AbstractThe objective of this study was to monotonically test two 7.32×7.32-m (24×24-ft) cross-laminated timber (CLT) diaphragms designed using the provisions of ANSI/AWC 2021 (AWC. 2021. Special design provisions for wind and seismic. ANSI/AWC SDPWS-2021, Leesburg, VA: AWC). Each diaphragm used twelve 1.22×3.66-m (4×12-ft) CLT panels and plywood splines or glulam beams at panel shear connection locations. Diaphragms were tested in simple-span bending in general accordance with ASTM E455 (ASTM. 2017. Standard test method for static load testing of framed floor and roof diaphragm constructions for buildings. ASTM E455-2017. West Conshohocken, PA: ASTM), used 8d common [3.3×63.5-mm (0.131×2.5-in.)] nails for panel-to-panel spline connections used proprietary 7.9×200-mm (5/16×7-7/8-in.) screws for panel-to-beam connections. The calculated allowable seismic shear design capacity for both configurations, based on the panel shear connections, was 60.5 kN (13.6 kips) per reaction. The diaphragm tested with load applied parallel to the long dimension of the CLT panels failed due to spline nail withdrawal at 4.0 times the allowable seismic design capacity. The diaphragm tested in the orthogonal orientation did not fail at the safe working capacity of the steel test frame, which was 6.0 times the allowable seismic design capacity. Although this testing provided empirical verification that the SDPWS design provisions met the minimum strength target underlying the design requirements, it also identified opportunities for potential future research to reduce design conservatism. Experimental results from a series of diaphragm connection tests correlated to the connections used in the full-scale diaphragm testing are described in the Part 2 companion study (Line et al., forthcoming).