system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does an engineer inspect a large building or bridge to know if it’s safe?

What are they look at / for ?
gpt
Are there cracks where there shouldn’t be any?  
Where cracks are expected are they bigger than they should be?  
Are any cracks showing signs of widening?  
Is there visible corrosion?  
Is concrete spalling? (Popping off the reinforcement). 
Is water getting in?  
Are beams/columns/walls/floors heavily deflected when they shouldn’t be?
Has anyone made any modifications to the structure - eg has someone cut a hole in a structural wall to install a door, or commonly in houses has someone cut pieces out of wood floor beams to install cables and pipes?  
Are there any other signs of damage?  
Is the current building use consistent with the loads it was designed for?