Temperature Effect And Time-dependent Behavior Of RC Structures Strengthened With Prestressed CFRP Plates

The use of fibre reinforced polymer composite in civil engineering applications is growing. It is a strengthening method with widespread use that bond FRP to the tensile face of an under-strength structure and improve the structrual load-carrying capacity using the high tensile property of FRP. The strength and rigidity of the strengthened structures is enhanced with no increament of dead load and nice corrosion resistance through this method. But there are some vice of such conventional FRP strengthening method, for example, the material utilization is low, the premature debonding occurs frequently, the original crack width of the structures cannot be lessen and the strain of FRP lags behind concrete. Prestressing FRP laminates can repair or slack these deficiencies and ameliorate the usability of the reinforced structures.There are a great many available research works of strengthening concrete structures with prestressed CFRP plates, but most of them are test room studies and theoretical investigations and the research of practical application is lacked. It was mainly limited by the means of prestressing and maintenance of prestressing. A majority of the prestressing and anchoring methods adopted in the past were only fit to apply lower prestressing to the individual members in the test conditions and cann't be used for the strengthening of practical structures. A strenthening engineering of a practical bridge using prestressed CFRP plates and the stretching and anchorage system was introduced in this thesis. The strengthening design and construction was described in the concrete and the field solution and precaution of the factors that required attention and impact strengthening effect. The strengthening effect was assessed through vehicle loading tests after strengthening. The measurement results of deflection and strain both showed that the carrying capacity and resistance to deformation was visibly improved and the expectant strengthening object was achieved.In addition, combining the monitoring results, the temperature effect of the strengthened bridge was analysed based on the thermal characteristics of materials and the formula of temperature strain was proposed. The actual measurement and theoretical analysis both indicated that the temperature stress was not neglectable and it was a important factor of the considerations of the structural long-term behaviour and fatigue life.At last, rational creep constitutive model of concrete and CFRP plate was adopted to study the time-dependent behavior of reinforced structures and the time-dependent strain of the strengthened bridge was simulation calculated with the formulae deduced in this thesis. The measurement result and calculation result indicated that the time-dependent reaction of the strengthened bridge was weak and had little influnce on the strengthening effect.