strain from a given load--and when the beam is vertical the weight
causes the least strain.


=Compression.= If we load a vertical post with a weight of 2000 lbs.,
the strain of compression exerted upon the post will be 2000 lbs. Now,
if we incline the post--the strain will be increased, as we have shown
above under the head of tension, and in like manner, dependent upon
the inclination.

But when wood, iron, or any other material is used for a pillar or
strut, it has not only to resist a crushing force, but also a force
tending to bend or bulge it laterally.

A post of circular section with a length of 7 or 8 diameters will not
bulge with any force applied longitudinally, but will split. But if
the length exceeds this limit--it will be destroyed by an action
similar to that of a transverse strain.

A cast iron column of thirty diameters in length, is fractured by
bending; when the length is less than this ratio--by bending and
splitting off of wedge shaped pieces. But by casting the column
hollow, and swelling it in the middle, its strength is greatly
increased.

Barlow's formula for finding the weight that can be sustained by any
beam, acting as a pillar or strut, before bending, is:--

WL² bd³ x 80 E
---- = bd³, whence W = -----------