FRP约束钢管再生混合混凝土柱力学性能及设计方法研究

A recently proposed recycling technique of waste concrete is to directly mix large pieces of recycled concrete lumps (RCLs) and fresh concrete to form the so-called “recycled compound concrete”. This novel technique has many advantages, such as its simplicity, cost-effective, as well as increased recycling ratio. However, the interfaces among RCLs and fresh concrete are generally weak and the strength of RCLs are generally low and non-uniform, leading to increased non-uniformity of recycled compound concrete. Fortunately, recent studies on compound concrete filled steel tubular columns and FRP-confined compound concrete columns revel that the non-uniformity of compound concrete can be largely reduced or even avoided under sufficient lateral confinement.. In this project, a novel FRP-confined compound concrete filled steel tubular column is proposed, which consists of an outer FRP tube, an inner steel tube and the compound concrete fill inside the steel tube. The advantages of the three constituent materials are fully made use of and their disadvantages are effectively avoided, leading to a “green”, high strength and high performance column form. To investigate the mechanical behavior of the new column form, a series of monotonic and cyclic axial compression test will be conducted on short stub columns in the first stage of the project. A stress-strain model will be proposed for compound concrete under combined confinement of FRP tube and steel tube. A design method for short columns under concentric compression will also be proposed. In the second stage of the project, both eccentric compression test and combined constant axial loading and cyclic lateral loading test will be conducted. A fiber section column model will be developed based on flexibility-based finite element method, taking into account the second-order effect and the interface slip between concrete and steel tube. The column model will be verified and modified by comparison with test results. The verified column model will then be used to conduct comprehensive parametric analysis, so as to develop an equation for limit slenderness ratio of short columns and to propose a design method for slender columns.

再生混合混凝土，即将废弃混凝土破碎成大尺寸的混凝土块并直接与新鲜混凝土混合振捣而成，是近年提出的一种新型混凝土回收方式。该回收方式具有简单高效、低碳环保、回收率高等优点。然而，废弃混凝土块强度往往较低且不均匀，其与新鲜混凝土之间的界面也比较薄弱，导致再生混合混凝土具有较大的离散性。现有的研究表明水平约束可以有效减缓甚至消除混合混凝土的这个缺陷。 .本项目拟研究的FRP约束钢管再生混合混凝土组合柱，是一种低碳环保、高强高性能的新型构件形式。为研究其基本力学特性，拟分两个阶段进行。首先，基于单调和反复轴压试验，提出一个适用于再生混合混凝土的应力应变模型以及短柱设计方法。然后，进行一系列偏压试验和低周反复荷载试验。建立一个基于柔度法的纤维单元柱子模型，考虑二阶效应和钢管与混凝土之间的粘结滑移，并通过试验结果进行验证和修正。采用修正后的柱子模型进行参数分析，进而提出一个长柱设计方法和抗震设计方法。

再生混合混凝土，即将废弃混凝土破碎成大尺寸的混凝土块并与新鲜混凝土混合振捣而成，是近年出现的一种新型混凝土回收方式。该回收技术具有简单高效、低碳环保、回收率高等优点。然而，废弃混凝土块强度往往较低且不均匀，其与新鲜混凝土之间的界面也比较薄弱，导致再生混合混凝土具有较大的离散性。现有的研究表明水平约束可以有效减缓甚至消除混合混凝土的这个缺陷。.本项目首次提出FRP约束钢管再生混合混凝土组合柱，采用FRP和钢管复合管对再生混合混凝土进行约束，形成一种低碳环保、高强高性能的新型构件形式。项目分两个阶段进行，第一个阶段中，对FRP约束钢管再生混合混凝土短柱进行了单调和反复轴心受压试验，基于试验结果，研究了核心混凝土的受力性能，建立了其本构关系，从而为短柱的设计计算提供参考；第二个阶段中，对FRP约束钢管再生混合混凝土长柱进行了轴心和偏心受压试验，研究了构件长径比和偏心距对其力学性能的影响。基于试验结果，采用纤维截面柱子模型对柱子进行理论模拟，获得较好的效果。然后采用理论柱子模型，通过大量数值构件的分析，提出一个适用于FRP约束钢管再生混合混凝土的长柱界限长细比计算公式，可直接用于该类构件的设计，为该构件的工程应用和推广提供技术支撑。