Study On The Flexural Behavior Of Steel-geopolymer Concrete Composite Beam

Geopolymer concrete is a new type of green and sustainable building material with the advantages of light-weight,high strength,good durability,strong bonding and high temperature resistance.The application of geopolymer concrete in steel-concrete composite beams can make up for the shortcomings of geopolymer concrete,such as brittleness,by using the advantages of the composite components.However,research has seldom been conducted on steel-geopolymer concrete composite beam,in this paper,the flexural behavior of steel-geopolymer concrete composite beam is studied.The contents are as follows:(1)A study on the composite mechanism of geopolymer concrete and steel was carried out.Nine sets of push-out tests were conducted on stud connectors embedded in geopolymer concrete to investigate the effects of geopolymer concrete strength,diameter and arrangement of stud,on the failure mode,load-slip curve,ultimate load capacity,shear stiffness and ductility of specimens,and compared with ordinary concrete specimens.(2)Comparisons were made between the experimental results and the predicted shear bearing capacity using design codes,such as GB50017-2017,GB50917-2013,AASHTO-2014 and EN 1994-1-1-2004 to analyse the applicability of the formulas on estimating the shear strength of stud connectors embedded in geopolymer concrete.Based on the design formula of GB50917-2013,the influence parameters such as elastic modulus and strength of geopolymer concrete have been modified to get the design formulas of shear strength of stud connectors embedded in geopolymer concrete.Loadslip models from Ollgaard,Lianguang Wang,Cederwall and Wang et al were also compared and discussed,it was shown that the model proposed by Cederwall can better simulate the load-slip curve of the push-out tests in this study,as a result,the model was modified to obtain the load-slip model for interface between steel and geopolymer concrete connecting with studs.(3)A pure bending test of five steel-geopolymer concrete composite beam specimens were carried out.The main experimental parameters are the degree of connection,concrete type,and concrete strength.The failure mode,bending momentdeflection curves,flexural bearing capacity,flexural stiffness,stress-strain development,and ductility were obtained.The test results show that the flexural bearing capacity was similar to that of composite beam with ordinary concrete,but its flexural stiffness is reduced and its ductility is better.Improving the degree of connection can effectively improve the bending capacity and flexural stiffness of steel-geopolymer concrete composite beam and reduce the slip and lift-off displacement.(4)A finite element analysis model of the steel-geopolymer concrete composite beam was established,and the calculated results were in good agreement with the experimental results,mechanistic and parametric analyses were performed.A method for calculating the load carrying capacity of steel-geopolymer concrete composite beams designed according to elastic and plastic theories is proposed;a method for calculating the flexural stiffness of steel-geopolymer concrete composite beams considering the modulus of elasticity of geopolymer concrete and the discounting of the stiffness of the composite beams by the slip between steel and geopolymer concrete is proposed.