Three-Dimensional Dynamic Nonlocal Beam Formulation for Simulation of Damage and Failure in Reinforced Concrete Structural Elements

钢筋混凝土（RC）结构占全国基础设施的最大份额。RC结构通常会受到地震、飓风和海啸等自然灾害的复杂动荷载条件，这些自然灾害会导致三维同步荷载。在如此复杂的荷载条件下，准确预测RC结构的损伤和破坏对于开发新设计和量化现有结构的脆弱性至关重要，并且已被确定为“NHERI五年科学计划：多灾害研究使世界更具弹性”的关键需求。通过提供这种能力，本研究将支持基于性能的设计和风险评估方法，包括联邦和州机构以及当地社区在内的利益相关者在决策的各个步骤中都要考虑这些方法。这项研究将通过准确评估新建和现有结构抵御自然灾害的性能、识别关键脆弱性、确定优先级并指导改造/升级工作、开发和改进新设计来提高结构和社区的复原力，从而保护人员和财产免受自然灾害的影响。这项研究将主要培训来自代表性不足的少数民族的研究生和本科生，将包括与少数民族占多数的学校的联系，并将允许开发一门新的研究生课程，与广泛的工程社区共享。本研究的目的是促进钢筋混凝土构件损伤和破坏的计算模拟和基本认识。在此过程中，本研究将建立一个计算单元公式，能够整体模拟（和预测）钢筋混凝土构件在三轴动荷载条件下的弯曲、剪切和扭转破坏，产生轴、弯、剪和扭转组合荷载。该公式标志着传统梁柱建模方法的范式转变：(i)通过通过截面子域建模确定的高阶截面运动学来准确描述构件内的三轴应力/应变状态，从而强制在截面上实现局部平衡；（ii）通过引入材料级和构件级特征长度来描述从材料级到构件级的损伤开始和传播，自然地再现强度和延性尺寸效应；（iii）通过速率相关的材料定律和构件动力学来一致地模拟加载速率效应。由于构件动力学与速率相关的本构律消除了拟静力解的多重性，降低了问题的非线性，因此该公式具有更好的计算收敛性，特别适用于结构损伤和破坏等高度非线性问题。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Reinforced concrete (RC) structures account for the largest portion of the nation’s infrastructure. RC structures are typically subjected to complex dynamic loading conditions from natural hazards, such as earthquakes, hurricanes and tsunamis, which result in simultaneous loads in three dimensions. Accurate prediction of damage and failure of RC structures under such complex loading conditions is essential to developing new designs and quantifying the vulnerability of existing structures, and has been identified as a key need in the “NHERI Five-Year Science Plan: Multi-Hazard Research to Make a More Resilient World”. By providing such a capability, this research will support performance-based design and risk assessment methodologies, considered in various steps of decision-making by stakeholders, including Federal and State agencies and local communities. This research will improve structure and community resilience in accurately assessing the performance of new and existing structures against natural hazards, identifying key vulnerabilities, prioritizing and guiding retrofitting/upgrading efforts, and developing and refining new designs in order to protect people and property from natural disasters. This research will train graduate and undergraduate students primarily from underrepresented minorities, will include outreach to minority-majority schools, and will allow the development of a new graduate course that will be shared with the broad engineering community.The goal of this research is to advance computational simulation and fundamental understanding of damage and failure of RC members. In doing so, this research will establish a computational element formulation capable of holistically simulating (and predicting) flexural, shear and torsional failures of RC members subjected to triaxial dynamic loading conditions generating combined axial, flexural, shear and torsional member loads. This formulation marks a paradigm shift from conventional beam-column modeling approaches by: (i) accurately describing the triaxial stress/strain state within members through higher order cross-section kinematics determined via cross-section sub-domain modeling that enforces the local equilibrium over the cross-section; (ii) naturally reproducing strength and ductility size effects by introducing both material- and member-level characteristic lengths to describe damage initiation and propagation from the material level to the member scale, and (iii) consistently simulating loading rate effects through rate-dependent material laws together with member dynamics. Because member dynamics together with rate-dependent constitutive laws eliminate the solution multiplicity of quasi-statics and reduce the problem nonlinearity, this formulation attains improved computational convergence properties, which makes it particularly efficient for highly nonlinear problems, such as those of structural damage and failure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.