Collapse behavior of fully prefabricated composite frames with segmented PC floor slabs in a middle column removal scenario

Fully prefabricated steel-concrete composite (PSCC) structures come into being when precast concrete (PC) floor slabs are used to replace cast-in-situ concrete slabs, which possess the advantages of time-saving and convenient construction without or with less cast-in-situ concrete. However, segmented PC slabs decrease the integrity of composite frames and enhance the collapse risk under extreme incidents. To investigate the collapse behavior of fully PSCC frames, a reduced-scale PSCC frame substructure with segmented PC slabs was designed and tested under the monotonic load in a middle-column-removal scenario. The test results show that PC slabs near the middle column were severely crushed during the collapse; and the fracture of the girder was observed at the large deformation stage, originating from a bolt hole in the upper girder flange nearest to one side column and the weld connecting the girder with the other side column. The steel girder sections adjacent to the gaps between adjacent PC slabs presented superior continuity in stress when the segmented PC slabs were connected with steel splice plates (SSP). Meanwhile, both flexural and catenary actions in the composite beams provide the collapse resistance, and the contribution of the catenary action in the beams to the collapse resistance should be prudently considered due to the local buckling of the steel girders. Parametric analysis referring to the test was performed in the finite element (FE) method. Numerical results indicate that connecting the adjacent PC slabs with SSPs could alleviate or eliminate the fluctuation of the bending moments in the girder sections around the gaps. PSCC frames with segmented PC slabs usually present two typical collapse failure modes, the primary difference of which lies in whether limited plastic regions appear in the steel girder sections near the gaps. A simplified theoretical method was presented to decouple the contribution of the collapse-resisting mechanisms to the collapse resistance, and the analysis showed that catenary action provided 81.0 % similar to 93.4 % of the total collapse resistance at the ultimate collapse stage.