Resources for strength calculation for an outside aluminium loft ladder and what about it becoming brittle in cold weather?

Question

I have been thinking for years about building an outside stair / loft ladder to climb from a platform to another one, one stair higher (3 meters). However, I never studied material strength, and I don't know anything about how to calculate my needs. Especially since talking with a friend, he mentioned that aluminium becomes brittle in cold weather and he has witnessed multiple accidents with ladders breaking in cold weather.

Here is the kind of material I wanted to buy

or

And here is the strength data

What do those mean, where can I find resources to (learn to) use those, and how should I add correction related with temperature variations?

Answer 1

Aluminum is generally not subject to low temperature embrittlement, unlike steel. Some alloys are used at cryogenic temperatures. Here is some very general information on low temperature properties. I don't think low temperatures are causing aluminum ladders to break. You should be able to find strength data as a function of temperature for any alloy you might be considering from an aluminum supplier.

Answer 2

Ferritic steels ( the magnetic stuff ) are the only metals that may have a severe toughness loss ( brittle) at low temperatures. As the temperature drops the ductility of all metals tend to be lower but not the potentially sharp reduction of toughness like a ferritic transition. Your aluminum ladder will become slightly stronger in cold weather; don't drink what your friend is drinking.