Loading Performance Study Of Frictional High Strength Bolts For Assembled Steel Bridges Of The Slow Traffic System

Slow traffic system is attracting attention as a short-distance green transport system that can provide good relief to urban traffic problems.In recent years,the continuous improvement in China’s steel production capacity,the development of new high-strength steel for bridges,and the popularity of green and sustainable construction concepts have driven the rapid development of assembled and modular steel bridge systems.The research on assembled steel bridges for slow moving traffic in China is still in its infancy and its related research is an urgent issue for design and construction at present.The frictional high-strength bolt connection is an important connecting element of assembled steel bridges,and accidents occur when both highstrength bolts slip and shear damage in advance.This paper takes the frictional high-strength bolts as the research object,and adopts the method of finite element numerical simulation,and conducts a systematic study on the frictional performance of high-strength bolts for four evaluation indexes,unlike the code which adopts the single design index of shear bearing capacity.The main research methods and findings of the thesis are as follows.(1)Through the established solid model of friction-type high-strength bolts,the law of the four evaluation indexes of the frictional performance of high-strength bolts of three different diameters existing in the code,namely the anti-slip bearing capacity,preload force,steel plate stress and frictional stress,was studied,and on this basis,the influence of different design parameters on their frictional performance was investigated using the sensitivity evaluation method.The study shows that the size of the anti-slip load capacity of high-strength bolts is positively correlated with the bolt diameter,the amount of preload loss decreases with increasing bolt diameter,but all within 5%,the peak stress of the steel plate in the slip phase is small and inefficient,the friction stress increases with the diameter of high-strength bolts,and the friction resistance is mainly affected by the size of the components.Sensitivity analysis shows that the four performance indicators of the frictional high-strength bolts,namely,slip resistance bearing capacity,preload force,centre plate stress and friction stress,are mainly influenced by the four parameters of cover thickness,centre plate thickness,hole diameter and nut diameter.(2)The agent model method is introduced into the optimization of high-strength bolts,and the optimization algorithm is used to optimize the design of the four models of anti-slip load capacity,preload force,plate stress and friction stress with single and multi-objective.The study shows that the performance of the frictional high-strength bolts affects each other and has obvious coupling,so it is easy to fall into local optimisation with a single performance objective.The relationship between the thickness of the cover plate,the thickness of the middle plate and the diameter of the bolt is within a certain range,so that the performance of the high-strength bolts can be maintained at a more excellent level;the optimal values of the hole diameter and the diameter of the nut are consistent with the values specified in the specification.(3)On the basis of the optimisation results,computer simulation techniques were used to determine the coefficient of variation of the splice section resistance and the statistical parameters of the load effect,and then the reliability design method was used to study the reliability of the load carrying capacity of the splice section of the assembled steel beam with high-strength bolts in the slow moving system.The results of the study show that the standard value of the high-strength bolt anti-slip load carrying capacity,which takes into account the effect of dispersion of random variables,has been discounted to a certain extent compared with the normative calculated value,and the high-strength bolt resistance sub-factor of 1.039 at the splice point of steel plate girders is obtained,and the proposed formula for the design value of frictional shear load carrying capacity of assembled steel bridges with slow moving system is proposed accordingly.The research results of this paper based on the resistance performance of the slow-moving system to high-strength bolts and its sub-factor can provide some theoretical reference for future research on assembled steel bridges for slow-moving traffic and the formulation of relevant codes.