Study of dynamic fracture of structure and anti-earthquake design under near-source earthquake

利用MSC/DYTRAN程序对高层建筑模型在近源强震作用下的初始暂态行为进行了数值研究。结果表明，在初始瞬变阶段，对于弹塑性建筑模型，许多柱的应力大于柱材料的屈服应力，而对于弹性建筑模型，许多柱的应力大于柱材料的抗拉强度。韩申-阿瓦吉大地震引起的结构意外断裂之一是尼尔森桥式桥梁承重部分的断裂。数值计算结果表明，当桥梁支座上下以大于5m/S的速度撞击时，支座上部会出现足以导致断裂的高应力。同时，过渡阶段产生的最大应力值强烈依赖于结构的尺寸和地震运动的加速度分布。为了保证结构构件的非弹性吸能能力，必须消除脆性断裂的可能性。基于足尺振动台试验，提出了一种新的计算方法。详细观察了脆性断裂对H型截面梁的极限吸能能力的影响，总结出一种保证极限吸能能力的简单方法：1.通过对旧材料的Charpy冲击试验，检测材料的极限吸能能力，通过检测材料的冲击强度来判断构件的脆性断裂；2.当材料满足极限吸能条件时，根据材料的抗拉强度估算极限吸能能力。3.由于构件的非弹性变形能力与构件端部的应力增量成正比，因此必须充分评价构件端部的强度传递效率(节点效率)。

Initial transient behavior of a tall-building-model due to a strong near-source earthquake has been numerically studied using the code MSC/DYTRAN.It is found that stresses greater than the yield stress of the column material, for an elastic/plastic building-model, and stresses greater than the tensile strength of the column material, for an elastic building-model, are achieved in many columns of the building-models, in the initial transient stage.One of unexpected fractures of structures due to the great Hanshin-Awaji earthquake is the fracture of a bridge bearing part of the Nielsen bridge type. The obtained numerical results show that a high stress sufficient to lead to a fracture appears in the upper part of the bridge bearing, when an impact of velocity higher than 5 m/s occurs between the upper and the lower parts of the bridge bearing.It is also illustrated that the maximum stress values occurred in the transient stage are strongly dependent on the size of the structure and the acceleration profile of the earthquake motion.In order to secure the inelastic energy absorptions capacity of structural members, the possibility of brittle fracture must be eliminated.Based on the full scale shaking table test, the ultimate energy absorption capacity of H-section beams influenced by the brittle fracture was minutely observed.A simple procedure to secure the ultimate energy absorption capacity is summarized as follows.1.Brittle fracture can be eliminated by detecting FTP condition through Charpy impact test of used materials.When2.FTP condition is satisfied, the ultimate energy absorption capacity can be estimated on the basis of tensile strength of materials.3.Since the inelastic deformation capacity of a member is proportional to the stress increase at the end of member, the efficiency in transmitting member's strength at the end of member (joint efficiency) must be adequately evaluated.