Penetration in Concrete Precast Panel Wall

[vm101]

Hi, I am supporting a project involving new piping through an existing 6" precast panel in a steel "butler" building (built in 1988). Contractor needs to make an opening for a 24" pipe (opening size will be ~26" diameter). Challenge is the only location for the pipe is at an elevation that it will interfere with the girt for the lower precast panel. See attached sketches. The panel is secured to the girt using Z clips that are welded to embeds in the panels. Contractor is recommending lowering the girt (~12") and reattaching the panels with modified (elongated) Z clips that would be welded to the existing embeds. Additionally, the diagonal braces would be cut and reattached to the girt and RF columns (shown in Option 1). Another suggestion (see Option 2) is to leave the girt in place so as not to disturb the majority of the panel attachments. To allow the pipe to pass through, an open square frame would be welded to the modified girt. Any panel connections disturbed by the removed section of the girt would be reattached with modified Z clips as suggested in Option 1. Biggest concern is panel attachment, not modification to girt. Location is remote and material options are limited (i.e., will take at least 3 months to receive materials after fabrication). Questions: 1) Which option seems more viable and less risky to future performance of panel? 2) W14x22 is not available so on-site fabrication of "square" would be necessary. We are looking for steel that could be used to fabricate the square to match the I beam's dimensions. If this is not possible, would HSS be acceptable?

 

[thaidavid40]

Your option 1 looks to affect the overall structural system the least. And it appears to have fewer "moving parts". That could be an advantage in a remote location where materials for field modifications could be difficult to come by (per your description).
Dave

Thaidavid

 

[hokie66]

I would reject Option 2 out of hand. Too "Rube Goldberg" for me.

Use Option 1, but don't use the embeds with long clips. Use drilled in anchors into the 6" wall panel.

 

[KootK]

I vote option one mostly because I don't care for option two. That member likely has tension, compression, and strong axis flexure in it. It would be difficult to evaluate the diamond thing for such loading. And the diamond thing would probably induce some unwanted flexibility in the member for axial loads. Is the bracing that we see part of the lateral system in the completed structure? If so, you might want to consider the degree to which you may be taxing your columns by creating a vertical offset between the strut within the frame and the struts outside of the frame. If that causes trouble for the column, you might also lower the end of the strut in the adjacent bay to match, making it sloped.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[vm101]

Thanks to all for chiming in -- Option 2 was actually my boss's (not an engineer) but I was leaning towards Option 1. The girt and bracing are part of the lateral system, but location (height) was driven more to support panel connection. We discussed the offset caused by lowering the girt and what impacts it could have in the neighboring bays. Because materials are scarce (not enough to extend neighboring girts so they can slope to lowered one), we were leaning towards adding a lateral brace above the new penetration made from angles or HSS (we fortunately have a great welding crew). Would this be acceptable, or is it preferred to have consistent connection points on either side of the columns?

 

[KootK]

I'm not sure that I understand what you're proposing. Are you able to provide a sketch?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[msquared48]

Since this is a "Butler" building, and perhaps a PEMB, I would not recommend messing with the bracing at all.

I would push for raising the duct above the level of the W14 horizontal brace.

So much less complicated... and compromising.

Mike McCann, PE, SE (WA)

 

[vm101]

KootK, please see attached sketch. Intent for new lateral beam above pipe is to balance forces on column from lowering existing girt and offsetting with girt on opposite side of column. The challenge is that the design was completed without full understanding of the building structure (please don't lecture the messenger). All piping is fabricated and on site. I've been told to redesign pipe location is not an option. My task is to recommend viable solution that allows pipe penetration at designed elevation. Everyone is comfortable with bracing the panel (from building exterior) while the girt is relocated and reattached. My concern is what does lowering a lateral support in 1 of 12 bays do to the structural integrity of building. Thanks for the feedback -- voices of reason are greatly appreciated!

 

[Thoughtclaw]

I would suggest contacting Butler. Their engineers understand their structures better than anyone else.