Experimental Research On Fatigue Mechanical Behavior Of Strengthened Existing Bridges Under Overloading

Existing bridge always suffers heavy truck load together with environment erosion during normal service stage, which inevitably cause structure damage such as rebar corrosion and concrete crack etc, and maintenance methods are adopted in order to ganrantee the servicbility. Therefore, the fatigue flexural performance of damaged bridge elements after reinforcement is very important. The thesis is an important part of the project of national natural science foundation(50808158)-"reliability analysis and remaining life prediction of reinforced concrete girder bridges under overloading". Static and fatigue performance of four group of experimental beams which are divided into reference beams without damage, reference beams reinforced without damage, beams reinforced after corrossion damage, beams reinforced after overloading damage were carried out in order to evaluate the influence of overloading on fatigue flexural performance of existing bridges. The development of the parameters such as tensile strains of rebar, strains of CFRP,strains of concrete,crack width and midspan deflection are discussed based on the experiment investigation. The contents of this thesis are as follows:1. Load survey data on main national freeway route are summarized and analyzed, the distribution and regular pattern of vehicle load are discussed. A traffic volume forecast method considering social economic effect is proposed based on gray theory and linear regression method,.2. Based on load survey date of Fudian Road, a truck model is proposed using fatigue damage analysis, the truck load effects in normal traffic state and in dense traffic state are studied. The results show that fatigue damage in normal traffic state is lager than in dense traffic state when considering same truck number and type.3. Static and fatigue performance of four groups of experimental beams are carried out. Test results show that the fatigue flexural performance is significantly affected by different loading level. The fatigue life prediction model is set up based on strains, deflection and crack information, Fatigue life prediction investigation shows that the fatigue life is controlled by rebar strain and midspan deflection. As the strain of rebar is always interfered by crack position.The midspan deflection is recommended as the main index to predict the fatigue life. 4. Rebar strain gauges sticked on the rebar are usually destoryed before the capacity experiment as the effect of corrosion simulation and fatigue loading. BOTDA is adopted to monitor rebar strains during the whole procession. The test results show that rebar and concrete strains of the beams reinforced after corrossion damage and overloading damage are decreased. The ductility is increased after the CFRP reinforcement.Because of the inefficiency of sampling frequency, the dynamic strain and deflection can't be collected very well. This special dynamic test system should be adopted to collect the above information.5. DH5937 is used to collect dynamic strain and dynamic deflection during the experiment. Fatigue life prediction model is proposed based on dynamic strains of CFRP and dynamic deflection of midspan. The investigation indicates that dynamic strains of CFRP has a priority to dynamic deflection of midspan.