Edificio con estructura de madera pasa los test de resistencia. SOM

19Aug16

Timber Tower Research Project

INITIAL RESEARCH REPORT

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.

SYSTEM REPORT

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.

Successful Timber Tower Test Paves the Way for Sustainably Constructed High-Rise Buildings

Developing sustainably constructed buildings is an urgent concern as cities look to decrease their ecological footprint. SOM sought to address this issue by exploring the potential of mass-timber to reduce the embodied carbon footprint of high-rise buildings. SOM and Oregon State University (OSU), with support from the Softwood Lumber Board, developed a comprehensive physical testing program that, to date, has included nearly 20 tests of varying sizes and configurations. On August 8th, the successful test of the final full-scale specimen provided strong evidence that the timber-concrete composite system can satisfy code requirements and compete with traditional construction methods.

The tested floor specimen—36 feet long by 8 feet wide—was modeled on a portion of a typical structural bay. The tested element was a Cross-Laminated Timber (CLT) deck topped with a thin layer of reinforced concrete to enhance the structural, acoustic, and fire performance of the system. The two materials were joined and made composite with connectors specifically designed for this application. The reinforced concrete topping slab was thickened at the supporting CLT beam to form a rigid connection between CLT decks, a feature which allows floors to span between beams with a relatively thin cross-section. For the test, the specimen was loaded with a hydraulic actuator and was recorded by 48 different sensors over the course of two hours.

The floor system provided greater stiffness than required by code and supported an ultimate load of 82,000 pounds: approximately eight times the required design load. The initial results are promising and will serve as the basis for verification testing—a series of tests that will address issues such as fire resistance—which will be required before the system can be used in high-rise buildings.

 



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