Shear Behavior Of RC Beams Strengthened With CFRP-UHPC Composite Plates

Reinforced concrete(RC)beams are the most basic stress-bearing components in building structures.However,unfavorable factors such as survey,design and construction errors during the construction of the structures,blind transformation during use,and hydrogeological disasters encountered will degrade the bearing capacity and durability of RC beams,seriously threatening the safety of the building.At present,the commonly used strengthening methods for existing RC beams have many shortcomings,such as poor durability,long construction period,or large environmental impact.Therefore,a more efficient,economical and secure strengthening method needs to be proposed.Ultra-high performance concrete(UHPC)has the characteristics of ultra-high compressive strength,high toughness and high durability.Fiber reinforced composites(FRP)have the advantages of light weight and high strength,but the high temperature resistance is weak.UHPC is reinforced with FRP bars to form a composite layer,which has the advantages of high strength,high toughness and high durability.This paper presents a method for strengthening RC beams using prefabricated CFRP-UHPC composite panels.The CFRP reinforcement is arranged in the UHPC to make the CFRP-UHPC composite panels.The CFRP-UHPC composite panel is firstly prefabricated in the factory,and then is installed onto the non-ductile RC beams by epoxy resin and mechanical measures(such as,tension bolts,or expansion bolts)on site.This strengtheningmethod can not only improve the bearing capacity,durability and ductility of RC beams,but also has advantages of short construction period and less environmental disturbance.This paper intends to study the shear behavior of RC beams reinforced with CFRP-UHPC composite plates by combining numerical simulation and theoretical analysis.And a shear design mehod will be also proposed.The method will provide a theoretical basis for its engineering application.The main research contents and results are as follows:(1)Through research and analysis,the constitutive models of concrete,steel bars,UHPC,CFRP and other materials were selected.And the FEA software DIANA was used to carry out numerical simulation analysis on three groups of UHPC-reinforced RC beams from literatures.The accuracy of the seleceted constitutive modelswere verified.(2)Based on the nonlinear finite element model verified by the test data,the whole force-displacement analysis process of RC beams strengthened by the CFRP-UHPC composite plate were simulated and analyzed,and the thickness of the UHPC plate,the reinforcement ratio of the CFRPstrips,the shear-span ratio,and the strengthening method were studied.The research shows that increasing the UHPC plate thickness and the CFRP reinforcement ratio can both improve the shear bearing capacity of the component and change the failure mode of the component;when the thickness of the reinforcement layer is the same,the shear bearing capacity of the small shear span is higher than that of the reinforced beam;It is suggested to use UHPC plate to strengthen the RC beam in the shear span,which can not only improve the shear bearing capacity,but also change the failure mode.The results about the influence law of parameters on the shear performance of RC beamshave provided a theoretical basis for establishing shear design schemes.(3)Based on the softening strut-tie model,a formula for calculating the shear capacity of RC beams reinforced with CFRP-UHPC composite plates was proposed,and then verified using the results from testand finite element simulations.The results show that the formula is accurate,continuous and safe,and can be used to predict the shear capacity of RC beams reinforced with CFRP-UHPC composite plates.Finally,a shear design method for RC beams strengthened with CFRP-UHPC composite plates was proposed,which can provide a theoretical basis for engineering applications.