FRP-Strengthening of Slender Reinforced Concrete Columns

在过去的二十年里，纤维增强聚合物（FRP）复合材料作为一种具有优越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。众所周知，垂直于RC柱轴线的单向frp粘接（即包裹）可以提高柱的轴向受压承载能力。平行于钢筋混凝土柱轴线的frp粘结只能增加其抗弯能力，在轴向荷载下没有明显的加固效果。对于具有低长细度效果的短柱来说，这是正确的。然而，对于长柱（细长柱）来说，情况就完全不同了，由于缺乏横向（弯曲）刚度，屈曲导致的破坏可能会发生。事实上，细长钢筋混凝土柱的强度是细长细细和受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着它的轴向强度。该建议的创新之处在于，与其他加固方法的关键区别在于，它主要通过粘合高模量纵向frp来增强柱的抗弯刚度，从而寻求细长RC柱所需的加固增益。本研究项目主要采用高模量frp对大型细长钢筋混凝土柱进行纵向加固，并在低偏心轴向荷载下进行室内试验。将研究圆形和方形截面、长细比、初始载荷偏心、FRP比、FRP模量以及纵向和横向FRP组合的影响。此外，将对FRP破碎和脱粘失效的力学进行深入研究，这可能会影响纵向FRP的性能。我们还将开发一个综合的分析模型，并根据实验数据进行验证，以研究大范围的截面、边界条件、材料特性和纤维取向的影响。研究计划完成后，预计将量化纵向FRP加固细长RC柱的行为，并提供一系列参数，以提出建设性和可靠的建议，以填补目前关于FRP加固细长RC柱的设计规定的空白。结果将高度适用于制造商和实践工程师。该研究项目的成果不仅有助于将加拿大提升到结构修复领域的领导地位，而且还将为该国老化的基础设施（如桥梁和细长柱的滨水结构）寻求创新和可持续的解决方案。

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.