Experimental Study For Long-term Deformation Of PC Box Girder With Corrugated Steel Webs Considering Shear Slip And Shear Deformation

In PC(prestressed concrete)box girder with corrugated steel webs,the corrugated steel webs,as the main shear resisting members with relatively high shear buckling strength,are generally thin and their shear deformation cannot be ignored.The usage of flexible shear connectors causes shear slip at interfaces of concrete and corrugated steel webs.The web shear deformation and shear slip result in the existence of ‘the secondary bending' of top and bottom concrete slabs around their respective neutral axes,and the plane section assumption will no longer be applicable.As a thin-walled structure,the shear lag exists in the upper and lower concrete slab of box girder with corrugated steel webs.Similar to the ordinary prestressed concrete structures,the shrinkage and creep of the upper and lower slab concrete and the relaxation of the prestressing tendons affect the service behavior of the girder.In this paper,the short-term and long-term behavior of PC box girder with corrugated steel webs were studied by model test,theoretical analysis and finite element simulation.The main work and conclusions are as follows:The indoor short-term and outdoor long-term test of three externally prestressed box girders with corrugated steel webs and one externally prestressed box girder with concrete webs were carried out.In the short-term test,the deformation,web shear force and cross-section normal stress distribution of box girder with corrugated steel webs were studied,with emphasis on the influence of shear connection types.In the long-term loading test,the mid-span deformation and prestress loss of box girder with corrugated steel webs were studied,with emphasis on the influence of shear connection types and effective prestress and compared with box girder with concrete webs.The indoor short-term test shows that the short-term deformation of box girder with corrugated steel webs and flexible shear connectors is larger than that with rigid shear connectors.At the sections near the concentrated loads and diaphragms for box girder with corrugated steel webs,the plane section assumption will no longer be applicable.The average normal stress at the upper and lower edge of the entire cross-section and the shear force carried by the concrete flanges increase while the web shear force decreases.For box girder with corrugated steel webs and flexible shear connectors,the phenomenon above is more serious.The shear lag effect exists in the upper and lower concrete flange of box girder with corrugated steel webs.The outdoor long-term test shows that the mid-span short-term and long-term additional deflection of box girder with corrugated steel webs are greater than that with concrete webs.The ratio of mid-span long-term deflection to short-term deflection of box girder with corrugated steel webs is smaller than that with concrete webs.The long-term prestress loss of box girder with corrugated steel webs is similar to that with concrete webs.The mid-span long-term additional deflection of box girder with corrugated steel webs using flexible shear connectors is larger than that with rigid shear connectors while the difference between their long-term prestress lose is small.The mid-span long-term additional deflection of box girder with corrugated steel webs decreases when the prestress increases.Based on the energy variational method,a theoretical model of box girder with corrugated steel webs was established,in which the shear deformation of corrugated steel webs,shear slip and shear lag of upper and lower concrete flanges were considered.The boundary conditions of diaphragm constraint on the secondary bending,shear slip and shear lag of concrete flanges were suggested.The analysis show that at the positions of diaphragms and concentrated forces,the constraint boundary condition for the secondary bending rotation will cause additional secondary bending(constraint secondary bending)in concrete slabs of sections around there.The stress concentrations of upper and lower concrete flange exist and the web shear force is reduced.The smaller the shear stiffness of shear connectors,the more serious the stress concentrations and the smaller the web shear force.At the positions of diaphragms and concentrated forces,the constraint boundary condition for the shear lag of upper and lower concrete flange will cause shear lag effect in concrete slabs of sections around there.The intensities of constraint secondary bending and shear lag effect decrease exponentially with the increase of the distance away from diaphragms and concentrated forces along the axial direction of girder.Using the exponential function,the distributions of intensities of constraint secondary bending and shear lag effect along the axial direction of girder was presented.Then a modified Timoshenko beam model was established,which can avoid solving complex analytical solutions and can be easily embedded into the existing finite beam element calculation module.Based on the theoretical model,the finite element calculation method of externally prestressed box girder with corrugated steel webs was established.The contributions of externally prestressing tendons and diaphragms to the overall stiffness matrix was embedded.Then,the relationships between the section strain(curvature)increment and the section force increment for box girder with corrugated steel webs considering concrete shrinkage and creep,relaxation of prestressing tendons and constraint of reinforcements(including the steel flanges)were presented.By combining these increment relationships with the finite element calculation method,the time-dependent finite element program for externally prestressed box girder with corrugated steel webs was developed.The calculation results are in good agreement with the results of outdoor long-term loading test.