could potentially replace concrete and steel in certain niches of the market, exacerbated by the increasing tally of Mass Timber exclusive buildings. Aggravating matters further, Mass Timber too often orates how it overcomes deficiencies of concrete and steel through its advantages rather than seeking cooperation with the building material paradigms. If concrete and steel perform better in cooperation than alone, could Mass Timber likewise perform better when included within the mix than unaccompanied? The duo formed by concrete and steel provide many benefits that either one individually might not be able to achieve, forging a close relationship between them that is regularly selected. Concrete pos- sesses high compression strength, moldability on site, variability in mix designs and applications, and imperviousness to combustion and moisture (provided no cracks form). Steel, almost concrete’s
Figure 3: Brock commons during its fast construction: concrete and mass timber working together to create UBC’s 18-story dorm.
counterpart, likewise boasts compactness, ingredient abundancy, high structural predictability, and high tensile capacity. Concrete covers steel’s weaknesses in compression strength, corrosion, vulnerability to heat, and workability. Steel accommodates concrete’s weaknesses in tensile capacity, weight, and cracking. The two, despite some of their individual deficiencies, integrate well and provide a strong, economi- cal (in material costs), and predictable option for buildings around the globe. As stellar as concrete and steel in tandem are, adding Mass Timber, particularly CLT, to the team could bring even more benefits. CLT can be built between 25% and 75% faster than similar reinforced con- crete and steel buildings on a square footage basis, has a 20% overall faster schedule, and uses 90% less construction traffic. CLT has a much higher strength-to-weight ratio than concrete or steel, providing lighter buildings on foundations if soil conditions are less than opportune. CLT, comprised of renewable resources, contributes significantly to a building’s environmental conscientiousness, particularly in buildings seeking certification, such as LEED. Likewise, joining concrete and steel can mitigate the construction unfamiliarity and high material costs of CLT. An example of such a building where CLT united harmoniously with concrete is the 18-story University of British Columbia’s Brock Commons Residential Hall, which uses a concrete core, CLT flooring and walls, and glulam columns. This provides both structural rigid- ity and seismic flexibility, construction familiarity and logistic speed,
lighter loads on a foundation and stability in wind events, and many other dichotomies frequently desired when designing a building. Upon completion, it was the tallest Mass Timber building in the world and the tallest wooden building in the hemisphere. Since then, codes have changed and taller Mass Timber exclusive buildings have been built, but Brock Commons proved that CLT and concrete can integrate effec- tively. Other examples of structures that incorporate some combination of Mass Timber, concrete, and steel are the John W. Oliver Design Building at UMass Amherst (all three), Woodland Trust’s Headquar- ters (Mass Timber and steel), The Cube in London’s ShoreDitch (Mass Timber and steel), and Hoho Vienna (Mass Timber and concrete). The prototypical building of the future could likely be a combination of the trio: a building where floors, shear walls, and roofs are CLT; long span beams or beams under extreme loads are steel; and foundations and cores are concrete. Such a structure would be able to provide con- struction speed, strength, seismic flexibility, fireproofing, construction familiarity, and environmental consciousness that display ingenuity and serve humanity. As with many systems, the combination of parts is more valuable than the parts individually. If concrete and steel’s preeminence led to such astounding progress in the last two centuries, imagine what adding another revolutionary material with its own set of benefits to the as- sembly can accomplish over the next two centuries.
AUGUSTUS RAYMOND is EI Project Manager at CE Solutions.
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csengineermag.com january 2020
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