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Re: 2 story retail/office building and lateral stability at the roof

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Alden,

        We are probably from different geographical locations so you may want to check my comments below with your local building code or your Mentor.

1.)    You should not have to provide additional steel joists at the roof level for lateral stability.  Although the roof trusses are designed "by others" you should have a truss schedule on your drawings which specifies exactly what loading they are designed for; it will be your duty to check that they comply.

2.)    The walls definitely require temporary bracing for stability during construction, however, where I come from, this is the responsibility of the Contractor.  You may, however, want to verify that what he is providing is sufficient.

3.)    It's a virtual certainty that, for a building this size, there will be roof mounted units somewhere on the structure.  Depending on your location and the roof shape this may mean that there are also snowdrift patterns which have a major effect on the roof design loading; this was discussed on this list as recently as a few weeks ago.  Your  boss (or your Mentor) should tell you whether you should: a) proceed and expect changes to your design after the information is known; b) wait for more information before proceeding; or c) design for a heavier roof loading in anticipation of the heavier loads you know are coming.

        Goofy?  I don't like mixing structural systems; but it's not really all that uncommon.  Here in Calgary, for instance, it's not really unusual to build the first few stories in concrete and then use wood construction above that.

        Hope this provides some assistance.

Regards,

H. Daryl Richardson

"Alden Manipula, E.I.T." wrote:

Hi, have a question regarding lateral stability during construction. I have a project that is a rectangular, 2 story building -  67' wide x 170' long - metal framed w/ metal stud & brick veneer curtain walls, and a gabled roof..  The architect has drawn some very large, triangular roof trusses - 20' tall x 33' long spaced at 24" o.c., these trusses are to be designed by a wood truss manufacturer. The second floor is going to be your typical floor joist + concrete slab construction.  At the roof level is whre i have some questions. 1)  Should I provide steel joists at the roof level for lateral stability or can I count on the wood trusses to provide this?  I can't see how i can count on the wood trusses since they are being designed by someone else.2)  Should I provide some sort of lateral stability assuming the wood roof trusses won't be placed immediatly after the steel erection?3)  There's talk about putting some rooftop units in a flat area of the roof where steel joists/roof deck will be.  So essentially this building will have 2 different roof systems:  1)modified roof /steel deck/roof joists 2) Asphalt shingles/felt/plywood/wood trusses.  Doesn't this sound goofy? Was this clear? TIA Alden Manipula