Abstract

Relaxation is one of the main sources of time-dependent stress losses in prestressed concrete construction. In the present study, an experimental investigation of the stress relaxation of the prestressing steel used in construction of the Confederation Bridge is undertaken. Relaxation is measured by monitoring the reduction in stress level in an elastically strained specimen and maintained at a constant extension. Two testing methods are adopted for the experimental program, namely, the release method and the lateral deflection method. A special setup is built for each of the two testing methods. Six specimens are tested using the release testing method. Of these, two specimens are tested at each of the three initial stress levels: 60%, 70% and 80% of the ultimate strength of the steel. The lateral deflection testing method is conducted on two specimens at two initial stress levels of 60% and 70% of the ultimate strength of the steel. The experimental results of this research are compared with steel stress relaxation estimated by the PCI expression and the CEB-FIP Code equation. These comparisons show that the available expressions underestimate the magnitude of stress relaxation losses. Based on the results of this research, an alternative equation to estimate stress relaxation of steel is proposed.