why do structures collapse?

http://o.canada.com/sports/soccer/world-cup/fifa-world-cup-gallery-brazilian-bridge-overpass-collapse

why do structures collapse?

• faulty design?

• faulty construction?

• faulty construction inspection and materials testing?

• all of the above?

An independent investigation is needed to determine why a structure fails. 
The independent investigation must address:

• the engineer, including how the engineer was selected, and the engineer's relationship with the government

• the builder, including how the builder was selected, and the builder's relationship with the government

• the construction inspector and materials tester, including how the construction inspector/materials tester was selected, and the construction inspector's relationship with the government

• public-private partnership? crony capitalism? 

http://en.wikipedia.org/wiki/Crony_capitalism

Without an independent investigation, we will never know why a structure collapsed.
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