Council on Tall Buildings and Urban Habitat
 

CTBUH Joins Chicago Seminar on Mass Timber Buildings
June 8, 2017

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CHICAGO – The Chicago Committee on High Rise Buildings (CCHRB) hosted a seminar titled The Heavy Timber High Rise: Building Tall with Wood in the 21st Century, which focused on new applications of wood as a structural material. The discussion revolved around new methodologies that permit multi-story construction, as well as the limitations, code compliance issues, and unfamiliarity that comes with utilizing new structural systems. CTBUH Executive Director Dr. Antony Wood spoke at the event, where he introduced the recent CTBUH Tall Timber TBIN Study and the upcoming timber workshop planned in conjunction with the 2017 Australia Conference. During the upcoming workshop, the Council will be attempting to define criteria for this new and innovative structural style.

The seminar began with a discussion of tall timber history. Timber construction in multi-story buildings is not necessarily a new concept; the eight-story, 145-foot-tall (44-meter) Butler Brothers Building in Minneapolis dates back to 1906, for example. It was also noted that the Chicago Building code recognizes the city’s extensive inventory of heavy timber framed buildings, and with a sprinkler system installed, such buildings are currently permitted to rise up to 120 feet (37 meters) in height. However, a distinction was quickly made between the traditional heavy timber construction common in North American warehouses and “mass timber,” which was the focus of the seminar. Mass timber is a new methodology in wood construction, which is pushing contemporary timber buildings beyond five floors in height.

Attendees filed into the auditorium, conversing amongst one another while they waited for presentations to begin. CTBUH Executive Director Dr. Antony Wood introduced the recent CTBUH Tall Timber TBIN study.

Mass timber refers to wood members made up of different layers, rather than the solid pieces of wood milled from large trees harvested from old-growth forests, as was typical a century ago. Such layered applications can be achieved in a few different methods, including glue-laminated timber (glulam), nail laminated timber (NLT), and cross laminated timber (CLT). Mass timber can be applied to typical post and beam construction, as was done with traditional heavy timber as well as modern day steel construction, but increasingly it is being applied to panelized construction, which allows for expedited construction and less waste than conventional techniques, as later presentations acknowledged.  

Case studies presented included:

  • The Tallwood House at Brock Commons in Vancouver, an 18-story university dormitory constructed of reinforced concrete cores with a framing system of wood columns and panelized floor slabs and façade sections;
  • A 92-room Candlewood Suites Hotel in Redstone Arsenal, Alabama, constructed entirely of CLT panels;
  • And the River Beech Tower, a conceptual 80-story building along the Chicago River utilizing a system of modules assembled from locally sourced wood and transported to the site by barge. 
Following the presentations, there was time for an engaging panel discussion and Q&A session. Pictured (from left to right): Jeff Morrow, Program Manager, Lendlease; Bernhard Gafner, Partner, Aspect Engineers; and Benton Johnson, Associate Director and Senior Project Engineer, SOM.

The seminar also included presentations on the results of various tests measuring the durability of mass timber construction against fire and forces subjected by an external explosion. Presentations also introduced the attendees to the studies and discussions now underway to recognize mass timber in the International Building Code (IBC). Currently, the IBC defines multi-story construction with heavy timber as Type IV; this type would be expanded to include three subcategories with different fire ratings, which could potentially determine the allowable heights on new high-rises constructed with various types of mass timber and hybrid structural systems. The seminar then concluded with a panel discussion between building design professionals and representatives of the Chicago and New York City fire departments offering their concerns about multi-story structures composed of combustible materials.

The general consensus among conference presenters was that mass timber, although still in an experimental and research phase for tall buildings above 12 floors in height, is poised to take on a growing share of mid-rise construction above five floors. As popularity grows, it is envisioned more buildings will become carbon sinks, sequestering the greenhouse gas through the sustainable management of forests where building materials can be locally grown, harvested, and prepared for construction.

Speakers included (from left to right): Jeff Morrow, Program Manager, Lendlease; Bernhard Gafner, Partner, Aspect Engineers; Benton Johnson, Associate Director and Senior Project Engineer, SOM; Dr. Michael Ramage, Director, Centre for Natural Material Innovation, University of Cambridge; Todd Snapp, Design Principal, Perkins + Will; David Weihing, Principal, Thornton Tomasetti; Amanda Kimball, Project Manager, National Fire Protection Association (NFPA) Research Foundation; Carl Baldassara, Principal, Wiss Janney Elstner and Associates; and William Tobin, Vice President of Timber & Innovations Group, Lendlease.