复杂边界下超高墩计算长度与二阶效应研究

tudy on the Effective Length and Second-order Effect of Ultra-high Piers with Complex Boundaries

为研究实际复杂边界下超高墩计算长度和二阶效应规范简化算法的准确性和适用性,以一刚构体系多跨矮塔斜拉桥的144 m双肢薄壁墩为研究对象,将其简化为一墩底固结、墩顶设转动与水平弹性约束的受压构件,并建立线弹性和非线性有限元模型,系统地分析了其计算长度随墩顶相对转动和水平约束刚度系数kθ、k F与偏心距增大系数随kθ、k F、荷载轴压比、截面配筋率、混凝土本构特性的变化规律,用于与新版桥规结果进行详细对比分析。研究表明:规范结果随个别参数的变化规律与有限元结果并不完全一致;后者表明提高配筋率可略微降低高墩的二阶效应;整体来看规范计算长度和偏心距增大系数普遍具有一定的保守性;采用约束混凝土本构后高墩达到极限状态时的二阶效应明显增强,而规范结果则明显偏低。

In order to study the accuracy and applicability of the code algorithm for effective length and second-order effect of ultra-high piers under actual complex boundaries,a 144 m double-legged thin-walled pier from a rigid-frame,multi-span,extradosed cable-stayed bridge was taken as the research object.It is simplified as a compression member with its bottom fixed and its top restrained by rotational and horizontal elastic constraints.Linear elastic and nonlinear feas are carried out systematically to study how effective length varies with the relative rotational and horizontal constraint stiffness coefficients,noted as kθ,k F,and how moment magnification factor varieswith kθ,k F,axial compression ratio,section reinforcement ratio,and concrete constitutive.Through a detailed comparison of the fea and the code results,it is shown that the two are not completely consistent along with the variation of some parameters;increasing the reinforcement ratio can slightly reduce the second-order effect according to the fea results;overall,the results of the effective length and the moment magnification factor from the code are generally more conservative.Using confined concrete constitutive will obviously enhance the second-order effect when the pier reaches the ultimate limit state;however,the results of the codeis lower than that of the fea.