Don't feel special Jim, I can't count the times she's reached around me to hand me the tool I'm looking for.
This is from the queenpost article;
"But trusses are not about bending. By definition, a truss is a framework that bears its burden via axial loading, in pure tension and compression. In this capacity, timber (and indeed all framing material) is many times stiffer than it is in bending. As a beam bridge, a 12-ft. 6x6 carries a midspan point load of 1000 lbs. with a half-inch of deflection. Stand the same stick up on end, load its top with half a ton and the newborn column will shorten a few thousands of an inch. Loaded axially the timber is a hundred times—two orders of magnitude stiffer than it is bending.
Conversely, consider the effect of an undersized truss member:
in bending (beam action) it can cause a local distortion of the
frame but, in buckling under axial load, it stands fair to bring
down the whole structure. As specified by the National Design
Specification for Wood Construction (NDS), the controlling design
value used to size a column or other timber loaded in compression
is compression parallel to grain (Fc) as modified by the column stability factor (Cp). Fc specifies maximum allowable axial compression stress by species and grade. To avoid the tendency of long thin members to buckle in compression, Cp lowers the working value of Fc via a complex calculation involving stiffness, slenderness ratio (effective length divided by least cross-section dimension), end conditions and other terms (Sect. 3.7.1, p. 22). Additional equations come into play if the timber in question in loaded in bending as well as compression."
That last sentence gets into section 15, if anyone can help me over a hump there I'd sure appreciate it.
Where my concern came from is the "Queenpost" earlier put the bottom chord in bending. A princepost wandering around on the bottom chord can put a kingpost truss bottom chord in bending. When an axially loaded member is handed too much bending, bad things can happen.
