Problem from book(adsbygoogle = window.adsbygoogle || []).push({});

"the roof of a 9m x 10m school has a total mass of 12600 kg. The roof is to be supported byt "2 x 4s" (actually about 4cm X 9cm) along the 10m sides. How many supports are required on each side and how far apart mush they be? Consider only compression and assume a safety factor of 12"

Well, I figured that the area of one support is [tex]4 cm \cdot 9 cm = 3.6 \cdot 10^{-3} m^2[/tex]

and that the total force of the roof is it's own weight [tex]F = 12600 kg \cdot 9.80 \frac{m}{s^2} = 1.23 \cdot 10^5 N[/tex].

The stress is given as [tex]stress = \frac{F}{A}[/tex], so the stress on one support should be [tex]\frac{stress}{x}[/tex] where x is the number of supports.

What should I do next (The Compressive strength is given in the book for wood; [tex]35 \cdot 10^6 \frac{N}{m^2}[/tex] parallel to grain and [tex]10 \cdot 10^6 \frac{N}{m^2}[/tex] perpindicular to grain)

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Compression problem

**Physics Forums | Science Articles, Homework Help, Discussion**