Experimental Study On The Fatigue Properties Of The Generally Simply-supported Steel-concrete Composite Beams

In this paper, the generally simply-supported steel - concrete composite beams were studied .Through experimental study on the fatigue properties of composite beams ,the main purpose is to investigate force characteristics of fully connected composite beams by double screw bolt under repeated loads ,and to analyse the fatigue life of various materials constituting composite beams,and to analyse the possible cause resulting in the destroy of composite beams, to propose reasonable formula for calculating the fatigue life of composite beams.In this paper, seven steel concrete composite beams are designed. In the fact,the test is completed for a total of four steel concrete composite beams under a two symmetrical concentrated load.Kinds of parameters for the four composite beams all are the same when designed, the only difference is the load applied on the beams.The SL-1 beam is tested under the static load . Mechanical properties tested include yield load , ultimate load ,the deflection in the middle span ,the strain at the top of concrete slab , the strain of the reinforcement in the concrete slab, the strain of the stud, the slip at the end of the beam,the distribution of the longitudinal strain along the hight of the cross section,the differential of strain for slip at different position in the longitudinal direction.The FL-2, FL-3 and FL-4 beam are all tested under cyclic load, the frequency of the cyclic load is 5HZ around ,the upper limit of the cyclic load is 58%,54%,38% of the ultimate load of SL-1 respectively,all of the lower limit of the cyclic loads are 45KN. The main mechanical properties tested are similar to SL-1.On the use of domestic and foreign research data related to the fatigue of steel. Concrete. bar and composite beam , the content of the paper include predicting the fatigue life of different part materials of the beam,finding the characteristic and cause of fatigue destroy of the beam,discoverying the characteristic of changes in the rigidy of the beams through the change of strain of the cross section,predicting the force applied to the stud to fit the S-N curve considering the previous experimental data at the same time,thus the curve has a wider significance,finnally proposing some suggestions about the fatigue problem of composite beams which is helpful to future researches hopefully. Key Words: beams under static load,experiment about figue,the amplititude of load ,fatigue life , the rigidy of cross section.