Strands instead of Rebars

[JohnRwals]

Hello!

ACI 318-14, 12.5.1.5 says non-prestressing STRANDS can be used for diaphragm reinforcement.
Can we use non-prestressing strands instead of reinforcing bars for regular beams or slabs?
Many precasters dispose of tons of left over strands after producing girders and walls.

-JRW

 

[BridgeSmith]

I suppose you could. Does ACI have provisions for how to calculate development lengths and lap lengths for strand? AASHTO doesn't seem to...

Rod Smith, P.E., The artist formerly known as HotRod10

 

[centondollar]

It would be more expensive and not of much use. Standardized collections of strands (tendons) are typically smaller in diameter than rebar, which nullifies the increased yield strength. Furthermore, tendons are not ribbed and will therefore not bond as effectively to concrete as ribbed rebar: longer development and lap length would be required, and the typical equations (based on assumption of ribbed rebar) would not apply.

The ultimate strain of strands is also much lower than ultimate strain of ordinary ribbed rebar, which leads to reduced ductility.

The answer is something along the lines of "sure, you can, but it is not useful", and you can observe this by looking at what reinforcement type the "high-performance" reinforced concrete industries (high-rise buildings, nuclear power plants, containment buildings, long-span bridges, defense applications etc.) use when prestressing is not applied.

 

[rapt]

I assume they are not debonded.

You would probably have to provide anchorages as development length from 0 stress is pretty large and diaphragm reinforcement needs to transfer the forces to the nodes. You could use the pre-tensioned strand development rules with starting stress of 0.

You could probably not justify using the full strand capacity.

 

[Ingenuity]

ACI 318-14, 12.5.1.5 says non-prestressing STRANDS can be used for diaphragm reinforcement.

It does, however, limit the value of the steel stress used to be the lesser of 60 ksi, or the specified yield strength. 60 ksi will govern assuming you are using high-strength prestressing steel.

For beams and slabs utilizing high-strength prestressing steel that is NOT prestressed (i.e. pre or post-tensioned) under flexure, you would never be able to utilize the high-strength tensile properties without excessive concrete cracking and significant curvature, if it did not debond sooner. ACI 318-14 limits the maximum yield to 80 ksi for flexural design calculations, and less for seismic systems.