So like the other answer said, get a contractor or an engineer to help you. Your existing strip footing won't be able to handle a point load that large, so you'll probably need to pour a new pad with a bunch of rebar there, and that size changes based on your soil type and conditions. You'll also need a new column the same size directly below it in the basement. The intermediate bearing post will have 18,000+ pounds on it, so you'll need a PSL or steel column. The best solution to open this up is to run a 3 ply 11-7/8" LVL full length but with an intermediate support in the middle making two 9.5' spans with 1 beam. With a 19' span (and completely guessing on the roof span and live loading for your area) you're looking at at least a 2 ply 24" LVL or a steel beam that would be impossible to install at this point. Nope, a 2 ply 1-3/4" x 11-7/8" LVL can't span that long with this much roof on it. So for your question about determining if your LVL beam will be enough, plug in your beam's information to step 2, calculate out each stud to see if they are enough or not. If the section modulus in step 4 is less than the required modulus times 2 (factor of safety) then the beam is not strong enough.So for a 2 by 6 beam with actual dimensions of 1.5 x 5.5 inches this would be: Section modulus for a wooden beam = (beam width * (beam depth)^2) / 6 Calculate the section modulus for the different beams you could use.Multiply the maximum bending moment of 900 ft lbs For example 1,150 lbs / in^2 is for pine 2 x 4's ( Max fiber stress by wood types). This requires you to look it up depending on what type of wood you have. Multiply the maximum bending moment found in step 2 by 12 to get inch-pounds and then divide that result by the allowable fiber stress in your wood beams to get the section modulus in inches cubed. This means that for the beam to work it must meet two requirements: supporting itself and having the rest of the support beams not to fail. To determine if it can or can't, do a similar calculation, finding the section modulus it needs to support and what it can support. What a horizontal beam does is divide the load between the two beams that support it, so long as the horizontal beam itself can take the load. For example if the span between two beams is 12 ft and 600 lbs is at this section then the maximum bending moment would be 12 x 600 / 8 = 900 ft-lbs. This would be determined by how much load at a given distance a beam has to hold. Actually calculate it out as this is one of the major factors.Ĭalculate maximum bending moment for each wood beam. For a flat roof with snow loading 25 lbs / ft^2 is usually used and 50 lbs / ft^2 for rooms heavily walked on. This means your resulting modulus should be 2 times what is required.:ĭetermine the total weight of the roof. Use a Factor of safety of 2.0 for structural loads. Of course every house and roof is different so modify to get better results. I see this question often in many forms so I will do my best to outline what is needed for a load calculation in general.
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