veneer pilaster

huangyhg

veneer pilaster
i am looking into the design of a masonry veneer for my client.  he would like to use as small a veneer pilaster to support the masonry veneer above (preferably 8").  he would like to have an 8' window, pilaster, 3'-4" door, pilaster and 8' window for the front of his building.  i have approx 20' of veneer above the openings.  
as far as i can see, the vertical stresses (due to vertical load only) on the veneer would be acceptable but i am having problems resolving the thrust created by the masonry arching over the openings.  by my calculations, the pilaster would have to be 24" wide to resist the unbalanced load (which generates bending in the 8' high pilaster). does this seem correct?

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yes, for arching action you do need to have some substantial masonry on either side of the opening.
if you lintel is designed to take the full vertical thrust of the brick above (instead of a triangular distribution of arching brick) then you've solved the lintel problem.  but there still might be a natural lateral arch thrust that would occur.
what you could also do is provide vertical columns behind the small pilasters and support the brick off column seats tied into the lintel.  the columns would go from ground all the way to the next structural level.   
thank you for your reply.  providing a steel post is the question i have to answer.  however, a loose lintel system is preferred.
if i have a symmetrical set of openings with no control joints in the veneer, wouldn't the thrust force be resolved?  i would only have to be concerned with thrusts near control joint and at the ends of the sets of openings (probably where the joints would be located.  see attached sketch.

yes, you are correct that the outside support areas have the lateral thrust.
is this under the irc or ibc?
under the irc, there are limitations on length of wall in table r602.10.5.
i don't believe there are direct limits on the veneer width in the ibc as it references asce 530 and it doesn't have any stated empirical limits.
the limit in the irc is based on two concerns - first, the table is limiting the number of openings in a structural shear wall.  second, the net wind uplift on the corners of a wall, for example, limit the number of vertical "though-studs" that connect the roof to the foundation.  with large openings like windows and doors there are only so many vertical studs that do the job and the engineer would have to design special hold-down studs to work.

so you are saying the internal thrusts do cancel.
this is under a state version of ibc 2003.  would you consider this a structural shear wall if it were only supporting itself?  i guess you could make an argument that a veneer shear wall resists the thrust.
fyi, the building is steel framed with braced frames and moment frames for a lfrs.  the veneer will have metal stud backup system for support of wind loads.

i normally don't use veneer as any sort of shearwall.  remember that the veneer is only connected to the building laterally by wire or gage metal straps.  so there is no lateral connection between the structure and the veneer.
having only 8" of veneer holding up 20 feet of brick just feels bad to me.