Flexural Performance Study On Simple-supported Concrete Box Girder With Web Openings Under Concentrated Loads

Concrete box girder especially suitable for medium span Bridges because of itsexcellent mechanical performance. By eliminating box girder horizontal clapboard tomake roof and floor to deck, at the same time, set up necessary holes on the web tomeet the requirement of ventilation, lighting and fireproofing, which can realizedouble deck traffic. The design method to solve urban traffic congestion hasimportant practical significance. This article is based on the national natural sciencefund project "stress mechanism and design method research of concrete box girderfor double-deck traffic"(approval No:51378202). Design the model of concrete boxgirder with web opening in1:6scales and conducted systematic experimentalresearch and theoretical analysis of its bending stress performance under the actionof concentrated double-deck load, the main conclusions are as follows:(1) Conducted large scale model experimental research of bending stressperformance in the elastic range of the simply supported concrete box girder withweb openings under the action of the concentrated double-deck load, and carried onthe finite element analysis to the influence of web holes on the mechanicalperformance. The research results can provide reference for concrete double-deckbox girder bridge design.(2) For the bottom deck side beam, the midspan deflection of bottom deck sidebeam is0.29mm when load on the roof deck side beam (condition1), the midspandeflection of bottom deck side beam is0.32mm when load on the roof side beam(condition3), which increase10.3%compare to condition1; For the bottom deckmiddle beam,the3/8span deflection of bottom deck middle beam is0.27mm whenload on the roof deck middle beam (condition2), the3/8span deflection of bottomdeck side beam is0.31mm when load on the bottom deck middle beam (condition4),which increase14.8%compare to condition2.So the load on the bottom deck haslarge effect on the deflection of box girders.(3) Conducted finite element analysis of the influence of web holes on themechanical performance of simply supported box. The analysis result shows that: thebottom deck side beam at the condition1~condition4, the midspan deflections of the beam without web holes are0.26mm、0.22mm、0.08mm、0.04mm；the midspandeflections of the beam with web holes are0.30mm、0.24mm、0.33mm、0.20mm,which comparing to the beam without web holes, the midspan deflections ofthe beam with web holes increase1.2times、1.1times、3times and4times.Comparing to the beam without web holes, under the condition1and condition2(both are roof deck load), the midspan deflections of the beam without web holesincrease1.15times,under the condition3and condition4(both are bottom deckload),the midspan deflections of the beam without web holes increase3.5times.Thebottom deck load has a relative great influence on the deflection of the beam withholes.(4) For the beam without holes, under the condition1,the roof and bottom deckshear lag coefficient range respectively are0.71~1.32and0.82~1.25at the condition1of1-1section, the roof and bottom deck shear lag coefficient range respectively are0.89~1.09and0.93~1.06at the condition1of2-2section. For the beam with holes,under the condition1,the roof and bottom deck shear lag coefficient rangerespectively are0.69~1.36and0.73~1.26at the condition1of1-1section, the roofand bottom deck shear lag coefficient range respectively are0.56~1.46and0.89~1.07at the condition1of2-2section. The shear lag of the beam with holesincreases under the load of every condition, the max increase is33.9%. As a result,web holes have relative great influence on the bending stress performance of simplysupported reinforced concrete box girder under double-deck load.