Research On Mechanical Performance Of New Composite Structure With Steel Cantilever To Widen Concrete Cover Beam

The high-speed development of the national economy has brought rapid growth in traffic volume.A lot of roads built in the early stage urgently need widening,but bridges are usually the technical difficulties for the widening in transportation lines.In recent years,as for the widening of bridge superstructure,domestic and overseas scientific research and engineering scholars have proposed multiple proposals,but there is a lack of research on the methods to widen the substructure of bridges which should be urgently carried out.This thesis proposes a method to widen the substructure of bridges,namely the method of widening concrete cover beam with steel cantilever beams.For this method,there is no need to add bridge piers,and the space under the bridge is less occupied.Thus,it is particularly applicable for cities with needs for widening or bridges with limited space under them.The specific content of the thesis is listed below:(1)Common and new domestic and overseas bridge widening methods were summarized and sorted out to compare their applicability,defects,and merits.Based on the widening background of a municipal simply supported beam bridge with a span of 30 meters in Yingkou City,the adoption of the bridge-widening method of widening concrete cover beams with steel cantilever beams was proposed.Besides,this method was adopted in proposing a design proposal targeting this bridge,the load-transferring mechanism of the widened cover beams as a whole was studied,and the construction process was explored.(2)Based on the principles and analysis methods of orthogonal experimental design,the impact of the concrete performance of the original cover beam,reinforcement ratio of the reinforced bars for the original cover beam,the number of steel-concrete connecting bolts,the external prestress,and the thickness of steel plate on the ultimate bearing capacity of steelconcrete composite cantilever structure was analyzed and 18 sets of structural design proposals were designed.Then the finite element analysis software ABAQUS was adopted to respectively establish 18 finite element models.Intuitive analysis and significance analysis were adopted in analyzing the result of the ultimate bearing capacity of computer models to determine the level of influence of different parameters of various stress components on the ultimate bearing capacity.Then,a mechanical analysis was conducted on various stress components to clarify the mechanical performance of various stress components under different load grades,thereby optimizing the proposal design for widening the concrete cover beam with steel cantilever beams and arriving at the optimal structural design proposal.(3)A scale model was produced based on the optimized design proposal on widening the concrete cover beam with the steel cantilever beam to do an experiment on the ultimate bearing capacity steel-concrete composite cantilever structure.Then,a comparative analysis was conducted between the results and the load-deflection relationship,steel structure stress,and concrete structure stress in the numerical simulation results respectively.The analysis results show that the experimental results are consistent with numerical simulation results,thus verifying the accuracy of the numerical simulation calculation.The experiment verifies the mechanical properties of the transfer components under different load grades and reveals the failure mechanism of steel-concrete composite cantilever structure.(4)Based on the theoretical model verified by experiments,a numerical simulation stress analysis was conducted on the construction stage and service stage of the widened concrete cover beam with steel cantilever under two working conditions.The analysis results show that the whole widened cover beam concrete structure,various components of steal cantilever,prestressed steel strands,bolts,and other load transfer components all meet the standardized stress requirement.Therefore,the new widening method that further widens the bridge surface through widening concrete cover beam with steel cantilevers is feasible.