Experimental study on bending behavior of narrow steel box-UHPC composite beam under negative bending moment
In order to improve the mechanical behavior of steel-concrete composite beams under negative bending moment,a new narrow steel box-ultra-high performance concrete(UHPC)composite beam was proposed.The reversed static load tests of 6 specimens were completed to obtain the load-deflection curves,load-strain curves,load-maximum crack width curves of midspan,and the crack development and failure pattern of specimens in the whole test process.Based on the simplified plasticity theory,the calculation formula of ultimate flexural capacity of composite beams was derived.The results show that the narrow steel box-UHPC composite beam has good mechanical performance under negative bending moment.Increasing the reinforcement ratio,steel fiber content and UHPC relative plate thickness can improve the ductility and increase the ultimate flexural capacity of composite beams to a certain extent.The reinforcement ratio of flange has great influence on bearing capacity.When the reinforcement ratio increases from 1%to 2%,the ultimate flexural capacity increases by 15%.The initial cracking load is greatly influenced by the steel fiber content and UHPC relative plate thickness.When the steel fiber content increases from 1%to 2%,the initial cracking load increases by 32%.When the UHPC relative plate thickness increases from 0 to 0.5,the initial cracking load is improved by 56%.The increases of steel fiber content and UHPC relative plate thickness can effectively control the crack width,reduce the number of main cracks,and improve the durability of composite beams.The calculated value of the ultimate flexural capacity calculation formula of composite beam is in good agreement with the test data,indicating that the plasticity theory is suitable for the calculation of the bearing capacity of the narrow steel box-UHPC composite beam.
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