The vast majority of modern bridges, as well as other constructions’ types, use the steel-concrete as a main material. It is relatively cheap, easily shaped, durable, and reliable. Steel is used as a skeleton of the construction, providing the strength and robustness. Concrete is an ideal filler with enough fluidity during the construction process. It solidifies within a short period and assumes the extreme hardness afterwards. This material is not exactly new, as Romans were already composing concrete with lime as a binder (Troyano, 2003). This paper presents a brief analysis of both advantages and drawbacks of the steel-concrete as bridges’ construction material.
Steel-concrete as a bridges’ composite material
There are numerous uses of the steel-concrete in constructions. According to Collings (2005), steel-concrete composite structures usually take a simple beam and slab form. Additionally, steel-concrete can be used for a considerable range of structures: “from foundations, substructures and superstructures through a range of forms from beams, columns, towers and arches, and also for a diverse range of bridge structures from tunnels, viaducts, elegant footbridges and major cable-stayed bridges” (Collings, 2005). The material is uncommonly universal and can satisfy most of the construction needs.
There are two simple components that undergo many transformations in order to take the final form of steel-concrete. Steel is one of the numerous iron’s forms, obtained from the iron ore and processed through the number of furnace operations. In order to achieve the construction quality, the level of carbon and impurities is thoroughly controlled. Concrete is an artificial stone, “composed of the gravel and sand mixed with a hydraulic conglomerate, cement, which hardens when mixed with water” (Troyano, 2003, p. 184).
Steel is a very strong material, in both tension and compression. Steel constructions can be assembled reasonably quickly, regardless of the environmental conditions. However, steel is much more expensive than other materials and highly liable to rust. Concrete, on the other hand, is cheap and strong, but extremely brittle. The combination of those steel-concrete features requires both the thorough design and bridges’ constructions maintenance. Otherwise, consequences can be catastrophic. “Collapses of prestressed concrete structures due to hydrogen embrittlement... of structure... built in the 1960s and 1970s have occurred even recently and generally without warning. The collapses occurred after service lives varying from a few months to 30 years (Pedeferri & Polder, 2004, p. 161). Reasons for such collapses can be multiple, but most often the explanations are quite simple: “these anomalies are essentially related to poor structural detailing, unsuitable concrete mixing, and negligent concreting operations” (Branco & De Brito, 2004 p.95). Thus, reliability of steel-concrete bridges can be achieved only by the comprehensive design and construction followed by the thorough maintenance.
There are no doubts that the steel-concrete will keep its leading position among other materials in bridge constructions. In order to achieve an increased robustness, traditional forms of the material are replaced by the reinforced steel-concrete. The number of new practices, the prestressing in particular, is applied to steel-concrete composite sections to control cracking or to increase the stress range of the structure (Ryall et.al, p. 444). Thus, further development of the steel-concrete composite material offers numerous benefits to the bridge construction industry.