![]() ![]() That extra half inch of thickness in the 4x4 accounts for the increase in section properties, nothing mysterious. ![]() The section modulus and the moment of inertia for the 4x4 are more than twice that of a 2x4. In that post you roughly equated a 4x4 to a 2x4 and suggested ignoring the the additional thickness. ![]() From my read of your original post (#2) it sounds like you are proposing using the 24" oc 2x4 table. In the op the 4x4 rafters are on 2' centers. I pointed out that we had a potential sheathing issue, flipped to the lumber sheathing table and I took him up to show that we were using T&G sheathing that was appropriate for the 4' spacing. It looked impressive but was structurally about the same as a stick framed roof, we were simply twice as thick and half as often. The new inspector came on a log and timber job I was doing a few years back, looked up at the roof framed of 4x10 DF and remarked that it had to be one of the strongest looking roofs he had seen. If we are engineering just from tables it would be fine to use the 12" oc 2x4 table for the allowable span. They are planning on voting this upcoming January on whether those design values that they put into play in June are valid (they are). Sistering a 2圆 to the existing scrapes by on paper. ![]() Allowable span for this situation dropped 8" due to the recent derating. MOE was 1.6 x 106psi so the deflection even using old values is 2.24". Overspanned based on strength alone but not horribly. With the higher bending strength material the section modulus required drops to 7.607"3. Using the old design values I get an adjusted Fb of 2156psi. This was probably pulled before 6/1/12 and who knows what is being enforced, so in trying to make the math fit the existing. Putting 4x4's on 12" ctrs still has 1.28" deflection. certainly passes l/180, 4圆's would have worked. Plugging in Rio's 5.45" depth deflection drops to. 2 Stress grade, and wet service conditions.I'm curious, Texas I'm assuming #2 SYP, which design values are you using in Strucalc? I tried it with new post 6/1/12 allowable design values and had an adjusted Fb of 1509 psi, which required a rafter section modulus of 10.89"3 remember a 4x4 is 7.146"3.īut the controlling factor is deflection, the new E value is 1.4 million psi giving a deflection of 2.56". Note: The span chart below is an example of how spans charts are presented. Because building code and lumber spans are updated from time to time, you should always check to make sure the span chart you are using is up to date. See the applicable code section, or the NDS to confirm the span chart you are using is correct.ĭimensional Lumber Deck Beam Spans Supporting a Single Span of Joists with or without Overhangs:Īssumes 40 psf live load, 10 psf dead load, L/360 simple span beam deflection limit, cantilever length L/180 deflection limit, No. The longer the joist, the more area of deck the joist supports, and thus the beam supports more area as well. In addition, many residents prefer the fell of a deck that is designed for higher loads. Building codes for residential decks only require 40 psf in some areas, but check your local requirements to make sure you are aware of any additional local guidelines. Beam span maximums are based on a maximum anticipated live load as well as other factors. Fewer posts on upper-level decks are typically more desirable to the occupants and this drives the use of larger framing materials for longer spans. The span of a beam is dependent on a few variables: The grade and species of lumber, size of lumber and the load it carries. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |