Problem $5\mathrm{.}4.$C$,$ Scenario a $-$ No$.1($from text$)$

Douglas fir$-$ larch rafters are to be used on $24-$in$.$ centers for a roof span of $16ft.$ Live load is

$20$ psf $($without snow$)$ and the dead load is $15$ psf$,$ including the weight of the rafters. Note:

you'll need to convert loads in $l\frac{b}{f}t2$ into $l\frac{b}{f}t$ by multiplying by the tributary width $(24in=2ft)$ th

a$)$ Compute the maximum bending moment. Note: you'll need to convert loads in Ib$/$ft$^2$

into $l\frac{b}{f}t$ by multiplying by the tributary width $(24in=2ft),$ then use the correct formula

$($Lesson $9,$ slide $16).$

b$)$ Assuming an allowable bending stress $(F_b)$ of $1,000$ and a $7$ day construction load, use

the load duration and repetitive load correction factors to compute the modified

allowable bending stress $(F_b^{\text{'}}).$

c$)$ Compute the required section modulus $($S$)$ and use this value with Table A$.8$ to find the

required rafter size based on bending.