FRP-Strengthening of Slender Reinforced Concrete Columns

在过去的二十年里，纤维增强聚合物(FRP)复合材料作为加固材料出现在土木工程中，用于既有钢筋混凝土结构的修复，具有优越的性能。众所周知，与钢筋混凝土柱轴线垂直粘贴单向FRP(即包裹)可以提高柱的轴压承载能力。与钢筋混凝土柱轴线平行粘结FRPS只能提高其受弯承载力，在轴向荷载作用下没有明显的加固效果。对于具有低细长效果的短柱来说，情况也是如此。然而，对于长(细长)柱，情况则完全不同，由于缺乏侧向(弯曲)刚度，可能会导致屈曲导致的破坏。事实上，钢筋混凝土细长柱的强度是其细长和由于其侧向变形和轴向荷载所引起的诱导弯矩的函数。因此，细长柱的弯曲刚度控制其轴向强度。这一方案的创新之处，也是与其他加固方法的主要区别在于，它主要通过粘结高模数纵向FRP来提高柱的抗弯刚度，从而寻求细长RC柱所需的加固收益。在本研究中，大型细长钢筋混凝土柱将主要在柱的纵向采用高模数FRPS进行制备和加固，并在实验室进行低偏心轴压试验。研究了圆形和方形截面、长细比、初始荷载偏心距、FRP比、FRP模数以及纵向和横向FRPS组合对加固效果的影响。此外，还将对可能影响纵向FRPS性能的FRP压碎和剥离破坏机理进行深入研究。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。该研究计划完成后，预计将量化使用一系列参数的纵向FRP加固细长RC柱的性能，从而可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。研究结果将对制造商和执业工程师具有很强的适用性。该研究计划的成果不仅将有助于将加拿大提升到结构修复领域的领先地位，还将为该国日益恶化的基础设施寻求创新和可持续的解决方案，如桥梁和细长柱子的滨水结构。

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.