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Re: Modeling Diaphragm Stiffness of Unreinforced Masonry

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Without code checking, and assuming that the top of the wall is adjacent to
the bottom of the girder,  I would look at using the horizontal shear
resistance of the top course for half the length of the wall as a diaphram
stiffness parameter.

The other courses contribute but since the displacement of the column is
greatest at the ends for this condition, then if the top course goes then
the next down will follow etc.,.

-----Original Message-----
From: Bill Polhemus <polhemus(--nospam--at)>
To: structx(--nospam--at) <structx(--nospam--at)>; seaint(--nospam--at)
Date: Monday, April 26, 1999 10:42 AM
Subject: Modeling Diaphragm Stiffness of Unreinforced Masonry

>I have a little project wherein I am trying to "check" the structural
>integrity of a 20-year-old building.
>It is three-story reinforced concrete with concrete joist floors, and in
>several locations has masonry wall infills that go clear from column to
>column and floor to underside of girder. However, there appears to be no
>vertical reinforcing in those walls, although the horizontal joints are
>reinforced. One entire floor of one side of the building, for istance, has
>this infill.
>It seems unreasonable to assume that these walls contribute no diaphragm
>stiffness, but I'm not sure how to model it on the computer.
>One colleague suggested that we assume a 4" thick concrete element with
>f'c=2000 psi. That seems reasonable, but I'd like to know what some of you
>N.B. Since I'm checking an existing building, it is necessary to add this.
>can't just neglect it as it gives me answers that just don't make sense in
>light of the way the "real life" building behaves.