huangyhg

another thread on lap splice length in cmu
let me begin by saying that i still specify 48 bar diameters for lap splices in cmu (yes, i know the ibc requires longer lap splice lengths for bars > #5).
anyway, the contractor on one of my projects called to say that he is using #6 x 7'-0" long bar lifts (he said you can't lift the blocks any higher than 7'). he builds 4'-0" of cmu, then grouts the cmu, then installs the next bar lift, lapping it 3'-0" with the bar below. what ends up happening, starting at the bottom of the wall, is you get a single bar for 4', two lapped bars for 3', a single bar for 1', two lapped bars for 3', a single bar for 1', etc. the contractor thought this was strange, but i told him it is correct.
now, just for fun, i calculated the more correct lap splice length for a #6 bar, using ibc, and came up with 48". if i had used this lap splice length, almost the whole height of the wall would be lap splices!!!
does anyone else think this is ridiculous???
daveatkins
find a job or post a job opening
daveatkins,
i had a similar discussion with a mason yesterday. he also said that 7' was the maximum lifting height which seems fairly obvious and reasonable.
as for the situation you describe above, i usually avoid it by using mechanical splices for two reasons. first, i agree that the required lengths are not always practical and can lead to a waste of rebar. many engineers dismiss mechanical splices because of a perceived increase in cost compared to lap splices. but just look at how much additional rebar you are using. at some point, mechanical splices become less expensive
the second reason i like mechanical splices is you get a higher quality splice. too many times i have seen a mason carelessly pound rebar into grout for a splice. maybe it ends up in the correct position, maybe not. even if the mason is careful to place the splice bar, it can become displaced when the cells are filled with grout.
for your projects that must adhere to the ibc, how do you justify the shorter lap length?
motorcity,
good point about mechanical splices. i will begin to think about using them.
i really can't justify, per code, using lap splice lengths based on the old asce/aci 530.
daveatkins
i prefer mechanical splices not just for cmu but for concrete as well. most contractors don't like them because they are unfamiliar with them and think they will cost more. however, i was adamant about using them on one project several years ago even tho the contractor fought hard not to use them. after about half way thru the project, the contractor told me he was glad i insisted.
daveatkins:
we more than agree that the masonry lap splices are ridiculus for #6's and above. we try to avoid #6's (or bigger) if we can just to avoid the splice length problem.
i guess i am wondering why aci changed. were masonry walls falling down becasue of improper splices? or is this a solution in search of a problem?
mechanical splices are more expensive. how do you justify the cost? what specific splice do you specify for masonry construction? for concrete construction?
i have specified them to help with the installation of reinforcing.

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