Simple Equations for Predicting the Strength of Slender Plain and Composite Columns

Abstract

The behavior of slender columns under axial load is more critical than short columns due to the elastic instability. In the structural design of composite members, determining the column capacity under axial load is essential when considering the length effect. Composite members like concrete-filled uPVC tubes (uPVCC) capture attention when ductility is the primary objective due to its significant elongation at failure 42% compared to less than three percent for super-advanced materials such as fiber-reinforced polymers (FRP). In the present study, six short and slender concrete-filled uPVC specimens (uPVCC) were tested under axial compression load. For comparison purpose, a similar number of specimens were tested without the plastic tube. Test results show that the plastic tube offers considerable confinement to the concrete and enhances the deformation capacity of the composite member by changing the failure mode from brittle to ductile. The columns without the plastic tube were more influenced by the slenderness ratio, undergoing 43-46% reduction in strength compared with 17-21% for the uPVCC. In order to evaluate the strength of the specimens a database of 128 data, short and slender plain and uPVCC specimens, was assembled and combined with present twelve test results were employed to develop simple equations for predicting the capacity of plain and uPVCC columns. Another thirty-two-test data from published literature were used to check the validity of the strength equations. Based on statistical indexes, the derived equations showed good performance with acceptable accuracy in predicting the strength of slender columns with and without the uPVC tube.