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Design of Mass Timber Diaphragms

and the new CLT Diaphragm Design Guide

When striving for material efficiency, the design of mass timber floor and roof systems to resist horizontal wind and seismic loading through diaphragm action is an important consideration. The design of diaphragms with mass timber panels typically follows one of two load path strategies. For diaphragms in nail-laminated timber (NLT), dowel-laminated timber (DLT), and glue-laminated timber (GLT) decking, a structural topping layer of wood structural panels is commonly used. For cross-laminated timber (CLT) diaphragms using CLT made from either solid sawn lumber or veneer-based structural composite lumber, the panels can be the primary diaphragm structural element. This presentation will provide detailed structural design and detailing recommendations for wind and seismic load-resisting diaphragms made from all of these products. It will also feature an in-depth review of the provisions for CLT diaphragm design in the American Wood Council’s code-referenced standard, 2021 Special Design Provisions for Wind and Seismic (SDPWS). To demonstrate practical design techniques, CLT diaphragm detailing options and examples will be presented based on WoodWorks’ new CLT Diaphragm Design Guide.

July 12, 2023 | 1:00-2:30 pm EST
Attendees can Earn 1.5 AIA/CES HSW LUs, 1.5 PDH credits or 0.15 ICC credits


Scott Breneman

Scott Breneman, PhD, PE, SE, Senior Technical Director, Mass Timber, WoodWorks 

Dr. Breneman is a licensed Structural Engineer and Professional Engineer in the State of California, a PE in the State of Washington, and Senior Technical Director – Mass Timber in the Project Resources & Solutions Division of WoodWorks. He received bachelor’s and master’s from the University of Florida and a doctorate from Stanford University. Scott has experience with structural design, seismic rehabilitation, and peer review of projects varying from single-family homes to high-rise hospitals. He is Past-President of the Structural Engineers Association of Central California, an associate member of the seismic subcommittee of ASCE 7 Minimum Design Loads for Buildings and Other Structures, and a member of the PRG 320 CLT product standard committee. At WoodWorks, he provides project support and education to individuals designing wood buildings and oversees the development of technical educational content.

Eric McDonnell, PE, Principal & Director of Mass Timber, Holmes

Prior to returning to Holmes as Principal, Eric worked in Christchurch, NZ on the rebuild effort after the 2011 Canterbury earthquakes. In Portland, he has led structural engineering efforts on the likes of the Rocky Mountain Institute Innovation Center, Framework, District Office, and the Adidas North American Headquarters Expansion.  Eric has also been at the forefront of mass timber research in the United States, including participating in the NSF/NHERI Collaborative Research project to develop a Resilience-Based Seismic Design Methodology for Tall Wood Buildings and co-authoring the CLT Diaphragm Design Guide and the U.S Mass Timber Vibration Design Guide published by WoodWorks.

Catalyst / MGA | Michael Green Architecture, Katerra / photo Andrew Giammarco