Weight of Precast Unit.

[Erasa]

Hi Engineers,
In calculating the weight of a precast unit is it the volume of concrete by the reinforced density of concrete only or is the volume of concrete by the the reinforced density of concrete plus the weight of rebar. I need clarification please.

 

[JedClampett]

I've never seen concrete weights refined any more than the volume times 150 lb. per cubic foot. But I guess it could be made much more complicated for a small increase in accuracy.

 

[Lomarandil]

For a typical concrete mix and typical reinforcement, 150pcf is pretty representative. Most concrete mixes really come in around 140-145pcf without the reinforcement.

I've occasionally used 160pcf for heavily reinforced sections, and I've once accounted for the actual weight and ratio of reinforcement (when the CG of a bridge section with concrete deck and steel truss members was critical to the operation).

 

[ColinPearson]

Usually I use 150pcf like these other folks said. That said, to directly answer your question, most of the time you are good just using that ballpark figure. W_reinf_concrete_unit = Vconc * 150pcf
You could get the density of the mix and multiply it by the volume of concrete MINUS all the volume of reinforcement, stirrups, etc. Then add to that the volume of steel times about 490pcf to get a total, but you'll find that it it usually isn't worth your trouble.

 

[Ron]

Agree with above. As an example, 1 cubic foot of concrete at 145 pcf + 1% min reinforcing yields a unit weight of about 150 pcf. Use 150 and the steel is included unless heavily reinforced as Lomarandil noted.