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Sidewalk Labs claims 35 storeys would be the highest mass timber building so far. The team modelled how it would perform compared to a traditional concrete building of the same size.
Sidewalk Labs has developed a digital "proto-model" of a 35-storey timber building for its proposed Waterfront Toronto smart city development.
The digital proof-of-concept – which Sidewalk Labs calls Proto-Model X, or PMX – provides insights into the hypothetical performance of the building made from factory-produced ‘mass timber’. The 3D model is rendered in Revit, a building design software from Autodesk, and hosted in BIM 360, a cloud-based tool that stores technical information about the building.
PMX was developed in collaboration with a team of architects, engineers and environmental designers.
PMX was developed in collaboration with a team of architects, engineers and environmental designers, including Aercoustics, Aspect Structural Engineers, Atelier Ten, CadMakers, Gensler, Integral, JE Dunn Construction, Michael Green Architecture, RDH, Sweco and Vortex Fire.
There is growing interest in timber buildings due to the development of mass timber, its potential to help address climate change and the fact that mass timber building parts lend themselves to efficient factory production, which can save time and cost.
Alphabet-owned Google sibling Sidewalk Labs claims 35 storeys would be the highest mass timber building so far. The team modelled how it would perform compared to a traditional concrete building of the same size.
The PMX building was approximately 2.5 times lighter than its concrete counterpart and behaved more like a building of 40 or 50 storeys during wind analysis.
The team realised that a traditional structural core made of timber would have to have walls five feet thick to deliver the required stiffness. This would be almost impossible to fabricate, difficult to assemble on-site and would also cause loss of floor space.
The PMX exoskeleton system solution is made of big timber beams crossing the facade of the building, based on a design tool pioneered by structural engineer Fazlur Khan, whose steel exoskeleton on Chicago’s 100-storey John Hancock Center in 1965 is widely held to have laid the foundation for modern skyscraper design.
Cara Eckholm, associate director, buildings, Sidewalk Labs, said: “Because the exterior lateral bracing is now doing the lion’s share of the work to keep the building standing, the core walls become lean – dropping from 5 feet thick to just 10 inches – and the interior is left open and flexible.
"The entirety of the 8,450-square-foot floor is preserved for tenant use, and future tenants would have the ability to knock down the non-structural wall between rooms,” she added.
"Because the exterior lateral bracing is now doing the lion’s share of the work to keep the building standing, the core walls become lean."
Even with the exoskeleton, PMX was particularly prone to swaying due to its lightness. After exploring several solutions, Sidewalk Labs settled on a 70-ton steel ‘tuned mass damper’. Tuned mass dampers are devices used by structural engineers working on super-tall buildings, such as Taipei 101. They reduce the amplitude of mechanical vibrations in structures.
“This targeted chunk of steel plays an essential role in making PMX comfortable for tenants while remaining less carbon-intensive than using concrete throughout the building,” Eckholm said.
The mass timber buildings that Sidewalk is planning would be produced in a factory that makes standardised parts, which can be combined to form many different types of buildings – much like LEGO bricks – to make the manufacturing process faster and more predictable, with their interlocking nature enables easy on-site assembly.
They will use “flooring cassettes”. The shell of each cassette is made of wood panels with acoustic and insulating layers. Each cassette houses pipes and wires that are part of the building’s mechanical, electrical and plumbing systems. Cassettes are slotted one by one into the envelope of the building, linking up to one another to form new floors.
It is still to be confirmed whether Sidewalk Labs proposal to create a smart neighbourhood in a disused area of Toronto’s Quayside district will go ahead. In November, the board of Waterfront Toronto unanimously agreed that the plan could proceed to more formal evaluation and further public consultation. The scope of the project was scaled back, though, including the amount of land, the oversight of data and the “lead developer” role.
Last month, the Board of Waterfront Toronto pushed the deadline for making a final decision back to May 20, from March 31, to allow more time for public consultation.
Sidewalk Labs’ proposal has faced ongoing controversy, with high-profile advisors standing down over concerns about privacy and personal data. A group of citizens launched the Block Sidewalk campaign to try and stop the deal and in April 2019, the Canadian Civil Liberties Association (CCLA) said it was taking legal action against Waterfront Toronto and the federal, provincial and municipal governments over citizens’ rights and “surveillance” relating to the project.
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