Penetrations thru existing slab on metal deck cutting through chord reinforcing bars

[jk2017]

I have a 3" NWC on 3" metal deck with #8 @ 12" chord reinforcing and unfortunately will need some small 6" diameter penetrations that will cut through some of those bars. Has anyone encountered this and what could be a solution to reinforce the chords? In the past, I have just added trim angles to redistribute the force into neighboring flutes, but not at chord reinforcing bars.

 

[KootK]

When you say "chord" reinforcing, do you mean diaphragm chord reinforcing? If so, how many bars total make up the chord?

 

[jk2017]

[/When you say "chord" reinforcing, do you mean diaphragm chord reinforcing? If so, how many bars total make up the chord?]

Yes, precisely - 9-#8@12" with the penetration happening at a splice, so 2 bars being spliced are getting cut, very unfortunate location. Pretty new to this so pardon the lack of detail in the post.

 

[KootK]

No worries. I was pretty sure that I knew what you were getting at. Some options:

1) If it's a chord and not a drag strut, you may not be at the peak moment location in the deck and may, therefore, require less reinforcing.

2) If you've got chord reinforcing on the other side of the deck, using it in compression may reduce the lever arm assumed in design and therefore the number of bars required. Some folks feel that compression bars need to be tied though.

3) Perhaps you can mobilize some nearby reinforcing not included in the chord originally?

4) Can you utilize a slab edge beam or deck angle locally to supplement the rebar.

Two of nine isn't a huge percentage of loss. There's likely some story that can be told that can avoid the need for a painful reinforcing exercise.

When you have a bolt hole in a flange, you can often make that section loss go away by utilizing Fu locally. I'll have to noodle on it some more but I wonder if a similar strategy could be employed here. Most diaphragms are designed to remain elastic rather than to develop plastic hinges etc.

 

[jk2017]

@KootK: Those are some great points. Indeed, not at a drag strut, and because it's at a splice location, there could be the argument that there are more bars there than needed. I do have chord reinforcement at the other side as well, I was thinking that could be a get out of jail card as you say. A deck angle is definitely an option and I was thinking of using that even if not necessary as they'll be installing deck angles in other areas of the slab (a whole other story...).