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# Re: Shear Wall Design

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Shear Wall Design
• From: NRoselund(--nospam--at)aol.com
• Date: Wed, 17 Nov 1999 00:32:26 EST

Andrew,

1) Has no holddown, and
enough to prevent the wall from overturning due to the applied lateral load;
then, the shear in the wall is not uniform.  In fact, the shear varies
linearly from zero at the vertical edge opposite the fulcrum, to twice the
average shear at the vertical edge at the overturning fulcrum.  If you design
the wall as if it has uniform shear, you actually get a wall that has
portions stressed to twice the design shear, and portions that aren't working
very hard.  As you increase the uniform dead load, more and more of the zone
adjacent to the fulcrum carries a uniform shear; however, no practical
uniform dead load will eliminate the zero shear at the edge opposite the
fulcrum, or keep the shear in the remainder of the wall from exceeding the
design uniform shear.

You can verify this by studying the free body diagrams of finite elements
within the wall.

An interesting effect of this arrangement is that the end of the wall
opposite the fulcrum will lift actually off the foundation under the design
load as the wall distorts in a curved shape.

You can see this effect pretty well by playing with a new soft vinyl eraser:
put its long narrow edge on the table and push laterally with your finger on
the top edge to simulate a lateral load, while applying varying amounts of
simultaneous downward pressure.  Place your pushing finger at different
positions along the top edge and see what happens; try to apply the force
along a length of you finger instead of just at the tip; when you have the
tension edge off the table, see what sort of "holddown" force it takes to get
it back down on the table.

Be careful who sees you doing this; there's a list circulating the Internet
on how to tell if your husband is an engineer -- this isn't on the list, but
it'll be a sure giveaway if someone is trying to figure you out.

Every plywood shear wall I design has a holddown at each end designed to
resist the total overturning force.

Nels Roselund
Structural Engineer