蚀钢筋混凝土圆柱进行加固,最后对加固后圆柱进行轴心受压试验,重点研究钢筋锈蚀率、FRP层数和种类对钢筋混凝土圆柱受压承载力的影响;基于对FRP条带间隔约束效应、钢筋锈蚀对混凝土截面及钢筋力学性能影响的研究与分析,提出FRP条带间隔约束锈蚀钢筋混凝土圆柱轴心受压承载力计算模型。试验实测值与模型计算值之比的平均值为1.020,变异系数为0.063,二者符合较好。     

FRP增强重组竹梁受弯性能数值模拟

通过有限元软件ABAQUS对纤维增强聚合物基复合材料（FRP）增强重组竹梁受弯性能进行了分析,有限元模拟结果与试验结果相一致,两者荷载-位移曲线相吻合,跨中截面应变发展过程基本一致,70 kN荷载时,截面应变误差在13.96%内,承载力预测具有很好的精度,预测最大误差为9.04%,FRP的增强使竹梁截面的应力重新分布,受压区竹材得到更加充分的利用;进一步参数化分析了截面宽高比、FRP层数、FRP种类对FRP增强重组竹梁受弯性能的影响。发现:FRP层数的增加对重组竹梁极限承载力和截面刚度提升作用显著;相同层数、相同种类FRP增强重组竹梁时,截面高度减小,极限承载力和截面刚度提高幅度增加;相同截面宽高比和FRP层数时,碳纤维增强聚合物基复合材料（CFRP）增强效果优于玄武岩纤维增强聚合物基复合材料（BFRP）增强效果。      

Evaluation of prestressed basalt fiber and hybrid fiber reinforced polymer tendons under marine environment

This paper studies the degradation of the tensile properties of prestressed basalt fiber-reinforced polymer (BFRP) and hybrid FRP tendons in a marine environment. Two levels of prestressing toward typical prestressing applications were applied in the experiment. The variations of tensile strength, elastic modulus and the relevant coefficient of variation (CV) were first investigated. The effect of prestressing on tensile property degradation was discussed. The characteristics of prestressed hybrid FRP tendons in a marine environment simulated by a salt solution were clarified. Moreover, a prediction model of BFRP tendons with different levels of prestressing in a marine environment was proposed. The results show that the BFRP tendons’ superior resistance to salt corrosion and the degradation rate of their tensile strength is nonlinearly proportional to the prestressing ratios, whereas the elastic modulus remains constant regardless the prestressing ratio and aging duration. Although prestressing on BFRP tendons accelerates degradation, it can still lower the variation of the strength of the BFRP tendon. Hybridization can lower the degradation rate of basalt and carbon FRP (B/CFRP) without prestressing, whereas basalt and steel-wire FRP (B/SFRP) exhibit much faster degradation due to the internal corrosive steel wires. The model regression by the Napierian logarithm equation well represents the degradation trend of BFRP tendons under different levels of prestressing.     

Performance of hybrid rebars as longitudinal reinforcement in normal strength concrete

Although steel is most commonly used as a reinforcing material in concrete due to its competitive cost and favorable mechanical properties, the problem of corrosion of steel rebars leads to a reduction in life span of the structure and adds to maintenance costs. Many techniques have been developed in recent past to reduce corrosion (galvanizing, epoxy coating, etc.) but none of the solutions seem to be viable as an adequate solution to the corrosion problem. Apart from the use of fiber reinforced polymer (FRP) rebars, hybrid rebars consisting of both FRP and steel are also being tried to overcome the problem of steel corrosion. This paper evaluates the performance of hybrid rebars as longitudinal reinforcement in normal strength concrete beams. Hybrid rebars used in this study essentially consist of glass fiber reinforced polymer (GFRP) strands of 2 mm diameter wound helically on a mild steel core of 6 mm diameter. GFRP stirrups have been used as shear reinforcement. An attempt has been made to evaluate the flexural and shear performance of beams having hybrid rebars in normal strength concrete with and without polypropylene fibers added to the concrete matrix.     

玄武岩纤维布约束高温损伤混凝土方柱轴压力学性能试验

对36个玄武岩纤维布增强聚合物基复合材料（BFRP）约束的高温损伤混凝土方柱和15个不同高温损伤的对比试件进行了轴压试验。试验表明,玄武岩纤维布横向约束能改变高温损伤后混凝土方柱的破坏形态,显著提高混凝土方柱的轴压强度和变形能力。其中三层玄武岩纤维布包裹的200℃、400℃、600℃和800℃高温损伤混凝土方柱轴压强度分别提高了48%、130%、206%和389%,轴向变形分别提高了433%、344%、319%和251%。采用典型的纤维增强聚合物基复合材料（FRP）约束常温未损伤混凝土轴压力学性能的设计模型预测FRP约束高温损伤混凝土的轴压强度和变形时存在较大的偏差。通过构建柱状膜结构静水压力平衡模型和约束混凝土方柱与FRP体积应变能平衡模型,分别改进了FRP约束混凝土方柱轴压极限应力和极限应变计算模型的基本形式。基于该基本形式和试验数据,分别确定了BFRP约束高温损伤混凝土方柱轴压极限应力和极限应变计算中与温度相关的参量,提出了适用于高温损伤混凝土方柱的轴压极限应力和极限应变的设计模型。      

纤维网格增强超高韧性水泥复合材料加固混凝土圆柱受压性能试验

为提升纤维增强聚合物复合材料（FRP）在加固材料中的优势和发挥效率,同时克服传统纤维网格增强砂浆的抗裂性差的缺点,将超高韧性水泥基材料（ECC）替代砂浆作为FRP网格无机黏结剂的新型复合材料已被提出,但仍缺乏相关的基础研究。本文以新型聚乙烯型ECC为基材,重点研究FRP grid/ECC加固混凝土柱的加固机制。以标准混凝土圆柱为试验对象,采用新型ECC材料为基材的FRP grid/ECC复合材料,以不同强度素混凝土、不同网格材料（玄武岩纤维增强聚合物复合材料（BFRP）与碳纤维增强聚合物复合材料（CFRP）网格）为试验变量,研究了该加固方式下对混凝土轴心受压性能的影响。试验结果表明,该加固方法可有效改善素混凝土脆性压溃破坏模式,提高峰值强度及受压延性。基于FRP grid/ECC材性特征,提出两阶段FRP grid/ECC加固机制,并基于该机制提出加固素混凝土圆柱承载力计算方法。      

Experimental and analytical investigation of reinforced high strength concrete continuous beams strengthened with fiber reinforced polymer

Carbon and glass fiber reinforced polymer (CFRP and GFRP) are two materials suitable for strengthening the reinforced concrete (RC) beams. Although many in situ RC beams are of continuous constructions, there has been very limited research on the behavior of such beams with externally applied FRP laminate. In addition, most design guidelines were developed for simply supported beams with external FRP laminates. This paper presents an experimental program conducted to study the flexural behavior and redistribution in moment of reinforced high strength concrete (RHSC) continuous beams strengthened with CFRP and GFRP sheets. Test results showed that with increasing the number of CFRP sheet layers, the ultimate strength increases, while the ductility, moment redistribution, and ultimate strain of CFRP sheet decrease. Also, by using the GFRP sheet in strengthening the continuous beam reduced loss in ductility and moment redistribution but it did not significantly increase ultimate strength of beam. The moment enhancement ratio of the strengthened continuous beams was significantly higher than the ultimate load enhancement ratio in the same beam. An analytical model for moment–curvature and load capacity are developed and used for the tested continuous beams in current and other similar studies. The stress–strain curves of concrete, steel and FRP were considered as integrity model. Stress–strain model of concrete is extended from Oztekin et al.’s model by modifying the ultimate strain. Also, new parameters of equivalent stress block are obtained for flexural calculation of RHSC beams. Good agreement between experiment and prediction values is achieved.