Enhancing Mass Timber Construction: New CLT Design Solutions

Cross-laminated timber (CLT) is gaining rapid popularity in the United States and worldwide. This engineered wood product is part of a broader construction method known as mass timber, which has grown significantly since Austrian engineer Gerhard Schickhofer developed CLT as a commercially viable product in the 1990s. CLT's appeal lies in its sustainable credentials, structural efficiency, and aesthetic benefits. When sourced from sustainably managed forests, CLT significantly reduces a building’s embodied carbon. Its biophilic properties create warm, natural spaces that are both architecturally pleasing and environmentally friendly.

Today, CLT is utilized in a variety of building types, from single-family homes to tall mass timber buildings up to 18 stories, thanks to the 2021 International Building Code. Its application spans office buildings, multifamily residences, schools, and more. The manufacturing of CLT has also expanded, with facilities across the U.S., Canada, Europe, and South America. The prefabricated nature of CLT panels allows for quick and easy on-site assembly, making it a favorite among builders for its efficiency.

To facilitate the design of CLT structures in compliance with U.S. codes, two new design tools have been developed. These tools, packaged into a single Excel workbook, enable engineers to design CLT for common applications quickly and accurately. The workbook includes tabs for calculating floor/roof panels and CLT walls, checking parameters such as cold strength, fire strength, deflections, and vibrations.

Design calculations for CLT are nuanced due to its composite nature with perpendicular layers. The tools take into account key properties such as allowable bending capacity, out-of-plane stiffness, axial loading capacities and rolling shear capacity. The calculation methods are based on standards such as ANSI/APA PRG 320 and the American Wood Council’s National Design Specification (NDS) for Wood Construction. These tools provide engineers with a detailed and precise approach to designing CLT structures, ensuring compliance with codes and optimization of structural performance.

The advancement of CLT and the availability of these innovative design tools mark a significant milestone in civil engineering. By facilitating the use of CLT, these tools help engineers contribute to the creation of sustainable and resilient buildings, reflecting a commitment to environmental stewardship and modern construction practices.

For more detailed information regarding the CLT design codes refer to Structure magazine.