Reinforcement Detailing for Local Cracking

在梁受剪切、温度变化、板和墙的干燥收缩或锚拔出的情况下，以轻配筋区为主的混凝土裂缝往往不稳定地逐渐发展。目前还没有建立计算方法来预测这类裂缝的扩展，因此，理论对钢筋细部是不够的。在假设裂纹扩展准则由线性断裂力学的应力强度因子决定的前提下，采用有限元分析方法，提出了一种适用于各种行为的计算模拟方法。发现该方法能够合理地模拟以下情况下裂缝的扩展：受剪切作用的梁的斜拉裂缝，锚杆拉出裂缝，以及由于钢筋在一定程度上抑制裂缝张开而引起的板的收缩离散裂缝。对于所研究的每一种行为，没有建立裂纹扩展应力强度因子的特征值。正因为如此，在预测裂缝在各个阶段传播直至结构破坏的外载荷时，精度并不令人满意。结果表明，该方法有助于预测所研究实例的裂缝分布和发育路径。因此，该方法被认为对详细配筋有帮助。

A crack in concrete dominant in lightly reinforced area tends to develop unstably and progressively in cases of beams subjected to shear, temperature change and drying shrinkage of slabs and walls, or anchor pull-out. Methods are not established for computation to predict propagation of such cracks, and consequently, theory is insufficient for reinforcement detailing.A method for computational simulations were developed for application to various behaviors using an assumption that a criteria for crack propagation is determined by stress intensity factors of linear fracture mechanics, and using finite element analysis.The method was found to be reasonably capable of simulating propagations of cracks in cases of : diagonal tension cracking in beams subjected to shear, cracking in anchor pull-out, and discrete cracking in slabs due to shrinkage where reinforcement restrained crack opening to a certain degree.Characteristic values for the stress intensity factors for propagating cracks are not established for each behaviors studied. Because of that, accuracies are not satisfactory in predicting external loads to propagate cracks at various stages up to strubtural failure. The method was found helpful for predicting distribution and paths of crack developments for the cases studied. Thus the method was deemed helpful for detailing reinforcement.