In wood-frame buildings of three or more stories, cumulative shrinkage can be significant and have an impact on the function and performance of finishes, openings, mechanical/electrical/plumbing (MEP) systems, and structural connections. However, as more designers look to wood-frame construction to improve the cost and sustainability of their mid-rise projects, many have learned that accommodating wood shrinkage is actually very straightforward. This publication will describe procedures for estimating wood shrinkage and provide detailing options that minimize its effects on building performance.
The growing availability and code acceptance of mass timber—i.e., large solid wood panel products such as cross laminated timber (CLT) and nail-laminated timber (NLT)—for floor, wall and roof construction has given designers a low-carbon alternative to steel, concrete, and masonry for many applications. However, the use of mass timber in multi-family and commercial buildings presents unique acoustic challenges.
While laboratory measurements of the impact and airborne sound isolation of traditional building assemblies such as light wood-frame, steel and concrete are widely available, fewer resources exist that quantify the acoustic performance of mass timber assemblies. Additionally, one of the most desired aspects of mass timber construction is the ability to leave a building’s structure exposed as finish, which createsthe need for asymmetric assemblies. With careful design and detailing, mass timber buildings can meet the acoustic performance expectations of most building types.
Buildings constructed for the U.S. Department of Defense (DoD) often have to meet blast-resistance requirements to mitigate the potential effects of terrorism. Terrorism is also a growing threat for civilian buildings (e.g., iconic structures, corporate headquarters, etc.), necessitating more building designers to incorporate blast resistance into their designs. The emergence of mass timber construction, and cross-laminated timber (CLT) in particular, offers a sustainable building material alternative that can also meet blast-resistance criteria in many circumstances.
A candidate cross-laminated timber (CLT) diaphragm analysis model approach is presented and evaluated as an engineering design tool motivated by the needs of seismic design in the United States. the modeling approach consists of explicitly modeling CLT panels as discrete orthotropic shell elements with connections between panels and connections from panels to structural framing modeled as two-point springs. The modeling approach has been compared to a developed CLT diapragm design example based on the US standards showing the ability to obtain matching deflection results. The sensitivity of the deflection calculations considering CLT panel-to-panel connection gap closure is investigated using a simple diaphragm example. the proposed modeling approach is also applied to the candidate floor diaphragm design for the Framework project, a winner of the US Tall Wood Building Prize Competition, currently under design. Observations from this effort are that the proposed method, while a more refined model than typically used during building design, shows promise to meet the needs of innovative CLT seismic designs where appropriate simpler diapragm models are not available.
Cross-laminated timber (CLT) has become increasingly prominent in building construction and can be seen in buildings throughout the world. Specifically, the use of CLT floor and roof panels as a primary gravity force-resisting component has become relatively commonplace. Now, with availability of the 2021 Special Design Provisions for Wind and Seismic (SDPWS 2021) from the American Wood Council (AWC), U.S. designers have a standardized path to utilize CLT floor and roof panels as a structural diaphragm. Prior to publication of this document, projects typically had to receive approval to use CLT as a structural diaphragm on a case-by-case basis from the local Authority Having Jurisdiction (AHJ).
This paper highlights important provisions of SDPWS 2021 for CLT diaphragm design and recommendations developed by the authors in the upcoming CLT Diaphragm Design Guide, based on SDPWS 2021.
Concealed spaces, such as those created by a dropped ceiling in a floor/ceiling assembly or by a stud wall assembly, have unique requirements in the International Building Code (IBC) to address the potential of fire spread in nonvisible areas of a building. Section 718 of the 2018 IBC includes prescriptive requirements for protection and/or compartmentalization of concealed spaces through the use of draft stopping, fire blocking, sprinklers and other means.
Changes to the 2021 International Building Code (IBC) have created opportunities for wood buildings that are much larger and taller than prescriptively allowed in past versions of the code. Occupant safety, and the need to ensure fire performance in particular, was a fundamental consideration as the changes were developed and approved. The result is three new construction types—Type IV-A, IV-B and IV-C—which are based on the previous Heavy Timber construction type (renamed Type IV-HT), but with additional fire protection requirements.
One of the main ways to demonstrate that a building will meet the required level of passive fire protection, regardless of structural materials, is through hourly fire-resistance ratings (FRRs) of its elements and assemblies. The IBC defines an FRR as the period of time a building element, component or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both, as determined by the tests, or the methods based on tests, prescribed in Section 703.
FRRs for the new construction types are similar to those required for Type I construction, which is primarily steel and concrete. They are found in IBC Table 601, which includes FRR requirements for all construction types and building elements; however, other code sections should be checked for overriding provisions (e.g., occupancy separation, shaft enclosures, etc.) that may alter the requirement.
As the height of mass timber buildings continues to grow, a new set of design and detailing challenges arises, creating the need for new engineering solutions to achieve optimal building construction and performance. One necessary detailing consideration is vertical movement, which includes column shrinkage, joint settlement, and creep. The main concerns are the impact of deformations on vertical mechanical systems, exterior enclosures, and interior partitions, as well as differential vertical movement of timber framing systems relative to other building features such as concrete core walls and exterior façades.
Wood-frame construction is a good choice for commercial and multi-family buildings, even in states where termites pose a higher risk. Wood buildings are safe, economical and sustainable. With the right precautions, they’re also durable and insect resistant. That includes proper design and detailing, good construction practices, and a pest management strategy that involves pesticides and/or physical barriers. Where termites pose a risk, it is good practice for the general contractor to engage a pest control specialist during pre-construction to map out an appropriate plan.
According to Faith Oi, PhD, Director of the University of Florida’s Pest Management University, the key to effective termite prevention is making the building inhospitable to termites. “Subterranean termites, which are the most damaging and economically important species in the U.S., follow pheromones and physical guidelines such as the outside of foundation walls. They can use any gap as a pathway—so it’s important to minimize hidden access and treat critical areas.”
This paper focuses on how to design and construct wood-frame buildings for termite prevention, and how to keep buildings insect-free over the long term. Intended for developers and design/construction teams, it covers building code requirements, best practices, control methods, costs, and ongoing maintenance. It emphasizes subterranean termites (including Formosans), and briefly covers drywood termites and other insects with the potential to cause damage.