8 rebar equivalant to how many 4s

huangyhg

#8 rebar equivalant to how many #4's?
i am told that to match our local code of one #8 bar top and bottom of footing walls one has to use 4 x #4 bars top and bottom. [redwood shores ca, reclaimed marshland]we only have 2x #4's top and bottom with much sagging and cracked wall problems. could somebody please verify this for me? thanks.
brem,
this sounds like pretty basic engineering and mathematics.
a #4 bar is approximately half the diameter of a #8 bar. it is therefore approximately 1/4 the area of a #8 bar.
based on this it is fairly obvious that 4 #4 would be needed to give the same area of reinforcement as 1 #8 bar.
as of 1 #4 bar, .2
as of 1 #8 bar. .79
therefore 4 #4s = 1 #8
a slight technicality but assuming the same minimum cover to the rebar 4 no. #4 bars would give you greater moment capacity as the lever arm would be greater.
stephena