Comparative Study Of Crack Resistance Of Two Types Of Flange Partially Filled Steel Box Continuous Composite Beam

There are two major problems of steel-concrete continuous composite beam,namely,the crack of the flange under tension and the buckling of the steel beam under compression.Steel box filled concrete in negative bending moment zone can increase the stiffness of composite beam and increase the ultimate flexural bearing capacity,but has no obvious effect on the crack resistance of the flange.Replace NC with UHPC in the negative moment zone to form UHPC flange-partially filled concrete steel box continuous composite beam,which can not only improve the overall bending stiffness of the composite beam,but also improve the overall bending stiffness of the composite beam.In addition,the cracking problem of the flange in the negative bending moment zone can be improved,and the crack resistance and durability of the composite beam can be improved.This paper relies on the National Natural Science Foundation of China and the Guangxi Natural Science Foundation of China.Based on the experimental research of the NC flangepartially filled concrete steel box continuous composite beam,the finite element method the software ABAQUS simulate and analyze its mechanical properties,analyze various parameters,and combine theoretical calculations to screen out the appropriate UHPC flange size,and select determine the reasonable system of UHPC flange-partially filled concrete steel box continuous composite beam.The main achievements of this paper are as follows:(1)Based on the static load test of three NC flange-partially filled concrete steel box continuous composite beams with different reinforcement ratios,the development process of cracks and cracks in the concrete flange of the composite beam during the loading process,as well as the local buckling,deflection deformation,failure mode and other phenomena,and then analyzing the causes of the phenomena,the load-deflection curve,load-slip curve,vertical strain distribution of the mid-span section and the mid-support section,and the characteristics of cracks were obtained.(2)The non-linear refined model of NC flange-partially filled concrete steel box continuous composite beam was established by ABAQUS finite element analysis software.The whole process of loading of the test beam was simulated by finite element,and the measured value was compared and analyzed.The deflection and cracks were average the error of the distance and slip value is less than 5%,which verifies the applicability of the finite element model,and lays the foundation for the subsequent simulation of the UHPC flange-partially filled concrete steel box continuous composite beam in the negative bending moment area.(3)Through the finite element method,the parameter analysis of 25 UHPC flange-partially filled concrete steel box continuous composite beams in the negative bending moment area shows that the composite beam stiffness is increased by 10%,the initial crack load is increased by about 2.3 times,and the ultimate load is increased by about 12%,the crack-observed load is7.6 times higher than the initial cracking load of NC.The longitudinal length of the UHPC in the negative bending moment area is 0.3 times the calculated span(1 800 mm),and the vertical thickness is 1/3(40 mm)of the total thickness of the flange,which is more economical and appropriate;the reasonable reinforcement ratio is 1.5%-2.0%.(4)Based on theoretical calculations,three calculated values: middle support section cracking moment,mid-span section yield bending moment,the cross section of the support in the beam can be substituted into the cracking moment to calculate the appropriate UHPC replacement length.In summary,the replacement length of the UHPC flange in the negative bending moment area is 1200mm-1800mm(0.2l-0.3l),and the replacement thickness is 40 mm(1/3 flange thickness).