钢管纤维自应力自密实混凝土柱设计理论研究

A new type of composite structure is developed by using fiber reinforced self-stressing and self-compacting high strength concrete as filling materials to improve the ductility of high strength concrete filled steel tube (CFST) columns, to overcome the difficulty in core concrete vibration, and to reduce the negative effect of the shrinkage and creep of concrete on structural properties. The optimal mixture proportions of fiber reinforced self-stressing and self-compacting high strength concrete are determined by analyzing the microstructure and mechanical properties of the core concrete and a design theory is then proposed for fiber reinforced self-stressing and self-compacting high strength concrete. A series of tests are conducted on composite structures under axial, eccentrical, and shear loads to study the effects of the type of fiber, the steel fiber volume fraction, the magnitude of self-stress, and the steel proportion on the mechanical properties of fiber reinforced self-stressing and self-compacting high strength concrete filled steel tube (FSH-CFST) columns. Based on the low-period cyclic load tests of FSH-CFST columns, the effects of the type of fiber, the steel fiber volume fraction, and the steel proportion on the hysteresis behavior and energy absorption capacity under the same axial-load level are studied. Long-term tests are carried out to investigate the shrinkage and creep of FSH-CFST columns under sustained load. Finally, theoretical analysis and numerical simulation are combined to propose a design method of FSH-CFST columns under axial, eccentrical, shear, and seismic loads. The equations are also formulated for calculating the shrinkage and creep of FSH-CFST columns.

为改善钢管高强混凝土柱的延性，解决核心混凝土振捣困难，降低收缩徐变对结构性能的不利影响，将纤维混凝土、自应力自密实混凝土和钢管高强混凝土技术相结合，提出一种新型组合结构—钢管纤维自应力自密实高强混凝土柱。研究纤维自应力自密实高强混凝土的配合比和工作性能，分析硬化后约束混凝土的宏观力学性能和细观结构，揭示纤维自应力自密实高强混凝土的膨胀机理，提出其自应力设计理论。在此基础上，通过钢管纤维自应力自密实高强混凝土柱的轴心受压、偏心受压和受剪试验，研究纤维种类、纤维掺量、自应力值和套箍率等因素对其力学性能的影响；通过新型组合柱低周反复加载试验，研究不同轴压比下，上述因素对其滞回特性的影响；通过新型组合柱的受压长期持载试验，研究其收缩和徐变特性。结合理论分析和数值模拟，提出钢管纤维自应力自密实高强混凝土柱轴压、偏压、受剪承载力及相应的抗震设计方法，建立收缩徐变计算公式。

为改善钢管高强混凝土柱的延性，解决核心混凝土振捣困难，降低收缩徐变对结构性能的不利影响，将纤维混凝土、自应力自密实混凝土和钢管高强混凝土技术相结合，提出一种新型组合结构—钢管纤维自应力自密实高强混凝土柱。本项目采用硫铝酸盐水泥和聚羧酸系减水剂，制备出达到预期自应力值、强度和自密实性的纤维自应力自密实高强混凝土，系统开展了纤维、水灰比、水泥对纤维自应力自密实高强混凝土膨胀性能、力学性能、工作性能的影响研究，确定了配合比设计原则。研究了纤维、水灰比等参数对混凝土时变膨胀变形的影响规律，提出了自应力值预测模型。该模型可较好地预测钢管三向约束下膨胀混凝土的自应力值，避免繁琐的测试过程。在此基础上，开展了钢管纤维自应力自密实高强混凝土柱的轴压、偏压、受剪、受弯等力学性能研究，结果表明初始自应力可提高试件弹性阶段的轴压、抗弯刚度，对试件的受压、受弯、受剪承载力均有显著的提升作用。纤维的掺入可有效提升试件峰值后的变形能力。结合试验及理论分析，建立了钢管纤维自应力自密实高强混凝土柱的受压、受弯、受剪承载力设计理论。通过界面推出试验，揭示了初始自应力对钢管与纤维自应力自密实高强混凝土的界面粘结-滑移性能的影响机理，建立了粘结强度的预测模型。开展了钢管纤维自应力自密实高强混凝土柱抗震、徐变性能的试验研究，揭示了纤维、自应力值等参数对试件耗能能力、延性、长期性能的影响规律。由此，建立了不同服役条件下钢管纤维自应力自密实高强混凝土柱的设计理论框架。