huangyhg

minimum 1% reinforcement for foundation column?
i am designing a foundation concrete column about 6' deep below grade for frostline reason, it will support a masonry column which will have very little load (for some art exhibition purpose). do i still need to let the concrete foundation column meet 1% minimum longitudinal reinforcement requirement?
thank a lot?
you can go down to 0.5% if you can show that the reduced section with the correct amount of steel can support the loads. you can't go below 0.5%, though. check the section with a 50% reduction in area and 1% steel (on the reduced section), if that works then you can use 0.5% on the full section.
structuraleit, thanks.
more questions: for its supported masonry column, the requirement minimum longitudinal reinforcement is only 0.25% based on bcrms, so how long should this 0.5% reinforcement in concrete foundation column extend into the supported masonry column?, if it needs to be extend a development length, then i can just use this oncrete foundation column longitudinal rebar as the masonry column longitudinal reinforcement, because the masonry column it self is only about 7' tall.
thanks.
@streit,
is the 0.5% reference in the code? i have looked for it myself previously. i was under the assumption that there was no lower limit, as long as you could prove that a column of a given cross section and reinforcing could take the load. anything above and beyond that was non-structural.
aci 318-05, section 10.8.4 talks about it. it doesn't specifically 0.5% reinforcement, but does word the section such that it is pretty clear that is the intent. it says that you can base the minimum reinforcement (i.e. 1%) on a reduced effective area, ag, not less than 1/2 the total area. 1% of 0.5ag is 0.5% of ag.
many thanks.
i don't use your design code, but if it can be designed as plain concrete there should be no lower limit on the reinforcement %.
can it be treated as plain concrete with continuous lateral support? the h/d ratio less than 3 or whatever your code allows? if so, then you may be able to put less than .5% reinforcing steel. the effect of reinforcing steel is neglected. i often use a single 15m (#5) bar in 16" dia piles.
dik
being below grade, is this column built integrally with a foundation wall? if so, per aci 318-02 (i don't have my '05 handy) 10.8.2, you can take your effective cross section as being 1-1/2" outside the tie reinforcement rather than using the full outer limits of the concrete.
it is best to use a minimum of 0.5% vertical reinforcement to resist potential frost forces. with frost adhesion on the sides of the pile or pedestal, you can develop significant tension. since you are assuming six feet for frost penetration, i assume you are in a cold region.
the distance the bars are carried into the masonry column can be nominal because there can be no tension in the masonry.
best regards,
ba

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