Research On Shear And Flexural Behaviors Of Steel-UHPC-Steel Composite Beams

Steel-concrete-steel composite structures(SCS)composed of external and internal steel plates and filled concrete have been widely applied in practical engineering,such as nuclear power plants,polar offshore structures and subsea tunnels.The synergy of steel plate and concrete of SCS is achieved by shear connectors including shear studs and cross ties,and the out-of-plane shear loads formed by uniform temperature,seismic loads,airplane or floating ice may be considered as governed loads for containment and ice wall of offshore structures.As a result,the shear and flexural behaviors of SCS composite structures are critical issues that needs to be investigated.Recently,the combination of novel materials with SCS composite structures has attracted a lot of interests.To meet the demand of large-scale complex structures,ultra-high performance concrete(UHPC)is applied to SCS composite structures to form S-UHPC-S composite structures.This kind of structures can effectively improve the mechanical behaviors,extend the expected service life in harsh environment and reduce the expected costs of maintenance actions.Moreover,UHPC with good fluidity and self-compacting performance can be combined with modular construction technology of SCS composite structures,which can significantly facilitate the construction of structures.However,a series of scientific issues are needed to be thoroughly investigated,including the influence mechanism of UHPC on mechanical behaviors of SCS composite structures,quantitative assessment on composite action between steel plate and concrete,and shear design methods of S-UHPC-S composite structures.To this end,the theoretical analysis on S-UHPC-S composite beams is conducted to propose the shear and flexural design methods of S-UHPC-S composite beams in this thesis,which is based on the experimental research works and combined with finite element simulations.The details of the research in the thesis are listed as follows:1.Through quantitative analysis on void ratio and packing density of cementsilica fume system,carbon content and particle distribution of silica fume,the influence mechanism of silica fume on fluidity of UHPC is revealed.Furthermore,based on analytic hierarchy process,silica fume selection model is developed to judge the fluidity of UHPC in terms of material properties of silica fume.Finally,selfcompacting UHPC under non-steam curing conditions is mixed on the basis of the selection model.2.Shear and flexural tests on four S-UHPC-S composite slender beams with shear span ratio more than 2.0 are carried out,in which the cross ties,spacing of shear studs and filled concrete are considered as the study parameters.The development process of cracks,strain variations of bottom steel plates,load-displacement curves,load-slippage curves and ductility coefficients are analyzed.Failure mechanism of SUHPC-S composite slender beams is revealed.3.Shear and flexural tests on fifteen S-UHPC-S composite deep beams with shear span ratio less than 2.0 are carried out,in which the shear span ratio,spacing of shear studs,thickness of steel plate,filled concrete and cross ties are considered as the study parameters.The development process of cracks,strain variations of bottom steel plate and cross ties,load-displacement curves and ductility coefficients are analyzed.Failure mechanism of S-UHPC-S composite deep beams is revealed.4.Considering the bond-slip between steel plate and concrete and fracture of shear connectors,the numerical model of S-UHPC-S composite beams is developed to validate the applicability of numerical models by comparing with test results.On the basis of this,parametric analysis on volumes of steel fibers,steel plates and spacing of shear studs,etc.is conducted.A series of indefinite quantitative relationships due to the limitations of test results are obtained,which can be used a data support for theoretical analysis.5.Based on experimental and numerical simulation results,quantitative assessment on composite action between steel plate and concrete is carried out.Considering bond-slip between steel plate and concrete,the theoretical calculation equations of ultimate bearing capacity for S-UHPC-S composite beams are proposed to validate the applicability of calculation equations.Monte Carlo simulation is used to conduct the reliability analysis on S-UHPC-S composite beams,in order to provide reasonable advices for engineering applications of composite structures.