Table 17. Strength of steel wires, 



Wires 



Ultimate Strength, 

 (MPa) 



Wires of varying diameters and make 

 Strands of 7 uncoated small wires 

 Strands of 19 or more galvanized wires 

 Strands of 19 or more uncoated wires 

 Bars 



1 379 - 2 275 

 1 586 - 1 862 

 1 379 - 1 517 

 1 517 - 1 655 

 965 - 1 172 



Table 18. Approximate yield point and proportional limit, 





Yield point 



Proportional 





at 0.2-pct set 



limit 





(f;) 1 



(f;) 1 



Wires as drawn 



0.75 



0.35 



prestretched 



0.85 



0.55 



time -temperature treated 



0.87 



0.70 



galvanized 



0.85 



0.55 



Strands, pretensioning as drawn 



0.85 



0.35 



stress -relieved 



0.90 



0.75 



Strands, posttensioning prestretched 



0.85 



0.55 



Bars 



0.90 



0.60 



Ultimate strength 



Table 19. Secant modulus at proportional limit, 





Secant modulus 





(MPa) 



Wires 



186 159 - 206 843 



Strands for pretensioning and 





stress -relieved 



186 159 - 199 948 



Strands for posttensioning and 





prestretched 



165 474 - 179 264 



Bars 



172 369 - 193 053 



cannot be easily measured for strands; only the wires making up the strands 

 are measured for ductility. 



(3) Steel, Creep Characteristics . One of the important character- 

 istics required of prestressing steel is minimum creep under maximum 

 stress. Creep in steel is the loss of its stress when it is prestressed 

 and maintained at a constant strain for a period of time. It can also be 

 measured by the amount of lengthening when maintained under a constant 



116 



