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end returns & footing design
are end returns only necessary for temp/shrink reinforcement in foundation design? if you have full development length for your flexural steel from the column face, there is no need to hook the bars right? also, can you use the (as req'd/as provided) reduction factor on the development length for flexural steel?
thanks in advance,
lee

by "end returns", if you mean hooks, then you don't typically need them at all in a footing.
anytime you can develop a bar on both sides of the critical plane of failure, then hooks are not required.
if full yield stress does not need to be developed for some reason, you can use the reduction factor.
daveatkins
with all that daveatkins noted i would only provide that in moderate to high seismic categories it is wise to use footing bars with 180 degree hooks.
regards,
qshake
eng-tips forums:real solutions for real problems really quick.
thanks, qshake. i am not in a seismic area.
daveatkins
i guess i'm having trouble with the wording of aci 318-02 7.12.2.3
"at all sections where required, reinforcement for shrinkage and temperature stresses shall develop the specified yield strength fy in tension in accordance with chapter 12."
where are the required sections? do i need to have the 180 degree hooks in order to develop fy to the ends of the pad?
highest stresses due to shrinkage and temperature do not tend to be near the free ends of a concrete pad where expansion or contraction can easily take place. the higher stresses tend to be nearer the middle of the pad or slab where you have much more restraining effects due to the size and weight of the rest of the surrounding slab. typically the reinforcement near the middle has enough concrete along its length to be developed. since reinforcement then is not really needed near the edge, say in the two or three feet of pad nearest the egde, you don't really need to develop the bar just for t&s. that's based on my engineering judgment and not hard numbers of calculations, but it seems to make sense to me.
if you have external loads requiring the development of a bar near the end, that is another matter.
perfect! thanks gents!

2009-09-08, 10:19 PM	#1
huangyhg 超级版主注册日期: 04-03 帖子: 18592 精华: 36 现金: 249466 标准币资产: 1080358888 标准币	end returns footing design end returns & footing design are end returns only necessary for temp/shrink reinforcement in foundation design? if you have full development length for your flexural steel from the column face, there is no need to hook the bars right? also, can you use the (as req'd/as provided) reduction factor on the development length for flexural steel? thanks in advance, lee by "end returns", if you mean hooks, then you don't typically need them at all in a footing. anytime you can develop a bar on both sides of the critical plane of failure, then hooks are not required. if full yield stress does not need to be developed for some reason, you can use the reduction factor. daveatkins with all that daveatkins noted i would only provide that in moderate to high seismic categories it is wise to use footing bars with 180 degree hooks. regards, qshake eng-tips forums:real solutions for real problems really quick. thanks, qshake. i am not in a seismic area. daveatkins i guess i'm having trouble with the wording of aci 318-02 7.12.2.3 "at all sections where required, reinforcement for shrinkage and temperature stresses shall develop the specified yield strength fy in tension in accordance with chapter 12." where are the required sections? do i need to have the 180 degree hooks in order to develop fy to the ends of the pad? highest stresses due to shrinkage and temperature do not tend to be near the free ends of a concrete pad where expansion or contraction can easily take place. the higher stresses tend to be nearer the middle of the pad or slab where you have much more restraining effects due to the size and weight of the rest of the surrounding slab. typically the reinforcement near the middle has enough concrete along its length to be developed. since reinforcement then is not really needed near the edge, say in the two or three feet of pad nearest the egde, you don't really need to develop the bar just for t&s. that's based on my engineering judgment and not hard numbers of calculations, but it seems to make sense to me. if you have external loads requiring the development of a bar near the end, that is another matter. perfect! thanks gents! __________________ 借用达朗贝尔的名言：前进吧，你会得到信心! [url="http://www.dimcax.com"]几何尺寸与公差标准[/url]