Homework SourseSelect a solid rectangle Eastern hemlock beam for a 16 ft si
Select a solid, rectangle, Eastern hemlock beam for a 16 ft simple span carrying a superimposed uniform load of 310 lb/ft.
Select a solid, rectangle, Eastern hemlock beam for a 16 ft simple span carrying a superimposed uniform load of 310 lb/ft.
Solution
L =16 ft, W= 310 Lb/ft
BM at centre = WL*L/8 = 310*16*16/8 = 9920 ftlb ( neglecting wt of beam at present)
I = bh3/12, b = breadth, h = ht of beam cross section
Bending shear stress MC/I = 9920* h/2/ (bh3/12)
From handbooks Eastrn Hemlock has limiting shear stress of 155 psi
Insert in the formula, get bh2 =4608
have a choice of h,b
if b = 2 ft, h = 13.8 in ( aprox 2x1) ft cross section
volume approx 16*2 =32 cft , wt at densty of 28 lb/ft3 896 lb
ditbtd wt 56 lb/ft
Recalculating, bh2 5440 ft3
if b=2 ft, h = 15 inch
