钢管再生细骨料混凝土柱静动力性能及非均匀约束作用机理研究

In the production of recycled coarse aggregates from construction and demolition waste concrete (CDWC), fine aggregate will take 20-50% as the by product. Using these fine aggregates to produce new concrete may become a solution for the natural sand resource depletion and increase the rate of recycling of the CDWC. Encasing recycled fine aggregate concrete (RFAC) inside steel tubes improves its mechanical behavior by changing the stress state of the concrete. Such innovative composite member, called as recycled fine aggregate concrete filled steel tubes (RFA-CFST), can widen the use of RFAC in structure application and solve the dilemma between increasing the recycling of CDWC and pursuing high performance structures (or members). Despite of the promising future of the RFA-CFST, the research work is limited. Besides, the available equations for stress-strain relationships of steel tubes and concrete core for circular CFST were all proposed based on the assumption that the concrete core is under uniform confinement along circumference. This may lead to overestimation of the structural (member) responses to eccentric or reciprocating loads when using line elements (or beam elements) to model CFSTs. In this context, this project will conduct extensive experimental and numerical study on RFA-CFSTs to investigate their static and seismic behaviors. Particular attention will be drawn on the mechanical behavior of core concrete under non-uniform confinement effects when subjected to eccentric or reciprocating loads. Stress-strain relationship for RFA-CFSTs will then be proposed accounting for the difference in confinement effects induced by sectional moments, and static and seismic design methods will then be established. The research in this project will improve the designing theory for circular CFST members.

再生骨料生产过程中将产生20-50%的细骨料，将其用于配制再生细骨料混凝土，是缓解天然砂资源匮乏，提高废弃混凝土资源化率的有效措施。钢管再生细骨料混凝土可从结构层次改善再生细骨料混凝土力学性能，扩大其在结构领域应用范围，解决废弃混凝土资源化与结构（构件）高性能化的矛盾，应用前景广阔，但目前相关研究刚刚起步。同时，现有圆钢管混凝土的钢管和混凝土纵向应力-应变关系均基于均匀约束本构建立，未考虑弯矩对约束效应的削弱，可能导致采用线(梁)单元研究结构（构件）偏压与往复荷载作用下的静力与抗震性能时，分析结果偏于不安全。为此，本项目将以圆钢管再生细骨料混凝土为研究对象，对其静力和抗震性能进行深入研究，重点揭示偏压和往复荷载作用下钢管对核心混凝土的非均匀约束机理，建立可考虑截面弯矩对约束效应影响的圆钢管再生细骨料混凝土纵向应力-应变关系表达式，及相关静力与抗震设计方法，进一步完善圆钢管混凝土设计理论。

将再生细骨料应用于混凝土中可有效缓解天然砂过量开采导致的自然灾害并改善建筑固废资源化率低的现状。然而，由于掺入再生细骨料会显著降低混凝土的力学性能，使其在结构混凝土应用中的限制极为严格。将再生混凝土置于钢管中形成钢管再生混凝土可以有效改善再生细骨料混凝土的性能，推广其在结构工程领域中的应用。目前，针对钢管再生细骨料混凝土力学性能的研究才刚刚起步，特别是抗震性能的研究尚属空白。同时，现有钢管混凝土本构模型尚未考虑弯矩对约束效应的削弱，分析结果偏于不安全。为此，本项目针对钢管再生细骨料混凝土静动力性能及非均匀约束作用机理进行了系统研究，具体工作如下：.1）进行了再生混凝土受压力学性能系统试验（90个立方体和72个棱柱体）。研究发现再生细骨料取代率对抗压强度影响小于10%。基于试验结果，建立了考虑再生粗、细骨料耦合作用影响的再生混凝土轴压应力-应变关系模型，填补了再生细骨料混凝土本构理论研究的空白。.2）进行了钢管再生混凝土轴压力学性能试验（54个短柱）。试验发现，再生粗、细骨料的耦合作用减小了再生骨料对试件力学性能的影响，极限承载力降低幅度仅为6.2%。建立了钢管再生粗、细骨料混凝土短柱轴压应力-应变关系模型与承载力设计方法，为钢管再生细骨料混凝土在结构工程中的应用奠定了基础。.3）基于前期研究成果，建立了可精确模拟弯矩对约束效应影响的钢管再生混凝土实体有限元模型。通过参数分析发现，在偏心率为0.6时约束效应的非均匀性引起的峰值荷载差异较为明显，差异可达19%。基于分析结果，建立了弯矩对约束作用影响的钢管再生混凝土偏压构件纵向应力-应变关系模型与承载力设计方法，填补了钢管再生混凝土非均匀约束效应的研究空白。.4）基于试验及有限元参数分析结果，建立了往复荷载作用下钢管再生混凝土纵向应力-应变关系表达式及恢复力模型，模型预测结果与试验结果承载力差异不超过5%。模型的建立为钢管再生混凝土的抗震设计奠定了基础。