The Case of the Failed Dallas Tower Crane
On a Sunday afternoon, a violent thunderstorm, with high winds between 75 and 80 mph, collapsed a tower crane and killed one innocent person and injured many others. The tower crane collapse extensive property damage to an apartment complex near the 5 story, concrete parking garage construction site. The construction company and owner claimed the tower crane was properly stowed for the weekend. The tower crane had been in service at the construction site for 15 months prior to the failure event. OSHA cited the company with numerous safety violations. Why did the tower crane collapse during the thunderstorm?
Samples from the welded tube structure of the failed tower crane were prepared for laboratory tests. Tube samples and welds were sectioned, mechanically tested, nondestructively tested, digitally photographed and subjected to expert inspections for several days. The alloy of the specimens were tested for hardness and high magnification investigations. Microscopy to X500, non-destructive tests by ultrasonic and penetrant testing methods, metallurgical grain structures and failed welded connections revealed possible causes for the tower crane failure during the thunderstorm.
There was visual evidence of defective welds on samples assessed in the laboratory. Lack of weld fusion, internal weld defects were readily observed in the welded connection of a diagonal tube from the tower structure. After welded connections were sectioned and prepared, weld defects were evident.
Welding specifications and requirements for the diagonal tube welds were unavailable from the overseas tower manufacturer or USA maintenance personnel. The Expert considered the observed weld deficiencies to be the primary reasons for the tower crane collapse during the thunderstorm.
The Lessons Learned:
Routinely inspect structural tube welds on tower crane structures. Tube welds on tower cranes should be properly welded and routinely inspected in accordance with sound practices and structural weld acceptance criteria when weather events may approach the limits of specified design considerations. Owners should specify simple, routine visual weld inspections of tower crane components.