Designing Resilience: NEESWood Capstone a Decade Later

In 2009, Simpson Strong-Tie participated in an unprecedented research event to highlight the importance of earthquake-resistant wood construction.

The event, the world’s largest earthquake test, was a collaborative Network for Earthquake Engineering Simulation project. It teamed academics, engineers, and industry researchers from around the world to subject a structure to what engineers refer to as the “maximum considered event” (MCE), a large, rare earthquake projected to occur, on average, approximately every 2500 years.
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Timber Tower Research Project

In 2009, Simpson Strong-Tie participated in the NEESWood Capstone Test, which was the final experiment in a multi-year study to test and evaluate the seismic performance of various wood-framed buildings. The Capstone Test was a six-story apartment building constructed and tested at the E-Defense test facility, located in Miki, Japan. More information about the Capstone Test is available here.

NEESWood Capstone Test. Photo credit: Simpson Strong-Tie.
NEESWood Capstone Test. Image credit: Simpson Strong-Tie.

I only mention the NEESWood testing because I thought six-stories was pretty tall for wood-framed construction, since U.S. building codes limit us to four or five stories in wood. I recently came across a research project by Skidmore, Owings & Merrill LLP (SOM) for something just a tad taller than that. Looking to minimize the carbon footprint by using timber as the main structural material, SOM published a report for the design a 42-story, 405-ft. tall building. The solution utilizes mass timber for the main structural elements with reinforced concrete at highly stressed areas. The project used the Dewitt-Chestnut Apartments, a 42-story reinforced concrete structure built in 1965, as the benchmark building.

SOM Timber Tower. Image credit: Skidmore, Owings, Merrill website.

Abstract for the Timber Tower Research Project along with links to the full report and sketches are on SOM’s website.

So, what do you think of a 42-story wood-framed building? Let us know by posting a Comment.

– Paul

Flexible or Rigid? Multi-Story Light-Frame Structure Design Considerations

I like to think I’m flexible, but I’ve been accused of being rigid at times. I guess that’s what therapy is for. If you were to ask a light-frame structure diaphragm that same question, you would likely get multiple conflicting answers. The 1988 UBC first introduced parameters to evaluate diaphragm rigidity. Earthquake Regulations Section 2312(e)6 stated:

Figure 1. Flexible Diaphragm Definition from ASCE 7-05

Provision shall be made for the increased shears resulting from horizontal torsion where diaphragms are not flexible. Diaphragms shall be considered flexible for the purposes of this paragraph when the maximum lateral deformation of the diaphragm is more than two times the average story drift of the associated story. This may be determined by comparing the computed midpoint in-plane deflection of the diaphragm under lateral load with the story drift of adjoining vertical resisting elements under equivalent tributary lateral load.

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