Please note: This is not an educated opinion. Merely observational. To put together such a structure engineers test materials and structural designs, get approvals based on those designs, while at the job site inspectors verify the work done while often taking samples of material at the site and taking photographs. When I do welding on something as simple as a petroleum tank a crew will come out and pass nuclear radiation through critical joints onto a photograph film. Results are saved for the record. Somewhere there are extensive files and documents on this structure. It's inconceivable to me that this structure failed in this manner due to shoddy construction. It's just not plausible.