| Corrugated steel web(CSW)combined box girders stand out in China’s bridge construction for their light self-weight,no web slant cracks,high prestressing efficiency and aesthetic bridge shape.However,its spanning capacity is still limited by the self-weight of the concrete,in addition,the positive moment zone in the span and the negative moment zone at the pivot point still use ordinary concrete,which has the risk of cracking.In response to these problems,the search for a new type of waveform steel web girder structure is particularly urgent.Ultra High Performance Concrete(UHPC)has many advantages such as high mechanical properties and high cracking resistance.In this paper,the top and bottom slabs of a combined box girder with variablesection waveform steel webs are replaced by UHPC,and a new type of combined box girder structure with variable-section prestressed CSW-UHPC is proposed.A static model test of a prestressed variable-section CSW-UHPC combined cantilever box girder with negative bending moment was designed and completed.Based on the test results,the shear hysteresis effect and the shear bearing ratio of the steel web were investigated.The main findings are as follows.The main research contents and conclusions are as follows:(1)A static model test of a large scale prestressed variable section CSWUHPC combined cantilever box girder with negative bending moment was designed and completed to analyse its basic force characteristics,especially its flexural and cracking resistance,and the accuracy of the test and finite element was verified by finite element software.The load-strain response,crack development mode,deflection and breaking load of the test beam were obtained through the model test,and the test results were compared with the finite element results,which were in good agreement;the shear hysteresis effect and shear bearing ratio of the steel web were investigated through the model test.The shear hysteresis effect was found in the negative moment zone at the root of the cantilever,with the shear hysteresis coefficient ranging from 0.942 to0.967;the web shear ratio showed a decreasing trend from the end to the root section,with the web shear ratio at the negative moment zone at the root of the cantilever being 2.15% under the breaking load,and the shear force was mainly borne by the bottom plate.(2)Considering the plastic development of UHPC in tension,the calculation modes of the initial cracking moment,the nominal cracking moment and the flexural load carrying capacity of the CSW-UHPC composite beam have been studied in depth,and it is recommended that the initial cracking moment and the nominal cracking moment be taken as 1.0 and 1.5 respectively,and that the k values be taken as 0.1-0.2 for the calculation of the load carrying capacity.The height of the relative limit pressure zone of this structure is investigated according to the relevant codes to provide a reference for the study of this structure.(3)Based on a 120 m main span CSW combined girder bridge in China,a variable section CSW-UHPC combined cantilever box girder scheme is proposed on the basis of the real bridge scheme in accordance with the principle of stiffness approximation,and the engineering feasibility and advantages of the variable section CSW-UHPC combined cantilever box girder scheme are analysed through finite element modelling.The results show that the CSWUHPC combination cantilever box girder solution with variable cross-section is a good solution for the bridge.The results show that the CSW-UHPC combined cantilever box girder solution is 35% lower in dead weight than the real bridge solution;the shear stress,overall buckling,local buckling and composite buckling of the two CSW solutions have been verified. |
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