Fire Safety Science Digital Archive

A systematic programme, undertaken co-operatively by the Building Research Station and the Joint Fire Research Organization, was carried out on linearly scaled beams of selected types of "full scale" beams to establish the factors which must be taken into account in the design of prestressed concrete beams with post-tensioned steel to give fire resistances up to 4 hours. Limitations of size imposed by the furnace anil equipment at the Fire Research Station made beams of 10 ft. span the largest which could be tested, and these are referred to as the 1/2-scale units in the series. Other beams of 3/8- and 1/4-scale were included for the purpose of discovering whether a relationship existed between fire resistance and scale which would enable extrapolation to full size. Fire resistance was measured by the test specified for beams in B.S.476: 1932. The results of the tests on the types of beams designated A, B and C, when plotted as fire resistance against scale, gave very nearly straight lines for types A and C beams under conditions of simple end support and a loading equivalent to the assumed dead load + 1 1/2 times the live load (1). Since extrapolation to full size represented an extension equal to 200 per cent of the range of data its validity was extremely doubtful and means were therefore sought to obtain points on the graph closer to full scale. Only one floor furnace exists which is larger than the Elstree furnace and which can give the heating conditions defined in B.S.476. This furnace is at the U.S. National Bureau of Standards and enquiry brought a generous offer of co-operation to carry out tests in accordance with British requirements on beams up to 4/5-scale, a total of six tests being agreed.