Mechanical properties of 1670 MPa parallel wire strands at elevated temperatures

High-strength prestressing steel cables serve as main load-bearing components for cable-supported structures, and exposure to high temperatures may result in their prestress loss, leading to failure and even collapse of such structures. This paper experimentally investigates the mechanical properties of 7-wire parallel wire strands with a tensile strength of 1670 MPa. The thermal elongation tests and steady-state tensile tests are conducted on 39 strand specimens at different target temperatures. The complete stress-strain curves including rupture strain are obtained by using charge-coupled device camera systems. The temperature-dependent thermal strain, Young's modulus, proportional limit, effective yield strength, ultimate strength, ultimate strain and rupture strain are recorded and compared to EC2, ACI 216 and other existing test data. The test results show that parallel wire strands experience obvious strain hardening before 300 °C, and their ductility is significantly improved after 400 °C. It is reasonable to define effective yield strength as the stress at a total strain of 2%. It is found that the existing design code and test data on single wires and twisted strands cannot be directly used for parallel strands. The EC2 provides conservative predictions for ultimate strain, proportional limit, yield strength of parallel wire strands, but fails to capture the full range of stress-strain curves of parallel strands due to ignoring strain hardening effect and underestimating rupture strain. The ACI 216 provides unconservative predictions for reduction factors of ultimate strength of parallel strands. Parallel wire strands have higher thermal strain, higher ultimate strain, higher rupture strain, lower reduction factor of proportional limit than single wires and twisted wire strands. Finally, calculation methods are proposed to mathematically determine the thermal strain, stress-strain curve and reduction factors of these properties, and dividing the stress-strain relationship into elastic, plastic, necking and rupture stage. © 2020 Elsevier Ltd