Cross-laminated timber (CLT) shear walls and diaphragms in the 2021 Special Design Provisions for Wind and Seismic (SDPWS).

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FIGURE 1. CLT shear wall for a) single panel configuration, b) multi-panel configuration, and c) multi-panel shear wall test. CLT shear walls in accordance with SDPWS utilize CLT panels meeting prescribed aspect ratios, prescribed nailed connectors to resist in-plane shear, and hold-downs to resist overturning.

The 2021 SDPWS contains new provisions for the design of CLT shear walls (see Figure 1). Design requirements include the use of CLT panels meeting prescribed aspect ratios, prescribed nailed connectors to resist shear, and hold-down devices to resist overturning. The system’s ductility and displacement capacity is from yielding of nails and metal connectors, and the combined rocking and sliding behavior of individual wall panels. System ultimate strength is governed by ductile nailed connection failure. Seismic design coefficients and the structural height limit of 65 feet proposed for inclusion in ASCE 7-22 Minimum Design Loads and Associated Criteria for Buildings and Other Structures are based on research that demonstrated adequate collapse performance for high seismic hazard areas using the FEMA P695 methodology (Amini et al., 2018; van de Lindt et al., 2020).

FIGURE 2. CLT diaphragm with nailed plywood spline (24’ x 24’ test diaphragm shown). CLT diaphragms in accordance with SDPWS utilize shear connections with calculated lateral design value controlled by NDS Mode IIIs or IV yielding and required capacity protection of other elements such as chords and chord connections.

The 2021 SDPWS contains new provisions for the design of CLT diaphragms (see Figure 2) intended to provide a minimum level of overstrength equivalent to that found in nailed wood structural panel diaphragms. Design requirements include the use of fastener design values in accordance with the National Design Specification® (NDS®) for Wood Construction, diaphragm shear connections with calculated lateral design values controlled by Mode IIIs or IV yielding as calculated by the NDS-2018, and required capacity protection of other elements such as chords and chord connections by use of design force increase factors.

The 2021 SDPWS is referenced in the 2021 International Building Code.

References:

Amini, M. O., van de Lindt, J. W., Rammer, D., Pei, S., Line, P., & Popovski, M. (2018). “Systematic experimental investigation to support the development of seismic performance factors for cross laminated timber shear wall systems.” Engineering Structures, 172, 392-404.

van de Lindt, J. W., Amini, M. O., Rammer, D., Line, P., Pei, S., & Popovski, M. (2020). “Seismic Performance Factors for Cross-Laminated Timber Shear Wall Systems in the United States.” Journal of Structural Engineering, 146(9), 04020172.

AWC SDPWS. 2021 Special Design Provisions for Wind and Seismic, American Wood Council, Leesburg, VA 20175.

AWC NDS. 2018 National Design Specification for Wood Construction, American Wood Council, Leesburg, VA 20175.