Computational Simulation of Local Damage in Structures

计算机模拟用于预测建筑物或桥梁对地震、爆炸或飓风引起的极端荷载的反应。当受到这些强烈的载荷时，损伤通常集中在结构内的小局部区域。局部损伤的计算机模拟及其与结构系统的结合是困难的，因为结构的模拟在大尺寸(超过10-20英尺)上运行，而局部损伤发生在小尺寸(几英寸)上。这一研究项目将创造一种新的方法来解决这种比例差异，从而能够准确地模拟极端载荷下的结构。这项研究涉及来自结构工程和计算力学的专业知识。这项研究的结果和软件产品将提高该国建筑物和桥梁基础设施的安全性和经济性。代表性不足的群体的参与和向学生传授新知识将产生更广泛的影响。当横截面或材料的强度损失(即软化)将损伤集中在构件的一个小区域时，结构构件中的局部损伤就会发生。准确的局部损伤建模是至关重要的，因为结构中的极端极限状态(如倒塌)对软化行为高度敏感，而软化行为通常伴随着局部损伤。目前用于模拟结构局部损伤的方法要么在复杂的情况下极其困难，要么对病理网格敏感，导致在这两种情况下都不能进行准确的模拟。这项研究试图通过使用非局部方法，通过在本构公式和单元公式中明确嵌入横截面和材料长度尺度，来弥合结构尺度和局部尺度之间的尺度差距。这项研究将包括对梁柱单元的非局部方法的理论发展，以产生与网格无关的、准确和稳健的钢筋混凝土和钢构件局部损伤的模拟。这一进展将由有限元模拟和现有的实验数据提供信息。随后将进行数值实施和验证。

Computer simulations are used to predict responses of a building or a bridge to extreme loading caused by earthquake, blast or hurricane. When subjected to these intense loads, damage is most often concentrated into small local zones within the structure. Computer Simulation of local damage and incorporating it with structural system is difficult because simulations of structures operate over large dimensions (more than 10-20 feet) whereas local damage occurs over small dimensions (a few inches). This research project will create a new method that will resolve this scale difference, enabling accurate simulation of structures under extreme loads. The research involves expertise from structural engineering as well as from computational mechanics. The results and software products resulting from this research will improve the safety and economy of the country's infrastructure of buildings and bridges. The involvement of underrepresented groups and the transfer of new knowledge to students will result in broader impacts. Localized damage in structural members occurs when cross-sectional or material loss of strength (i.e. softening) concentrates damage in a small region of the member. Accurate modeling of local damage is critical, because extreme limit states in structures (e.g. collapse) are highly sensitive to softening behavior that typically accompanies local damage. Current approaches to simulate local damage in structures are either extremely difficult in complex scenarios, or are pathologically mesh-sensitive, leading to inaccurate simulations in either case. This research seeks to bridge this scale gap between structural and local scales through use of a 'nonlocal' approach, by explicitly embedding cross-sectional and material length scales within constitutive and element formulations. The research will include theoretical development of nonlocal approaches for beam-column elements, to produce mesh-independent, accurate and robust simulations of local damage in reinforced concrete and steel members. This development will be informed by finite element simulation as well existing experimental data. This will be followed by numerical implementation and validation.