Last month, we analyzed the floor
structure of an 18x20-foot living
room. The floor system has an
18-foot-long central girder supporting
10-foot-long 2x8 joists running to the
outside walls. The joists are #2 Doug
fir 2x8s 16 inches on-center. Using a
design floor load of 40 pounds per
square foot, we calculated the load on
the girder to be 33.3 pounds per inch.
Through analysis of bending strength,
we arrived at a beam with enough raw
strength to handle this load — a
quadruple 2x12 girder built up from
select Doug fir. But raw strength is
only one of the elements we have to
check out in designing beams. In
this column, we'll look at two other
ways