Degree Name

Doctor of Philosophy


School of Civil, Mining and Environmental Engineering


Strengthening concrete columns by externally wrapping fibre reinforced polymer (FRP) around the perimeter of column sections is rapidly growing. This strengthening technique confines the column cores thus increases their carrying loads and ductility. This thesis is concerned with the confinement mechanism of FRPconfined concrete. Particular attention is given to a new technique for strengthening existing concrete columns.

The confinement mechanism of FRP-confined concrete is comprehensively investigated and analysed, which resulted in confinement models for FRP-confined concrete columns. The confinement model for FRP-confined circular concrete columns covers a wide range of unconfined concrete strengths with higher accuracy than other existing models. The confinement model for FRP-confined rectangular concrete columns takes the stress concentration at the corners of sections into account, which has not been done by previous studies. In addition, this study introduces the use of artificial neural network (ANN) to generate analytical equations for calculating the compressive strength and strain of FRP-confined rectangular concrete columns. These equations significantly increase the accuracy compared to existing models.

Additionally, the progressive failure mechanism of FRP-confined concrete that has not been previously investigated is experimentally studied. Experimental results show that the maximum usable strain of 1% recommended by ACI 440.2R (2008) and Concrete Society (2012) is un-conservative for FRP-confined concrete. A new model is then proposed to calculate the residual strength of a concrete core at a given axial strain.

Finally, a new practical method called circularisation technique is proposed to strengthen existing square reinforced concrete columns. The new technique significantly increases the axial capacity of the existing square columns. Through experimental studies, the proposed technique was verified for not only normal strength concrete but also high strength concrete. Two sets of experimental testing proved the viability of the proposed circularization technique.