基于有限单元柔度法和刚度法的非线性梁柱单元比较研究

分别基于有限单元柔度法和有限单元刚度法理论,采用纤维模型梁柱单元编制了钢筋混凝土杆系结构非弹性分析程序。基于柔度法的梁柱单元模型的特点在于以单元截面力插值函数作为出发点,在不考虑几何非线性的前提下,总能保证单元内部截面力场分布满足平衡条件。通过构造的数值算例及钢筋混凝土双向弯曲柱反复加载试验结果与两种方法模拟分析结果的对比,对柔度法与刚度法的分析效果进行了比较研究,并对纤维模型梁柱单元解决空间杆系结构非弹性分析的有效性进行了验证。结果表明:对于结构处于强非线性阶段,尤其是对于处理下降段(软化)问题,基于柔度法的梁柱单元无论从计算效率还是计算效果上都明显优于基于刚度法的梁柱单元;纤维模型梁柱单元是目前处理空间杆系双向弯曲与变轴力耦合问题最为实用有效的单元分析模型。

COMPARISON BETWEEN FLEXIBILITY-BASED AND STIFFNESS-BASED NONLINEAR BEAM-COLUMN ELEMENTS

Flexibility-based and stiffness-based fiber-model beam-column elements are investigated in this paper. Flexibility-based beam-column elements are based on force interpolation functions that reproduce the variation of internal element forces in a strict sense in the absence of geometric nonlinearity. Numerical examples and tests of reinforced concrete columns under biaxial bending have been selected for computational effectiveness comparison between the two methods and verification of fiber model beam-column elements. The results show that flexibility-based beam-column element are apparently superior to stiffness-based beam-column element in dealing with softening problems of structures in strong nonlinear phase. Fiber model beam-column elements are presently one of the most practical and efficient element models handling biaxial bending and variable axial force coupling problems of frame structures.