Experiment And Method On CFRP-retrofitted RC Frames Damaged By Progressive Collapse

This paper presents an efficiency retrofitting method by using FRP(Fiber Reinforced Polymer)which can enhance the progressive collapse behavior of RC frame structures.RC frame structures would likely be subject to disproportionate collapse under accidental loads.But a considerable amount of the structures damaged in progressive collapse could continue to use after repair and retrofit,and FRP can be effectively used in progressive collapse mitigation.Carbon Fiber Reinforced Polymer(CFRP)have been widely applied in repairing and retrofitting existing structures to improve structural behavior due to the excellent mechanical properties,such as high strength,light weight,easy construction,corrosion resistance,fatigue endurance,good damping property,etc.In this paper,an efficiency method for improving the progressive collapse resistance of frame structures is proposed,which can be used for retrofitting the RC frame structures subjected to progressive collapse by using CFRP and grouting.Nonlinear analyses on the test are carried out by using finite element method.By comparing the progressive collapse behavior of CFRP-retrofitted with that of un-retrofitted RC frame structures,the retrofit effect is evaluated.Specific research contents include:(1)A quasi-static experiment method was adopted to test the progressive collapse behavior of four-bar and two-story CFRP-retrofitted frame specimen.The test content including crack development,failure mode,capacity of different stages,and the changes of steel strain were discussed.The retrofitting effects of CFRP-retrofitted RC frame structure after loss of a column to resist progressive collapse were studied by comparing the un-retrofitted RC frame structure's test results.The experimental results demonstrate that the retrofitting technology enhances the bearing capacity of substructures.(2)Nonlinear analyses on the progressive collapse behavior of CFRP-retrofitted RC frame structure are carried out by using finite element method.These details including the load versus displacement curves,the distribution of internal forces have been simulated.The calculated results are found to be accordant with test results.The design method of new retrofitted method is carried out.(3)Buildings are exposed to multiple natural hazards over their service period.For these structures,earthquake and progressive collapse are two of the most commonly encountered hazards.Considering that the progressive collapse retrofitted design of the RC frame may lead to an undesirable failure mode(i.e.,“strong-beam-weak-column”)under earthquakes,which indicates that a seismic redesign is necessary subsequent to the progressive collapse design.Fragility curves are used to assess the seismic resistance.Case study is carried out to analyze the progressive collapse design andseismic redesign suggestions are proposed.