axial tension for reinforced concrete column

huangyhg

axial tension for reinforced concrete column
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?
i've always used the following:
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   
req'd as    =     pu
                      -------
                      ?fy
i messed it up again....just to clarify the equation, here's a third try:
req'd as    =     pu
                      -------
                       φfy

thanks jae
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   
i would take the service limit as a limit on cracking.  it may be based on experience or research, but if a text has made it to the 11th edition, then the authors are probably pretty knowledgeable.  i wouldn't just discount their recommendation without a lot of thought.  
i would provide much more reinforcement than required just to limit cracking.
". . . to provide adequate safety, the force permitted in a tension   
something else to keep in mind is the anchor bolts.
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.
thanks everyone! all your comments are greatly appreciated.  with the reinforcing i will be calling out, my service load will be less than 1/2p.  so i do also meet this limit as the text book suggests.
jkw05-yes, i will be responsible for the anchor bolt length.  i will be verifying embedment, edge distance, etc.