Currently, the strength of common used concrete is 20一40 n/mm. It is not difficult to produce the concrete of 80一100 N／mm if necessary. In order to lighten self-weight, concrete with light weight but high strength gets big development.
Due to the continuous improvement of material strength, the application scope reinforced concrete and prestressed concrete is expanding. In recent 30 years, reinforced concrete and prestressed concrete have achieved remarkable development in long-span structure and high-rise building structure. For instance, Germany builds a roof beam of hangar with scope of 90m by adopting prestressed lightweight concrete; the scope of bridge in Japan reaches 239 m.
During this period, design theory also has new development. Since the 1970s, structural reliability theory has gradually stepped into the stage of engineering practical on the basis of mathematical statistics, which makes the limit design method more improved and scientific. In the meantime, structure calculation theory of reinforced concrete gets great development and is widely used in the designs of plate, continuous beam and frame.
In the late 1960s, with the deep research on concrete deformation property and the application of electronic computer, the unique finite method is used in the situation analysis of reinforced concrete and develops rapidly later. By constantly being improved, the new branch “modern reinforced concrete mechanics” is gradually formed. The electronic computer, finite element theory and modern test technology are used in reinforced concrete theory and experimental study, so its calculation theory and design method are becoming perfect and toward a higher stage.