Experimental investigation and design method of axial compression behavior of T-shaped partially encased steel-concrete composite stub columns

Abstract

The implementation of special shaped Partially Encased Steel-concrete Composite (PEC) columns represents a viable approach to avoid the protruding of PEC columns with conventional cross-sections in tall buildings. Nevertheless, there is a lack of clarity regarding the load-carrying capacity and failure mechanisms associated with special shaped PEC columns. To comprehensively investigate the mechanical behavior of special shaped PEC columns under axial loading, this paper conducts an experimental analysis focusing on the compressive behavior of 9 T-shaped PEC (TPEC) short columns. The study examines the influence of critical design factors, including the content of section steel, spacing between transverse links, aspect ratio of the section, and the strength of concrete, on the axial load-carrying capacity of the members. Subsequently, the failure mode, ultimate load, initial stiffness, strain response, ductility index, and strength characteristic index of TPEC short columns were thoroughly explored. The results show that TPEC short columns exhibited damage patterns characterized by flange buckling, concrete spalling, accompanied by buckling of some transverse links and fracture of connecting joints. The steel ratio and transverse links spacing have substantial influence over the ultimate capacity and ductility of the columns. Notably, an augmentation in the steel ratio leads to an increase in both the ultimate capacity and ductility, while an increase in transverse links spacing results in a decrease in these characteristics. Comparatively, the section aspect ratio and has a relatively minor impact on the capacity and ductility. Additionally, it can be observed that the strength of concrete has a significant influence on the load-bearing capacity of short columns, while its effect on ductile behavior remains relatively insignificant. Finally, the applicability of the current design guidelines (i.e. the ACI318-14, Eurocode 4 and T/CECS719-2010 codes) are evaluated and a new design method for assessing the axial compression resistance of TPEC stub columns based on the constrained partitioning theory and the principle of superposition is proposed. This study can serve as a substantial theoretical foundation for the engineering utilization of TPEC short columns.