Many researches were carried out both experimentally and numerically for a beam with diagonal bar as a reinforcement. However, specifically, limited attention has given to the flexural resistance, stiffness contribution and shear resistance underestimation of the diagonal bar connected to the main bars of the beam. The research is aiming to investigate comparatively the flexural behaviours and span coverage of the beam with diagonal bars welded to the main bars of the beam over the same beam without the existence of diagonal bars. In parallel, the research indicates the shear resistance underestimation of the beam with diagonal bar connected rigidly to the main bars. The analysis done with the two beam types having the same beam geometry but with and without diagonal bar existence. In this study, the geometric parameters and the number of rows of diagonal bar in width of the beam cross-section were taken. Six models with diagonal bar and one model without diagonal bar were analysed numerically. A 3D solid model was applied to grasp accurately the actual contact surfaces between the bar and the concrete and in between of diagonal and main bars.The concrete damaged plasticity model was selected since it is capable of representing the complete inelastic behaviour of concrete in tension and compression including damage. While for reinforcement bar, elastic perfectly plastic model is applied. For verification, Abaqus was calibrated with an existing experimental work results carried out by Leopoldo Tessier. For further numerical models, approximated analytical analysis is applied. The results indicate a good agreement in general, and in failure mechanisms, maximum failure load and crack patterns determination are with an excellence accuracy. In conclusion, diagonal bar welded to the main bars develop an effect to the span coverage, flexural failure mode and resistance. The analysis indicates that the diagonal bar does not affect flexural crack pattern. The research also directs about the beam has to be designed with due consideration of the diagonal bar’s flexural contribution. This study has revealed the difference between the two beams with and without the diagonal bars welded to the main reinforcement bar. It is hoped that the beam will adapted in Ethiopia to cross the span that the conventional beam cannot cross economically. In addition, a unified design procedure for such beam will developed.