Experimental Study On Shear Performance Of Steel-UHPC-NC Composite Beams

A new type of steel ultra-high performance concrete ordinary concrete composite beam(referred to as steel UHPC-NC composite beam)is proposed to solve the problems of easy cracking,insufficient durability,and low toughness of the bridge deck during use.The shear resistance of steel-concrete composite beams is a key issue related to the safe performance of structures,and its shear analysis is the controlling calculation content of the ultimate bearing capacity design of composite beams.As a new type of composite beam,there is currently no literature on the shear performance of steel UHPC-NC composite beams,and the shear failure mechanism of this structure is still unclear.In order to explore the shear performance of steel UHPC-NC composite beams,shear failure tests were conducted on steel UHPC-NC composite beams.The failure morphology and shear mechanism of the test beams were analyzed,and a numerical analysis model for shear resistance of steel UHPC-NC composite beams was established.Based on the experimental and numerical analysis results,a formula for calculating the ultimate shear bearing capacity of steel UHPC-NC composite beams was proposed.The main work and achievements completed in the thesis are as follows:(1)Two steel UHPC-NC composite beams with different interface treatments and one steel NC composite beam were designed and manufactured,and shear failure tests were conducted.The failure process and morphology of the experimental beams were obtained,and the results showed that significant web shear buckling failure and concrete wing shear compression failure occurred in all experimental beams;Due to the different composition and interface treatment methods of the wing plates,the failure process and morphology of the concrete wing plates are different.The NC wing plate of the steel NC composite beam shows a shear compression crack when the load drops to 0.81 Fu,while the steel UHPC-NC composite beam without connecting steel bars shows a shear compression crack at the ultimate load.The steel UHPC-NC composite beam with connecting steel bars shows a shear compression crack when the load drops to 0.98 Fu,Shear compression failure occurs at or after the ultimate shear bearing capacity.Comparing two steel UHPC-NC composite beams with different interface treatment methods,the UHPCNC interface peeling occurred before the ultimate shear bearing capacity.The difference is that the steel UHPC-NC composite beam with interface connecting steel bars delayed the development of UHPC-NC interface peeling cracks under the tension of the connecting steel bars.This indicates that setting connecting steel bars at the UHPC-NC interface can effectively prevent brittle shear failure at the interface.(2)The experimental results show that the shear bearing capacity of the steel UHPC-NC composite beam with connecting steel bars at the UHPC-NC interface is 11.1% higher than that of the steel NC composite beam;The shear bearing capacity of the steel UHPC-NC composite beam without connecting steel bars at the UHPC-NC interface is less than 1% higher than that of the steel NC composite beam.It can be seen that setting connecting steel bars at the UHPCNC interface significantly improves the shear bearing capacity of steel UHPC-NC composite beams.(3)Establish a numerical model of steel-UHPC-NC composite beam,and the shear deflection curve obtained is in good agreement with the experiment.On this basis,variable parameter analysis of parameters such as UHPC compressive strength,UHPC layer thickness,concrete compressive strength,and steel beam web height was conducted on the steel-UHPCNC composite beam.The results indicate that the impact of UHPC compressive strength on the shear bearing capacity of steel UHPC-NC composite beams is relatively small,while the thickness of UHPC layer,concrete compressive strength,and steel beam web height have a significant impact on the shear bearing capacity of steel UHPC-NC composite beams.(4)Surface fitting was performed on the numerical analysis results of UHPC compressive strength and UHPC thickness parameters,and a formula for calculating the shear bearing capacity of steel UHPC-NC composite beams with interface shear connection steel bars was proposed.The formula for calculating the shear bearing capacity of the proposed steel-UHPCNC composite beam was validated,and the results showed that the calculated values of the formula were in good agreement with the experimental results.Comparing the ultimate shear bearing capacity of the steel UHPC-NC composite beam obtained from experiments and numerical analysis with the calculated shear bearing capacity of the composite beam in the current code,the results show that the calculation results in the current code tend to be conservative.