Study On Mechanical Performance Of Bridges With Super Longitudinal Slope

Due to the limit of topographic and planning condition at bridge location,super longitudinal slope which exceeds the allowable value stipulated by current specifications,was empoyed in the design of many bridges.In the absence of corresponding specifications,there are problems that need to be solved urgently in internal force distribution,automobile braking force effect,disease analysis,etc.of bridges with super longitudinal slope.In this thesis,the effects of super longitudinal slope in a continuous beam bridge in Shaoguan City were investigated.Through theoretical and numerical analysis with finite element models,the distribution of various internal force indexes of piers and beams changing with super longitudinal slope were evaculated.The action mechanism and value taking method of the automobile braking force of the continuous beam bridge with super longitudinal slope were summarized and analyzed.The influence of support leveling defects on the internal force and displacement of piers and beams were quantified,and the causes of its defects were analyzed.The main work is as follows:1.With the comparison of the results by theoretical derivation and numerical analysis of several finite element models with two software,the accuracy and reliability of finite element models with super longitudinal slope are verified.The internal force distributions of the upper and lower structures of the bridges under different longitudinal slope conditions are compared with respectively,and the variation rules of various indexes with longitudinal slopes are quantified and the reasons are summarized.It is found that the bending bearing capacity and the cracking resistance of the beam section of the bridge with super longitudinal slopes need to be properly strengthened,and the shear force of the beam and the internal force of the pier are less affected.2.According to the characteristics of frequent setting slope changing points in sections with super longitudinal slopes,the calculation models of the beams on small radius vertical curves under the conditions of multi-stage longitudinal slopes are compared and analyzed.The distribution characteristics of internal force of piers and beams under this condition are obtained,and the variation trends of beam section stress caused by the radial force of steel tendon within the range of vertical curves are quantified.3.Through comparison and analysis,it is found that the internal force of upper and lower structures caused by automobile braking force has low correlation with longitudinal slope.By describing the braking process of the vehicle,analyzing the generation mechanism of braking force and the vehicle motion equation when braking on a slope,combining with the braking characteristics of vehicles driving downward,the slope-resistance coefficient is introduced to modify the braking distance in specifications,and a method for determining the braking force of vehicles driving downward based on the braking distance is proposed.4.Through numerical calculation,the influences of support leveling defects under various longitudinal slopes are compared and analyzed,the variation trends of beam-end displacement and pier-top internal force with the support leveling degree are revealed,the generation mechanisms of the displacement disease of piers and beams are analyzed,and the coping strategies and matters needing attention in the design and construction process are put forward.