Study On Strength And Fatigue Of Bridge Expansion Joints Under Vehicle Load

Bridge expansions are important but weak parts of a bridge structure,and they are prone to strength or fatigue failure under repeated wheel loads and their maintenance cost can be up to twenty percent of the total maintenance cost of the bridge.Therefore,the problems of strength and fatigue of bridge expansion joints is an important issue in the field of bridge engineering.We study the strength and fatigue problems of two kinds of common bridge expansion joints and put forward some optimization suggestions.First of all,we introduce the structure of two kinds of common bridge expansion joints(RBM160 modular expansion joint,RBKF160 finger-type bridge expansion joint)and put forward the calculation method of the vertical wheel load.Between them,the vertical wheel load of modular expansion joints is obtained by the numerical analysis method based on the distributed spring-damping element and the vertical wheel load of the finger-type expansion joints is obtained by the assumption of the technical document.Then,we analyze the transient dynamic response of the bridge expansion joints under the wheel load by using finite element method and evaluate the strength of the bridge expansion joints.Finally,the hot spot stress history of the two kinds of bridge expansion joints is transformed into the fatigue stress spectrum by using the rain flow counting method,the effect of mean stress on fatigue life is considered by using the Goodman formula and the fatigue life of the hot spot is estimated by using linear fatigue cumulative damage theory.Besides,we also study the problem of thread loosening in finger-type bridge expansion joints under the repeated action of wheel load.The results show that:(1)For modular expansion joints,the analysis results of impact factor of wheel load in vehicle bumping is similar to the recommended values in the technical document,therefore,the value of the technical document is reasonable.(2)For modular expansion joints:(1)Under the action of vertical wheel load,strength failure is unlikely to occur.(2)The fatigue life of the welded joint between the middle beam and the transverse beam is the shortest and increasing the weld fullness can increase the fatigue life of it.(3)For finger-type bridge expansion joints:(1)The concrete in the edge of the cavity under the cross-cavity plate is prone to strength failure and it is also the shortest fatigue life position of concrete.Steel fiber reinforced concrete can be used to enhance the durability of the concrete.(2)Anchor bolt thread and anchorage zone concrete areprone to fatigue failure.Because of the obvious stress concentration phenomenon in the local screw,the fatigue life of which is shorter than that of anchorage zone concrete and the initial loosening of the thread is caused by the fatigue failure of it.(3)Relative to the non cantilever structure with bilateral support,the cantilever structure with unilateral support is more unfavorable to the fatigue resistance of the anchor bolt and concrete.