| Under the influence of topography,high and low pier bridges often appear in the Loess gully area of China,with significant differences in pier height.The sufficient pile length of the pile foundation is prone to decrease in the slope area,which leads to the significant differences in the dynamic characteristics of bridges;slope top pile foundation-the response of the slope system and the slope distance of the pile foundation are closely related.It is more complicated than the stress on the flat pile foundation.The description of the slope distance of the slope top pile foundation in the existing specifications is not based on sufficient evidence;under seismic effects,the pile foundation is subjected to more unfavourable stresses due to the complex soil action.This paper uses a finite element method to analyze the variability of dynamic characteristics of high and low pier continuous beam bridges,the response and stability of the slope distance to the slope top pile foundation-side slope system,and the dynamic response of the pile foundation after the completion of the bridge,based on a highway bridge project in a yellow soil gully area.The work is mainly as follows:(1)In order to investigate the nature of the differences in the dynamic characteristics of high and low pier girder bridges in mountainous areas,the author uses MIDAS CIVIL modeling software to analyze the dynamic characteristics of four typical mountainous terrain continuous girder bridges,compare the differences in the dynamic characteristics of various types of high and low pier girder bridges and analyze the influence of the changes in pier height and sufficient pile length due to terrain on the dynamic characteristics of high and low pier continuous girder bridges.The topographic changes in the Loess area directly affect the pier height,effective pile length,mainly affect the pier’s longitudinal and transverse thrust stiffness and structural vertical vibration caused by different topography under the high and low pier bridge self-vibration frequency,period and various order of vibration type shape is different.And that is the essence of the reason for the gully area high and low pier beam bridge dynamic characteristics of the difference.(2)In response to the problems of cracking at the top of the slope and excessive local displacement during the construction of the pile foundation of a highway assembly bridge,it was suggested that the pile design should take into account the distance between pile and slope.Based on the finite element software ABAQUS and strength reduction analysis theory,the influence of the slope distance between the pile foundation and soil at the top of the steep slope on the stability of the side slope and the bearing performance of the pile foundation was investigated.It is recommended that when analyzing the distance between pile and slope of the top pile foundation,the potential sliding surface of the bridge site should be found first.If the top pile foundation is in the sliding surface of the slope,the pile foundation will play an anti-slip role,and the slope will be passively reinforced,then the anti-slip design of the pile foundation should be considered,which gives the basis for the description of the provisions of the Technical Specification for Building Pile Foundations in China regarding the slope distance of the slope top pile foundation(3)To understand the response of slope top pile foundation under seismic effect,the two-dimensional dynamic analysis model of slope top pile foundation-soil with infinite element boundary was established by using finite element software ABAQUS,and the influence of slope of pile front edge and bridge superstructure quality on the dynamic response of pile foundation under horizontal seismic effect were compared and analyzed.The changes in pier top displacement,top pile displacement,peak soil pressure,and peak bending moment under different parameters were obtained.The slope and superstructure quality does not affect the displacement of the pier pile time change trend.There a positive correlation between pier top displacement peak,pile top displacement peak,pile body peak soil pressure of pile body and peak bending moment of pile body and slope and superstructure quality.The effects of slope to dynamic response of pile foundation is more significant. |
