Enlargement of Tilt Panel Opening

[Busman]

I have been tasked with enlarging existing roll-up door openings and am in a very preliminary phase of the design. The current 7 1/4" thick panels are approximately 28' wide by 25' high and currently contain two 10' wide by 10' high doors. The client needs to enlarge these doors to 12' wide by 16' high. My tentative plan to achieve this is to remove the portion of the panel between the existing door openings and replace it with a central tube steel column. I will essentially be left with 2'(width) of panel on each end. I also plan to case the openings with channels with regularly spaced anchors to the panels. I have good drawings on the existing reinforcing steel so I am confident I will be able to appropriately size the channels for the overhead condition, supplement the jambs of the opening, and size the new central column. I am simply inquiring about general thoughts on the design approach and experience with similar conditions. I am curious about three things in particular:

(1) I may supplement the shear capacity of the newly cut panels by reinforcing the new steel channel/column frame with gusset plates welded to the jamb/head corners and was curious if anyone had found it necessary to do so or has used a different technique.

(2) What is the potential for cracking at the corners of the newly cut openings and is there a way to reduce this potential?

(3) Although I have not been asked to design the demolition and means and methods used to perform the work, I am assuming it will come up. Although I have not yet ran the numbers, my instinct tells me that the panel may need to be shored at the new 24' span prior to cutting. How is this typically accomplished? I did read a thread about coring holes at the new corners prior to cutting and I like that idea, but I have not seen much about shoring prior to cutting (maybe because the new opening spans are not as long as this case).

Any thoughts and things to consider would be greatly appreciated.

 

[msquared48]

The tube steel side columns will have to go floor to ceiling to take the lateral and vertical load of the opening, and the header at the top of the door will have to be sized for vertical and lateral too. You might even consider a double header here - one near the roof, and one at the top of the door. You could even install diagonals between the top and bottom members if you needed to, but I do not think you will.

I would install the vertical and horizontal members on the inside of the structure before the sawcuts are made, so the new permanent framework becomes your shoring during removal too.

As for cracking, in an event, you may see some, but only as much as the adjacent panels in the line see too doe to parallel loads. I don't think you will see any cracking due to transverse wind or seismic loads if you give the steel tube sections enough "I".

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JAE]

Agree with Mike that using vertical struts behind the wall, from floor to the overhead diaphragm would be a good idea. We usually use significant tube steel for this with intermittent clip angles to bolt/attach the panels to the tubes - all this to resist lateral wind forces.

Item 3) above - I think it is important to sometimes provide the SEQUENCE of the work - not necessarily the means and methods of the work. Probably a good idea to use notes on the actual details emphasizing that the contractor is responsible for shoring and methods. If shoring is required, at the least, the engineer can assist in providing applicable dead loads on the shoring, once you know where the shoring will be placed.