This paper presents a numerical investigation on aluminium alloy welded columns of channel section. Non-linear finite element models were firstly developed and validated against non-welded column test results. The materials considered in this study were aluminium alloys 6063-T5 and 6061-T6. The validated finite element models were used for parametric studies to generate numerical results for columns containing welds. In the finite element models, both ends of the columns were transversely welded to aluminium alloy end plates. Finite element models of welded columns were developed by dividing the column into two part: non-welded region and heat-affected zones. Material properties of non-welded aluminium alloys and heat-affected zone were adopted in the models. A total of 100 numerical results were newly generated from the parametric study. The numerical results were compared with design strengths predicted by the existing American, Australian/New Zealand, European and Chinese standards. The column strengths were also compared with the design strengths by the direct strength method (DSM) and the continuous strength method (CSM). Modified DSM and CSM approaches with the consideration of heat-affected zone softening effects were proposed in this study. Both modified DSM and CSM approaches were found to yield more accurate and consistent predictions for aluminium alloy welded columns. In addition, reliability analyses were performed to evaluate the reliability level of all the existing and newly proposed design rules for channel section columns containing transverse welds.