FRP-Strengthening of Slender Reinforced Concrete Columns

在过去的二十年中，纤维增强聚合物（FRP）复合材料作为具有上级特性的加固材料出现在土木工程中，用于修复现有的钢筋混凝土（RC）结构。在钢筋混凝土柱上粘贴垂直于柱轴线的单向FRP（即缠绕）可以提高柱的轴压承载力。平行于钢筋混凝土柱轴心方向粘贴FRP，只能提高其抗弯承载力，在轴向荷载作用下没有明显的加固效果。这对于细长效应较低的短柱是正确的。然而，对于一个长（细长）柱的故事是完全不同的，其中屈曲引起的故障可以支配由于缺乏横向（弯曲）刚度。实际上，细长钢筋混凝土柱的强度是其细长度和由侧向变形和轴向荷载引起的弯矩的函数。因此，细长柱的抗弯刚度控制其轴向强度。该建议的创新方面，以及与其他加固方法的关键区别在于，它主要通过粘结高模量纵向FRP来增强柱的抗弯刚度，从而寻求细长RC柱的所需加固增益。在本研究计划中，将制备和加固大型细长RC柱使用高模量FRP主要是在柱的纵向方向，并将在室内进行测试，在轴向荷载下具有低偏心率。将研究圆形和方形截面、细长比、初始荷载偏心、FRP比率、FRP模量以及纵向和横向FRP组合的影响。此外，将对可能影响纵向FRP性能的FRP压碎和剥离失效的力学进行深入研究。还将开发一个全面的分析模型，并根据实验数据进行验证，以研究广泛的横截面，边界条件，材料特性和纤维取向的影响。研究计划完成后，预计将量化的行为与纵向FRP加固的细长RC柱的参数范围内，到一个点，建设性和可靠的建议，可以填补目前的设计规定的差距，关于FRP加固细长RC柱。研究结果对制造商和实践工程师具有很高的适用性。该研究计划的成果不仅将有助于提升加拿大在结构修复领域的领导地位，而且还将为该国恶化的基础设施寻求创新和可持续的解决方案，如桥梁和细长柱的滨水结构。

In the past two decades, fiber-reinforced polymer (FRP) composites have emerged in civil engineering as strengthening materials with superior characteristics for the rehabilitation of existing reinforced concrete (RC) structures. It is well-known that bonding unidirectional FRPs perpendicular to the axis of an RC column (i.e. wrapping) can increase the axial load capacity of the column in compression. It is also accepted that bonding the FRPs parallel to the axis of an RC column can only increase its bending capacity, without significant strengthening effect under axial loads. This is true for a short column with low slenderness effects. However for a long (slender) column the story is completely different, where buckling induced failures can govern due to lack of lateral (flexural) stiffness. In fact, the strength of a slender RC column is a function of its slenderness and induced moment due to its lateral deformation and axial load. As a result, the flexural stiffness of a slender column controls its axial strength. The innovative aspect of this proposal, and the key difference from other strengthening approaches, is that it seeks the desired strengthening gain of a slender RC column primarily by enhancing the flexural stiffness of the column by bonding high-modulus longitudinal FRPs. In this research program, large-scale slender RC columns will be prepared and strengthened using high-modulus FRPs mainly in longitudinal direction of the column and will be tested in laboratory under axial loads with low eccentricities. The effect of circular and square cross-sections, slenderness ratio, initial load eccentricity, FRP ratio, FRP modulus, and combination of longitudinal and transverse FRPs will be studied. In addition, an in-depth study will be performed on the mechanics of FRP crushing and debonding failures that may affect the performance of the longitudinal FRPs. A comprehensive analytical modeling will also be developed and verified against the experimental data to study the effect of a broad range of cross sections, boundary conditions, material properties, and fiber orientations. The research program, upon its completion, is expected to quantify the behavior of slender RC columns strengthened with longitudinal FRPs with a range of parameters, to a point that constructive and reliable recommendations can be made to fill the gaps of current design provisions regarding the FRP strengthening of slender RC columns. The results will be highly applicable for manufacturers and practicing engineers. The achievement of the research program not only will serve to elevate Canada to a leadership position in the area of structural rehabilitation, but also will seek innovative and sustainable solutions for the country’s deteriorated infrastructure, such as bridges and water front structures with slender columns.