$570M Seattle high rise 'game changer' in seismic and wind resistance
- The successful completion of an 850-foot-tall, rebar-free skyscraper in Seattle could usher in a new era of safer, faster and more cost-effective high-rise construction, according to Engineering News-Record.
- The 58-story Rainier Square Tower's actual cost of construction is $370 million, a 2% savings from a previously considered concrete-core model that would have required more administrative expenses due to the longer schedule, and would have necessitated more equipment, like cranes and hoists. The shorter schedule also allows developers to start seeing earlier revenue streams from leasing.
- The modular system of cross-tied, steel-plate walls, which will be filled with concrete in the field, will offer an earthquake-resistant core and a building capable of resisting lateral wind and seismic loads, according to designers. The construction process should take 31 months – versus 40 months if a concrete core had been used – with top-out scheduled for August 2019 and the certificate of occupancy for April 2020.
Work on the project officially got underway in October, with construction of a mock core to test the concept. One of the primary benefits of a rebar-free core is that designers will not have to consider the effects of rebar congestion, which can result in honeycombed concrete. A significant amount of rebar can prevent concrete from filling forms completely leading to voids that oftentimes must be repaired.
Researchers are also making headway with a new type of concrete that could eventually be used in earthquake-prone areas. Eco-friendly ductile cementitious composite (EDCC), under development at the University of British Columbia, is reinforced by polymer-based fibers and is similar to the molecular makeup of steel. Its cement also uses a mix containing a more sustainable 70% fly ash.
Researchers have successfully tested EDCC by coating inferior walls with a 10-millimeter-thick layer of the material and then subjecting it to earthquake strengths of up to 9.1.
Concrete structures are very expensive to retrofit in order to make them more quake-resistant. Los Angeles owners of buildings constructed of non-ductile concrete could find themselves paying millions in order to comply with the city's new seismic ordinances. The city recently sent out notices that these owners must present a retrofit checklist prepared by a civil or structural engineer within three years, followed by a compliance plan and then proof of compliance within 10 years. All retrofits must be completed within 25 years unless there are grounds for an exemption.
- Engineering News-Record Rainier Square Tower's Composite Steel Frame Called a Game-Changer
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