Study On Mechanical Performance And Design Method On Partially Precast Steel Reinforced Concrete Beams

Partially precast steel reinforced concrete beam,which is abbreviated as PPSRC beam,is a composite beam composed of two parts,the precast outer-part and the cast-in-place inner-part.The application of PPSRC beams can efficiently simplify the constructional procedures on site and avoid braces and scaffolding to promote the building industrialization.With the advantages of flexible combination in cross section and material,the PPSRC beams proposed here are superior in high bearing capacity,low cost,good quality and wide range of application.Therefore,PPSRC beams may have a promising future in structural engineering.To investigate the flexural performances of PPSRC T-beams,static loading experiments were carried out on nine specimens.On the basis of test result and numerical analysis,the effects of the compressive strength of concrete in the inner-part and section shape were critically explored.The crack load,ultimate bearing capacity,ductility and strain development were also thoroughly examined.From comparison of the test results,the deformation of PPSRC beams agrees with the section assumption and the mechanical performance and ductility of PPSRC beams are similar to the entire cast-in-place SRC beam.Based on the traditional method in calculating stiffness and flexural bearing capacity of SRC beams,a set of proposed calculation methods is presented here and verified to be valid by the comparison of test and calculated results.To investigate the shear performances of PPSRC T-beams,static loading experiments were carried out on twenty seven specimens.The effects of the compressive strength of concrete in the inner-part,aspect ratio and section shape were thoroughly explored to investigate the shear performance of PPSRC beams with H-shaped steel and castellated steel under positive and negative bending.Meanwhile,the numerical analysis was employed to investigate the effects of width of concrete flange and rectangle section.On the basis of test and numerical results,the compatible truss-arch model for SRC beams is proposed here and verified to be valid by the comparison of test and calculated results.By means of ABAQUS,the development of stress and deflection of PPSRC beams in precast period and service period are analyzed to explain the stress state and deflection under construction load and to propose a reasonable method for the selection of precast cross-sectional dimensions.Technique of birth-death element is applied here to monitor the stress and deflection of entire construction period to build the calculation method for the deflection of each period.On the basis of test and analyzed results,the results of the optimization of a practical prestressed reinforced concrete large-span beam indicates that PPSRC beams meet the relevant requirements with no extra braces,formwork and prestressed rebar with the comparison of the former plan,therefore,PPSRC beams are verified to be superior in large stiffness,high capacity and low cost and take full advantage of concrete and steel.Therefore,PPSRC beams could be regarded as an advisable choice for such heavy-load and large-span beams.