Summary
The paper reports a series of tests of beams prestressed on a system, developed by Mr. Donovan Lee, which utilizes alloy steel bars with an ultimate tensile strength of about 70 tons per sq. in. in diameters up to 1 ⅛ in. The beams were constructed and tested at the Field Test Unit of the Ministry of Works, which has since become the Building Operations Research Unit of the D.S.I.R. Details are given of the five test beams of I- and U-shaped cross sections. Some Were assembled from precast elements and others were monolithic. The spans varied from 21 ft 6 in. to 46 ft 6 in. and the total prestressing force from 27·5 to 89·1 tons.
The method of loading, the sequence of the tests and the recording of deflexions and strains are described. Typical strain and deflexion curves are given, and the results are presented in tables showing loads at cracking and failure, deflexions at working loads and ultimate load factors.
Measurements on the steel were obtained in one of the beams, and data on the strain during prestressing, anchoring and loading are also given.
