### STRUCTURES: FORCE VS. STRESS

f = P / A

where

f = stress

P = force

A = cross section area

Note: stress can be compared to allowable stress of a given material.

Force is the load or action on a member

• Stress can be compared to allowable stress for any material, expressed as:

F ≥ f (Allowable stress must be equal or greater than actual stress)

where

F = allowable stress

f = actual stress

The type of stress is usually defined by subscript:

Fa, fa (axial stress, capital F = allowable stress)

Fb, fb (bending stress, capital F = allowable stress)

Fv, fv (shear stress, capital F = allowable stress)

The following examples of axial stress demonstrate force and stress relations:

Note: The heel would sink into the wood, yield it and mark an indentation

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