Double Deck Traffic Oriented Cantilever Box Girder Concrete Experimental Study On Shear Lag Effect

With the development of our country’s economy and the increase of traffic flow, there ismuch more traffic jam in the city every day by the most have been built single-deck trafficconcrete box girder. On account of that, building double-deck traffic bridge canmultipurposely use bridge location and make land and space saving and resouce sharingrealized. Double-deck traffic concrete box cantilever girder put double-deck traffic intopractice through the reasonable improving the structural form of concrete box girder, whichmeans that enlarge the section size to ensure the necessary clearance requirment and throughcanceling the general setting diaphragm in the box girder, making the both roof and floor bethe bridge decking and meeting the requirements of ventilation, natural lighting and fireprotection with some necessary holes. Consequently, Research on double-deck trafficconcrete box girder bridge has important practical significance.In connection with the practical application of double-deck traffic concrete boxcantilever girder, the writer made a1:6scale model to research the cantilever model girder’stest of the shear lag effect under the effect of elastic stage. And this thesis mainly researchedthe deflection, roof concrete strain distribution and roof concrete shear lag effect of thismodel which is on the function with roof and floor uniform load and roof uniform load orfloor uniform load. Simultaneously, the writer uesd ANSYS to build a double-deck trafficconcrete box cantilever girder’s finite model, made an analog computation to its procedures.On this basis, this thesis further numerical analysis by taking full advantage of finite element.The main research results are as follow:1. The double-deck traffic concrete box cantilever girder’s deflection increase linearlywith the loads’ raising when it’s under the effect of double-deck uniform load or single-deckuniform load. And the deflection is equal to that under the same loads. That could explain themodel bridge is in a stretch functional mode.2. In the connection with double-deck uniform load or single-deck uniform load. withthe increasing loads, the roof bearing section’s strain is the maximum at the intersection of ribwith roof. And it’s smaller at the further sides, which demonstrated visible positive shear lagphenomenon. However, in the place from the one half of bearing section demonstratednegative shear lag phenomenon that the data is the minimum at the intersection of rib withroof but larger at the further sides. 3. Under the condition of different load position, the writer learned that the shear lageffect of this double-deck traffic concrete box cantilever girder is the clearest when it’s underthe effect of roof uniform load, the second when roof and floor uniform load worked, and theweakest when floor uniform load reacted. So, the writer suggested that it would be safer toplan the loads on the basis of shear leg effect under the work of roof uniform load in thedouble-deck traffic concrete box cantilever girder.4. The research compared the experimental results with the ANSYS analysis result. Itshows that ANSYS result is in good agreement with experiment’s result, which proved thefeasibility of ANSYS analysis resule. On this premise, through analyzing the change rules ofconcrete box cantilever girder model’s roof shear leg along cantilever’s length, the writer gotthe results that there is a positive shear lag phenomenon and negative shear lag phenomenonalternation at concrete box cantilever girder’s cantilever part. Besides the clear positive shearlag phenomenon and negative shear lag phenomenon on the roots of cantilever girder,negative shear lag phenomenon also existed with increasing distance between the controlsection and bearing section and became clearer when it’s closer to the free section. So, as foruniform load, the writer thinks that builder should think about the influence of positive shearlag phenomenon and negative shear lag phenomenon alternation on structural design counting.The research also shows that when the roof uniform load works, the positive shear lagphenomenon and negative shear lag phenomenon’s demarcation point is the closest to theroots of cantilever girder(about one sixth cantilever part length from the support saddle), thedouble-deck uniform load’s effect took second place(about one fifth cantilever part lengthfrom the support saddle)and the furthest under the effect of floor uniform load (about onefourth cantilever part length from the support saddle). That means double-deck trafficconcrete box cantilever girder’s positive shear lag phenomenon and negative shear lagphenomenon’s demarcation point concerned with the loading positions.