Todd Pattist wrote:

In other words: If the pilots had not extended the airbrakes, the
Nimbus would not have disintegrated.


I don't think this is quite the correct way to look at it.
It implies that opening the brakes was the direct cause. I
don't see it that way.

Each part of the wing can produce a certain lifting force.
The g-force you feel is the result of the total lifting
force produced - applied to the mass of the glider.
Opening the brakes prevents portions of the wing from
producing their share of the lifting force. For structural
reasons, the remaining parts (tips especially) cannot safely
produce any more lift than they were producing before the
brakes were opened, so the total lift force is reduced and
the g-force drops automatically. Thus, it's not so much
opening the brakes that breaks the wings, it's the use of
the elevator to increase the AOA after the brakes are opened
to try to hold the higher g-force.

I think this may not be a correct analysis. In my ASW 20, during steady
straight flight, I could open the spoilers while holding the stick
steady. The glider would maintain it's attitude, but begin sinking. The
G force was reduced very momentarily, then returned to 1 G. The wing
tips would bend upwards, indicating they were producing additional lift.
The additional sink rate increased the angle of attack of the wing, and
this caused the additional loading on the wing tips. In other words, the
lift tends to shift to the wing tips without the pilot doing anything
besides opening the spoilers.

I haven't tried it, but I assume this would also happen in a 3 G turn.
If true, the only way to avoid exceeding the "open spoiler G limit"
would be reduce the G loading before opening the spoilers.