RCC Column Minimum Reinforcement ???

[TekEngr]

I am designing a RCC column and under the loading (moment +axial) 250mmx250mm size of column is enough but due to the anchor bolt concrete cover requirements I need to increase the column size 750mmx750mm so my question is that I need to place the minimum area of reinforcement in the column according to the 250mmx250mm or 750mmx750mm.
If I follow 750x750 the minimum area of steel bar (1% x Ag) will be too much, so any one can provide the better solution in this regard???
thanks in advance

 

[hokie66]

Some codes allow using 0.5 percent in cases such as you described.

 

[MacGruber22]

Why is 1% too much? Contractor complaining?

hokie - do you really use .5%? All the OG's trained us to stick with 1%. They only let us use .5% for lightly loaded pedestals.

"It is imperative Cunth doesn't get his hands on those codes."

 

[bridgebuster]

@shahg123 - I've done something similar on a road reconstruction project where I was designing drilled shafts for to support a bunch of miscellaneous structures - bus shelters, water features, sculptures, light poles, low-rise seating walls, etc. First, I would check my design using 1% rebar with the minimum diameter required for strength then design the larger section with that rebar and compare my results. Typically I would up the rebar to 0.%5 of the larger section; in one case I was permitted to use .25%. However, I didn't have any situations where the ratio of diameters was 3 to 1.

 

[hokie66]

MacGruber,
Yes. Not sure of the OP's code, but some do allow 0.5 percent of the oversized section.

 

[wannabeSE]

In ACI 318-11, the 0.5% percent for oversized sections can be achieved with §10.8.4

For a compression member with a cross section larger than required by considerations of loading, it shall be permitted to base the minimum reinforcement and strength on a reduced effective area Ag not less than one-half the total area . . .

 

[MacGruber22]

Nice. That is good to know.

"It is imperative Cunth doesn't get his hands on those codes."

 

[dik]

Can you revisit the column conditions and see if you can reduce the column size a bit... going from a 250 column to a 750 column seems excessive.

Dik

 

[msquared48]

Why are there any anchor bolts at all for a concrete column? Is this a precast element?

Mike McCann, PE, SE (WA)