Web Based Tools for Diaphragm Design
Using web based tools can save time and increase efficiency during structural analysis, and often these tools are the most up-to-date resources which include changes and updates to the code. Are you aware of the many online resources available to assist with calculating the shear strength and stiffness of steel deck diaphragms?
In the July 2023 SEU session, Mike Antici, PE, from Vulcraft, and Thomas Sputo, SE, PE, from Sputo and Lammert, LLC, presented, on behalf of the Steel Deck Institute, Diaphragms Are More Than Just Deck and Fasteners. Tom and Mike explained how traditional shear mechanics are applicable to diaphragms and how the shear stiffness analysis can be used in lieu of designing a diaphragm as rigid or flexible. They also reviewed capacities and limitations of joists, deck, and fasteners.
During the presentation, Tom and Mike mentioned several online tools and analysis resources for diaphragm and fastener checks. For example, SDI has a Diaphragm Interaction Calculator which produces deck capacities based on the user’s input of various deck profiles, thickness, and spans, as well as different fastener sizes and spacings. Tom noted the importance of using the correct number of spans in this online tool since the stiffness of the deck is proportional to the number of spans, while the deck strength is inversely proportional to the number of spans. This free online tool calculates the shear strength and stiffness of the diaphragm as well as the interactive allowable shear strength under combined loads with uplift.
Mike noted that SDI is not the only tool available; many deck and fastener manufacturers have also developed online tools. Hilti offers its users PROFIS DM Diaphragm which is offered as a free software download. Nucor offers its customers a Bare Deck Diaphragm tool as well as a Deck-Slab Diaphragm tool which is available free for registered users. Also, New Millennium Building Systems offers a web based calculator, Deck Tools, for deck diaphragm capacities. This online tool allows for roof deck, composite deck and form deck calculations with various fastener patterns. Simpson Strong-Tie has developed a Steel Deck Diaphragm Calculator as well, which can be used to produce the necessary diaphragm capacity tables for your deck configuration.
Tom and Mike highlighted a number of recent changes within the code which affect the capacity of deck diaphragms, and Mike strongly recommended using these online tools in favor of published manufacturers tables which may be outdated or not include these new code provisions. Deck diaphragms are a critical component of the lateral force resisting system, and using these free, available resources can validate that all aspects of the diaphragm are capable of providing a continuous load path for your structure.