Reid Zimmerman is the Technical Director for the Portland, Oregon office of KPFF Consulting Engineers (reid.zimmerman@kpff.com).
This is the second of a two-part series on the Kahramanmaraş Earthquake Sequence which occurred on February 6, 2023 in Turkiye. The first article was printed in the STRUCTURE magazine July 2023 issue and presented a background on regional seismicity, seismic design and practice in Turkiye, and the authors’ observations from the field. This article focuses on observations relevant to structural practice in the U.S.
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Mass timber construction has experienced a significant increase in adoption in recent years due to its architectural appeal and sustainable nature. As its use has spread into regions of high seismicity, the need for reliable and economic seismic force-resisting systems compatible with this type of construction has arisen. Lateral systems incorporating Buckling Restrained Braces (BRBs) complement the desirable benefits of mass timber, and several methods have been developed for their incorporation in mass timber buildings. Three of these methods will be highlighted: a timber/steel hybrid system which collects lateral forces over large areas and concentrates them into steel BRBFs that are able to handle the relatively high resulting forces; a timber BRBF system which resists the lateral forces on a more local level but which must develop the BRB demands into timber members, rather than steel; and a novel timber shear wall system utilizing vertically-oriented BRBs as hold downs at the base of the wall. Each system has its advantages for certain building configurations and will be illustrated through completed projects.
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Cross-laminated timber (CLT) has become increasingly prominent in building construction and can be seen in buildings worldwide (Figure 1). Specifically, CLT floor and roof panels have become relatively commonplace as a primary gravity force-resisting component. Now, with the 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.
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The new Multnomah County Central Courthouse is an approximately 300-foot-tall concrete building located in Portland, Oregon, completed in the summer of 2020 (Figure 1). It includes courtrooms, judicial offices, security facilities, and expanded public spaces. Built to serve as the new central courthouse for Multnomah County and to replace the historic courthouse several blocks away, the owner and design team selected enhanced, multi-objective seismic performance goals for the building. Nonlinear response history analyses revealed the unique characteristic of multi-story mechanism formation in tall concrete moment frames like those in the Multnomah County Central Courthouse. The performance-based seismic design then leveraged fluid viscous dampers to improve that performance. Finally, a partnership between the owner, design team, contractor, Oregon Department of Geology and Mineral Industries, and the U.S. Geological Survey succeeded in seismically instrumenting the building with a dense array of accelerometers.
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“Danger. Extremely Flammable. Fire/Explosion Hazard.” These words are printed in cautionary lettering on a little green propane
tank used for my camping stove. Equally interesting, though not quite as dramatic, is the word “overbuilt” printed just above the manufacturer’s name. In context with the outcome of failure – an explosion – overbuilt seems stout, safe and ultimately reassuring. …