力法非线性梁柱单元的合理单元长度划分

REASONABLE DISCRETE ELEMENT LENGTH OF FORCE-BASED NONLINEAR BEAM-COLUMN ELEMENTS

针对目前结构非线性分析中最常用的力法非线性梁柱单元模型,从理论上分析出了能消除其计算失真问题的合理单元长度及对应积分点数量。然后基于OpenSees有限元程序,使用该理论分析结果建立了一组单墩循环推倒试验的数值分析模型,通过加载点力-位移滞回曲线的对比分析和墩底截面曲率滞回曲线的对比分析验证了理论结果的正确性。结果表明:使用力法非线性梁柱单元模型进行结构的非线性数值分析时,其单元长度划分应根据积分点数量确定,确定原则应基于使单元屈服后变形增长的分布长度与塑性铰长度相等进行计算;在实际使用中,可利用等效塑性铰长度计算积分点数量与单元长度的关系,初步确定单元划分的合理长度;在保证单元长度与积分点数量的对应关系前提下,力法非线性单元的积分点数量越多,计算结果越稳定。

Force-based nonlinear beam-column elements are frequently used in structure nonlinear analysis. In this study, the reasonable discrete element length and the corresponding integration point number are derived theoretically to eliminate computational errors. Subsequently, a numerical model is established, using the OpenSees finite element program, for a set of single-pier cyclic pushover tests. The derivation is verified by comparing both the force-displacement hysteresis curves for load point and the section curvature hysteresis curves at the pier bottom. Results show that: the discrete element length should be determined on the basis of the integration point number when force-based nonlinear beam-column elements are used, and the relationship between the discrete element length and the integration point number is to ensure the length of plastic curvature increments in FEM equal to the plastic hinge length in the actual structure. In practice, the equivalent plastic hinge length can be used to pre-calculate the reasonable discrete element length. If the aforementioned relationship is ensured, the more force-based nonlinear beam-column element integration points are employed, the more reliable the results are.