Axial tension for reinforced concrete column
Axial tension for reinforced concrete column
(OP)
Situation where I have axial tension on a reinforced concrete column. I don't due alot of concrete design so please bear with me. Crack control isn't an issue as in like a water tank design. My 11th edition of Design of Concrete Structures equation 1.14 says P=fy*As, but the next proceeding line states "to provide adequate safety, the force permitted in a tension member under normal service loads should be of order of 1/2P". I don't understand the service load portion? Can't I just use my .9 phi factor and use my ultimate load in equation 1.14?






RE: Axial tension for reinforced concrete column
Req'd As = Pu
-------
φfy
where Pu is the factored axial tension force
fy is the yield of the rebar (usually 60 ksi)
This gives you the required strength check for the member as the steel takes everything and concrete takes nothing.
For serviceability I'm not sure what to say here as the natural tendency is for the reinforcing bars to stretch and the resulting cracks in the concrete would vary depending on the uniformity of the load application and the distribution of the reinforcing (i.e. you should have more, smaller bars instead of fewer, large bars).
RE: Axial tension for reinforced concrete column
-------
?fy
RE: Axial tension for reinforced concrete column
Req'd As = Pu
-------
φfy
RE: Axial tension for reinforced concrete column
I have a fairly large prefab metal building (225'x350'). I'm tying the bases of each column for each frame together to take out the horizontal thrust loads. My loads are great enough where I need actual grade beam/tension member to take out my tension. I'm going to use (8) #7. I'm going to bundle my bars in sets of two. I think with all my clear distances and so forth I will be able to use a 16"x16" grade beams. The bundled bars seem to work since I can wrap them at the anchor bolts of the columns.
Is it fair to say that I meet spacing and clear distance requirements for my rebar that I will be able to transfer my load sufficiently (i.e. have enough concrete to transfer the load) through my lap splices?
Another question I have..... This large grade beam can also see compression (not nearly the tensile load). The grade beam will have soil on 4 sides. The top side of the beam will unfortunetly have only 8" soil above it. Can I consider it to be fully braced. Obviously if I can't I will never get a column that long to work.
Sorry for the long post. Thanks for your help.
RE: Axial tension for reinforced concrete column
RE: Axial tension for reinforced concrete column
Tension members will almost definately crack if only the minimum required strength steel is added.
csd
RE: Axial tension for reinforced concrete column
I have the 9th edition, and this sentence is followed by:
"Because the concrete has cracked at loads considerably smaller than this, it does not contribute to the carrying capacity . . . It does serve, however, as a fire and corrosion proofing . . ."
So it would appear that the intention is to minimize crack sizes.
RE: Axial tension for reinforced concrete column
With uplift at the column base, consideration will have to be given to the anchor bolt embedment, and how that tension load is transferred to the rebar, verifying adequate edge distance at your piers, and consideration of possible conflicts between anchor bolt locations and vertical rebar and pier ties.
On the last metal building foundation I did, the metal building manufacturer would not specify the anchor bolt length, so you might want to tie down who is responsible for that.
RE: Axial tension for reinforced concrete column
RE: Axial tension for reinforced concrete column
RE: Axial tension for reinforced concrete column
RE: Axial tension for reinforced concrete column
RE: Axial tension for reinforced concrete column
RE: Axial tension for reinforced concrete column
RE: Axial tension for reinforced concrete column
RE: Axial tension for reinforced concrete column
if you are intrested in details! just ask.
regards
RE: Axial tension for reinforced concrete column