大跨CFST拱桥考虑成拱过程的地震响应分析方法

Analysis method for seismic response of large-span CFST arch bridge considering arch forming process

摘要:

为探究成拱过程对大跨钢管混凝土（concrete filled steel tube,CFST）拱桥地震响应的影响机制,阐释了典型成拱过程与拱肋截面应力累积历程,提出考虑成拱过程的非线性动力接续分析方法,并通过Midas/Civil专业施工分析模块验证分析方法对成桥初始状态的分析精度。从钢管和管内混凝土地震应变响应、主拱地震位移响应等角度对比分析成拱过程的影响规律,基于“中介效应分析”剖析成拱过程对大跨CFST拱桥地震响应的影响机制。建立了考虑成拱过程前后钢管与管内混凝土地震应变响应的映射关系,提出地震响应简化修正分析方法。结果表明:提出的分析方法可达到与Midas/Civil专业施工分析非常接近的精度,钢管峰值应力误差仅为6.8%,管内混凝土应力曲线几乎重合；考虑成拱过程后,钢管和管内混凝土应变不再符合平截面假定,在地震作用下考虑成拱过程与否会导致CFST主拱进入不同的弹塑性状态,其差异随峰值地面加速度（PGA,a_PG）的增大而增大；在主拱截面塑性发展程度较低时,成桥初始状态差异起决定性影响,而在塑性发展程度较高时,材料塑性发展程度差异成为关键影响因素；所提出的简化修正分析方法精度较高,钢管及管内混凝土峰值应变误差均值分别仅为2.9%和5.5%。

Abstract:

In order to explore the influence mechanism of arch formation process on the seismic response of large-span concrete filled steel tube (CFST) arch bridges, the typical arch formation process and the stress accumulation history of the arch rib section are first explained. A nonlinear dynamic sequential analysis method is proposed for large-span CFST arch bridges considering the construction process, and the accuracy of the proposed method in obtaining the initial state of bridge is validated against Midas/Civil professional construction analysis module. The influence laws of the arch formation process are investigated from the perspectives of seismic responses of steel pipe and infilling concrete strains, as well as seismic response of the main arch displacement. Based on the "mediating effect analysis", the influencing mechanism of the arch formation process on the seismic response of large-span CFST arch bridges is addressed. Finally, a mapping relationship between the seismic strain responses of steel pipe and infilling concrete obtained with and without considering the arch formation process is established. A simplified corrective analysis method is proposed for seismic response of large-span CFST arch bridges. The research results indicate that the proposed analysis method can achieve accuracy very close to that of Midas/Civil professional construction analysis, with a peak stress error of only 6.8% for steel pipes and almost overlapping stress curves for infilling concrete. When considering the arch formation process of the main arch, the strain distribution of the steel pipe and infilling concrete no longer conforms to the plane section assumption. Under earthquakes, whether the arch formation process is considered leads to different elastic-plastic states in the CFST main arch, with the discrepancies increasing as the peak ground acceleration (PGA, a_PG) rises. When the plastic development degree of the main arch section is low, the differences in the initial state of the completed bridge are critically influential. Conversely, when the plastic development degree is high, the degree of material plasticity becomes the key influencing factor. The proposed simplified corrective analysis method has high accuracy, with average peak strain errors of only 2.9% for the steel pipes and 5.5% for the infilling concrete.