DISCUSSION. THE FIRE-RESISTANCE OF PRESTRESSED CONCRETE BEAMS.

Abstract

face instead of three, as in a beam. 56. He had been rather disadpointed to see, in 5 28, which summed up the discussion on model testing, that the early hopes in this respect had not been justified, There would obviously be considerable difEculties with prestressed concrete work, since it dealt with structures of very long span, if it was always essential to insist on having full-sized members tested. Some of the results showed that the least that could be said was that the model testing had been extremely encouraging and that the reasons for the various differences which occurred with the larger members needed further exploration. 57. What were the Authors' views on scaling down the concrete aggregate? In some beams +-in. aggregate had been used but in most of them s i n. He thought it was possible that if further attention had been given to the scaling down of the aggregate there might have been better correlation between scale and fire-resistance. 58. The results seemed to indicate a further restriction to the development of continuous structures in prestressed concrete. There had been considerable diiliculties in regard to structural design as compared with reinforced concrete, and it was difficult in some cases to see the advantages of continuity. Any plans for a further investigation into the fireresistance of continuous structures would be of considerable interest. He believed that the new furnace at Boreham Wood now gave those facilities. 59. In $50, referring to aggregates, the Authors seemed to indicate that there would be no advantage with other aggregates. All the tests had, of course, been carried out with gravel aggregate, which was possibly the worst type of aggregate for Wresistance. With other forms of construction, particularly reinforced concrete, there was some advantage in fire-resistance clauses for the use of limestone, and he thought that there might also be some advantages with blast-furnace slag aggregate which in its manu-factwe had been subjected to considerable heat. Why did the Authors think that there would be no advantage with other aggregates? 28 t Proc. Instn civ. Engrs, vol. 17, pp. 15-38 (Sept. 1960). Downloaded by [] on [15/02/23].