Let's start with the outer wall upstairs plate, the roof carry beam. In other words the main floor beams carry the main floor only, the second floor beams carry the second floor, that load is not carried through the walls down to the main floor beam. Each floor and the roof is carried on beams that floor by floor carry their loads over to and then down the posts. I'm going to assume the load paths of the building consist of vertical posts stacked over the piers all the way to the top plates. A poured concrete or block wall foundation costs more but is faster. If you have more time than money there is plenty of building stone there, a 16" thick rubblestone foundation is not expensive but does take some time. It doesn't matter how well you build the rest if the foundation fails. I've spoken with an engineer who called that method a collapse mechanism. A pier foundation is specifically called out in the code for engineering for a reason, they have a pretty dismal failure rate when put to nature's tests. That was long winded, my finger's tired have a go and if you need help holler with an example and I'll walk through it with you.Ī chain doesn't break at the strong link. The "simple beam, uniformly supported" is the most commonly encountered situation, a typical rafter or joist. For timbers that experience snow loads increase base design value for bending strength, Fb, x 15% (multiply by 1.15), leave all other values at base design strength.įor eastern white pine these are the base design values for beams and stringers 5x5 and larger in #2 grade. Adjustments are fewer for heavy timber, I use just one. So species, then basic geometry of the cross section, then grade will give you base design values. B&S is more rectangular in section, deeper than wide, generally beams. P&T is roughly square in section with the measure of adjoining faces within 2" of each other, generally posts. When wood gets to 5x5" and larger you are into heavy timber, look further to the back of the supplement for design values for posts and timbers, or, beams and stringers. It then used the adjusted design value in working the problem and determining span. Each time you clicked a box after that the calc multiplied the base design value by a strength adjustment factor. The calc looked up the bending strength, stiffness and shear strength of that lumber. on the calc you linked to, you first selected a species and grade. Wood that is 2-4" thick is called dimensional lumber and has one set of design values and adjustment factors. More often though once you start playing with heavy timber those wussified tables aren't going to help with the problem in front of you, you'll need to understand a little more about what is behind them and solve the problem more manually. They also have "Supplement to the NDS, Design Values for Wood Construction" It gives the allowable design strength values of many species, it is where the design values used in the calc you linked to come from. There are some tables in "Wood Structural Design Data" a free pub on the awc.org site
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