April 2010 — 1
Ron Hunsicker, P.E.
Brick Veneers in Earthquakes
Most research into the behavior of masonry in earthquakes involves reinforced, load bearing, concrete
masonry. Generally, it is assumed that the reinforced concrete masonry absorbs all the energy from an
earthquake and that masonry veneers contribute nothing. Masonry veneers are only expected to remain
attached to the building—not fall to the street or sidewalk below.
Recent research, summarized in the attached article from the December issue of The Construction
Specifier, Seismic Performance of Modern Masonry.Construction Specifier.200912.pdf, indicates that clay
brick masonry veneers contribute to resisting forces generated during earthquakes. Additionally, they do
so while sustaining remarkably little damage.
The motion of the 1994 Northridge earthquake was duplicated during the testing. This motion is often
used because the ground accelerations during that earthquake were some of the highest ever recorded in
an urban area in North America. (For comparison, the recent Haitian earthquake involved the release of
about three times more energy than the Northridge earthquake; Mw 7.0 versus Mw 6.7.) Regardless, there
was no damage to the veneers until the accelerations generated by the testing table were 20% greater
than those found during the Northridge quake.
Before you view Figures 11 and 12 and scream “How can a brick guy show that!” in the language of
earthquakes, these two figures show “light” damage. The bricks did not fall off the building, the building
did not collapse, and the structure can still function as intended. Although the cracks are large (to an
East Coast or Midwest eye), they represent phenomenally good performance. If a building can still
function after a large earthquake, it has done very well.
Interestingly, when portions of the veneer fell from the residential building, it was not because the 22
gauge corrugated ties pulled out of the masonry. It was because the nails attaching the ties pulled out of
the studs. Lesson: In higher seismic zones, use screws, not nails.