Today I was supposed to participate in a mapping party, and then this happenes: 
… 
I don’t think I’ll buy an Alu-frame again…
Is this the fault of the alu bicycle frame or your own bulky frame? 
(sorry, couldn’t help myself. No pun intended!)
Maybe you just need a longer seat post so that the forces are spread over a larger section of the bicycle frame…
Prolly related yes… 
But from what I understand alu-frames degrade heavily after 2-4 years of use.
Not sure what you mean with longer seat post, you mean it should go all the way down?
Damn…
Nothing wrong with ally frames and I believe that a steel frame of similar design would have failed in a similar fashion. Mine (mid-range Eaton tubing in a conventional design) is only a year younger, has copped a hiding and is still going strong. I have seen a few frames fail, but it has always been a result of damage (not saying that is the case here though) or weird design (makes me think Giant). I suspect, as does Lambertus I think, that the seat post did not go far enough into the frame to properly support the loads. My general rule of thumb is a minimum of 100mm insertion and most importantly it must extend at least 50mm (more is better) past the bottom edge of the top tube. That puts the seat loads directly from the seat post into the frame proper instead of hanging out in the breeze. Thin-walled tubing (even steel) is not up to the task of supporting seat loads above the top tube on its own and it looks like you needed a post at least 100mm longer.
Cheers
Thanks, I’ll take a look how much it was inserted. It’s a good thing to know, I’ve never thought of this before. I usually want my saddle high, makes it easier to spot in the parking (and comfy)…