Effect of Band Width & Spacing of Fibre Reinforced Polymer Strengthening on Axial Capacity of Non-Slender Square Concrete Columns

This article presents an experimental investigation on factors affecting the contribution of carbon fibre reinforced polymers (CFRP) and woven sisal mats to the strength gain of non-slender, square reinforced concrete columns. The main parameters considered in this research were the effect of the ratio of band width of confining material to the smallest lateral dimension of column, the ratio of band spacing to the smallest lateral dimension of column and the use of woven sisal mat as a replacement for commercial CFRP. Reinforced column specimens were cast, then left to cure in water for 21 days. After 21 days, they were taken out of water, wrapped in CFRP or woven sisal, then left to dry in the open for 7 days. On the 28th day, compressive tests were carried out on 60 samples (100mm wide x100mm long x 300mm high) to ascertain the axial capacity of confined and unconfined columns. They were categorised based on bandwidth, spacing and type of confining material, then axially loaded to failure. Results showed that when the confinement area of various specimens is kept constant, an increase in band width and spacing had a negative effect on axial capacity of confined columns and vice versa. C16/20 columns with ratios of band width to the smallest lateral dimension of 0.375, 0.75 and 1.5 resulted in strength gain of 107.39, 104.98 and 73.21%, respectively. Increasing the ratio of band spacing resulted in reduced strength gain. In C20/25 columns, ratios of 0.25, 0.5 and 0.75 resulted in strength gains of 91.58, 85.26, and 74.74%, respectively. Longer, unconfined zones of the columns resulted in premature failure, before confinement action was triggered, thus reducing the contribution of confining material. The samples with confinement material distributed at short intervals across the length of the column recorded the highest increase in axial capacity. The results indicated that a woven sisal mat can be used as an alternative to CFRP. Partial confinement of C16/20 and C20/25 columns in sisal registered strength increase of 67.13 and 50.5%, respectively. Failure modes showed varied outcomes depending on bandwidth, spacing and location of confinement material.