考虑混凝土贡献的修正变角桁架模型

Modified variable-angle truss model considering contribution of concrete

为提高有腹筋RC(钢筋混凝土)浅梁抗剪承载力的预测准确性和稳定性,提出一种考虑混凝土贡献的修正变角桁架模型。首先,基于变角桁架模型得到箍筋的抗剪贡献值计算公式,并结合塑性下限定理确定斜裂缝倾角的取值;其次,通过混凝土浅梁受压区的劈裂破坏模式得到混凝土项的抗剪贡献值计算公式,并利用尺寸效应系数考虑了混凝土项的脆性破坏特征;最后,将箍筋项和混凝土项提供的抗剪承载力进行叠加,建立有腹筋RC浅梁抗剪承载力计算公式。基于有腹筋RC浅梁抗剪承载力试验数据库ACI-DAfStb对本文、GB50010、ACI及AASHTO规范中抗剪计算公式的预测准确性进行对比评估,结果表明:文中抗剪承载力公式不仅能够体现配筋率、剪跨比和混凝土强度等主要抗剪参数的影响规律,还能考虑尺寸效应和斜裂缝倾角对抗剪承载力的修正;同时,在抗剪承载力预测准确性和稳定性方面,相对规范方法有所较高。

To improve the prediction accuracy and stability of the shear capacity of reinforced concrete （RC） shallow beams with web reinforcements, a modified variable-angle truss model considering the contribution of concrete was developed. Firstly, the shear capacity calculation formula of stirrups considering the contribution of concrete is presented based on the variable-angle truss model, and the value of diagonal crack dip angle is determined according to the plasticity lower bound theorems. Secondly, the shear capacity calculation formula considering the contribution of concrete is presented according to the splitting failure mode of RC shallow beam compression zone, and the brittle failure characteristics of concrete are also considered by the size effect coefficient. Finally, the shear capacity provided by the stirrup and concrete is superimposed to establish the shear capacity calculation formula of RC shallow beams with web reinforcement. The prediction accuracy of shear capacity calculation formulas in this study, GBS0010, ACI and AASHTO standard are eontrastively evaluated based on the database ACI-DAfStb of shear capacity of RC shallow beams with web reinforcement. The results indicate that the proposed shear capacity formula can not only reflect the influence rule of reinforcement ratio, shear span ratio, concrete strength and other shear parameter, but also consider the size effect and the modification of diagonal crack dip angle to the shear capacity. Furthermore, the prediction accuracy and stability of shear capacity are improved when compared with that using the methods in current standards.