Hi Antonio,
I pick the first two as evoking ideas of empty power that has outlasted purpose and life. These to me being to mind existential thoughts of the importance of the strong things we rely on. It may not be them that fail us, rather, life moves on and they cannot move with life.
This picture stands out as having more than just an impression I'd see and walk off never to think of it more. There's some anthromorphioc feeling in the curved elements as if muscles are being flexed. With the weathered patina and decay, it is somewhat defiant. Like an old man guarding his village after the rest of population have moved on.
The second picture has a similar feeling, as if to see, in spite of time, and there being nothing to guard, I'm still competent to block you access. The stength of the vertical bar, (yet rusted) and the convergence to infinity, suggest being there for a long time. It emphasizes the present and it is devoid of meaning. We have great stength but nothing to guard anymore. The present has no meaning.
Thanks for sharing,
Asher