Experimental Study On Strengthening Precast Reinforced Concrete Frame Using Fiber Sheet/Rope To Mitigate Progressive Collapse

In the existing buildings,the reinforced concrete(RC)structures are widely used.Among them,the robustness of the frame structure is relatively poor,especially the precast frame structure.At present,very little consideration has been given to the design of progressive collapse resistance.With the improvement of design standards,it is bound to face the need of the strengthening of progressive collapse resistance.However,researches on the strengthening of progressive collapse resistance are rare.There are two difficult problems in the traditional strengthening method,which is used to the strengthening of progressive collapse resistance:First of all,for structures that have no problem with seismic performance,How to strengthen without violating the principle of "strong column and weak beam";Secondly,whether the traditional beam strengthening method can be applied to the large deformation failure form of progressive collapse.In this paper,assembly integral substructure,the most commonly used in precast reinforced concrete frame structure,was studied by strengthening test.First of all,the traditional strengthening method of externally bonded carbon fiber sheet is improved,the CFRP sheets were anchored with hybrid fibre reinforced polymer(HFRP)anchors;Secondly,a new method of external strengthening using T700 carbon fiber rope(non-impregnated adhesive)with aramid fiber is put forward.Given a certain amount of pre-relaxation,and aiming at the key problem of reinforcement,that is the anchoring problem,two kinds of anchoring methods are put forward,that is,artificial binding kNot and post-installed with expansion head.Four assembled concrete frame structures which removing the middle column were designed and made in the scale ratio of 1:2 in this paper.One of them was strengthened with carbon fibre reinforced polymer sheets on the beam sides,the middle parts of the CFRP sheets were anchored with hybrid fibre reinforced polymer(HFRP)anchors.One was strengthened with T700 carbon fibre rope which was anchored into concrete.The third one was strengthened with T700 carbon fibre rope and anchored with a special kNot.The last one was not strengthened.An effective lateral constraint is set at side columns of two ends of the substructure,and a vertical load controlled by displacement is applied to the middle column.By comparing with the unstrengthen specimen,the collapse failure mechanism of the fabricated concrete frame structure,the failure patterns of three kinds of substructures and the strengthen effect are studied.Based on the experimental results,the suggestion of design and construction measures of preventive strengthening against fabricated reinforced concrete frames are proposed.The test results show that the method of strengthened with CFRP sheets which anchored with T700 rope on the beam side can effectively improve the progressive collapse resistance of substructures before the ultimate deformation of the structure specified by DOD2010(0.2L),but after that,due to the large deformation of the structure,the CFRP can be stripped off and destroyed.The strengthening failed.The strengthen method of T700 rope adopted in this paper,and two kinds of anchoring measures(planting T700 rope with extended head and directly binding T700 rope)can ensure that the anchoring of T700 rope don't fail before fracture.The effect of T700 rope strengthening on the stage of " flexural action " and " compressive arch action " of substructure is very small.After the substructure enters the catenary action,the T700 rope helps the beam to bear the suspension force of the upper load,improves the bearing capacity of the substructure effectively in the catenary action,and improves the progressive collapse resistance of the substructure.Based on the experimental results,the design and calculation method and construction method of strengthened with CFRP sheets on the beam sides,strengthened with T700 rope anchored,strengthened with T700 rope bound and anchored with a special kNot are proposed in this paper.The method of strengthened with T700 rope anchored plays an important role in the stage of catenary action.The calculation formula of the design of strengthened with T700 rope has the characteristics of simple force model and simple calculation.