混凝土翼板完全断开的钢-混凝土组合梁弹性刚度分析

Elastic rigidity analysis of composite steel-concrete beams with whole openings in concrete slab

由于结构功能的需要,常常需要在钢-混凝土组合楼板上开洞。洞口的存在将削弱组合梁的承载力及刚度。基于3根翼板完全断开的钢-混凝土组合梁的试验研究成果,利用通用有限元软件ANSYS对试验梁进行了模拟,考虑了钢与混凝土界面的滑移,结果表明,弹性有限元方法对开洞组合梁弹性刚度的计算结果准确。通过理论分析推导出了翼板完全断开的组合梁弹性换算截面对应的跨中挠度计算公式,并用不考虑滑移的弹性有限元模型进行了验证。理论公式计算结果与有限元计算结果吻合良好。有限元计算所得的钢与混凝土界面滑移曲线表明:最大滑移并未出现在梁端,而是洞口边缘的滑移最大,这一点在试验中也得到了证明。在折减刚度法的基础上,结合洞口边界条件,推导出了考虑洞口影响的钢与混凝土界面滑移所引起的开洞组合梁跨中附加挠度计算公式。通过各种计算方法的比较证明本文提出的理论公式计算结果与实测值吻合良好,同时也表明洞口开在支座边缘对于组合梁的整体刚度影响非常小,即使不考虑开洞的影响,按照未开洞的组合截面计算,带来的误差也不大。通过大量数值计算,回归出了不同荷载工况下的刚度折减系数简化计算公式,并针对实际工程中的非典型荷载工况提出了等效计算方法。本文提出的计算方法可为翼板完全断开的组合梁的正常使用阶段的挠度验算提供参考。

Openings often exist in the concrete slab of a composite floor due to the function requirements of the structures, and would reduce the strength and rigidity of the composite steel-concrete beams. Based on an experimental study of composite steel-concrete beams with whole openings in concrete flange, the elastic rigidity of the composite beam is analyzed. Finite element analysis is conducted to simulate the composite beams with whole openings in concrete slab, taking account of the slip between steel and concrete, and the results show that the elastic FEA is accurate for calculation of the elastic rigidity of composite beams with whole openings in concrete slab. The calculation method is proposed through analytical analysis of the deflection of the composite beams with whole openings in concrete slab, without considering slip effects. The deflections predicted by the analytical method agree well with the FEA results without slip effects. The slip distribution along the beam calculated by FEA shows that the value of the slip at the end of the beam is not maximal, and the maximum value of slip appears at the edge of the openings. The effects of the openings and the slip between steel and concrete are both considered in another analysis. The deflections predicted by the analytical method agree well with the test results. It is verified further that there exist little effects on the deflection at mid-span when the openings are near the supports. The error is small even without considering the effects of the openings near the supports. The simplified method of calculating the rigidity reduction factor is established through regression analysis, and an equivalent simplified method for the atypical load conditions is also proposed. The analytical method can be used for the serviceability limit state design of composite steel-concrete beams with whole openings in concrete flange.