We typically put a full height (floor to roof) steel tube or channel member
on each side of the new opening, and either a new channel or angle
horizontally at the top side of the opening. Vertical member is sized for
out of plane forces (usually wind since the opening removes mass for seismic
forces), and horizontal member is sized for the weight of the remaining
masonry plus any tributary roof load. Also, in plane shear should be
checked, since you are reducing the strength of the wall.
It seems like you do need a full height member on each side of the opening,
unless the remaining wall adjacent to the opening has sufficient strength
for out of plane forces on a tributary area equal to half the width of the
opening plus some length of wall (probably not more than two or three times
the wall thickness).
As for the steel being visible and the architect not liking it, would he
like it better when the wind blows the wall in and the roof caves in on top
of it? Wouldn't a nice architectural interior window mullion look better
than a large hole and collapsed roof?
Another option would be to remove the masonry full height and build a new
frame into the wall capable of taking out of plane forces. With this
option, watch out for severing the diaphragm chord steel.
Conrad Guymon, P.E.
----- Original Message -----
From: "HariA" <haria_pe(--nospam--at)yahoo.com>
To: "Mail Server @ SEA International" <seaint(--nospam--at)seaint.org>
Sent: Wednesday, April 25, 2001 2:11 PM
Subject: New Openings in (E) CMU/Concrete Bldg
> Wanted to get an opinion on the design of new wall openings in existing
> conc/cmu building. The general method used in our office has been to
> provide a frame around the opening ie., about 6" beyond the opening on top
> and two sides. Angle at the top anchored to the wall and strongback
> from floor to roof. The angle takes the vertical (based on a triangular
> load) from the wall and roof above while the strongback transfers the
> vertical to the wall and also acts as a strongback to take the
> lateral forces of the wall. The architect is not too much for this design
> since steel is going to be visible all across the wall.
> But I have seen other engineers put a channel around the opening which
> into the door or window rather than on the wall. How effective is this
> the lateral forces. Building we desing are mostly in the southern calif.
> Thanks for your input.
> Do You Yahoo!?
> Get your free @yahoo.com address at http://mail.yahoo.com
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