Research On Flexural Mechanism Of RUHPC-RC Composite Beam

Ultra-High Performance Concrete(UHPC)is a kind of high performance,high toughness,low porosity,high performance cement-based composite with excellent mechanical properties and high durability.One research direction is to combine UHPC as a prefabricated unit and combine it with cast-in-place reinforced concrete(RC)into a new sustainable composite structure.UHPC has excellent compressive ductility,which enhances ductility and energy dissipation of UHPC-RC composite structures.In addition,the slip between fiber and UHPC matrix during the crack development also consumes energy,which is beneficial to the structure energy consumption.However,in the existing research,the research on the energy dissipation performance of UHPC-RC composite structure is lacking,and the research on UHPC tensile energy consumption is also less.So in this paper,the following aspects have been carried out:Firstly,a new process: stone modular methed was invented to manufacture RUHPC-RC composite beam.The bending test of sagging and hogging area of the RUHPC-RC composite beam was carried out.The experimental results show that the crack load,peak load and ductility of RUHPC-RC composite beam is improved compared with ordinary reinforced concrete beams.Secondly,Fiber reinforcing model was proposed,which use mesoscale fiber pull out performance to reflect macroscale UHPC tension and energy dissipation performance.The model can predict the residual tensile strength of UHPC after cracking and the dissipating energy during the crack development.It provides the mechanism of the contribution to the structural bearing capacity and the ductility for UHPC.The computational model also gives a scientific reference for other fiber reinforced composites.Thirdly,a simplified design method for the ultimate bearing capacity of RUHPC-RC composite beams is proposed.The gradient effect of the relative size of permanent formwork on the bearing capacity of composite beams is studied.Forthly,based on fiber-reinforcing model,an approximate analytical solution for the energy dissipation of the sagging and hogging area of RUHPC-RC composite beam is derived,which can accurately calculate the energy dissipation from the loading to the failure of the composite beam.Analysis result shows that,the high compressive strength and ultimate compressive strain of UHPC increase the ultimate curvature of the composite beam section,steel fiber pulled out from UHPC matrix also consumes energy,make the energy dissipation of the RUHPC-RC composite beam significantly higher than that of the ordinary reinforced concrete beam.The gradient effect of the relative size of the permanent formwork on the energy dissipation performance of the sagging and hogging area of the composite beam is studied.A new energy ductility coefficient is proposed,which can more realistically and conservatively reflect the energy dissipation performance of the RUHPC-RC composite beam than the traditional displacement ductility coefficient.