Timber Tower Research Project


The goal of the Timber Tower Research Project was to develop a structural system for tall buildings that uses mass timber as the main structural material and minimizes the embodied carbon footprint of the building. The research was applied to a prototypical building based on an existing concrete benchmark for comparison. The concrete benchmark building is the Dewitt-Chestnut Apartments, a 395-foot-tall, 42-story building in Chicago designed by SOM and built in 1965.

SOM's solution to the tall wooden building problem is the Concrete Jointed Timber Frame. This system relies primarily on mass timber for the main structural elements, with supplementary reinforced concrete at the connecting joints. This system plays to the strengths of both materials. The result is an efficient structure that could compete with reinforced concrete and steel while reducing the carbon footprint by 60 percent to 75 percent.

SOM believes that the proposed system is technically feasible from the standpoint of structural engineering, architecture, interior layouts, and building services. Additional research and physical testing is necessary to verify the performance of the structural system. SOM has also developed the system with consideration to constructability, cost, and fire protection. Expert reviews and physical testing related to fire-safety are also required before this system can be fully implemented in the market. Lastly, the design community must continue to work creatively with forward-thinking municipalities, and code officials using the latest in fire engineering and performance-based design, to make timber buildings a viable alternative for more sustainable tall buildings.


This report responds to the recommendations of the initial Timber Tower Research Report, which advocates for additional research and physical testing. It consists of detailed analysis of the gravity framing components of the Concrete Jointed Timber Frame system. This was chosen as the first subject for additional research because the gravity framing components represent the majority of materials used in the structure. Therefore, these components are also the primary consideration in project cost and carbon footprint. It was also chosen because the gravity framing system involves untested connection detailing not typical of timber construction.

The purpose of the report is to provide detailed structural system information and expected behavior that could inform a physical testing program of the gravity framing system.


This report summarizes the results of the SOM-led testing program at Oregon State University. The testing program investigated composite timber and concrete floor systems for use in high-rise buildings. The testing and report build on the major findings from the initial Timber Tower Research Project and Gravity Framing System report.

The purpose of the testing program was to research cross-laminated timber (CLT) floor systems with a composite concrete topping slab that improves the structural, acoustic, and fire performance of the floor system. The program researched key behaviors of timber-concrete floor systems, including the effectiveness of composite action, two-way bending stiffness, and continuous beam behavior. The program consisted of more than 20 tests on 14 full-scale specimens. Full testing descriptions and detailed results are available upon request from Oregon State University.

The testing results show that composite timber floor systems are able to increase the spanning capabilities and two-way behavior of CLT floor systems. Existing calculation techniques used to estimate the composite stiffness appear to be adequate for the behaviors studied.


This research study investigated structural steel frames with timber floors for use in high-rise residential buildings. SOM engaged with the American Institute of Steel Construction (AISC) for this study. The study is an application of the findings revealed in the OSU testing report. The proposed structural system combines shallow steel framing and a composite CLT and concrete floor system, which maximizes the advantages of each material. Structural steel framing is provided for its superior spanning capabilities and the composite timber floor system is provided for its lightweight properties. The resulting combination is able to achieve column bay sizes consistent with flat plate concrete construction and a flat soffit condition.

The proposed structural system was studied by comparing it to a benchmark building that uses a conventional concrete structure. This approach gave context for the structural details selected and showed that the proposed system could be marketable in terms of bay sizes and floor openings. The comparison to the benchmark building illustrates that the proposed system could be viable in the high-rise residential market.