Buildings are naturally affected by the forces of nature, and also by artificial forces. Elements such as gravity, wind, snow, earthquakes, retained soil, water, impact by an object, and mudslides can all have negative effects on a building.
This chapter will give you a basic understanding of the forces that affect buildings, and some helpful information on the framing methods used to resist those forces.
Although you may not be responsible for designing structural requirements for buildings, it is important to have some understanding of a building’s structural loads. When you are aware of the reasons behind the decisions engineers and architects make, it is easier to interpret the plans, and to make sure that the structure is built accordingly.
The forces of nature can have devastating effects on buildings. The following photo shows an example of how destructive the elements can be. This photo is quite dramatic; you can see that the ground literally fell out from under the house. But the photo also shows the strength of good framing— the house stayed together even though the ground collapsed under it.
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Source: APA, The Engineered Wood Association |
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As the forces of nature contact a building, they travel throughout seeking a weak link. Ultimately, if a weak link is not found, the force or energy will be transferred to the ground, which will absorb the force. Each component of the building must be strong enough to transfer the load in a path to the ground. The components are:
• Foundations
• Walls
• Floors
• Roofs
• Connections
To achieve the strength needed, a building’s walls, floors, and roof must work together as a unit.
The vertical elements that are used to resist forces are commonly called shear walls, and the horizontal elements (like floors and roofs) are called diaphragms. The path of energy to the ground is called the load path. The diagram on the next page shows the load path for transferring the forces to the ground.
