QUASI-IMPULSIVE STRUCTRAL FAILURE DUE TO NEAR-SOURCE EARTHQUAKE

1995年神户地震(神户地震)对结构的破坏促使作者开始研究近源地震的准脉冲效应及其导致的脆性结构破坏。自1999年以来，在科学研究补助金的资助下，开展了为期三年的国际合作研究。在重要的研究成果中，特别关注了神户Ashiyahama高层公寓楼和桥墩发生特征破坏的主要原因：1.在应力波的作用下，结构响应的瞬变阶段起着重要作用，在近源地震等严重地震的情况下，结构响应的暂态阶段对随后的振动阶段反应影响很大，并可能造成重大破坏。这种重要性的程度取决于地震动剖面、场地条件和结构特性，如形状、大小、边界或支撑条件等。2.实际上严重的破坏位于结构部分附近，这些部分的能量传递肯定发生了突变。3.重钢骨架的实际主破裂发生在该位置附近，并被认为是由这种影响引起的。4.支撑-柱节点附近发生的特大型断裂是由较大的拉力轴力和横向剪切共同作用引起的支撑断裂所致，并传递到相邻的柱截面，导致完全断裂。5.屈服铰集中在一个重合的故事中会导致严重的整体坍塌。当发生在结构对地震的反应的早期阶段时，这种情况尤其危险。这些现象是从精确的三维有限元动力分析中发现的。

Structural damage suffered from the 1995 Hyogoken-nanbu Earthquake (Kobe Earthquake) motivated the authors to initiate investigation into the quasi-impulsive effects of near-source earthquakes and the resulting brittle type of structural failure. An international cooperative research has been carried out for three years since 1999, funded from Grant-in-aid for Scientific Research. Among, significant research results, the following is abstracted with special attention on main causes of characteristic failure undergone at Ashiyahama high-rise apartment complex and bridge piers in Kobe: 1.Governed by stress waves, the transient phase of structural response plays an important role, affecting heavily the following vibratory phase response, and possibly causing subsequent significant damage, in the case of severe earthquakes such as a near-source earthquake. The degree of this importance depends on ground-motion profile, site conditions and-structural properties, such as shape, size, boundary or support condition, etc. 2.Actual severe damages were located near structural portions where abrupt changes, in energy transmission must have taken place. 3.Actual main rupture in the heavy steel skeleton occurred near such a location, and is understood as caused by this effect. 4.The particular large scale rupture experienced near a brace-column joint was initiated by the brace breakage, which was caused by the combination of a great tensile axial force and transverse shear, and was transmitted to the adjacent column cross-section, which resulted in complete rupture. 5.Concentration of yield-hinge occurrence in a coincident story can cause severe whole story collapse. This is particularly dangerous, when occurred in an early phase of structural response to an earthquake. These phenomena have been found from an exact three-dimensional finite element dynamic analysis.