Ever since the 1989 Loma Prieta
Earthquake, which registered 7.1 on
the Richter Scale, seismic codes for
new construction in California have
become stricter. It's now common to
see engineered seismic bracing details
even on plans for a simple addition.
The most common detail is the shear
wall, a framed wall with structural
sheathing, designed to resist the lateral
forces that an earthquake exerts
on a building (see Figure 1). Any
wall properly sheathed with plywood
has considerable shear strength, but
the term "shear wall" is reserved for
walls designed by engineers. A shear
wall incorporates special construction
details and materials specified by
code to resist the forces that rack a
building during an earthquake or
high winds (see Figure