Experimental Research On Mechanic Performance Of UPC Continuous Beams Strengthened With CFRP Laminate

Unboned prestressed concrete continuous beams still have good ability of resuming deformation after it is destroyed subjected to load, and the residual deformation is very small after unloading. It is significant to explore the mechanical properties and design method of unboned prestressed concrete continuous beams strengthened by carbon fiber reinforced polymer (CFRP) laminate after clearing away the crushed concrete, repairing the beams with epoxy-resin-sand mortar and sealing the crack with special glue.In the current"Technical specification for strengthening concrete structures with carbon fiber reinforced polymer laminate"(CECS146:2003), the strengthened beam is only the normal concrete beam whose carrying capacity does not reach the limit state. The beam in this dissertation strengthened by CFRP laminate is prestressed concrete beam, and it has reached the limite state and failed. So the design methods and calculation formulas in this specification can not be applied to this kind of beam. In this circumstance, the special analysis and research is needed.Considering the above problems, experiment and research on 10 destoryed unboned prestressed concrete continuous beams strengthened by CFRP laminate are carried out. The distribution of strain in critical section at mid-span and support proves that the plane section assumption is still correct. Two failure modes of beams are gotten from the test phenomena, one is CFRP is broken and the other is the fringe of compressive concrete is crushed. After analyzing constitution relation of materials, the calculation formulas of flexural carrying capacity under different failure modes are prsented. The calculation formula of short-term stiffness of this kind of flexural member is put forward after considering the influence of prestress, area of unbonded tendon, area of non-prestressed reinforcement, area of CFRP laminate, the residual strain of material and other factors to the stiffness. The calculation formulas of ultimate curvature, yield curvature and yield moment of section for this kind of beam are derived. The calculation method of length of plastic hinge is discussed. Based on these results, the law of redistribution of inner force of these 10 destoryed unbonded prestressed concrete continuous beams strengthened by CFRP laminate is obtained. Then, the relation curve of moment modification amplitude and relative rotating ability of plastic hinge of middle support is proposed briefly, and the calculation formulas of moment modification coefficient suitable for plastic design are presented.