Load carrying capacity and ductility of circular concrete columns confined by ferrocement including steel bars

In order to significantly increase not only the load carrying capacity but also the ductility of existing circular concrete columns, a method to strengthen the columns with ferrocement including steel bars (FS) jacket was proposed. To evaluate the behaviour of the FS strengthening columns more objectively and thoroughly, a comparatively experimental study on uniaxial compression behaviours of concrete columns wrapt with three different confining systems, namely bar mat-mortar (BM), FS, and fibre reinforced polymer (FRP), was carried out. Fifty-one specimens were produced. The load–strain responses, failure modes, ultimate loads and ductilities of various strengthened columns were investigated. The experiment results showed that the mortar cover crack spaces of FS columns were basically equal to the wire mesh spacing, leading to the occurrence of much more cracks compared with that of BM columns. As a result, on the premise that the concrete compressive strength of the FS columns increased 30% compared with that of the BM columns, the ductility of the former reached about twice as that of the latter. When the confined concrete strength of FRP strengthened columns was similar to that of FS strengthened columns, the ductility, energy absorption capacity and deformation capacity of the former were obviously lower than those of the latter. In the light of a formula for calculating the ultimate load of concrete-filled steel tube (CFST), an empirical formula for predicting the ultimate load of the FS strengthened concrete column was proposed. The calculation results by using the proposed formula show a good agreement with the test results.

Research highlights
► Ultimate load can increase significant by using ferrocement including steel bars.
► Multiple cracks of cover bring the ductility of strengthened columns to a high level.
► Proposed formula can predict ultimate load of strengthened columns satisfactorily.