Experimental Study On Fatigue Behavior Of The Beams Strengthened By Steel Fiber Reinforced Self-stressing Concrete Layer

The strengthening method of converting simply-support into continuous for multi-span T shape free beam bridge divided into prestressing and non-prestressing methods. Prestressing strengthening method is good technology, but there are also disadvantages such as high technical requirements, complicated application technology, the problem of corrosion of prestressed steel and prestress loss. Non-prestressing strengthening method technology is simple, but there are also some problems such as interfacial bond quality of laminated layer, bearing capacity of concrete in negative moment area, crack control capacity and durability are relatively worse and etc. Steel fiber reinforced self-stressing concrete can combine advantages of steel fiber reinforced concrete and self-stressing concrete, so it is a excellent composite with high cracking resistance and good toughness. If using steel fiber reinforced self-stressing concrete into the negative bending regions of continuous composite beams which strengthened by non-prestressing technology, the crack resistance of surface course and fatigue durability of the member would be improved. And then the key technical issues of non-prestressing strengthening method will be solved.In this paper, fatigue tests of the composite beams with steel fiber reinforced self-stressing concrete layer have been carried out. Fatigue failure patterns of the flexural member are analyzed. Fatigue strength, reinforcement stress, crack width and fatigue deformation are mainly addressed.First of all, the horizontal section assumption is feasible according to experimental results and deformation modulus calculation formula is put forward. The stress growths of steel bars in the beams under fatigue load are compared. The calculation formula of steel bar stress in the beams is deducted. Upon the observation of experimental courses and the analyses of experimental results, steel bar rupture is a mainly cause of beam destruction. The fatigue strength calculation formula is set up according to stress range of the reinforcement.Secondly, the cracks development of the beams strengthened under fatigue loads is analyzed on the basis of experimental results. Then the calculation formula is set up by the initial crack width and magnified coefficient, which is available through regression analysis to experiment data, and the calculated values, fit favorably with the test results. Finally, the deformation rule of beams strengthened under fatigue loads is analyzed according to experimental results. Then, residual deflection and loading deflection are taken into consideration discussed; the calculation formula of the total deflection is obtained.