Why do buildings move?
In short, gravity. Gravity is always trying to get things closer to the ground, and strong buildings resist gravity. Buildings also move because of environmental forces, and live loads inside and on the building.
There are two ways a building usually fails to resist gravity:
- If the soil the structure is built on is poor.
- If the structure is weak and cannot bear live and dead load.
What are live loads and dead loads?
- Live loads are things like furniture, people, wind, snow, and earthquakes.
- Dead load is the weight of the building itself.
Wind can push, pull, or lift buildings; buildings must be strong enough to resist lateral and uplift forces caused by wind, and the downward force of gravity. As seen here in the Ottawa Valley on September 23rd, 2018, wind can significantly damage a building.
“Environment Canada meteorologist Peter Kimbell on Saturday confirmed that two tornadoes struck the area on Friday. The first, which struck Dunrobin just before 5 p.m. and crossed the Ottawa River into Gatineau, rated a high EF3 on the Enhanced Fujita scale with winds of 150-155 mph. The second tornado touched down about 6:30 p.m. in Ottawa’s Arlington Woods neighbourhood. Kimbell said it was a high EF2, with wind speeds of 137-143 mph.”https://weather.com/storms/tornado/news/2018-09-21-ottawa-canada-tornado-damage
Earthquakes, soil/geological erosion are often few and far between, but have detrimental consequences to the structure.
Component failures due to inappropriate installation of building materials, rot, insects, fire and mechanical damage can cause a great structure to fail.
How does all this affect components in the structure?
Components in the structure are affected by two main forces:
Compression is when you squeeze something, and tension is when you pull. Many of the components of a home will feel both these affects at the same time.
These components, made from different materials will fail in different ways. Some will shear, for example when a beam splits, or a brick cracks, it’s because of shear. Some components bend. When a component bends downward, the top is under compression and the bottom tension.