Physical and geometrical non-linear behavior of precast beams on elastomeric supports

Abstract The stability of long and slender precast beams has been associated with structural collapse during the transitory phase of construction. The inevitable deviations regarding the execution between the support cross-section and midspan aggravate the instability problem, thus causing the beams to become even more susceptible to its effects. The focal point of this study is the numerical and behavioral evaluation of concrete beams that present geometric imperfections on elastomeric supports and analyze the influence exerted by the variables of: strength characteristics of concrete, physical non-linearity of the concrete and the compression stiffness of the bearing pad. The numerical analyses were developed on a computer program based on the finite element method (FEM). Among the principle conclusions drawn from the study, one finds that the increase in the characteristic strength of the concrete provides the beam with a higher degree of stability, and the consideration of the physical non-linear behavior of the material did not allow the equilibrium point on the numerical model to be found in some of the cases that were evaluated. The rotational stiffness of the pad decreases as the skew angle increases. Therefore, one needs to remember that in very critical situations, it may not be possible to find the point of equilibrium, thus leading to collapse.摘要 细长预制梁的稳定性与施工过渡阶段的结构坍塌密切相关。支承截面与跨径区间的施工偏差不可避免，此类偏差会加剧失稳问题，使梁体更易受失稳效应的影响。本研究的核心内容为：对弹性支座存在几何缺陷的混凝土梁开展数值分析与性能评估，并分析三类变量的影响效应：混凝土强度特性、混凝土的物理非线性行为，以及支座垫板的压缩刚度。本次数值分析基于采用有限元法（FEM）开发的计算机程序完成。本研究得出的主要结论包括：提高混凝土特征强度可提升梁体的稳定性；在部分评估工况中，考虑材料的物理非线性行为后，数值模型无法找到平衡点。支座垫板的转动刚度随偏斜角增大而降低。因此需注意，在极端临界工况下，可能无法找到平衡点，进而引发结构坍塌。