Question 1: if I’m reading the span tables correctly (and I may not be), two 2x10. Roof pitch is 6:12 with architectural shingles and solid sheathing. Common, jack, and hip rafters will be 2x8 spaced 16 on center. You still need to check horizontal shear, V and deflection the formulas for these are in the pic. Planning a 12’ x 14’ hip roof (outside to outside), set on 6圆 pressure treated southern yellow pine 2. That fiber is allowed to safely withstand 978 pounds per square inch of stress. The extreme fiber is the one furthest from the neutral axis of the beam, in this case the extreme bottommost sliver of wood, the one that would first tear in the middle bottom of the beam under bending stress. That doesn't mean it participates in extreme sports or is under extreme stress. Looking that up in the front of the supplement (We can trial and error it the hard way,bd^2/6, I'm being lazy and will look it up)6x14 works as does an 8x12 and a 10x10 is so close I'd consider it. Looking it up as a solid sawn beam in table 4D in the supplement it has an allowable base Fb (extreme fiberstress in bending) value in #2 grade of 850 psi.I'm going to bump that 15% for roof use so Fb 978 psi. The w is load per inch of beam, 3750 lbs/300" span=12.5 lbs per inch uniformly bearing on the beam.īamalama is full of fine southern yellow pine. Maximum bending moment is in the center of the beam (notice the graph) Scroll down that page and pick up DA-6 and the 2005 Supplement-Design Values for Wood Construction There is a pamphlet of beam formulas for various conditons here Assuming very, very light loading of 10 pounds per square foot I'll call the load 3750 pounds uniformly distributed along the length of this simple span. The tributary area would be half the 30' (15' bears on the beam, 15' bears on the back wall), times 25' (the beam's span)=375 square feet of roof bearing on the beam. That is another topic but must be considered carefully. Floor Joist Spans 1 12 and 1 14 Clear Opening 12 (See Requirements for Use on page 23, and Key, Example and Notes on this page) Table 21 No. The ceiling joists must restrain this force. Back to the rafters, at low pitches the horizontal thrust becomes tremendous as the rafters try to snap through. It sounds as though this would be trussed rafter construction, rafters and a ceiling joist spliced over a kingpost arrangement for a 30' clearspan. The building supply contractors desk will have sizing software for them. Typically they are less expensive than glulam or steel. I'd check into LVL's (laminated veneer lumber, ~plywood beams) if cost is an issue. First,I think you'll find that pitch inadequate
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