Desinged a few, built a few more, never did any real beam calcs though. ground snowload 30/105.wind speed 85 exp. I'm looking at the design criteria/snowload figures on the county website again. the website wouldn't load yesterday so I was guessing from memory. I don't recall where I came up w the 80/130 figure. The building is 14'x24' w/a 1'-0" popout for a 25' span overall sitting on a concrete foundation. My gut says not enough but that is not the way to check a beam. I had my copy from back in the day so passed a few of his manuals on to our new engineer intern yesterday. A retired engineer friend gave me his old copy last week in a box full of his manuals. You don't want to have to buy it for one beam. If you get stuck holler I do have an old '80's copy of their timber construction manual. If I remember right the publication is AITC-117 but the titles on their pubs page should tell. I believe you can download span tables from the (google this) American Institute of Timber Construction the strength varies according to what they glued together. There is a code stamped usually on the top edge of the beam, something like 16F-V1 which relates to the design strength of the beam according to the species, grade, and layup of the beam. I use the full ground snow load because I've seen it all stick on a 12/12 metal roof before after freezing rain followed by snow, all it takes is once, but your call. I think the 80/130 numbers you gave are wind/snow design loads? You are correct on the allowable deduction for a slick roof with no obstructions that would tend to hold snow. Where access to the roof is provided in addition to that necessary for cleaning and repair, the imposed uniformly distributed load should be taken as a minimum of 1.50 kN/m².Just a carpenter here but maybe some help. The imposed load should be calculated in accordance with BS 6399:Part 3:1988 Code of practice for imposed roof loads, as a rule of thumb for altitudes not exceeding 100m you can use a uniformly distributed load of 0.75 kN/m² and for most other areas exceeding 100m but not exceeding 200m you can use 1 kN/m², for parts of Scotland, Pennines, North East England and heights over 200m you will need to refer to BS 6399 Part 3. Joists are to have minimum end bearing of 40mm. Wane as allowed in BS 4978:2007+A2:2017 is permitted in all sections included in these span tables. Holes drilled at the neutral axis (centre line) are not to exceed 0.25 of the depth of a joist and are not to be less than three diameters (centre to centre) apart and are to be located between 0.25 and 0.4 of the span from the support. Notches are not to exceed 0.125 of the depth of the joist and are to be located between 0.07 and 0.25 of the span from the support. Timber to be covered, these span tables do not apply to timber which is fully exposed to the elements. These span tables apply only to flat roof and roof with a slope of up to 10 degrees. If insulation is placed on top of the flat roof joists and as such the joists are not fastened to the boarding above, the depth to breadth ratio of the joists should not exceed a ratio of 4 to 1. The dead loads shown at the top of span table above do not include the self weight of the joists, however, the joist self weights are included (in addition to the dead loads) in the calculations used to determine permissble clear spans. The allowable clear spans have been calculated in accordance with BS 5268-2:2002 Structural use of timber - Part 2: Code of practice for permissible stress design, materials and workmanship and BS 5268-7.2:1989 Structural use of timber - Section 7.2 Joists for flat roofs. * Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 Dead load per square metre (in kN/m²) supported by joistsĬentre-to-centre spacing of joists (in mm)
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