Canadian Consulting Engineer

News

Construct Canada session shows Murphy’s Law at work

Judging from a session at Construct Canada Conference and Trade Show last week, construction is no industry for the timid and faint of heart.




Judging from a session at Construct Canada Conference and Trade Show last week, construction is no industry for the timid and faint of heart.

Nastassja Pearson, P.Eng. and Andrea Yee, both project managers at Halsall Associates, presented on “Murphy’s Law: Unintended Consequences in Building Envelope Design and Construction,” on December 4. The well attended session was one of scores held at largest construction conference, which took place over two days at the Toronto Convention Centre downtown.

Pearson and Yee outlined trends in architecture and construction that are creating potential problems and need special attention from engineers and designers.

First they talked about glass. It is being used everywhere in large panels for floor-to-ceiling walls, in balconies and in imaginative building forms, but it has also received lots of attention for breakage and failures.

For example, designers want to create “cleaner” looks with minimum framing for glass. But this requires complex glass support systems, which in turn require more complex engineering analysis.

Another trend is for glass to be used as balcony guardrails, but fitted well outboard of the balcony slab and often with minimum framing for support. Some well publicized failures in Toronto during 2011 and 2012 prompted new regulations in the Ontario Building Code (see https://www.canadianconsultingengineer.com/news/structures-glass-fallout/1001954101/)but even these new regulations leave some design questions unanswered. And there are issues related to the glass quality because manufacturing heat-soaked tempered glass, for example, requires the ovens to be carefully calibrated in order to avoid imperfections.

As a designer it’s also necessary to make sure that the product that arrives on site is what was specified. Yee said. Quality control programs are critical. On their site inspections, for example, they have several times found that the argon filling specified for insulating glass units was missing.

The trend for architecture to be more individualized, such as with twisting glass-walled towers, irregular forms, and special cladding features, demands more engineering attention. Pearson cited a campus building where a patterned metal screen was added outside the glass wall envelope to provide shading. A catwalk was provided between the two vertical walls and gave enough room for crews to clean and maintain the glass. However, there was not enough space to manoeuvre when it came time to replace a glass panel. So cranes had to be brought in.

Another project, in Calgary, was designed with a terracotta outer screen wall. Anticipating potential problems, Halsall recommended testing a scale model of the wall in a “cold room” to show how snow and ice may build up on the façade.

Glare and reflections from glass can create unforeseen problems. Pearson cited a case in the southern U.S. where sunlight reflecting off glass melted the siding on a neighbour’s house. The neighbour’s response: install a mirror and shine the light right back.

There can also be problems with large prefabricated cladding panels. These are “fast, flexible, and have great textures.” They have the advantage of being manufactured under quality-controlled conditions. But problems can come when they arrive on site and hundreds, sometimes thousands, of them have to be assembled. The joints and transitions between panels and materials need careful detailing to maintain the external water and air barrier. Pearson showed an infra-red photograph of a building under positive pressure where heat could be seen escaping through the panel joints. Detailing the panel joints might represent only 10% of the entire job, she suggested, but “to do it right might take 90% of the time.”

Insulation is another issue. You may not achieve your expected R20 wall if the fasteners, drip edges and connectors, for example, create thermal bridges, said the presenters. In some cases insulation can ruin historic brick buildings by cutting off the interior heat source to the outside walls and exposing them to greater freezing and thaw risks. If improving energy efficiency is the goal, it may make more sense to look for ways to make the building air tight.

With flooring problems sometimes occur due to the shift to low-VOC adhesives. Pearson and Yee reported seeing blistering, debonding and lifting floors, which can be a costly problem to fix in facilities such as hospitals. Concrete floors are often poured at the end of a project and not enough time is left for the concrete to cure and dry out before an impermeable floor material is installed.

With Murphy’s Law (what can go wrong, will go wrong), we might be tempted to just give up, Pearson said. But she had some remedies to offer.

First, do a collaborative design review with all the major players involved as early as possible. That way the architects, engineers, contractors, etc. can all discuss the intent of the project, provide their specialist input, and discuss plan B if new conditions should arise.

Second, do more testing. This includes laboratory tests, such as cold room scale testing and quality control field tests to ensure you are receiving the upgrades that your client is paying for.

Pearson’s final advice: “Plan ahead, and communicate with the whole project team.”