Effect of compressive strength of concrete on transmission length of pre-tensioned concrete systems

This paper presents an experimental study on L t in pre-tensioned concrete (PTC) members made of four values of compressive strength of concrete. Also, it presents a comparison between the formulations of transmission length (L-t) given in various codes and other literature. A test specimen consisted of a concrete prism (100 x 100 x 2000) mm with a prestressed seven-wire strand (12.7 mm diameter) at the center. The values of average compressive strength for concrete at transfer (f(ci)) were 23, 28, 36, and 43 MPa. The challenges involved with the measurements of DEMEC readings, difference between the readings from surface-mounted discs and the inserts are discussed. The results indicate that L-t could decrease by 33% when the f(ci) increases from about 23 to 43 MPa. Based on this data, a new bi-linear formulation to determine the L-t as a function of f(ci) is proposed. Further, it is shown that higher estimates of L-t as per the available formulations, will lead to lower estimate of bursting tensile stress in concrete generated during transfer. Hence, a precise estimate of L-t as a function of the strength of concrete at transfer is expected to provide more rational design of transmission zone reinforcement.