Steel is 3 times stronger than aluminium. It is also 3 times heavier.
Anything that weighs the same as a steel frame will do it.
Nobody usually hauls the weight I do on my GM.
Lets see.
On an alloy frame much weaker then the above and no rear shockies. I strap 27kgs of lead to the frame the . Then I place a approx 32kg child on the back rack with a pillow. Then I place a child 22kg on the front bar on a pillow strapped ontop of the SLAs. The I put a 5kg trailer onto my bike and a full grown adult of 57kg sits in the trailer.. I ride 16kms without any failure.
Lets see.
My alloy bike weighs 22kg
Lead acid pack. 27kg
GM hbs hub 5kgs
rack, rubber straps and what not 5kg
first child 37kgs
second child 22kg
Me 70kg.
Thats 166 kg with out the bike frame. and 188kg with frame
Trailer and passenger 63kgs.
Now we are up into the 250kg limit. Then ride this bike doing similar stuff around for over a year at speeds exceeding 40kph. Until I melt the poor 36v motor.
Proof of melted motor.
My first 48v SLA build on an alloy frame. I took the crate off and fastened a pillow to the rack and rode 3 children to school and back.
My rear dropout. Rather small compared to some aluminium frames.
How is his frame going to break in 5 seconds?
Many people have problems with the drop outs with front hubs a alloy forks.
Providing your dropouts are nice and strong don't worry unless you are a very large person.
If anything you may need a stronger rear shock. Thats all and nothing more.