Understanding Duration Of Load Of 1 6 For Roof

L r l o r 1 r 2.

Understanding duration of load of 1 6 for roof.

Full time loading floor joists serves as the benchmark value. Anything hung from or attached to the structural framing is a collateral dead load. Roof live load may be reduced by the following equation. Greater than 10 years 0 9 permanent 10 years 1 0 normal floor ll 1 year 1 075 long term temporary load 2 months 1 15 snow load 7 days 1 25 roof live load 10 minutes 1 6 wind or seismic load less than 2 seconds 2 0 impact load e g.

The load factors are all greater than 1 0 since we want to compare the result to the ultimate. How long will the members be loaded. Benchmark values are multiplied by 1 15 to yield snow load values and by 1 25 for 7 day loading. Roofs are under a lot of pressure.

Static loads also known as dead loads are the permanent loads of the structure. Don t worry about the calculations. Factor is equivalent to the earlier use of a 1 3 wind load factor in that the newer wind load provisions of asce 7 98 include separate consideration of wind directionality by adjusting wind loads by an explicit wind directionality factor kd of 0 85. The span would be 11 5 3 4.

R 1 0 6 for a t greater than or equal to 600 psf. Dead loads consist of the weight of the building itself plus the weight of all fixed items like walls roof and carpeting. Roof live load reduction. All loads are listed as pounds per square foot of horizontal projection footprint area.

Here each square foot of roof system delivers 50 pounds of live load and 15 pounds of dead load 65 psf total to the structural support system. The factor for dead load 1 2 is lower than the factor for live load 1 6 because dead load is more predictable than live load. Using lrfd lc 2 the combined design load equals 1 2 times the dead load plus 1 6 times the live load or 15 6 kips. So consider a simple gable roof on a 24 foot wide ranch framed with 2 6 exterior walls and a 1 1 2 ridge.

This is the horizontal distance from the inside surface of the supporting wall to the inside surface of the ridge board. Rather the span is based on the rafter s horizontal projection. Since the wind load factor of 1 3 included this effect it must be adjusted to 1 5 in. R 1 1 for a t less than or equal to 200 psf r 1 1 2 0 001 a t for between 200 psf and 600 psf.

Where l r shall not be less than 12 psf and not more than 20 psf. In commercial or industrial buildings for each floor or portion thereof designed for live loads exceeding 50 psf 2 40 kn m 2 such design live loads shall be conspicuously posted by the owner or the owner s authorized agent in that part of each story in which they apply using durable signs. Load limits on the roof of a building. Tables automatically handle this adjustment.