Experimental Study On Shear Performance Of Lightweight Ultra-High Performance Concrete Deep Beam

Deep beam is simply supported beam with a span of less than 2 times the height of the beam or a continuous beam with a span of less than 2.5 times the height of the beam.The beam has a high beam body,large shear capacity and strong bending resistance.It is widely used in engineering structures.The light-weighting of high-performance concrete is a current research hotspot.Our research group has developed a Lightweight Ultra-high Performance Concrete(LUHPC)with the apparent density of less than 2100kg/m~3,the compressive strength of greater than 110MPa,the splitting strength is greater than 12MPa and the elastic modulus is greater than 3.8×10~4MPa.It will significantly reduce the self-weight of the structure and increase the load-bearing capacity of the structure when applied to deep beam structures.At present,the shear performance test of LUHPC deep beam still lacks targeted research so that it is very necessary to carry out the experimental study of the shear performance of deep beam.This paper relies on the Hubei Province Science and Technology Innovation Major Project"Development of Lightweight Ultra-High-Performance Concrete and Its Application in Prefabricated Assembled Bridge Engineering(2018AAA001)",carried out LUHPC uniaxial compressive and tensile constitutive relations.Five LUHPC deep beam test models with shear-span ratio in 0.26,0.44,0.62 and span-to-height ratio in1.43,1.67,2.00 were designed and manufactured.It was studied that the variation law of the shear limit load,deflection,strain of steel bar and concrete of LUHPC deep beam.According to the law,the formula for calculating the shear strength of LUHPC deep beams is proposed.This work provides a certain theoretical and experimental basis for the application of LUHPC new materials engineering.The main work completed is as follows:(1)The effect of different steel fiber content on the basic mechanical properties of LUHPC was studied.The experiment showed that when the steel fiber content was2.5%,the basic mechanical properties of LUHPC were great main performance indicators:28d compressive strength is greater than 110MPa,the apparent density is only 2080kg/m~3,split strength is 14.39MPa and the elastic modulus is 4.05×10~4MPa.(2)The LUHPC uniaxial compression and uniaxial tensile test of 2.5%steel fiber content was studied.The LUHPC axial compression,axial tensile failure morphology and stress-strain curves were measured.The LUHPC uniaxial tensile and compression constitutive equation was established.Taking into account the effect of the steel fiber content_f on the axial compression curve,the steel fiber volume content parameter is introduced to establish the uniaxial compressive constitutive relationship of the LUHPC under different steel fiber content.(3)Five pieces of LUHPC deep beams specimens were designed and produced,and the shear performance test was carried out.The shear performance of LUHPC deep beams was compared and analyzed under the influence of different shear span ratios and span height ratios.All the test beams were damaged by oblique compression,the shear-span ratio increased from 0.26 to 0.62,the shear bearing capacity decreased by only 4%,but the mid-span deflection increased significantly.The span-to-height ratio was reduced from 2.0 to 1.43,and the shear capacity was increased by 26.4%.Tests showed that the change in shear-span ratio has little effect on the shear bearing capacity of LUHPC deep beams.After reaching the ultimate load,the load of LUHPC deep beams declines slowly without brittle failure.LUHPC deep beams have good ductility.(4)Considering the influence of LUHPC strength on shear resistance,according to the test data,the concrete strength correction parameter?=1.6 was determined.The LUHPC deep beam shear capacity calculation correction formula was proposed.