The American Society of Civil Engineers is preparing to publish the world’s first standard for the design of critical structures to resist the impact of tsunamis. The document, which includes interactive digital inundation maps, is intended to serve as a model for the creation of standards in vulnerable coastal areas around the globe.
“In the U.S., tsunami hazard has not been considered at all,” said Gary Chock, president of Martin & Chock Inc. and chair of ASCE’s tsunami loads and effects subcommittee, at the ASCE 2016 Convention, held Sept. 28 to Oct. 1 in Portland, Ore. “We have filled the gap by providing a means of improving community resilience for critical infrastructure.”
Chock has long maintained that tsunamis should be factored into the planning, siting, design and construction of at-risk coastal buildings. “It is now my hope that communities around the globe will also benefit from this work of ASCE and develop their own maps using this approach,” he said.
The groundbreaking effort includes creation of the digitally interactive inundation maps for tsunami-vulnerable coastal areas in Washington state, Oregon, California, Hawaii and Alaska. The maps reveal that nearly 3.5 million residents are at risk, according to ASCE.
For the maps, which graphically depict the extent of tsunami inundation in specific regions of the U.S.—including those proximal to the Pacific Ocean’s earthquake-vulnerable Cascadia Subduction Zone—ASCE collaborated with the University of Washington’s Joint Institute for the Study of the Atmosphere and Ocean (JISAO) and AECOM.
The tsunami design zone maps—part of the new ASCE Geodatabase-Version 2016-1.0—tell engineers the inundation distance and run-up elevation factors for calculating tsunami effects on specific structures, said Yong Wei, a JISAO research scientist and a tsunami loads and effects subcommittee member.
The tsunami design provisions, debuted at the convention of 850 registrants, are scheduled to be published early next year as the sixth chapter in “ASCE 7-16: Minimum Design Loads and Associated Criteria for Buildings and Other Structures.”
The new chapter includes the 42-page standard and 60 pages of commentary. It was approved by the structural committee of the International Code Council for inclusion as a reference document in the model 2018 International Building Code (IBC), subject to confirmation at the ICC final action hearing later this month.
However, the National Association of Home Builders and the Asphalt Roofing Manufacturers Association are trying to reverse the adoption of ASCE 7-16 for reasons not related to the sixth chapter. To prevent this, ASCE’s Structural Engineering Institute is asking its members to support the adoption of ASCE 7-16 during upcoming public-comment hearings at the 2016 ICC Annual Conference, to be held Oct. 19-25 in Kansas City, Mo.
If the standard becomes part of the IBC, it can be adopted into local building codes by jurisdictions in the five western states. “It is hoped the IBC adoption process will occur in 2020,” said Chock.
To date, one vertical refuge center—the Westport, Wash., Ocosta Elementary School, which opened in June—has been built under the new standard.
The tsunami standard mostly considers high-risk essential structures in vulnerable areas, not single-story and commercial buildings. Structures covered “shall be designed for the effects of the maximum considered tsunami, including hydrostatic and hydrodynamic forces, waterborne debris accumulation and impact loads, subsidence and scour effects.”
The standard’s writers performed probabilistic tsunami hazard analysis to determine the offshore tsunami amplitudes. The standard’s development process then involved inundation modeling of the run-up—the accumulated water mass—to define the ground elevation where the tsunami inundation reached its horizontal limit.
The run-up data set for the standard includes geo-coded points that define the locations and elevations of the run-up. The inundation limit on land is the interconnection of the run-up points. The tsunami design zone essentially consists of the land area between the inundation limit line and the coastline.
The map-data layers consist of geo-coded inundation limit and run-up reference points, which are organized by segments of coastline for each of the five states. Tsunami Design Geodatabase Information Products will be hosted on an ASCE electronic-database web interface.
The standard took five years to create—considered a short time. But that effort was helped by earlier groundwork, beginning in 2001, when Washington state held a meeting on the impact of waves on structures.
The devastation caused by the 2004 Indian Ocean tsunami led to increased research and development of tsunami warning systems and evacuation strategies. It also provided the impetus for increased laboratory research on tsunami loads and effects, including a 2005 project to develop performance-based tsunami engineering, led by researchers at the University of Hawaii, Manoa, and funded by the National Science Foundation and the Network for Earthquake Engineering Simulation Research (NEESR).
In 2008, the Federal Emergency Management Agency published FEMA P-646: Guidelines for Design of Structures for Vertical Evacuation From Tsunamis, developed by the Applied Technology Council (ATC). “The 2008 document was a good starting point for the ASCE standard,” said Ian Robertson, a professor of structural engineering at the University of Hawaii, Manoa, and a chapter-six subcommittee member.
In 2010, the University of Hawaii led an NSF-NEESR project to develop loading expressions for floating-debris impact.
Based on the research, Chock, principal investigator on the NEESR projects, assembled 30 experts on tsunami modeling and loading and scour effects. He then proposed the ASCE subcommittee, which was officially formed in February 2011.
On March 11, the Tohoku tsunami devastated the northeast coast of Honshu Island, Japan. Members of ASCE traveled to the inundated area and did field surveys, gathering data that was used to validate the earlier laboratory experiments (ENR 5/9/11 p. 12).
“The field reconnaissance helped to confirm that experimental results in the lab do scale up to full scale,” said Robertson, who was on the first of seven ASCE survey teams. “That was very reassuring.”
Work on the standard itself is complete, but there is more to be done. To provide structural engineers with support as they design structures, ASCE plans to publish, likely late next year, “Tsunami Loads and Effects: Guide to the Tsunami Design Provisions of ASCE.” The guide, which will be hundreds of pages, will provide fully worked examples of tsunami-resistant design for structural engineers unaccustomed to the discipline of hydrodynamics, says Robertson, lead author.
Under a contract with ATC, Robertson also is updating FEMA P-646 to align it with ASCE 7-16.
The all-volunteer tsunami loads and effects subcommittee consisted of 16 full and 14 associate members. ASCE approved the standard, but only after eight ballots and the clarification of more than 1,000 comments, according to Chock.
“As this work progressed, some outsiders expressed uncertainty about whether this effort was worthwhile,” said Chock, adding, “This was a mission that could not be allowed to fail. To fail would mean there might never be any engineering approach to mitigating tsunami risk.”