huangyhg

definition of "fatigue loading" on adhesive anchor
i am considering the use of a proprietary mechanical sleeve-type anchor to resist tension loads. the anchors are to be installed in vertical holes on the underside of an existing concrete flat slab. the tension load will vary from 0.3k to 4.5 k many times during the life of the anchor (the anchor is helping attach mobile medical equipment). the icc-esr for this anchor (i am designing under ibc '06) has a note that says the anchor should not be used for situations where there is fatigue or shock loading. unfortunately it does not define what those are. spoke to the anchor manufacturer and they were not much help. they could only say that fatigue/shock situations were not investigated during the testing of the anchor. is there a generally accepted definition of what a fatigue load is, or when a load would be considered a "shock" load?
an app d acceptable alternative to this sleeve anchor is a type of adhesive-attached dowel by the same mfgr, but i am hesitant to use the adhesive because of concerns about loss of adhesive strength in a fire. (i also have concerns about installation quality, but would ask for a proof testing program on every adhesive anchor if in the end they were specified).
hi samdamon
have a look at this link:-
adhesive anchors must meet ac58 and ac308 to be used for extended tension service considering creep. to my knowledge, there is only one anchor that meets the criteria to date (a fallout of the big-dig collapse) and it is made by hilti. contact them or go to their website.
if you "heard" it on the internet, it's guilty until proven innocent. - dcs
for steel design, aisc says that fatigue is not an issue when the number of load cycles is under 20,000 over the life of the structure. i don't know about concrete or anchors, but this may offer some perspective.
the reason the icc report states that the anchor cannot be used for dynamic/cyclic/fatigue loads is that no such test exists in the u.s. therefore, the icc report cannot state that it can be used in those conditions. most mfg's should have external testing that could support a products use for those type of conditions, you should see if that testing exists for the product used. typically, undercut anchors and heavy duty sleeve anchors are used for these types of loads.
i have used pretensioned anchors before, in this case the anchor is set with the design load for its entire service life and thus all tension loadings lower than design do not stress the anchor within the pre-compression zone of the concrete. you would have to check the actual protruding steel shank for fatigue though.
hth
vod

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