Return to index: [Subject] [Thread] [Date] [Author]

Re: Reinforcement of massive pedestals

[Subject Prev][Subject Next][Thread Prev][Thread Next]
     If you look at ACI 318, section 15.8.2.1, it states that a steel ratio 
     of at least 0.005 times the gross area should be used for pedestals, 
     which this is.  UBC has the same wording.  Other code provisions lead 
     us to the conclusion that this is a firm requirement in zones 3 &4.  
     This works out to 74 - #11 bars vertically.  I think most people would 
     agree that this is excessive, except for rebar suppliers.  :-)
     
     What I would propose, is that you look at a "shell" of concrete that 
     will take all the design loads.  Maybe the outer 6" would do it. 
     Consider this your structural section and use the 0.005 ratio of steel 
     in this area.  Leave the remainder of the concrete in the middle as 
     plain concrete. It is just a filler.   
     
     We have been using much less than the 0.005 ratio for years on our 
     massive pedestals, with no structural problems or building official 
     questions that I know of.
     
     Ed Haninger
     Fluor Daniel

_____________________________ Reply Separator _________________________________
Subject: Reinforcement of massive pedestals 
Author:  "Vyacheslav Gordin" <scgordin(--nospam--at)hotmail.com> at fdinet
Date:    5/26/99 8:11 AM


I need to design a footing for a large vertical vessel in a highly 
seismically-active area.  Soils are good, though, and allow the footing pad 
to be 20'x20'x36." The loads (including considerable weight and seismic 
shear and uplift/pullout) are applied through three baseplates @120 degrees 
connected to a 12'x12'x4'-6" pedestal centered on the footing. The pedestal 
height is dictated by the technological process.
     
Within the contact areas I installed rebar cages similarly to short  tied 
"columns."  I also tied the tops of the three "columns" together with rebars 
to resist considerable shear.
     
Unsure about the reinforcement of the rest of the pedestal. Both the ACI 
0.0018 and Caltrance's 0.0025 reinforcement ratios appear to be excessive.
     
Any thoughts about how to reinforce the pedestal away from the areas of 
contact (apparenly, minimum reinforcement)?
     
Steve Gordin, S.E.
Irvine CA