new openings in existing tilt-up wall panels

huangyhg

new openings in existing tilt-up wall panels
what is the design process for reinforcing new openings in existing tilt-up wall panels?  the as built drawings are not available.  what is the best way to reinforce these new openings?  
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not knowing what the reinforcing in the panel is, i would assume that it spans vertically, unless it has pilasters, then it would span horizontally.  i would use interior metal tube steel after-set bolted to the wall with steel angles that are welded to the tube columns.  based on which way the steel in the panels runs, these tubes would take the lateral loads normal to the panel and span them either vertically or horizontally.  seen this done many places like costco where they are constantly changing things.  done several modifications this way too.  simple installation in the field.  only drawback is what the owner/architect wants to see in the final product.  if the building is a warehouse, it shouldn't matter much though.
mike mccann
mccann engineering
i have done this a few times but usually i have had existing drawings.
unless there are already existing openings in the area, your reinforcement will be welded wire mesh evenly distributed with some additional trimmers around the edge.
you can often justify a door in the bottom of the panel by showing that the moment at the top of the opening is less than the maximum moment and taking the moment capacity as proportionate to the width.
if you only have discreet supports at each end of the panel then you will also need to justify the panels ability to span between these as a deep beam . this takes a bit more thought.
csd
wwm seems way too light to me - usually #4 and #5 bars at 12 to 18" oc depending on the span and lateral loading.  tilt-up panels are usually the shear element of the structure too and have minimum shear reinforcing - .0025bt.  for a 5.5" panel, this shear steel would be a minimum of #4 @ 10" oc, irrespective of bending.   
mike mccann
mccann engineering
in any event though, once the cut through the panel is made, you should be able to see the size and spacing of the bars used to verify/rectify any assumptions made.  additionally, priorto any cutting, you should be able to determine the spacing and location of the reinforcing with a deep scan metal detector.  the use of this instrument has worked well for me in the past.  mine is an old (10 years) zircon videoscanner, but still works fine.  i don't know, but some now just may be able to tell you the bar size - i don't know why not if they can tell a quarter from a nickel.
mike mccann
mccann engineering
msquared48,
the min. shear reinf. required what section in aci is that? what if the wall is a shear wall, but not load bearing?
thanks
you can use structural steel to reinforce new openings if it is required.  single and double angles as well as channels may reinforce the "header".  the jambs may require reinforcement also.  tubes are commonly used around my area.  you then have to check connections and footings, as usual.  
if the wall is not load bearing, but not a shear wall, it would still have to be reinforced to take the bending stresses induced by wind and earthquake forces, plus it still sees it's own dead weight vertically.
mike mccann
mccann engineering
bpanning, you may also consider an inspection to determine what the existing reinforcing is should you want that information.
i would expect around #4 at 12 each way, but who knows?
a decent testing and inspection firm can go out and do rebar location using a pachometer (fancy stud finder).  this can determine the spacing and the ones with the bells and whistles can determine the size of the bar.  there are of course other options, ground penetrating radar, x-ray, etc.