Experimental Research On Fatigue Of Concrete Bridges Strengthened By Transforming From Simply-supported To Continuous Beams

Damaged simply-supported beam bridges were strengthened by transforming the simply-supported beam bridges into continuous beam bridges under non-prestressed which could increase the beating capability and normal usage performance of the structure system effectively.As the deadweight was excessive large,the fatigue check was not considered in the design code of reinforced concrete highways and bridges in our country.But in the continuous beam system that was strengthened,as the mid-bearing section only bore the negative moment produced by the secondary dead loads and live loads and the efficiency of the live loads was greater bigger than that of the secondary dead loads,the middle support section was easy to be damaged due to fatigue.This article took the key scientific research project of Liaoning Province Department of Communications(200514) as the research background and carries out a series of fatigue test researches of the concrete bridges strengthened by transforming the simply-supported into continuous beams:(1) Researches in negative bending fatigue test were conducted for 7 steel fiber reinforced self-stressing concrete composite beams through inverted loading mode.Fatigue formula for reinforced steel bars in the composite layers was established and fatigue check method for steel fiber reinforced self-stressing concrete composite beams was proposed.The test results show that the steel fiber reinforced self-stressing concrete restricts greatly the crack width and rigidity loss of the composite beams and that when the fatigue cycle reaches 2 millions times,the structural durability and normal usage performance requirements will be satisfied.(2) Researches in fatigue performance tests of the composite beams under the negative moment were conducted respectively when the reinforcement ratios of an interface are 0, 0.082%and 0.164%.The test result shows that the structural steel bars are able to make steel fiber reinforced self-stressing concrete composite layer to work collaboratively with the old concrete beam and make the steel fiber reinforced self-stressing concrete give full play to its anti-crack performance,which could reduce consequently unfolding of crack on the structural surface and improve the normal usage performance and durability of the structural negative moment areas.(3) 3 kinds of concrete were used to strengthen the damaged simply-supported beams respectively.The fatigue performance of two continuous beams strengthened by different concretes was researched through the fatigue researches.The test results show that the continuous beams strengthened by the steel fiber reinforced self-stressing concrete can effectively reduce the reinforcement stress amplitude,middle support section curvature and crack width.Compared to the continuous beams strengthened by the common concrete,the max crack width in the negative moment areas after 100,000 fatigue cycles drops approx. 25.0%～32.0%.(4) With reinforcement ratio of structure reinforcement at junction of wet-joint as reference,research of the fatigue performance at junction of wet-joint was conducted.Test results show that the structural reinforcement is able to improve the fatigue shear resistance and cracking resistance performance at the junction of wet-joint,indirectly improve the fatigue bending resistance performance of middle supports and mid-span reinforcement and at the same time reduce the overall rigidity loss of the structure.It is advised that content of structural reinforcement at the junction of wet-joint should be increased and it shall be no less than 0.003bh₁.(5) Fatigue tests of double-span continuous beams which were strengthened by steel fiber reinforced self-stressing concrete were conducted.Compared with non-damage continuous beams in simply-supported stage,fatigue performance of continuous beams strengthened by transforming the simply-supported beams into continuous beams was analyzed.The test results show that after these two kinds of beams which were damaged and non-damage in simply-supported stage were applied 1,000 fatigue cycles,reinforcement stress amplitude and mid-span section rigidity loss of mid-span and middle support exhibit good consistency.Middle support and mid-span section fatigue check result shows that the middle support section flexural rigidity of the continuous beams strengthened by steel fiber reinforced self-stressing concrete is remarkably higher than that of the mid-span section and that the internal force of the mid-span section is adjusted to the middle support,which improve consequently the bearing capability of the structural system.