huangyhg

embedment in concrete
i am starting another thread hopping i will get some responses this time.
i have been searching for a good approach on the design of post embedment in concrete slab that varies in thickness from 4" to 7". aci 6.3 discuss this subject but it does not in any way describe a method of design. the post is subject to a lateral load of about 640lb on the top of the post due to wind and due to the fact that the post is a member of a glazed railing. as you know the minimum load that the railing should be designed for is 50 lb/ft along the top rail and 200 lb at any point along the rail. however, when the railing is glazed railing and is subject to high wind pressure the load increases. therefore, the embedment in concrete slab must be improved. how would you approach this problem?
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assuming decent quality soil:
1) thicken the slab around the post area
2) add cont. reinforcing bars around the posts in these thickened areas
3) place post in a concrete pier for the embedment length required beneath the slab
4) design the embedement length/diameter of pier according to ubc embedment formulas
i am not an expert. but, is it not easier to bolt the post ? or is it going to be more expensive.
i have designed many railings of this style utilizing a 3d frame analysis program. designing one post like a flag pole is asking for problems. the entire railing should be considered a unit. keep the posts 5'-0"+/- c/c. if there is a 4" high toe guard, use it in the anchoring design. post base plates with epcon anchor bolts work well with cosmetic covers of alum. or stainless stl.
with a high moment and little vertical load, you may end up with a very large footing if you don't use a pier. using a program to model this would be too time consuming to me.
for an application such as this (glazed or solid insert), the loadings on the post can be tremendous. if you have no opportunity to stabilize the top rail by attachment at the ends, then the post must be designed like a "flagpole". while you can get some capacity increase by using a unit or segment analysis, it will likely prove to be minor.
assuming you have this condition at other than a ground floor (elevated slabs), then the embedment condition becomes somewhat difficult. for high moment at the embedment, the tension component of the couple created in the concrete can be quite high and will require auxiliary reinforcement with a loop or hairpin bar wrapping each embedment area. this is necessary to prevent blowing off the edge of the concrete. due to the potential for reversals, this reinforcement should be top and bottom.
i don't have much better advice than you've already had but i recently looked at handrail post design for a manufacturer of stainless steel posts. the conclusion i came to was that most handrails (certainly in this part of the world) do not comply with the requirements. they are quite often post fixed with bolts and this simply does not work unless you have a massive base plate and can keep your post a decent distance from the edge of the slab. both of these solutions are usually not aesthetically acceptable. the only way to make it work is to have an embedded post or plate and then the considerable bending forces near the edge of the slab need to be contained as ron said with reinforcement. one solution is to have a post base bracket with reinforcement welded to it going back into the slab.
carl bauer

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