3 sided metal diaphragm

huangyhg

3 sided metal diaphragm
we are currently designing a retail building that cannot use any braced frames along an entire front side of the building and the owner wants to stay away from moment connections because of cost.  can anyone point me to a reference regarding how to design a 3 sided metal deck flexible diaphragm (shear resisting elements on only 3 sides)?  i've designed my share of rigid diaphragms that may not have shear resisting elements on all sides and can resist torsion, but i have not designed a flexible diaphragm with this requirement.
hi,
what do you call a "flexible diaphragm"?
you can achieve a diaphragm effect using diagonal bracing.
have you tried to use a 3d analyse software?
alternatively, you can design rigid connections between beams/columns along the facade (at top) and pin connection between columns/foundations (at bottom).
flexible as defined by steel deck institute relating to diaphragm stiffness.  normally metel deck diaphragms end up on the flexible side where concrete roofs are on the rigid end of things.  
it has been my experience that flexible diaphragms cannot resist torsion and distribute shear loads based on trib only, where rigid diaphragms can resist torsion, and distribute shear based on shear resisting element relative stiffness.
diagonal horizontal bracing is an option, but in this case will not do anything more than the diaphragm will for us.
we are using 3d software, but i'm not sure how that will help additionally here.  rigid connections are to be avoided because of cost.
traditionally, steel deck diaphragms have been considered "flexible", which means they must always be designed as a simple span between bracing elements (thus, an open sided diaphragm is forbidden).
however, i think most engineers would concede that such a diaphragm can function as open sided.  for example, the ibc allows the design of open sided wood diaphragms, and wood diaphragms have been considered flexible in the past.
it gets down to your comfort level, as the engineer of record.  personally, i would be ok with designing an open sided steel deck diaphragm.  if you are not completely comfortable with this, and you don't want a moment frame along the open side, you could design the columns on the open side as "flagpoles" (columns that cantilever from the base).
daveatkins
i'm assuming you are suggesting that the flexibile diaphragm be designed assuming it can transmit the resulting torsion to the bracing elements in perpendicular direction to the load.   have you seen any documentation like published examples regarding designing flexible diaphragms like this?  
i think you are correct that this is done in practice and is valid way to go assuming small loadings.  it would be nice to be able to hang my hat on something published.
thanks for your help and very useful input.
micowestruct - i have a design guide for 3-sided diaphragms produced by vulcraft that i use on a regular basis.  also includes a deflection calculation for your 3-sided monster. i can fax it if need be.

if you can't find anything, i would go for the bracing at the roof suggested by morokanu.  i've done this in the past and it works out when you need that rigid behavior without a rigid diaphragm.
ars001, can you scan and e-mail the design guide?  i've designed diaphragms like this before, but i would like to find some more documentation about the design process.
ars001, do you have a link to where that design guide can be purchased instead?
nutte- give me a day or so and i'll scan it.  i have a couple fires i'm trying to put out.  give me an email address.
ucfse- i called vulcraft and got the info from them.  i'm sure you could do the same.  otherwise i can email you the info.
ars, i ask because we don't use the site as a medium for exchanging copyrighted documents, and we don't give out email addresses.  the best thing to do then is to post a link to where the guide can be purchased or downloaded for free.