The four most common forms are: (1)~Simple tension,~ in which there is a direct pulling in two of the wood on the under side of the beam due to a tensile stress parallel to the grain, (See Fig.

17, No.

1.) This is common in straight-grained beams, particularly when the wood is seasoned.
[Illustration: FIG.

17 .-- Characteristic failures of simple beams.] (2)~Cross-grained tension,~ in which the fracture is caused by a tensile force acting oblique to the grain.

(See Fig.