Many factors must be considered when selecting the working stress. This selection should not be made by the novice; usually the working stress is set by a group of experienced engineers and is embodied in building codes and specifications. A discussion of the factors governing the selection of a working stress starts with the observation that in many materials the proportional limit is about one-half the ultimate strength. To avoid accidental overloading, a working stress of one-half the proportional limit is usually specified for dead loads that are gradually applied. (The term dead load refers to the weight of the structure and other loads that, once applied, are not removed.) A working stress set in this way corresponds to a factor of safety of 4 with respect to __ and is recommended for materials that are known to be uniform and homogeneous. For other materials, such as wood, in which unpredictable