Twenty years ago, one of the tallest skyscrapers in Chicago, known then as the Amoco Building, was found to have a deteriorating marble facade, with cracking and bowing of panels. Owners ended up replacing more than 44,000 panels at a cost of more than $80-million (U.S.) at the time.
Last month in Toronto, the tallest skyscraper in Canada, First Canadian Place, had a marble panel on the building's facade break loose, dropping more than 50 storeys and temporarily closing roads in the city's financial district.
The owner, Brookfield Properties Corp., says it has enlisted the assistance of facade specialists and a geologist to investigate and will not speculate on a cause.
"I am not aware of the Amoco Building situation in Chicago," said Melissa Coley, vice-president of investor relations and communications at Toronto-based Brookfield. "We have taken care of any immediate risk and safety concerns. We are not prepared to comment more at this time, until all our studies have been completed."
But striking similarities between the two buildings and the spectre of climate change offer a cautionary tale for Brookfield.
Later renamed Aon Center, the Amoco Building was built in 1972 and utilized the same type of marble that was used in the construction of First Canadian Place, which was completed in 1975. The panels, about 3.5 centimetres thick, came from Carrara, Italy.
Aon Center now has a replacement facade made up of five-centimetre-thick granite panels from Mt. Airy, N.C.
Michael Scheffler, an engineer and senior consultant with WJE Associates Inc., said the Chicago-area firm was brought in to investigate the Amoco Building facade in the late 1980s after one marble panel was found to be "bowing."
WJE went on to develop recommendations for the building, and Mr. Scheffler said the entire facade replacement was done "before anything fell off" the skyscraper.
Among the WJE findings:
Testing revealed the marble panels had lost about 40 per cent of their original strength;
Loss of strength was found to be a result of 16 years of exposure to heating and cooling cycles;
Laboratory-accelerated weathering testing estimated that the marble panels would lose about 70 per cent of their original strength after 26 years of exposure;
Structural analysis revealed panels could not support design wind loads with the strength loss.
Once the problem was determined, all panels were braced with straps until a new facade was designed and put in place in the late eighties and early nineties, said Mr. Scheffler, who has been involved in more than 600 investigations of deterioration and distress in buildings.
He stressed that climate variations played a significant factor in the breakdown of the marble panels' effectiveness.
"We found that the use of thin marble in an environment that experiences a lot of temperature variation and moisture is not good," he said. "The marble came from Italy. Well, Italy is not Chicago or Toronto. What worked well in Italy did not work so well here."
A Canadian structural engineer, who requested anonymity, said situations such as First Canadian Place and the Amoco Building are not design flaws, but more likely based on a lack of knowledge about the materials at the time of construction.
"In these cases, the possible infiltration of rainwater into panels and the potential for it to see many cycles of freeze and thaw over the years may have the same effect as we see on our roads. Higher wind forces on upper floors would also put stresses on the cladding and in the case where a defective or weakened panel was concerned, could help loosen it."
The effect of climate change cannot be underestimated, he added.
"Climate change is probably allowing more frequent and more dramatic temperature variations to occur in regions that normally see less of this," he said. "Personally, I believe that climactic data must now be followed more closely in order to adjust to the changes as soon as possible and determine what kinds of inspections and maintenance must be done to various structures and cladding before it becomes problematic."
While it was decided to replace the marble on the Amoco Building, that fate is not necessarily in the cards for First Canadian Place.
Depending on the strength of the marble and the design, the panels and their connections to the building's subsurface may have sufficient strength to support loads prescribed by the local building code, Mr. Scheffler said.
If the marble's strength is determined to be insufficient, remedial work, such as installing supplemental anchors may be required, if they can adequately engage the structural elements behind the panels, he said. Other factors to consider for this repair would be the cost and aesthetics, he added.
Jim Laughlin, Toronto's deputy chief building official, said Brookfield has confirmed that routine and frequent inspections of the marble cladding by professional engineers had been done prior to the First Canadian Place incident and the company has assured that enhanced monitoring and maintenance will continue.
He said the City of Toronto has a property standards bylaw that requires landlords to maintain their buildings in good repair, structurally sound and free from loose or unsecured objects and material.
"An order to remedy the unsafe condition was issued and we have been monitoring the progress of the repairs to ensure the building is safe," Mr. Laughlin said.
He said the city would be obtaining an engineer's report from Brookfield on the remedial action taken at First Canadian Place, as well as what measures it will undertake to prevent future occurrences.
Prominent Toronto developer Harry Stinson said he considers Brookfield to be a highly respected and competent building manager.
"If it [falling panel]happens again, it won't be because of the neglect of that company," Mr. Stinson said. "... If you look at the odds, look at the sheer scale with thousands and thousands of these tiles ... it is rather surprising there aren't more examples."
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