Experiment And Theoretical Analysis On The Mechanical Properties Of Gfrp-Concrete-Steel Composite Beam Bridges

The glass fiber-reinforced polymer(GFRP)-concrete-steel composite beam bridge is a novel type of bridge,which consists of GFRP-concrete decks,steel beams and shear connectors.The load in the bridge transverse direction is borne by GFRP-concrete decks,the load in the bridge longitudinal direction is borne by GFRP-concrete-steel composite beams,the shear force between steel beams and composite decks is borne by shear connectors.In the construction process the GFRP plate could be used as a stay-in-place form,which could reduce the construction process and save the amount of wood formwork.In the state of serviceability,the GFRP plate can replace part of the bottom reinforcement,protect the bottom of concrete deck from environmental attack and improve the durability of composite beam bridges.In order to study the design method of GFRP-concrete-steel composite beam bridges,the mechanical properties of GFRP-concrete composite decks,GFRP-concrete-steel composite beams and GFRP-concrete-steel shear connectors were studied.The main research work is as followed:1.In order to study the static mechanical properties of simply supported decks and explore the way to improve the ductility of composite decks,five GFRP-concrete composite decks with different connection degrees were tested,and the way to improve the ductility of GFRP-concrete decks was explored by changing the connection mechanism before and after the interface failure.The experimental results showed that a variable gravel coverage changed the failure model,the ultimate load,and the ductility of the composite deck.The GFRP-concrete deck with a reasonable gravel coverage could exhibit good bending stiffness before interface failure and have a better ductility after interface failure.Moreover,the ultimate load could be not reduced significantly.2.In order to investigate the static mechanical performance of GFRP-concrete continuous decks and study the calculation method of continuous decks under service load,three continuous decks with different reinforcement ratios were tested.Experiment and theoretical analysis showed that plane sections in the positive and negative moment remained plane before the steel rebar yielded.With the enhancement of reinforcement ratio,the deformation of continuous decks decreased.During the whole loading process,the moment redistribution was obvious.The negative moment could continue to increase after reinforcement yielding,because the bending moment was shared by GFRP ribs.The moment redistribution could be predicted by using the conjugated beam method.The crack width and the deformation could be calculated by using the reinforced concrete structure method.3.The nonlinear analysis method of GFRP-concrete decks before the ultimate load was studied,and the calculation method of shear capacity at the failure of specimens was explored.Based on the cross-section analysis,the nonlinear analysis model of GFRP-concrete decks with effective connections was presented.The consistency of theoretical results with experimental results demonstrate that GFRP bottom plate strain,deflection at mid-span section,moment redistribution could be predicted by using the theoretical method.Based on the comparison of the previous calculation method as well as the analysis of GFRP plate shear force distribution,a shear capacity calculation method of GFRP-concrete decks was proposed.4.In order to study the static mechanical performance of GFRP-concrete-steel composite beams,the push-out test of GFRP-concrete-steel specimens,the bending test of simply supported GFRP-concrete-steel beams,and the bending test of continuous GFRP-concrete-steel beams were conducted.The research showed that the GFRP plate exerted no obvious effect on shear stiffness and ultimate load of shear connectors.On account of the confining effect of GFRP plates,both the ultimate strain on the concrete top surface and the ultimate deformation of composite beams were increased.Besides,the failure process was also changed.The flexural capacity of composite beams in the positive and negative moment sections could be predicted by using the plastic flexural capacity calculation method without consideration of GFRP bottom plates.5.In order to study the deformation calculation method of GFRP-concrete-steel composite beam before the cross section stress achieve the strength of materials,the cross section analysis method was improved.An analysis method was proposed,which could consider concrete nonlinearity,stiffness nonlinearity of shear connector,unequal spacing arrangement of shear connectors,and variable cross-sections.The theoretical model could predict the deformation of steel-concrete/GFRP-concrete-steel composite beams with full and partial shear connections.In addition,based on the parametric studies,a simplified deformation calculation method of GFRPconcrete-steel composite beam was exhibited.6.Based on the research results,the design method of GFRP-concrete-steel composite beam bridges was presented.After the concrete torsional crack occurred an anti-torsional structural measure consisting of ring bars,concrete,and GFRP plates was proposed to prevent the GFRPconcrete decks without bottom transverse bars from failure.At last,based on the research results,an engineering example of GFRP-concrete bridge decks was analyzed.