Summary
Bond stresses between concrete and steel may perform the function of transferring prestress from the prestressing tendon to the concrete, or may arise due to shear or due to flexural cracks. The last two are difficult to separate quantitatively, and may be referred to together as flexural bond stresses.
The paper discusses the results of investigations into bond carried out at the Portland Cement Association Laboratories near Chicago. There were two major series of tests; one series was concerned with the prestress transfer bond, and the other with the flexural bond stresses.
The first series of tests was performed on prisms 2 × 2 in. in cross-section and 72 or 96 in. long, with a single pretensioned wire located at the longitudinal axis. Both the size of wire and its surface condition were varied. Strains of the wires and the concrete were measured by electric resistance strain gauges.
The flexural bond stresses were measured on centre-loaded 6 × 10 in. beams, the major variables being the size of wire, its surface condition and the degree of prestress.
The results of the tests are given in graphical form, and the relationship between the bond strength and the ultimate strength of pre-tensioned concrete is discussed.
