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Re: Commercial Construction Standards

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In a message dated 98-07-29 01:19:39 EDT, you write:

<< 
 I am starting a commerical project this week. It's been a long time since I
 have done anything but custom residential, cold-form and retrofit work. This
 appears to be very easy, but I have a few questions on engineering standards
 which some of you might be able to help with:
 The project is a Starbucks Coffee and five other storefronts. Wood frame,
 TJS roof trusses (parallel chord) with sloping wall plate, tee-bar ceiling,
 three solid sides and one openfront, slab on grade. A few unique features
 such as a small parapet type tower structure (facade), and a covered portola
 (walkway).The building is essentially 57' x 120 feet long. The trusses
 (TJS)clear span the 57 feet. there diaphragm is 5/8" struct I plywood, all
 side walls are fully sheathed from plate to plate. Overall plate height
 rises from 12 feet to about 16 feet (3/8" per foot roof slope). Here are a
 few questions:
 
< 1.  Would you recommend welded wire fabric in the slab or a more durable #3
 rebar arrangment. What is the conventional layout of #3 rebar (6" o/c, 12"
 o/c or 18" o/c).>

I would use either #3 at 18 or #4 at 24 (if you are in Los Angeles, then you
have to use #4@16 for the slab-on-grade (Los Angeles City Code change,
effective  April 1998).  I am sure the contractor will want to use mesh
(cheaper), but it will end up in the sand.

< 2. The stores are approximately 15 feet wide, however the owner does not
 want any interior partitions for load bearing. He wants to be able to
 combine stores if wanted. What is the maximum slab area for installation of
 expansion joints? What is the conventional slab thickness (4" or 6")>

The slab thickness we would use is 4" concrete over 2" sand over membrane over
2" sand.  The sand requirements vary with the soils report requirements
usually and depends upon floor covering moisture sensitivity.  If the project
you are talking about is in the desert, you may already have the sand as your
base.

I have heard recently, that you should not space your construction joints
furthur than 15 feet apart in each direction (15'x15') to help control
cracking.  I would not go more than 20 feet x 20 feet, with a ratio of 2:1
max.

The biggest problem probably is that they want to pour in the morning or
afternoon and sawcut the next morning (common construction practice) because
the cracks have already occurred.  Ideally they need to cut it as soon as they
can walk on it.  I  know that there are different curing compounds to reduce
cracking and you could add fibremesh to the concrete mix (some contractors
like fibremesh, others don't).  
 
<3. I intend to use embedded steel in the open front - pendulum type
 columns - which conforms with the clients past conventions. Rather than
 embedding into post foundations, I plan to use the foundation as a grade
 beam with erection pads below (which will be bearing pads as well). I want
 to develop lateral moment in the grade beam. This posses two questions:
 a) should I place the grade beam below and independent of the slab edge? I
 think it is a good idea since the grade beam will be f'c=3000 psi concrete
 with special inspection required and also it will keep the structural
 gradebeam independent of the non-structural slab. Any other thoughts?>

I would place the grade beam independent, of the slab edge.  Provide dowels
from the grade beam up into the slab.  This slab is probably going to be a
exterior sidewalk slab poured after the main building slab-on-grade which will
have a turned down footing at the glass storefront.  Top of grade beam should
be at least 12 inches below lowest adjacent finished grade.  You can also
provide dowels from the sidewalk slab into the main building slab-on-grade.

<b) Should I follow '94 code and distribute lateral according to an Rw of 6
 or follow the '97 code and take the penalty for the pendulum condition?
 Also, if I follow '97 UBC convention should I use the lateral component for
 the entire building or just the embedded poles?>

I would use the penalty of the 97 UBC (especially if it is suppose to be
adopted in Jan/Feb 1999).  I don't think the lateral component for the entire
building will make that much of a difference in the longitudinal direction
(depending on number of openings in the rear wall).  Obviously, the transverse
direction will have a higher loading, but will your plywood walls still work
anyway with slightly more nailing(?).
 
 <4. 3(b) leads to this question - Has the SEAOSC code committee taken a
 position yet regarding embedded column lateral design. It was suggested in
 their minutes that they intended to take the position that only the columns
 be loaded with higher shear in order to compensate for story drift. Any
 comments yet?>
 
I don't know what SEAOSC code committee has decided, but I would probably
check the flagpole deflection for the higher loads and design the rear wall
for 95-100% of the
total load based upon Rw=6.
 
 <5. I have recomended the use of TS (Timber Strand) studs. This is a low
 budget project, but I am under the impression that the labor savings in
 taller walls with dimensionally true and straight lumber will compensate for
 the labor cost and scrap necessary to deal with crowned, warped and twisted
 studs.>
 
I have not worked with the timberstrand studs, but if they are straighter it
will probably work better.  Especially for axial load and out-of-plane wind
loads since I imagine its design values are better than #2 grade douglas fir,
but then again your rear stud wall may end up being 2x8's.  I assume the top
plate will be 3x and do you have a restriction as to how far from the studs
the trusses can be located if they are top chord bearing (not that the framer
is going to pay any attention to this).

 Any comments you might have would be greatly appreciated. At the least,
 please let me know if you think I am on the right track.
 
 Thanks in advance for all advice.
 Sincerely,
 Dennis S. Wish PE
  >>

Good luck Dennis

Michael Cochran