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Wednesday, March 26, 2025
Mass Timber: Advanced Topics
Rooms C123–124Presentations in this session include:
- Past to Future: Historic Timber Connections to Inspire Future Developments
- Why WOODEN You? Efficient Timber to Timber Connection Detailing
- Fire Design Considerations for Type IVB Mass Timber
- Testing Without Standards: Seismic Deformation Compatibility and Fire Performance of Mass Timber Gravity Connections
- Service Conditions and Durable Design for Fasteners in Mass Timber Construction
- Screw Failures in Mass Timber Construction: The Role of Hydrogen Embrittlement
Moderator:
Scott Breneman
WoodWorks - Wood Products Council
Past to Future: Historic Timber Connections to Inspire Future Developments
The Pacific Northwest has a long history of timber construction, passing through many different eras of growth. This history — and the historic structures that remain — provides many fascinating examples of performative, low-resource timber connections. As the timber industry continues to search for the next generation of mass timber joinery that minimizes the use of metal fasteners, these historic examples can be appreciated in a new light.
This presentation will show and discuss a selection of historic timber structures in the Pacific Northwest and their connection details. The discussion will highlight their material basis, tools used, fabrication process, and logic of assembly. Examples will include native houses of the Coast Salish, block houses and log cabins built by various immigrant groups, and depression-era CCC (Civilian Conservation Corps) park structures and mountain lodges. Though built with limited resources, these structures reveal an impressive level of timber knowledge and construction ingenuity. Digital models of these timber connections help extract their defining geometries, show their structural behavior, and bring forth their contemporary benefits.
With new fabrication methods enabling a wider range of mass timber connections than before, these historic examples can help inspire and advance new directions in timber connection design.
Why WOODEN You? Efficient Timber to Timber Connection Detailing
While timber is the only structural material that is able to replenish in nature, this does not mean we should use it in one project and consider it disposable. If mass timber products can be re-used in the future, not only does this add value to the initial trees harvested and produced, but it also extends the time that the embodied CO2 is stored in the product while reducing the energy used to make new products. And it allows other trees to be harvested in the future rather than the present.
Fire Design Considerations for Type IVB Mass Timber
The use of Type IVB construction is an enticing option for high-rise projects, given the favorable carbon footprint when compared to other construction materials, and the ability to expose a significant amount of the structure. With 2-hour ratings required at all primary structural elements, special attention must be paid to detailing at connections to ensure that both aesthetic goals and fire rating requirements are met. While off the shelf connections and fireproofing products are becoming more and more available on the market, applicability to specific conditions of each project must be considered when interfacing with the AHJ.
This presentation discusses detailing lessons learned from Julia West House — a type IVB housing project currently under construction in the city of Portland, Oregon. Topics include the relationship of steel components, wood, and non-combustible cover; how to use existing testing; where engineering judgements can be utilized; and bringing on a fire protection engineer to support strategies.
Interpretation of newly adopted building codes is also an important consideration when bringing first-of-their-kind tall mass timber projects through permit, so this presentation also outlines recommended strategies for interfacing with the AHJ to keep projects on schedule through permitting.
Testing Without Standards: Seismic Deformation Compatibility and Fire Performance of Mass Timber Gravity Connections
Two important performance characteristics of mass timber connections are seismic deformation compatibility and fire resistance. ASCE-7 requires structures in Seismic Design Category D thru F to have their gravity connections be adequate for the combined effects of gravity load and seismic forces resulting from displacement due to the design story drift. The IBC requires load-bearing structures, including connections, to achieve a fire resistance rating once a building exceeds certain heights and/or area. However, for both of these criteria, there are no standards to guide the testing requirements to demonstrate adequate connection performance. Testing is needed to allow specifiers to use pre-engineered connectors to improve the efficiency of mass timber construction.
The presenters will highlight the seismic deformation compatibility and fire testing of concealed beam hangers performed by Simpson Strong-Tie to provide background on current testing approaches and acceptance criteria that have been utilized. The presenters will summarize current methods for testing to inform the audience on the suitability of standardized pre-engineered connections.
There will also be recommendations and questions for the audience to consider as the presenters advocate for the industry to develop standard criteria for seismic deformation compatibility and fire resistance testing of mass timber connections.
Service Conditions and Durable Design for Fasteners in Mass Timber Construction
This presentation explores how service conditions critically impact the performance and durability of fasteners in mass timber construction. Fasteners are a key component in the integrity and lifespan of structures, especially when exposed to varying environmental factors such as moisture, pollution, and corrosive marine environments.
Attendees will gain insights into the different service environments—dry, wet, and waterfront — and their direct effects on fastener connections. The discussion will cover the impact of moisture content on fastener performance, highlighting moisture content adjustment factors both at fabrication and in service. Additionally, we will examine heightened corrosion risks, particularly in chemically treated wood, and explore advanced mitigation strategies, including metal compatibility and protective coatings.
A significant focus will be on hydrogen embrittlement and bimetallic contact corrosion, addressing guidelines for preventing these conditions. Practical design considerations will also be shared, emphasizing fastener spacing, installation techniques, and accommodating wood movement.
The presentation will be grounded in real-world case studies, offering lessons learned from successful mass timber projects. Engineers, architects, and construction professionals will walk away equipped with knowledge to ensure fastener durability in diverse service conditions, advancing the resilience of mass timber construction.
Screw Failures in Mass Timber Construction: The Role of Hydrogen Embrittlement
The reuse of construction elements is gaining importance in promoting sustainability. This includes the potential for reusing wood screws, with one possible application being lifting and transport systems. This study seeks to evaluate whether screws, typically designed for single use, can be safely reused in these specific contexts.
By combining a literature review with experimental testing, this presentation will assess the mechanical integrity of screws after repeated cycles of use. The results will guide the development of tools to determine screw reusability and may contribute to future updates in standards. While this study focuses on lifting and transport, the findings could open doors to future exploration of screw reuse in broader construction applications, advancing circularity in the industry.
