Performance of square steel tubular stub columns in-filled with fly ash and silica fume self-compacting concrete under concentric loading

Abstract

Concrete filled steel tube (CFST) column is a composite member comprising of structural hollow steel tube and concrete core. This paper evaluates the effect of fly ash (FA) and silica fume (SF) on square CFST stub columns’ behavior under concentric loading. The self-compacting concrete (SCC) grade used is M60 with the addition of 50% FA and 10% SF as a partial replacement of Portland cement. The performances of the fly ash-silica fume selfcompacting (FSS) CFST columns are examined through the axial compression capacity, the load-shortening response, and the failure mode of stub columns. The axial load of the FSS CFST columns is compared with the international design codes to validate the available design codes’ accuracy. The results yield that the FSS CFST columns’ ultimate axial load capacities range between 1408.80 kN and 808.70 kN, while the reference CFST columns’ capacities range between 1332.80 kN and 789.20 kN. FSS concrete improves the concrete contribution ratio and strength index of the square CFST stub columns. However, reference CFST columns demonstrate better ductility than FSS CFST columns. This is attributed to the brittleness of the FSS concrete. All the square CFST stub columns fail via local buckling. Eurocode 4 slightly over predicts the square CFST columns’ ultimate capacity by an average of 4.58%. The American Concrete Institute (ACI) code, on the other hand, over predicts the axial capacity of the CFST stub columns by an average of 17.46%.