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当考虑大应变时梁抗弯能力的增强及钢与混凝土之间的相对滑移时,组合梁的弹塑性分析很重要。通过将组合横截面的平衡考虑为应变分布的函数,提出了一种简化弹塑性分析方法。采用抛物线-矩形应力块单元模拟混凝土,当应变超过0.0035时,混凝土强度退化。将组合梁的抗弯能力表示为下翼缘应变的函数,并与基于欧洲规范4和美国AISCLRFD规范的全塑型设计进行比较。研究了各种参数对组合梁塑性抗弯能力的影响,如:截面不对称、钢材强度、设置或不设支撑、大应变时钢材的应变硬化及混凝土的强度退化、界面滑移、梁腹板开口等。对有支撑梁,达到2～4倍屈服应变时,组合梁达到95%的塑性抗弯能力;对无支撑梁,达到5～10倍屈服应变时,组合梁达到95%的塑性抗弯能力。考虑钢材的应变硬化时0.95的极限塑性弯矩对应的下翼缘应变比不考虑应变硬化减小了30%。
The elasto-plastic analysis of composite beams is important when considering the increase of beam bending resistance and the relative slip between steel and concrete under large strain. By considering the balance of the combined cross-sections as a function of the strain distribution, a simplified elasto-plastic analysis method is proposed. The parabola-rectangular stress block is used to simulate the concrete. When the strain exceeds 0.0035, the concrete strength is deteriorated. Bending capacity of the composite beam is expressed as a function of the lower flange strain and compared to the all-plastic design based on European Specification 4 and the U.S. AISCLRFD Code. The effects of various parameters on the plastic bending resistance of composite beams are studied, such as asymmetry cross-section, strength of steel, setting or no support, strain hardening of steel and strength degradation of concrete under large strain, interface slip, Opening and so on. For a supported beam, the composite beam achieves 95% of the plastic bending resistance when it reaches 2 to 4 times the yield strain. For a non-supported beam, the composite beam achieves 95% of the plastic bending resistance when it reaches 5 to 10 times the yield strain. The lower flange strain ratio corresponding to the ultimate plastic bending moment of 0.95 for strain hardening of steel is reduced by 30% without considering strain hardening.