BRITTLE FRACTURE BEHAVIORS OF BUILDING STRUCTURES

我们研究了在构件中存在初始裂纹的建筑结构的断裂行为。基于断裂力学原理，采用边界元法对裂纹扩展行为进行数值分析。应用边界元法分析了矩形脆性梁和宽翼缘脆性梁的端弯矩-端旋转关系，它们代表了裂纹扩展的不稳定平衡路径。在此基础上，提出了简单有效的旋转弹簧模型来代替裂纹单元。这些旋转弹簧模型对于含裂纹单元的建筑结构脆性断裂行为的数值分析是有效的。对于单元中存在初始裂纹的脆性结构，裂纹扩展稳定性将受到不含裂纹部分的结构刚度的影响。如果不含裂纹部分的结构刚度较大，则裂纹扩展会迅速扩大。提出了结构刚度矩阵的特征值和特征向量可用于确定结构在裂纹扩展过程中的稳定性，并提出了用其压缩刚度矩阵代替刚度矩阵的方法。该方法适用于具有多个初始裂纹的结构。进行了多次裂纹扩展试验，并给出了裂纹扩展的一些特征。深缺口试件试验包括钢板的拉伸、宽翼缘钢梁的弯曲、钢梁与钢柱节点的弯曲、t形苯乙烯梁的弯曲。

We have researched on fracture behaviors of building structures with initial cracks in the elements. Based on the fracture mechanics, Boundary Element Method is applied to numerical analysis of crack growth behavior. Applying the BEM crack growth analysis, we determined the end moment-end rotation relations for, the, rectangular brittle beam and wide flange brittle beam, which represent unstable equilibrium paths for the crack growth. On the basis of them, we propose the rotation spring models as simple and effective substitute for the crack elements. These rotation spring models are effective for numerical analysis of brittle fracture behaviors of building structures with crack elements. On the brittle structures with initial cracks in the elements, the stability on crack propagation will be influenced by the stiffness of the structure without the crack part. If the stiffness of the structure without the crack part is large, crack propagation will grow rapidly. We presented that eigen-value and eigen-vectors of the stiffness matrix of the structure are useful for determination of the stability on crack propagation, and that its condensed stiffness matrix can be used instead of the stiffness matrix. This method can be applied to the structures with plural number of initial cracks. Many, crack growth tests are examined and some characteristics of the growth are presented. Deeply-notched specimen tests consist of the extension of steel plate, bend of wide-flange steel beams, bend of steel beam and steel column joints, and bend of T-shaped styrene form beams.