Are Reinforced Concrete Girder Bridges More Economical Than Structural Steel Girder Bridges? A South African Perspective

This study investigated the cost-effectiveness of steel girders compared with conventional reinforced concrete girders used in bridge construction in South Africa. The investigation considered an existing bridge which required widening as a result of increased traffic flow. The consulting engineers chose two 10 m reinforced concrete girders for the end spans, while two 22 m post-tensioned reinforced concrete girders were used for the central spans. To determine the cost-effectiveness of the consulting engineer’s choice, steel girders were designed for the 10 m and 22m beams based on the relevant South African design codes of practice. The analysis was conducted for both non-composite and composite action between the steel girders and the reinforced concrete bridge deck. Based on the design calculations, a cost comparison was performed. The investigation revealed that steel girders are an economically viable option when off-the-shelf steel sections up to 10m in length are considered. For the 10 m girders, a significant cost saving was achieved for both noncomposite and composite construction compared with reinforced concrete. However, for the 22m spans, the post-tensioned reinforced concrete girders are significantly more cost-effective compared with steel plate girders. Thus, bridge design engineers should consider steel girders as an option during the conceptual design stage for end spans. A survey was also conducted among senior engineering professionals to determine the reason(s) for the apathy towards using structural steel sections as girders in bridge construction in South Africa.