column reinforcement (bundled)
column reinforcement (bundled)
(OP)
good day!
i recently started working in structural designing. i have little actual experience so there are a few things that i am unsure of.
right now i am designing a 2-storey residential building. due to the architectural requirement, my columns are limited to 200mm width. however, some are unable to resist moment unless i place more bars on the base. but if i put more, it wouldnt comply with the minimum spacing required. i would like to ask if it would be okay to place 3 pcs bundled 16mm rebars on the each corner? these columns are placed in the middle and 450mm length. i have 2 which wouldnt pass the required capacity. and by doing this would result to total of 14 bars. is it okay?
thank you very much
i recently started working in structural designing. i have little actual experience so there are a few things that i am unsure of.
right now i am designing a 2-storey residential building. due to the architectural requirement, my columns are limited to 200mm width. however, some are unable to resist moment unless i place more bars on the base. but if i put more, it wouldnt comply with the minimum spacing required. i would like to ask if it would be okay to place 3 pcs bundled 16mm rebars on the each corner? these columns are placed in the middle and 450mm length. i have 2 which wouldnt pass the required capacity. and by doing this would result to total of 14 bars. is it okay?
thank you very much






RE: column reinforcement (bundled)
BA
RE: column reinforcement (bundled)
RE: column reinforcement (bundled)
It is possible to use bundled bars but you should pay strict attention to code requirements regarding development of bundled bars at a tension splice.
BA
RE: column reinforcement (bundled)
Are you sure that your column is large/strong enough? Keep in mind that 8" column capacities need to be reduced in most jurisdictions in order to maintain fire ratings.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: column reinforcement (bundled)
For Canadian code assuming not exposed the clear cover is either 20mm or the equivalent bar diameter of your bundle, or your max aggregate size (typically 20mm). For 3-16m bars an equivalent diameter is 28mm.
Assuming 10m ties then your actual clear space between bars is 200-2*28-2*10-2*28 = 68mm. Your min spacing is the max of 30mm or 1.4*equivalent bar diameter = 40mm. Therefore you are technically ok but that's going to seem like a ton of reinforcing in a small area.
Although it's only slightly less reinforcing to go with 25m bars than the 3-16m bars, it looks cleaner and is easier to review. And as noted by BA when this vertical reinforcing is spliced it is much nicer to only have 2 bars at each splice instead of 6. And correct me if I'm wrong, but isn't the splice lengths for bundled steel increased?
RE: column reinforcement (bundled)
and also another thing. a few of my beams require having 8-9 rebars. and are 200x450mm in dimensions. i am thinking that this is a bit too big. but i cant find any other way. i really wanted to increase my rebar diameter but was advised to use only 16. im not sure if it was as per clients request or by the architect
anyway thank you. i'll check on that splicing requirements
RE: column reinforcement (bundled)
ah. but i would only need the bundled bars on the ground floor. on the 2nd floor, 175x300 would be adequate
RE: column reinforcement (bundled)
I don't know if you've done this yet, but you should draw this cross-section out to scale at the rebar splice location to get an idea of what this will look like. Remember, someone eventually has to take your drawing and make it real.
What are your floor to floor heights?
RE: column reinforcement (bundled)
My sense here is that you may be pushing too hard to achieve small member sizes. For a two story column, it's usually cheaper to keep the column size the same on both floors so that the formwork can be reused. This document is an excellent resource for practical proportioning of concrete things: Link. It's even got a table for the maximum number of bars in one layer of a beam.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: column reinforcement (bundled)
Do not reduce the second floor columns to 175x300; stay with the same column size through two floors. There was a time not too long ago in Canada where 10" (250 mm) was the minimum column dimension permitted. That was dropped for some reason (probably to satisfy architects) but I would never reduce the minimum column dimension below 200 mm.
BA
RE: column reinforcement (bundled)