The crane that toppled over a Halifax building in the winds of post-tropical storm Dorian, damaging multiple buildings, evacuating residents and closing a busy street for two months, collapsed due to a “weld failure,” according to the provincial government’s investigation.
The Department of Labour and Advanced Education released the report into its investigation on Thursday afternoon as a highly-anticipated news conference detailing new restrictions due to COVID-19 was starting.
The 73-metre high crane was manufactured by Manitowoc Company, owned by Lead Structural Formwork Ltd., and erected at Wadih Fares’ Brenton Suites development. It collapsed on Sept. 7, 2019 at the height of the post-tropical storm at about 4pm.
It hit the corner of the Trillium condo building, and fell over a building under construction on South Park, known as the Olympus Building, and partially onto the street below. No one was injured, but there is a proposed class action lawsuit before the courts naming the developer and the manufacturer and owner of the crane, on behalf of businesses who suffered losses.
As Fares said in an interview at the time, “The crane wasn’t supposed to collapse; however, it did.”
Winds at the time of the collapse were between 97 and 107 km/h, according to the provincial report. Tower cranes like this one are meant to withstand winds of up to 160 km/h, the report says, and workers on the site had prepared the crane for the weather.
“Rigging was taken off the hook, the block was raised to its highest position, trolley was locked in place, the slewing brake was manually disengaged, and the counter jib was checked for any unsecured objects,” the report says.
“The crane was placed in weather-vaning mode by computer and confirmed it would vane properly.”
A few months before it collapsed, in June 2019, the crane wasn’t weather-vaning properly:
On June 4, 2019, the Safety Branch was advised by the general contractor that the turntable at the top of the tower crane had seized, preventing it from “weather-vaning” when subjected to wind loads. Weather-vaning is the ability of the crane to rotate freely into the wind when not in use. This is intended to reduce the effect of the wind on the structure. The general contractor advised that the top section of the crane, consisting of the cabin, turntable, and jib would be repaired or replaced as soon as possible to deal with the inability to weathervane.
That work was done, engineered, tested, approved and certified. None of the new components contributed to the collapse.
The investigation into the collapse began the day after, Sept. 8, and by Sept. 12, it was deemed safe to inspect the base of the crane in the development on Brenton Street.
“A possible failure point was initially identified in a lower mast section at the northwest corner of the crane tower (later referred to as Section 2) where a hollow diagonal tube had become separated from a solid vertical post at a point where it had previously been welded together (Photo 2),” the report says.
The province brought in a contractor, BMR Structural Engineering, to review the crane, and they confirmed the area where it failed.
“The jib, top mast, transition piece, and mast sections directly below the transition piece were undamaged. Based on their examination and other information collected by inspectors, including videos taken just prior to the incident, the engineer determined there was no structural failure in the top sections prior to the incident,” the report says.
“The bolts in the crane base were undamaged, indicating this did not contribute to the failure … The engineer’s report concluded that the crane collapse was the result of the failure in the second section of the mast approximately 6 to 9 meters above the base (initially identified by inspectors in Figure 3).”
In October 2019, the province issued an order to the owner of the crane, Lead Structural Formwork Ltd., “for a metallurgical assessment of the diagonal brace and node identified as the point of failure and an assessment of the turntable.”
There was a delay due to COVID-19 in the results of that assessment, but the province received them in August 2020, “indicating there was a lack fusion, corrosion, pores, and a crack, which propagated from the inside diameter to the outside diameter of the area of the weld. The report also mentioned other welding defects on other welded connections.”
In September 2020, the province received another report assessing the turntable of the crane, the part that had seized in June 2019 and was replaced, indicating there was “no defect or abnormality that would have existed prior to the crane collapse or contributed to the collapse.”
“The two reports confirmed that there was no abnormality in the turntable that would have contributed to the incident and that the defect in the weld on the second mast section contributed to the collapse of the crane,” the report says.
The investigation determined that the crane had undergone all the proper inspections, although it did find “that the crane operator’s logbook did not document the daily inspections from August 15, 2019 to September 6, 2019.”
The operator was issued a two-day suspension and the owner was fined $500, but “it was determined that the failure to complete the logbook was a deficiency, but did not contribute to the collapse of the crane.”
In conclusion, the report says the crane collapsed “as a result of the failure of a weld where a diagonal tube had been connected to a vertical member of the crane mast between 6 and 9 meters from the base.
“The weld failure caused the diagonal tube to separate from the vertical member of the mast, transferring the weight supported by the mast’s 4 vertical posts to only 3 of its posts, causing the tower section to rotate and fail, which resulted in the total collapse of the crane.
“The investigation determined the tower crane owner and operator met the applicable legislative and regulatory requirements to prevent this event from occurring and no further regulatory action will be taken with regards to the collapse of the crane.”
The department plans to meet with crane owners and operators to review the findings. It will also “require structurally critical welds in the masts and booms of all tower cranes in Nova Scotia immediately undergo a thorough cleaning for visual inspection of welds, non-destructive testing on any welds as found to be necessary, and any deficiencies repaired by a person as specified in the regulations or standards.”
It also plans “to develop and implement an industry leading code of practice or standard for enhanced tower crane mast and boom weld inspection, testing, and maintenance in Nova Scotia.”
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