Innovative pool design

The Grandview Heights Aquatic Centre in Surrey features a dramatic wood roof.
Monday, July 4, 2016
by Cheryl Mah

The long-anticipated Grandview Heights Aquatic Centre is making a big splash in South Surrey.

Officially opened in March 2016, the Aquatic Centre is an architecturally striking facility that will meet the recreational needs of a growing community while providing the capacity to host competitive swimming and diving events.

Designed by HCMA Architecture + Design, the $55 million project serves as an anchor for the developing area and is the first to be completed on a “super block” that is part of Surrey’s long range vision for a regional campus of health, wellness and sports excellence.

“The City of Surrey set the bar very high, wanting a world class facility with iconic architecture,” says Melissa Higgs, associate and project architect at HCMA Architecture + Design.

Programmatically the design had to balance recreational needs with the unique needs of swimming and diving competitions.

“It was important to figure out how to orient the pools to meet those needs,” says Higgs. “The pools are arranged end to end rather than side by side, allowing us to bring the activity of the leisure pool onto the corner, while creating a separate and quieter environment for the competition pool.”

A key design objective was to have the activity within the building be highly visible. The design team chose to do that by maximizing glazing towards the street and placing the leisure pool and waterslide close to the corner of 24th Ave and 168 St.

The 95,000-square-foot aquatic centre includes a 10-lane, 50-metre FINA certified competition pool, 10 metre high dive tower and a leisure pool with a waterslide.

Other features are two hot tubs, universal change area, fitness centre overlooking the natatorium and seating for up to 900 spectators.

But the most dramatic and defining feature is the mass timber roof that resembles an undulating wave form.

“Swimming pools have a very long span from a structural perspective so we looked at different solutions,” says Higgs. “Instead of going the short span – across the lap pool, we came up with the idea of a cable hung structure.”

Wood was chosen because it met a number of important design considerations including Surrey’s Wood First policy. “Wood also performs very well in pool environments and aesthetically it creates a warm atmosphere,” notes Higgs. “We were able to get the full span we needed with a very shallow wood structure. In a way it’s really a form follows function – very efficient solution to the problem.”

Glulam “cables” were used instead of conventional steel roof trusses, reducing the effective structural depth by 90 per cent. This strategy also served to reduce the building volumes and energy costs, as well as sequester carbon.

When coming up with the roof structure design, Fast & Epp project engineer Derek Ratzlaff explains that they had to work within the constraints of the dive tower on one end and the water slide on the other end. With the two structures creating natural high points, the concept was to create a timber catenary roof suspended between concrete end buttresses and a central V-column support. The sections span 180 feet and 120 feet long. While suspended catenary steel cable systems are not uncommon particularly on bridges, the use of timber as long spanning tension cables is rare. The result is what the project team believes to be the world’s most slender and longest span timber roof ever built.

“The innovation is in the material choice. Wood is unusual in tension instead of a cable,” says Ratzlaff, noting the buttresses are doing double duty supporting the roof and serving as the dive tower.

Execution of the innovative design required a high level of technical accuracy from the construction team.

“The biggest challenge was making sure the glulams met the tolerances between the buttress columns,” says EllisDon Construction project manager Gary Watt. “It took many painstakingly long days to make sure everything was all lasered and surveyed in correctly.”

Construction took 20 months with EllisDon achieving substantial completion in December 2015. Peak manpower was just over 100. Installation of the roof was a key milestone.

The 532,000 lbs of glulams for the roof were manufactured by Western Archrib in Edmonton and trucked to the site. The extensive preplanning by the project team allowed Seagate Structures to assemble and install the roof structure in 12 days, completing the work ahead of schedule.

More than 100 rafters measuring 120 and 180 feet long were raised over 74 feet and set in place with two 2.5 inch steel pins on each side. Each assembly is made up of paired glulam beams, each measuring only 5 inches wide and 10.5 inches deep.

All the buttresses are post tensioned, which was another undertaking in itself.

“The post tensioning required extra planning and careful mock ups… before the work was done and a lot of that work had to be done high in the air,” says Watt.

A unique envelope connection design was also required to accommodate the roof. Like a suspension bridge, the roof will move under different loading conditions (eg. wind, snowfall). The design team had to ensure the deflection of the roof would not exceed 200mm.

“Because of the movement in the roof, all the walls had to be sleeved at the roof line – that was tricky,” says Ratzlaff, explaining a long slotted-hole connection was used as the solution.

Considerable time was spent developing a glulam cable to concrete connection and glulam mid span splice connection that would be structurally sound, aesthetically pleasing and easy to erect.

To avoid unsightly exposed mechanical ducting, the vertical steel facade columns along the south wall were used as ducts to eliminate condensation at the exterior glazing.

“We actually have the ducts for the mechanical systems in the columns – highly unusual. We drilled holes into the steel columns and air is piped right into the columns from underneath the pool deck and shoots across the glass,” says Ratzlaff, adding it’s another unique example of the structure doing double duty.

Additional highlights of the building engineering include an exhaust system to extract trichloramines (chlorine odour) from the pool surface, which provides a more pleasant and healthy environment for swimmers.

“This is the first pool design that we’ve done that has a trichloramine exhaust system, which is constantly extracting air across the surface of the pool water and removing trichloramines,” says Higgs, noting the LEED certified building’s mechanical system is highly efficient and uses heat recovery.

Watt cites installing the mechanical equipment was another challenge. “Instead of being on the roof because of the design, the mechanical equipment is all in the basement. It all had to be put in place during construction. It was a very tight space for all these large electrical and mechanical equipment. Lots of careful planning and BIM modeling to make sure everything would work and fit.”

The unique nature of the building meant plenty of custom work for the various trades. For the structure to come together, sequencing of work was not as straightforward as building top to bottom. “It required work to be done in different areas at a certain time,” says Watt.

The innovation and technical expertise required to make the roof a reality has already earned the project two prestigious awards. It was honoured with a 2016 AIBC Lieutenant Governor of British Columbia Merit Award in Architecture and a 2016 ACEC-BC BC Lieutenant Governor’s Award.

“It was a bit of surprised but we’re really proud to be honoured like that,” says Ratzlaff, who also worked on the Richmond Olympic Oval. “It is definitely a highlight project.”

Higgs says, “the roof makes it a beautiful experience inside the pool and a striking building on the outside. We’re proud of the architecture, but the real success is the huge impact it will have on the community. The amount of use from the public has been high – upwards of 2,500 a day in the first week it opened.”

Watt says the pool is definitely not a typical project.

“We had a very good team that worked together to resolve any issues quickly,” he says. “I will probably never do another one that looks like this in my career – lots of challenges and different construction techniques and thinking outside the box. This definitely wasn’t a box.”


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