Book 12, Question 44
Why Do Old Brick Buildings Crack in Earthquakes While Wooden Houses Bend?
Old brick buildings are stiff and brittle, which means they crack instead of bend. Wood-framed houses can bend and flex, like a diving board. Flexible things are often stronger in a quake!
More fun facts
- Unreinforced masonry means brick or block walls built without steel bars inside to hold them together.
- Unreinforced brick walls are weak when shaking pushes them sideways or bends them outward.
- Mortar is the glue between bricks, and when it cracks it snaps suddenly, much like the bricks themselves.
- Older brick buildings were often built with much weaker mortar than today's rules require, and mortar also weakens over time.
- Diagonal stair-step cracks along the mortar lines show that a brick wall could not resist the shaking.
- A single brick weighs 6 to 12 pounds, and just one square foot of a typical brick wall weighs 120 pounds or more.
- Short walls around the edge of a roof, called parapets, along with chimneys and decorative ledges, are especially likely to fall.
- Long Beach, California, where a big earthquake struck in 1933, was the first city to require old brick buildings to be strengthened.
Sources: madcad.com
Questions kids ask
Can old brick buildings be made safer?
Yes. Fixes range from simply anchoring parapets to big engineering projects that strengthen the whole building.
Why is falling brick so dangerous?
Bricks are heavy, so pieces falling from walls or chimneys can hurt people inside and on the sidewalk below.