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Where can I find information on the loading capacity of particular precast units in a mature structure?
In the past (particularly in the 1950s and 1960s) a wide range of precast beams and slabs were manufactured for use in buildings, either to form a floor directly or as the main components of beam and block floors. Cross-sectional shapes and dimensions varied considerably. Individual manufacturers would quote safe working loads for various spans, with or without a structural topping, in accordance with the appropriate design codes and regulations in force at the time.
Information on the properties of many of the systems available in 1965 was brought together in Prefabricated floors for use in steel framed buildings, which was prepared by the British Constructional Steelwork Association; a copy is held by the Society along with other achieve material. It should be noted that Imperial units (pounds, feet and inches) were generally in use at the time. Nowadays precast units are standardised and information on properties can be obtained from British Precast. Alternatively, if the amount and position of the reinforcing steel is known, the capacity of the unit may be calculated using the standard approaches given in text books, bearing in mind that the strength of the steel will be in accordance with the design codes in use at the time and will be significantly less that available today.
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Acknowledgement: The Concrete Society
Other references:British Constructional Steelwork Association, Publication M2, “Prefabricated floors for use in steel framed buildings“, 1965