密实截面组合梁的竖向抗剪强度Ⅱ:受负弯矩作用的组合梁

Vertical shear strength of composite beams with compact steel sections. Part Ⅱ: Composite beams subjected to hogging moment

在负弯矩区段,虽存在严重的混凝土开裂,但组合梁的竖向抗剪承载力仍远大于钢梁腹板抗剪名义值。采用通用有限元程序ABAQUS 6.5,对密实截面组合梁负弯矩区的弯剪强度问题进行研究。分析结果表明,提出的有限元分析方法可以准确预测组合梁的弯剪强度,同时对组合梁的变形刚度也可以较准确地模拟。在此基础上,利用有限元方法,对剪力连接程度、混凝土强度、力比、混凝土翼板截面尺寸、剪跨长度等参数进行计算分析,回归得到组合梁负弯矩区截面考虑力比影响的竖向抗剪强度公式。研究发现,在负弯矩区段,组合梁竖向抗剪强度的提高,只来源于混凝土翼板的抗剪作用,组合作用的贡献可以忽略;采用建议的抗剪强度公式可以不考虑组合梁负弯矩区截面弯矩与剪力的相互影响。

In the hogging-moment zone of a composite beam,the vertical shear strength exceeds the nominal shear strength of steel joist,even though the concrete slab has seriously cracked.In this paper,a three-dimensional FE model,using the general-purpose finite element software,ABAQUS version 6.5,has been developed to investigate the strength of composite beams with compact steel sections under combined hogging bending and shear.This FE model can predict the ultimate strength and the entire load-deformation history of composite beams to an acceptable degree of accuracy,and is verified by experimental results.The verified model is then employed to study the parameters that influence the shear capacity of composite beams,such as the degree of shear connection,the concrete strength,the force ratio,the dimension of concrete slab,and the shear span,etc.It is shown that the vertical shear strength of composite beam is higher than that of steel beam,which is attributed to the contribution of concrete slab but not the composite action.Based on the numerical results,empirical formulae that incorporate the effect of the force ratio are proposed to obtain the vertical shear strength of composite beams subjected to hogging moment.It is also found that the interaction between bending and shear strength in hogging-moment zones of a composite beam can be neglected when using the proposed formulae.