Research On Bearing Capacity Of Monolithic Precast Concrete Beam-column Subassemblages Under Corner Column Removal Scenarios

The alternative pathway method is one of the common methods to analyze the progressive collapse resistance of structures.The interior,exterior and corner columns are often defined as the removed members in frame structures.The edge beams are often considered as cantilever beams when analyzing the concrete frame structures under corner columns removal scenarios,the bearing capacity of frames is controlled by the flexural strength of cantilever beams.In practical concrete frames structures,two edge beams connected to the removal corner column are subjected to the bending-shear-torsion combined loading due to the coordinated deformation of beams and slabs.The bearing capacity of such edge beams differ from that of bending members.This paper presents an experimental and analytical investigation on monolithic precast concrete beam-column subassemblages to assess the bearing capacity of subassemblages and investigate the effect of torsion-bending ratio on bearing capacity.The finite elements method is also involved in this paper to expand tests conclusions.Five monolithic precast concrete(PC)beam-column subassemblages and one cast-inplace reinforced concrete(RC)beam-column subassemblages subjected to monotonic loads were tested in this paper.Three different types of beam-column connections were used in PC specimens,including 90° hooks connections,lap-splice connections and headed bars connections.Three different torsion-bending ratios were applied to study the effect of torsion-bending ratio on mechanical behaviors of specimens.The effect of connection types and torsion-bending ratios were discussed by comparing the specimens’ failure mode,bearing capacity,ductility index and strain distribution.The differences between PC and RC members under combined loading were also investigated in this paper.It is observed that the section bearing capacity of PC subassemblages under bending and torsion decreases with the increase of torsion-bending ratios.The peak applied loads of specimens declined by 15.9% and 40.4% respectively compared with that of bending specimen when the torsion-bending ratios of specimens were 0.127:1 and 0.254:1 respectively.The mechanical behaviors of PC beams with 90° hooks connections can be regarded as the same as those of RC beams under combined loads.Based on the formulas in Chinese,American and European concrete codes,the assessment method of bearing capacity of PC members under combined loading was also discussed in this paper.Besides,the ABAQUS models of specimens were established and the parameter analysis was carried out to expand experimental results.Both bendingtorsion interaction and bending-shear-torsion strength relationship of PC members were discussed using test results and finite element analysis data.It is shown that the design formulas in Chinese,American and European concrete codes can all be used to design PC members subjected to combined loads.The safety margin of design formulas is acceptable.