徐变对PC连续梁支座沉降附加内力的影响

Influence of creep on additional internal force of PC continuous beam due to bearing settlement

为分析徐变对PC连续梁支座沉降附加内力的影响,提出一种通过体系转换描述连续梁支座沉降附加内力状态的思路,借助现行桥梁设计规范给出的连续梁徐变内力重分布公式以及徐变应变的积分表达式,推导出老化系数的计算公式.假设支座沉降的发展规律与混凝土徐变发展规律相同,建立考虑徐变影响的总变位协调方程.选取咸河大桥5跨连续梁为算例,分别计算缓慢沉降和瞬时沉降条件下的徐变次弯矩及最不利弯矩.结果表明:徐变对连续梁支座沉降引起的弹性弯矩有很大的消减作用,使实际最终弯矩不足弹性弯矩的1/2,瞬时沉降时的徐变次弯矩可达到缓慢沉降时的3倍;连续梁支座沉降引起的徐变次弯矩及最不利弯矩均与抗弯刚度成正比,与跨度的平方成反比;连续梁支座沉降最不利弯矩的峰值发生在中间支座截面处,其值为第一个内支座截面最不利弯矩的1.25倍.

In order to analyze the effect of creep on the additional internal force caused by bearing settlement of prestressed concrete continuous beam, a way to reflect the internal force state of continuous beam due to bearing settlement through system transformation is proposed. The calculation formula of aging coefficient is derived by applying the internal force redistribution formula of continuous beam due to creep in current bridge design codes and the integral expression for creep strain. Assuming that the development law of bearing settlement is the same as that of concrete creep, the compatibility equation for total displacement considering the influence of creep is established. The five-span continuous beam of Xianhe bridge is selected as an example, and the creep-induced secondary bending moment and the most unfavorable bending moment under slow settlement and immediate settlement are calculated, respectively. It is shown that creep greatly reduces the elastic bending moment caused by the bearing settlement of the continuous beam, making the actual final bending moment less than half of the elastic bending moment. The creep-induced secondary bending moment under immediate settlement can reach three times that under slow settlement. Both the secondary bending moment and the most unfavorable bending moment caused by the bearing settlement of the continuous beam are proportional to the flexural rigidity of cross section and inverse proportional to the square of span. The peak value of the most unfavorable bending moment caused by the bearing settlement of the continuous beam occurs at the middle support cross sections and equals 1.25 times that at the first inner support cross sections.