The Four Basic Forces
There are four basic forces in construction and any structure must be built to withstand these forces. When built correctly, ICFs provide exceptional protection against all of these forces.
Compression (Also known as Crushing)
- Columns and posts are defined as vertical structural elements. A column or post transfers load from a roof or a floor down to a foundation. For a simple column, most of that load is an axial force that transfers downward.
- Imagine a column, say a wood 6 × 6 under a wood outside deck, with an axial load. That load puts the column in compression and the weight is transferred down to the foundation and ground beneath.
Tension (Expansion/Pulling/Stretching)
- A steel cable attached to a cable winch illustrates tension force quite well. As the cable winch is tightened, the steel cable stretches tighter.
- The tension stress in the steel cable increases and the slack in the steel cable is less. Once the maximum design stress is reached the cable will be fully loaded.
If more tension force is applied the cable will snap.
Torsion (Tearing/Twisting)
- A beam carries the load (usually horizontally) from floors and roofs and transfers it to columns.
- A simple beam must be designed to resist both shear and bending moments.
A great example of torsion force is when you twist open a bottle of water or soda. The bottle is twisted one direction (or held immobile) while the cap is twisted in the opposite direction.
Shear (Sliding)
- Shear can be illustrated by tearing open a potato chip bag. As your hands grip the bag and pull in opposite directions, the bag starts to tear in a shear failure.
- Using tension, you would grip either end of the bag and pull along a line, but in opposite directions. Opening the bag in this manner, with too much gusto, could be very messy.
Trying to open that bag using axial force (compression) would only smash the chips.
