Project Lead: Thomas Miller

Project duration: 3/1/16 – 9/30/19 (NCE)

Understanding how roof and floor systems (commonly called diaphragms by structural engineers) that are built from Pacific Northwest-sourced cross-laminated timber (CLT) panels perform in earthquake-prone areas is a critically needed area of research. These building components are key to transferring lateral forces from wind and earthquakes into the shear walls and down to the foundation. The tests performed in this project will provide data on a commonly used approach to connecting CLT panels within a floor or roof and the performance of the overall system and the screw fasteners. Structural engineers will directly benefit through improved design guidance. A broader benefit will be increased confidence in the construction of taller wood buildings in communities at greater risk for earthquakes.



  • Phase 1): 1) Determine strength and stiffness of common self-tapping screw connections used in diaphragms with fastener spacing used in practice; 2) Find ductility (energy dissipation) of the connections to contribute to more accurate structural performance characteristics for seismic design.

  • Phase 2: 1) Evaluate seismic design parameters related to overall and connection behavior using full-scale 15 ft. x 15 ft. CLT diaphragms tested monotonically and cyclically; 2) Compare performance to behavior of inter-panel connections using surface splines from Phase 1; 3) Apply the results to seismic design using ASCE 7-16 provisions and calculate the diaphragm design force reduction factor Rs for use in its alternate design method; 3) Compare results to those from a related ARS project (CLT Fastener Solutions for Tall Wood Buildings), related values from the Phase 1 tests, and from precast concrete and light-frame wood diaphragm testing; and 4) Supplement the efforts of others: FEMA P695 development; CLT diaphragm design white paper team; NEES-CLT group; other university researchers.

Presentations, posters,etc.
  • C. Beairsto, T.H. Miller, and R. Gupta (2019), “Large-Scale Monotonic and Cyclic Testing of CLT Diaphragms,” TDI Symposium, Oregon State University, Corvallis, OR.
  • C. Beairsto, T.H. Miller, and R. Gupta (2019), “Monotonic and Cyclic Testing of Large-Scale CLT Diaphragms,” International Mass Timber Conference, Portland, OR.
  • C. Beairsto, T. Miller, and R. Gupta (2018), “Monotonic and Cyclic Testing of Full-Scale CLT Diaphragms,” Poster at International Mass Timber Conference, Portland, OR.
  • K. Sullivan, T.H. Miller, and R. Gupta (2016), “Behavior of Cross-Laminated Timber Diaphragm Panel Connections with Self-Tapping Screws,” World Conference on Timber Engineering, 8 pp.
  • K. Sullivan, R. Gupta, and T. Miller (2016), “Behavior of Cross-Laminated Timber Diaphragms, Poster at 70th International Convention of the Forest Products Society.
  • K. Sullivan, R. Gupta, and T. Miller, “CLT Diaphragm Panel-To-Panel Connections,” 58th International Convention, Society of Wood Science and Technology (Pre-project presentation)

Publications, thesis citations

  • K. Sullivan, R. Gupta, T. Miller (2018), “Behavior of Cross-Laminated Timber Diaphragm Connections with Self-Tapping Screws,” Engineering Structures,

doi: 10.1016/j.engstruct.2018.04.094, pp. 505-524

  • K. Sullivan (2017), “Behavior of Cross-Laminated Timber Diaphragm Panel-to-Panel Connections with Self-Tapping Screws,” MS Thesis, Oregon State University, Corvallis, OR.