Experimental Tests of Wide Aspect Ratio Cross Laminated Timber – Steel Diaphragms for Hybrid Building Applications

Abstract

The purpose of this investigation is to identify the behavior of wide aspect ratio, cross-laminated timber (CLT) diaphragms, with steel gravity members, designed to meet the code requirements given in the 2021 Special Design Provisions for Wind and Seismic (SDPWS) (American Wood Council, 2020). To do so, three configurations with varied inter-panel connections were tested. To identify the impact of different inter-panel fasteners, metal surface splines with nails and screws were evaluated. The metal surface spline along the beam lines was then removed to test the use of the panel-beam connection as the inter-panel connection. Testing revealed an excess in strength capacity with the ASD design strength exceeded by a factor of 4.5-6 across all configurations compared to the required overstrength of 2.8. Due to the large overstrength, the diaphragm can be expected to remain elastic at design forces. Across the ASD design range, the configuration that included metal surface splines with screws had the highest stiffness followed closely by the configuration that relied on the panel-beam connection alone. The metal surface spline configuration with screws had a stiffness double that of the configuration with nails. The three deflection methods included in the investigation were able to more closely predict the diaphragm displacement when the fastener type included was limited to nails. When screws were introduced to the calculation, the deflections had larger overpredictions.