headed bar in Pedestal

[McGill10]

Hello All,
I have a question related to anchor bolt/ Pedestal design. This project is in seismic design category D, where we can't reduce development length base on excess reinforcement per ACI.This giving tall pedestal, we are looking options to get reasonable pedestal ht.

1)To reduce the height of pedestal, is headed bar is the good option? Pedestal supporting a steel column has anchor bolts with tension forces which has to be taken by vertical bars on pedestal. Hooking the bar at top makes it congested, so I got suggestion of using headed bar. But I am not feeling comfortable, as I see the bearing head (of headed bar) being at the top of the pedestal, there is a significant concrete breakout at the top. It seems I transfer the problem from bottom of anchor bolt to the top of headed bar.

Any experience on use of headed bar on similar situations will be greatly appreciated.
Thank you
Mcgill

 

[Agent666]

Perhaps a section showing the relative dimensions might help to understand the concern.

If bolts and bars are in tension effectively lapping with one another, when you say you are worried about the headed bars breaking out in tension as long as you follow the rules in ACI318 regarding spacing of the headed bars and the size of the bearing head I believe any sort of tension breakout (side blowout perhaps with load acting towards the base of the plinth?) is precluded.

In these situations to alleviate conjestion I tend to finish the vertical bars straight and then add an additional Ubar with legs lapping with the vertical bars. This allows some flexibility to move the u bars around to miss bolts, etc, rather than clashing with many layers of hooks turning in any which way.

 

[Agent666]

By the way, headed bars pretty much have the same development length as a hook as far as I remember.

 

[KootK]

[highlight #FCE94F][/highlight]

But I am not feeling comfortable, as I see the bearing head (of headed bar) being at the top of the pedestal, there is a significant concrete breakout at the top.

As Agent666 pointed out, a headed bar is really not much different from a hook other than the congestion improvements. The breakout at the top is likely from the lateral component of the strut that transfers anchor bolt tension into the pier verticals. And you'll have that with either the hooks or the headed bars.

How short are you trying to make this pier? At some point, it may behoove you to simply anchor your anchor bolts within the foundation element below and bypass the pier as far as anchor bolt tension is concerned.

 

[McGill10]

Based on the replies from all of you and with some research, I now feel comfortable using headed bar instead of hooked bar in similar situations.