Question

Consider a 10 ft long 12×20 timber stringer.  The stringer is made of Alaska Spruce and is of Select Structural grade.

1. Find the following properties of the section. State the correct units.

1. Nominal size …………………………………………………..
2. Standard dressed size …………………………………………
3. Area …………………………………………………..
4. Moment of Inertia (I) about x-x axis ………………………………………………
5. Moment of Inertia (I) about y-y axis ……………………………………………
6. Section modulus (S) about x-x axis …………………………………………
7. Section modulus (S) about y-y axis …………………………………………

2. Find the self-weight of the stringer in pounds, given the density of wood is 40 lbs/ft³

…………………………………………………..

3. Find the modulus of elasticity to be used in the design calculations of this stringer

…………………………………………………..

Answer 1

Nominal size is the given size which is 12x20.

Standard dressed size is the standard width and height which is 11.5inch x 21.5inch (as per National design specifications).

Area = 11.5x21.5

= 247.25 inch^2

Moment of Inertia (I) about x-x axis

Moment of Inertia (I) about y-y axis

Section modulus (S) about x-x axis

Section modulus (S) about y-y axis

The self-weight of the stringer in pounds, given the density of wood is 40 lbs/ft3 = 68.68 lbs/ft (as per National design specifications).

The link for the national design specifications is  https://awc.org/pdf/codes-standards/publications/nds/AWC-NDS2018-Supplement-ViewOnly-1805.pdf