Experimental and numerical studies on composite structures under lateral cyclic loading: precast l-plate encased composite columns and wide U beam-column joints

Due to several advantages like the requirement of less construction time and labor works for installation and removal of formworks, enhanced quality of construction etc., composite structural components are being used extensively by the construction industry. Composite structures in this study refer to structures comprising precast components that will later be infilled with cast-in-place concrete. The precast components perform as the permanent formwork while casting the cast-in-place concrete and become parts of the final structural component of the system after the cast-in-place concrete is hardened. Two composite structural systems were studied: L-shaped precast plate encased composite column and post-tensioned composite wide U beam-column joint systems. In this research, a study on the seismic behavior of composite structures was performed based on numerical simulations and experimental studies. The study on selecting a suitable concrete material model and contact algorithm was performed to depict composite structures' behavior by simulating the composite columns available in the research database. With the verified modelling concept, the performance of the L-shaped precast plate encased composite column was investigated. Also, some modifications were suggested to enhance the interface shear strength between the outer precast encasement and inner cast-in-place core concrete to achieve composite action. The modelling concept verified from the numerical study of composite columns was also adopted to study the behavior of full-scale L-shaped precast plate encased composite column and modified wide beam-column exterior and interior joint systems. Extensive numerical studies were performed to investigate the effects of spandrel beam and confining transverse tendons on seismic upgrading of composite full-scale wide beam-column exterior and interior joints.Moreover, this study reports an experimental investigation performed to explore seismic performance comparison of two half-scale wide beam-column interior joint systems. The two tested interior joints include one control and another modified, of which the latter is an improvement of the control with the addition of spandrel reinforcement in the joint core and confining transverse tie bars. Hence, the seismic behavior of composite structures comprising of a composite column and composite wide beam-column joint was studied in this research. Finally, the seismicity of Thailand was explored, and an L-shaped precast plate encased composite column, and precast wide U beam-column joint systems which are suitable for all seismic zones of the country were proposed. From the simulation results, continuous surface cap (MAT_159) and kinematic plasticity (MAT_003) material models were found suitable to model concrete and reinforcement for analyzing the behavior of RC structures subjected to lateral cyclic loading. Moreover, a numerical model using the tied with failure (tiebreak) contact algorithm could capture the test results of the tested composite columns with satisfactory accuracy. With this modeling approach, numerical studies of the L-shaped precast plate encased composite columns and the full-scale wide beam-column joint systems were performed. The numerical model could capture the test results of the L-shaped precast plate encased composite columns and the half-scale wide beam-column joints. Hence, depending on the severity of the seismic hazard and soil site conditions in various regions, the proper L-shaped precast plate encased composite columns and wide beam-column joint models proposed in this study are suggested for each location in Thailand. The composite control column and joint model were found to be safe only in regions with very low seismicity, even on soft soil sites. However, the modified composite column and joint models could be adopted depending upon the levels of seismicity and soil site conditions. Therefore, it can be concluded that the proposed modified composite columns and wide beam-column joint systems can be used for all seismic zones in Thailand.

鉴于模板（formwork）拆装所需施工时长与人力成本更低、施工质量更优等多项优势，组合结构构件（composite structural components）已在建筑工程领域得到广泛应用。本研究中的组合结构指由预制构件（precast components）构成、后续需填充现浇混凝土（cast-in-place concrete）的结构体系。预制构件在现浇混凝土浇筑阶段充当永久模板（permanent formwork），待现浇混凝土硬化后，将成为最终结构构件的组成部分。本研究共考察两类组合结构体系：外包L形预制板组合柱，以及后张法（post-tensioned）组合宽U形梁柱节点体系。本研究通过数值模拟（numerical simulations）与试验研究（experimental studies），对组合结构的抗震性能（seismic behavior）展开了系统性探究。为精准复现研究数据库中的组合柱以刻画组合结构的受力行为，本研究开展了适配混凝土材料模型（material model）与接触算法（contact algorithm）的选型工作。基于验证后的建模思路，本研究对L形预制板外包组合柱的受力性能进行了深入分析。同时，为实现组合作用，本研究提出了若干优化方案，以提升预制外包件与现浇内部核心混凝土之间的界面抗剪强度（interface shear strength）。本研究沿用经组合柱数值模拟验证的建模方法，对足尺（full-scale）L形预制板外包组合柱以及改进型宽梁柱内、外节点体系的受力行为展开研究。本研究开展了大量数值模拟工作，以探究连梁（spandrel beam）与横向约束预应力筋（confining transverse tendons）对足尺宽梁柱内、外节点的抗震加固效果。此外，本研究还报告了一项试验研究，旨在对比两种半缩尺（half-scale）宽梁柱内部节点的抗震性能。所测试的两个内部节点分别为对照节点与改进节点：后者通过在节点核心区增设连梁钢筋（spandrel reinforcement）与横向箍筋（transverse tie bars），对对照节点进行了优化。因此，本研究针对包含组合柱与组合宽梁柱节点的组合结构体系的抗震性能进行了全面探究。最后，本研究对泰国的地震活动性展开了调研，并提出了适配该国所有地震烈度区的L形预制板外包组合柱与预制宽U形梁柱节点体系。模拟结果表明，采用连续表面帽模型（continuous surface cap，MAT_159）与运动学塑性模型（kinematic plasticity，MAT_003）分别作为混凝土与钢筋的材料模型，可有效模拟承受低周反复侧向荷载（lateral cyclic loading）的钢筋混凝土（RC, Reinforced Concrete）结构的受力行为。此外，采用带失效准则的粘结接触算法（tiebreak contact algorithm）构建的数值模型，可较为精准地复现试验中组合柱的受力结果。通过该建模方法，本研究对L形预制板外包组合柱以及足尺宽梁柱节点体系开展了数值模拟。该数值模型可准确复现L形预制板外包组合柱与半缩尺宽梁柱节点的试验结果。因此，结合泰国各地区的地震危险性等级与场地土条件，本研究建议为泰国各地选用适配的L形预制板外包组合柱与宽梁柱节点模型。研究发现，仅在地震活动性极低的区域（即便场地为软土地基），未做优化的组合柱与节点模型才可保证安全。而改进型组合柱与节点模型则可根据地震烈度与场地土条件灵活选用。综上，本研究提出的改进型组合柱与宽梁柱节点体系，可适配泰国所有地震烈度区的工程需求。