Steel, an ideal material for bridges, is widely used around the globe for the construction of bridges of sizes ranging from the very large to the very small. Steel has long been recognized as the economic option for a range of bridges. It dominates the bridge constructions for long span bridges, railway bridges, footbridges, and medium span highway bridges. It is now increasingly the choice for shorter span highway structures as well. Steel is an essential part of modern bridges because it is strong, can flex without fracturing and has a long life, even in the harshest conditions. It can be used to build bridges of any length because of its durability and ease of manufacture and maintenance. New grades of steel increase the economic advantages of steel, while ensuring that it meets the increasing demands for high performance.
Steel offers many advantages and this has led to it being widely used for all forms of bridge construction around the world, from simple beam bridges up to the longest suspension bridges. The advantages offered by steel bridge solutions are not only from the material itself, but also from its broad architectural possibilities.
High strength to weight ratio – The high strength to weight ratio of steel minimizes substructures costs, which is particularly beneficial in poor ground conditions. Minimum self-weight is also an important factor in transporting and handling components. In addition, it facilitates very shallow construction depths, which overcome problems with headroom and flood clearances, and minimizes the length and height of approach ramps. This can also result in a pleasing low-profile appearance. The lightweight nature of steel construction combined with its strength is particularly advantageous in long span bridges where self-weight is crucial. In case of bridges with modest spans the reduced weight minimizes substructure and foundation costs, which is beneficial in poor ground conditions. Minimum self-weight is also an important factor for lift and swing bridges, as it reduces the size of counter-weights and leads to lower mechanical plant costs.
Material with high quality – Steel is a high-quality material, which is readily available in different certified grades, shapes and sizes. Prefabrication in controlled shop conditions has benefits in terms of quality. Trial assembly can be done at the fabrication shops to avoid fit-up problems on site. All these activities lead to high quality work at minimum cost. The quality control extends from the material itself and follows on through the processes of cutting, drilling, welding, fit-up and painting. These testing procedures provide confidence to the bridge builder and engineers who specify steel.
Speed of construction – The prefabrication of components means that construction time on site in hostile environments is minimized which results into economic and safety benefits. The speed of steel bridge construction reduces the durations of rail possessions and road closures, which minimizes disruption to the public using those networks. The light-weight nature of steel permits the erection of large components, and in special circumstances complete bridges may be installed overnight.
Versatility – Steelwork can be constructed by a wide range of methods and sequences. Installation may be by cranes, launching, slide-in techniques or transporters. Steel provides the erection contractor flexibility in terms of erection sequence and construction programme. Girders can be erected either singly or in pairs, depending on plant constraints. Components can be sized to suit access restrictions at the site, and once erected the steel girders provide a platform for subsequent operations. Steel also has broad architectural possibilities. The high surface quality of steel creates clean sharp lines and allows attention to detail. Modern fabrication methods facilitate curvature in both plan and elevation. The painting of steelwork introduces colour and contrast, whilst repainting can change or refresh the appearance of the bridge.
Modification, demolition and repair – Steel bridges are adaptable and can readily be altered for a change in use. They can be widened to accommodate extra lanes of traffic, and strengthened to carry heavier traffic loads. When the bridge is no longer required, the steel girders can easily be cut into manageable sizes and recycled, which is a benefit in terms of sustainability. Steel bridges can readily be repaired after accidental damage. In case the bridge is damaged, the affected areas can be cut out and new sections welded in. Alternatively, girders can be repaired by heat straightening. Heat straightening is by a heat treatment technique, based on the theory of restrained expansion. It is an economic and less disruptive solution in case a deformed bridge girder is to be straightened.
Recycling – Steel is a sustainable material. Steel is the most recycled construction material and choosing it for bridges represent a sustainable management of natural resources. When a steel bridge reaches the end of its useful life, the girders can be cut into manageable sizes to facilitate demolition, and returned to steel plants for recycling. Some 99 % of structural steel either finds its way back into the steelmaking process where it is used to create new steel products or is reused. There is no degradation in the performance of recycled steel. Alternatively, component parts of steel bridges can be reused in other steel structures.
Durability –Steel bridges now have a proven life span extending to well over 100 years. Steel has a predictable life, as the structural elements are visible and accessible. Any signs of deterioration are readily apparent, without the need for extensive investigations. Corrosion is a surface effect, which rarely compromises the structural integrity of a bridge, and any problems may be swiftly addressed by repainting the affected areas. In addition, the latest coatings are anticipated to last well beyond 30 years before requiring major maintenance.
