Use of J type bolts

This may be off-topic, but I've always wondered why j-bolts will straighten out under tensile loads, but 180 degree hooks on rebar apparantly do not. Does anyone know why 180 degree hooks behave differently than j bolts?


chichuck

This is in the 3rd edition AISC, Load and Resistance factor design. Look at page 14-10. It states that hooked anchor rods should be used for members subject to compression only.

Notice it is only a recommendation. If you go through all the engineering, you can still use hooked rods. You will find that you have a disproportionately large diameter and/or embedment requirement when compared to a headed rod for a given load, hence they are not recommended.

this is just a personal opinion.
90 degree hooks on rebar have requirements for minimum extension length for developing the bar whereas J bolts extension is much shorter and thus not developing its strength.

blame it to my limited knowledge ..but why anybody would use J type bolt when they are not good in tension.....
for compression one can straightaway use simple straight rod ...
for tension use bolt with anchor plate..

It is also recommmended in the AISC Base Plate Design Guide (to not use hooked anchor rods). The reason is that they have a tendency to straighten under tensile load and pull out of the concrete. This has been demonstrated in tests. Other people may have different opinions, but I would NEVER consider using a hooked anchor rod for this reason. See page 5 of AISC Design Guide #1 (the second paragraph on the right hand side of the page). Additionally, it is easier and cheaper to fabricate a straight rod with a nut welded on the end so there is no benefit to using a hooked rod.

SHBH, Exact clause ACI318M D.5.3.5

chichuk, rebars behave differently because the ribs on the bars transfer the load more or less uniformly while a plain bar can easily de-bond, transferring the load to the anchorage.