Mechanical properties and bonding strength of twisted wire strands at elevated temperatures.

This paper experimentally investigates the mechanical properties of 1860 MPa twisted wire strands and the load capacity of hot casting sockets at elevated temperatures. The stress-strain curves of the strands at the temperature in 20 °C to 600 °C range are reported, and the elastic modulus, yield strength, ultimate strength, ultimate strain and rupture strain are obtained and compared to EC2 and other existing studies. The failure mode, load capacity, failure displacement and critical temperature of the sockets at the temperature in 20 °C to 440 °C range are acquired. The test results show that 1860 MPa twisted wire strands have significantly improved ductility in necking stage after 200 °C, which is underestimated in EC2. The strands with hot casting sockets rupture before 180 °C, and are pulled out from the sockets after 230.5 °C. The load capacity drops after 150 °C, and the failure displacement dropped after 300 °C, indicating significant influence of the sockets on the fire resistance. Based on thick-walled cylinder model, calculation methods are proposed to determine the bonding strength and load capacity of the strand with hot casting sockets. The prediction of the failure modes and load capacity agrees well with test results. The parametrical analysis by the calculation methods shows that the load capacity of the strands with sockets increases as the embedded length or internal diameter of socket increases, or the diameter of the strands decreases in a limited range. For fire protection, it is recommended to keep the socket temperature under the critical temperature in accordance with load ratio. • Mechanical properties of 1860 MPa twisted wire strands at elevated temperatures are presented. • A novel stress-strain model of high-strength twisted wire strands is proposed. • The load capacity of hot casting sockets at elevated temperatures is presented. • The critical temperature of hot casting socket as a function of load ratio is proposed. • An analytical method is proposed to determine the bonding strength of the strand with hot casting sockets. [ABSTRACT FROM AUTHOR]