Axial strength and elastic stiffness behaviour of partially confined concrete columns

Abstract

The confinement mechanism for concrete columns utilizing carbon fibre wraps is well recognized to be an economic solution for rehabilitation and strengthening works. Partial application of this strength enhancement approach is evaluated in this paper for columns with concrete strength varying from low grade 6 MPa up to 50 MPa grade. Much research has been conducted on the confinement of low strength concrete columns given the need to improve the seismic performance of structures constructed according to old standards or without sufficient construction practice, particularly in developing countries. In addition, understanding strength improvement for low concrete strength columns is becoming important with the growing interest in utilizing inherently low strength recycled aggregate concrete in the construction industry due to its social, environmental and economic benefits. Twenty-one low strength concrete columns, partially confined with various lengths of confinement were tested and their strength behaviours were evaluated. A mathematical expression between the confinement lengths and the columns elastic stiffness was developed. Based on the experimental results, finite element models were developed for 80 partially confined concrete columns with ranging the concrete strength from 5 MPa to 50 MPa. The estimated elastic stiffness results for the modelled columns were found to accurately fit a Poly 2D function, which was in turn represented by a surface-based expression that provides the elastic stiffness of a partially confined column based on the function of the concrete strength and confinement level. Noticeable strength and stiffness improvements were found to be gained when more than 50% of the columns’ heights are confined, understanding the strength and stiffness behaviours of partially confined columns provides efficient and economic opportunities to improve the dynamic behaviour and eventually the seismic performance of buildings constructed with low-grade concrete.