高强钢材力学性能与普通钢材具有显著区别，对钢框架抗震性能具有重要影响。论文对高强钢框架抗震性能及设计方法展开研究，取得的主要研究成果如下：（1）开发了结构钢材全过程弹塑性本构模型。通过材性试验研究了Q550和Q690两种高强钢材的单调和滞回性能，无明显屈服平台，且随动强化特征十分显著。基于试验结果分别提出了有屈服平台和无屈服平台结构钢材的循环弹塑性本构模型，探讨了基于单拉应力－应变曲线和经验关系标定其材料参数的方法，并在通用有限元程序ABAQUS中成功实现，应用于钢结构材料、构件和节点的非线性分析，充分验证了其精度和数值稳定性。（2）完成了高强钢框架抗震性能的足尺试验。对按我国新版《钢结构设计规范》设计的1个Q345普通钢框架、2个Q460高强钢框架、2个Q345梁－Q460柱和1个Q345梁－Q890柱混合钢框架共6个单跨两层钢框架足尺试件进行了循环加载试验，分析了其破坏形态、承载力、变形、延性和耗能能力，探讨了梁柱构件和盖板加强型梁柱节点的受力性能，基于承载力下降15%确定了各个试件的极限位移角，同时基于能量等效评估了各个试件的实际地震力折减系数。结果表明采用延性较好的节点构造和截面类型后，高强钢框架的滞回性能稳定，表现出良好的变形和耗能能力，各个试件亦均满足规范大震下的不倒塌性能要求。（3）建立了高强钢框架抗震分析的数值模型。以可考虑构件局部屈曲和梁柱节点变形的精细壳单元有限元模型为工具，利用开发的结构钢材循环弹塑性本构模型，对高强钢框架足尺试验进行了模拟和预测。结果表明建立的数值模型能够准确地描述框架整体和节点局部的滞回曲线以及柱脚屈曲形态，并验证了梁－壳高效多尺度模型的可靠性。（4）进行了高强钢框架抗震性能的参数分析并提出了设计建议。建立了三跨六层高强钢和混合钢框架算例的高效多尺度模型，通过静力推覆和动力时程分析研究了钢材等级、截面宽厚比对承载力和变形需求的影响，分析了基于首次屈服承载力的地震力折减系数，结果表明按我国新版《钢结构设计规范》设计的高强钢框架能满足大震不倒的性能要求，并对其建议了最小性能系数和节点转动需求。本论文获得国家自然科学基金项目（51478244）和国家自然科学基金优秀青年基金项目（51522806）资助。
The difference in mechanical properties between high strength steels and ordinary strength steels plays a significant role in the seismic behavior of steel frame structures. This dissertation mainly investigates the seismic behavior and design methods of high strength steel frames, and the main research works and results are as follows:(1) Full-range elasto-plastic constitutive models for structural steels are developed. The monotonic and cyclic behavior of Q550 and Q690 high strength steels is studied by coupon tests, and no yield plateau but significant kinematic hardening is observed. Based on those observations on various coupon tests, cyclic plasticity models for structural steels with and without yield plateau are proposed, respectively, and the simplified calibration procedures are discussed in detail to determine the material dependent parameters by using the monotonic stress-strain curve and empirical formulas. Furthermore, both constitutive models are successfully implemented in the general-purpose FE software ABAQUS, and are applied to the nonlinear analysis of various materials, members and connections in steel structures. The accuracy and numerical stability have been fully verified.(2) Full-scale experiments to examine the seismic behavior of high strength steel frames are conducted. In total, cyclic tests on six single-bay two-story frame specimens designed according to the new “Code for design of steel structures” in China were performed, including one frame using Q345 ordinary strength steels, two using Q460 high strength steels, two hybrid frames using Q345 beams and Q460 columns, and another one using Q345 beams and Q890 columns. The failure modes, loading and deformation capacity, ductility and energy dissipation are assessed and the mechanical behavior of beams, columns and cover-plate reinforced connections are analyzed. The ultimate drift ratio corresponding to the 15% decrease in lateral strength from its peak value, and the total seismic force reduction factor based on energy equivalence are evaluated for each frame specimen. With ductile beam-to-column connections and cross-sections, the high strength steel frame specimens exhibit stable hysteretic behavior and excellent deformation and energy dissipation capacities. All frame specimens satisfy the no-collapse performance requirement under rare earthquakes.(3) FE models for the seismic analysis of high strength steel frames are established. Using the elaborate shell model to account for the local plate buckling and nonlinear connection deformation, and the proposed cyclic plasticity models for structural steels, the full-scale experiments are simulated and accurate predictions on the global or local hysteretic curves and local buckling in column bases are obtained. The beam-shell mixed model is also verified to reduce computational cost.(4) Parametric studies on the seismic behavior of high strength steel frames are carried out to propose appropriate design methods. Based on the beam-shell mixed models of three-bay six-story example frames using high strength steels in both beams and columns or only columns, the influence of steel grade and cross-section slenderness on the loading capacity and deformation demand is quantified by nonlinear static pushover and dynamic time-history analyses. The seismic force reduction factors with reference to the initial yield strength are evaluated, and it can be concluded that high strength steel frames designed according to the new “Code for design of steel structures” in China have considerable potential to exhibit no-collapse under rare earthquakes. As a result, minimum behavior factors and corresponding rotation demands for beam-to-column connections are proposed to guide the design of such frame structures.This dissertation is sponsored by the National Natural Science Foundation of China (Grant No. 51478244) and the Excellent Young Scientist Programme of the National Natural Science Foundation of China (No. 51522806).
