On 08/08/2016 08:26, RuudH wrote:

I was lucky to discover the sheared forward bolt before my 1200 km trip to the French Alps this spring
This bolt was exactly the same position as in your picture. Only the head was gone, with the rest of the bolt still in.

https://dl.dropboxusercontent.com/u/...obra-bolts.jpg

That photo shows a classic fatigue failure. But it has failed through
the shank not the threaded portion. Rather it appears to match the
corrosion marks on the remaining bolt. It also looks like the brittle
fracture area is quite a large portion of the total area, which implies
that it is quite highly stressed.

Solution? Bigger bolts, more bolts or stronger bolts, or all of these.

Ian