So, if structural is in some blocking foes everything get destroyed, only the object or how would this work?

I can remember reading about this but cannot remember how it happens

First, always helps to post the text:

Structural Integrity Field
Blocking terrain and walls 6 or fewer squares from this object can't be destroyed.

Gamma Bomb (just the pertinent part)
When the red line is crossed, deal 3 damage to each character and destroy each object, wall, and square of blocking terrain within 8 squares and then remove this object from the map.

First, keep in mind that SIF couldn't be in blocking, it would have to be beside blocking or walls.
Normally SIF would prevent the terrain within it's area of effect from being destroyed (although figures would still take damage.) However, I believe we got a ruling that the active player could choose the order of destruction/damage, so if I wanted to negate the effects of SIF I'd choose to have it be the first thing destroyed.

Note that SIF has received a very much needed errata and now reads:

Heavy: Blocking terrain (but not blocking terrain markers) and walls 6 or fewer squares from this object can’t be destroyed. This object has no effect when held.