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Pier Reconfiguration—A Seismic Focus

Pier Reconfiguration—A Seismic Focus

Pier 4

Pier 4 completed with cranes installed. Photo: The Northwest Seaport Alliance

Local ports must evolve to meet industry needs, or ships and jobs will simply go elsewhere. The Northwest Seaport Alliance (the Ports of Tacoma and Seattle) needed to accommodate some of the largest shipping vessels in the world. A 18,000 twenty-foot equivalent unit (TEU) Ultra-Large Container Ship is longer than two Space Needles, and the Port of Tacoma’s General Central Peninsula couldn’t accommodate such a vessel. Part of the reason was that Pier 4 stuck out diagonally into the Blair Waterway, narrowing the waterway and creating a chokepoint.

Pier 4 had to be completely reconfigured and aligned with Pier 3 to create a single 3,000-foot-long berth. This required demolition of the existing pier structure and cutting back the shoreline to accommodate the reconfiguration.

Hart Crowser supported multi-discipline engineering firm KPFF Consulting Engineers on this project, which involved demolishing the existing wharf, dredging 460,000 cubic yards of sediment (a volume equivalent to a football field stacked with 215 feet of sediment), constructing a new 1,750-foot-long concrete wharf structure, erecting a new 7,000-square-foot, two-story marine operations building, and improving utilities throughout the site.

Brand-New Seismic Code for Wharves and Piers

Cranes arriving

Eight new post-Panamax cranes came from overseas. Photo: KPFF

The Port of Tacoma Pier 4 Reconfiguration project was the first major port development in the Pacific Northwest to follow the new code standard. The new code standard for seismic design of piers and wharves (ASCE 61-14 ) encourages using “performance-based seismic design” to calculate how the soil and structures will act and interact during an earthquake.

It’s usually the differential deformation (the difference in movement from one location of the structure or soil to another location) that makes a structure unusable after an earthquake. Hart Crowser used dynamic finite element modeling and close collaboration with KPFF engineers to analyze the forces and displacement in the structure caused by earthquake ground motions. Hart Crowser’s work was used to provide input to KPFF’s structural analysis and to optimize the stone column ground improvement layout. This analysis makes the resulting design safer, more resilient, and less expensive than alternative design methods.

Ground Improvement for Seismic Stability

Stone column installation

Installing stone columns to strengthen soil.

The soil at port and waterfront sites is often weak, and the Port of Tacoma is no exception. In many places there are river deposits or large areas of fill that have been deposited in the past. To strengthen the soil, the team installed stone columns, which are basically pillars of rock inserted into the ground. A hollow probe (or tube) is vibrated into the soft ground to the specified depth then filled with gravel which is injected into the surrounding soil. This vibration and volumetric displacement makes the surrounding soil denser and stronger. When the probe is removed, the gravel stays behind, forming underground columns. This can mitigate earthquake-induced liquefaction—in other words, keep the soil from turning to quicksand in an earthquake, and keep the underwater slope from failing in an earthquake.

The ability to design and install stone columns is not common and requires knowledge and experience. Plus, some stone columns needed to be installed on land and some in water, and there was a high water table to contend with. Construction had to be timed for dealing with tides so that workers could get close enough to create the hole before the tide came in. During the stone column installation, old undocumented pier structures were found. Hart Crowser made recommendations for over excavation of the structures in some places and a revised stone column layout to avoid underground obstructions in other places.

A Successful Outcome

The American Council of Engineering Companies of Washington awarded Hart Crowser a 2019 Silver Best in State Award for complexity for this project. The reconfigured dock now supports the largest container cranes on the West Coast and can accommodate some of the largest container vessels in the world. These new ships use 35 percent less fuel per box than smaller vessels and produce around 50 percent less carbon emissions. Hart Crowser was honored to be a part of the new Pier 4 – a world class marine cargo facility that will serve the Port of Tacoma, the Northwest Seaport Alliance, and the community for many years to come.

Performance-Based Seismic Design for Safer High-Rises

F5 Tower

The City of Seattle knows that building codes for downtown Seattle are not safe for tall buildings in a strong earthquake. That’s why it now requires performance-based seismic design for all buildings over 240 feet tall.

What is Performance-Based Seismic Design?

Seismic design usually follows a prescriptive code, sort of like following a cookbook. Performance-based seismic design is a more rigorous seismic analysis, performed by a team of experienced geotechnical and structural engineers. Because the design doesn’t follow the cookbook code, this alternate design procedure must be done by top engineers, so that it meets the intent of the code while also going beyond the code in certain respects. It must also be peer-reviewed by experienced engineers—often the people who participated in developing the code in the first place.

Doug Lindquist, a principal geotechnical engineer with Hart Crowser, describes it this way: “Performance-based design is a design method where the geotechnical and structural engineers proactively evaluate the performance of a structure in terms of displacements, forces, moments, and damage level. Performance-based design often results in a more resilient, constructible, and valuable structure compared to prescriptive/reactive methods.”

In the early 2000s, Hart Crowser was the first local geotechnical firm to use modern performance-based seismic design methods in the Pacific Northwest. Our engineers have incrementally improved on our proprietary methods and procedures over the last 18 years.

When and Where is Performance-Based Seismic Design Used?

Performance-based seismic design is used for buildings taller than 240 feet—around twenty-four stories or higher. It is used in areas zoned for high-rises, and only when allowed by the local permitting jurisdiction (e.g., Seattle and Bellevue).

Examples of our 20+ performance-based seismic design projects include:

  • Rainier Square Tower, Seattle (850 feet tall)
  • F5 Tower, Seattle (660 feet tall)
  • Russell Investments Center, Seattle (598 feet tall)
  • Lincoln Square Expansion, Bellevue (two towers, 450 feet tall)
  • Cirrus, Seattle (440 feet tall)
  • Midtown 21, Seattle (322 feet tall)

Major western United States cities allowing performance-based seismic design include Seattle, Bellevue, Portland, San Francisco, San Jose, Oakland, Los Angeles, and San Diego.

Advantages

Safer Design

Typical building design following the International Building Code (IBC) is based on the Design Earthquake (DE), which is defined as two-thirds of hazard level of the Risk-Adjusted Maximum Considered Earthquake (MCER). Using performance-based seismic design, the geotechnical engineer works closely with the structural engineers to analyze the building under both the DE and the MCER hazard levels. Because the building is analyzed under the higher MCER loading, the engineers have a better understanding of how the building will behave when subjected to strong ground motions. After review of many performance-based design projects, the City of Seattle identified deficiencies in the typical building design methods and now requires performance-based seismic design for all buildings taller than 240 feet.

Faster Construction and Lower Development Costs

When a building is so tall, the building code requires a dual seismic restraint system. This is like wearing both a belt and suspenders. If it’s a good belt, you don’t need the suspenders, and vice versa. Using performance-based seismic design allows you to build using one or the other. Just as it’s faster and more economical to dress donning only one fashion accessory, it’s faster and more economical to build only one structural system. This is allowed when the design engineers perform detailed analyses showing that the single system achieves the desired performance goals of the structure.

Improved Views and Higher Building Value

Eliminating cross-bracing or other exterior seismic restraint systems improves the building’s views, allowing floor-to-ceiling windows, which make the building more desirable to tenants.

Recent Advances

ASCE 7-16

Although it will not be required for use until 2020, improved methods in ASCE 7-16 have been used by Hart Crowser engineers since 2015. Certain provisions of this new code document allow for the removal of some of the extra conservatism built into the current building code. Hart Crowser was the first to use these methods in the Pacific Northwest, which result in reduced construction costs compared to older methods.

Ground Motions

Horizontal pairs of ground motions are provided by the geotechnical engineer to the structural engineer, who simulates the seismic response of the building subjected to these motions using a building model in the PERFORM 3D. There are thousands of ground motions in multiple public databases for geotechnical engineers to choose from to give to the structural engineer for design. Over the last 18 years, Hart Crowser has developed tools and techniques to identify, select, and scale the optimum ground motions that meet the source characteristics (e.g., magnitude, mechanism, spectral shape, site conditions, and source-to-site distance) and reduce the error between the target spectrum and ground motion spectra. This eliminates unnecessary conservatism and reduces construction cost compared to using less ideal ground motions.

Seattle Basin Amplification

The Seattle Basin amplifies ground motions compared to motions outside of a basin. Hart Crowser has been at the forefront of the practical implementation of research on the Seattle Basin into building design. Doug Lindquist has presented at both the 2013 and 2018 workshops on the subject organized by USGS and the City of Seattle.

Future Improvements

Future improvements will include enhanced scenario modeling to determine the strength of shaking at a building site (e.g., the M9 project) and additional advancements on incorporating basin amplification into design.

Lincoln Square Expansion

Lincoln Square Expansion in Bellevue, Washington.

Oregon Public Broadcasting’s Resiliency Blitz Starts January 26

Allison Pyrch of Hart Crowser

Allison Pyrch at a base isolated hospital near Ishinomaki, Japan, talking to Ed Jahn, OPB Producer. With Jay Wilson, Clackamas County Emergency Manager (left) and the hospital engineer. Listen January 26-28 on OPB radio’s Morning Edition between 7 and 9 am and at www.OPBnews.org.

For the last year, Allison Pyrch, a geotechnical engineer with Hart Crowser in Portland, Oregon has been the American Society of Civil Engineers representative to support Oregon Public Broadcasting in the preparation of a 2015 “media blitz” highlighting Oregon’s dire need for improved seismic resiliency.

Allison, the section secretary and a member of the ASCE Technical Committee on Lifeline Earthquake Engineering, travelled to Japan with the OPB Field Guide crew in September to highlight the damage and engineering successes that were observed after the 2011 subduction zone earthquake and tsunami.

The Japan footage, as well as footage from within Oregon, will be used throughout the year to bring awareness to the need for seismic resiliency here at home. The work will culminate with an hour-long documentary in October 2015.

The first segment of coverage will air January 26-28 on OPB radio’s morning Edition between 7 and 9 am can be found now on the OPB website here and here. The series will discuss critical structures in tsunami zones. The January 28th segment will feature Allison and cover how Japan constructs base isolated hospitals that are ready for business immediately after a major seismic event. Tune in and listen!

The Aftermath of the Big One

Building Damage – Concepcion, Chile 2010

Building Damage – Concepcion, Chile 2010

Collapsed Bridge – Route 5 – Chile 2010

Collapsed Bridge – Route 5 – Chile 2010

Tsunami Building Damage – Japan 2011

Tsunami Building Damage – Japan 2011

Tsunami-Damaged Sea Wall, Geotechnical Engineer Allison Pyrch – Japan 2011

Tsunami-Damaged Sea Wall, Geotechnical Engineer Allison Pyrch – Japan 2011

Investing in “resiliency” now can make the difference between thriving or not recovering at all.

To be resilient is to be able to restore to a strong, healthy, and/or successful state within a short period of time after experiencing misfortune or change. Because many global communities have recently experienced a string of natural disasters, we are now considering how “resiliency” applies to society and our infrastructure and, of course, we’re asking about our own communities in the Pacific Northwest. How will we fare after a major natural disaster?

The Pacific Northwest is reasonably resilient when it comes to storms, flooding, and landslides—all natural occurrences we have dealt with on a regular basis. Our public agencies have well-tested plans to get basic, and then full services up and running within hours or days. However, the current projections for damages due to global warming or earthquakes and tsunamis are not so optimistic. Based on the most current data, the Pacific Northwest is overdue for an 8 to 9 magnitude subduction zone earthquake and the resulting tsunami, much like those that hit Chile in 2010 and Japan in 2011. Based on evaluations recently completed by Oregon and Washington, widespread damage and casualties are anticipated. Deaths due to collapsing unreinforced or under reinforced masonry and concrete structures are anticipated including those in many historic downtown areas, schools, and public buildings. Widespread damage to utilities and infrastructure is also expected.

The resiliency plans passed by both Oregon and Washington legislatures predict these specific things:

  • Utilities—including electricity, water, wastewater, and natural gas services—will be out for months, if not years;
  • Our aging transportation infrastructure (already rated poor under normal conditions) will not perform well during the design seismic event; and
  • Total destruction is anticipated in tsunami inundation areas.

Both reports indicate that as things now stand, the Pacific Northwest is not seismically resilient. Not by a long shot.

Achievable?

Getting to “resilient” is a formidable and expensive task for communities. The Cascadia scenario includes an overwhelming list of damage and problems that seems impossible to solve in a timely way, especially given current funding challenges. However, the scale and complexity of the problem does not allow communities to ignore the problem altogether. The Oregon and Washington resilience plans proposed a timeline of 50 years to significantly increase the region’s sustainability, and have proposed putting seismic resiliency at the forefront of planning for the states. The Oregon Department of Transportation (ODOT) and Washington State Department of Transportation (WSDOT) have both started down the path to resiliency.

Having recently completed a large-scale evaluation of their systems, ODOT developed a prioritization plan based on infrastructure quality, the anticipated damage, and public priorities after a Cascadia event. They incorporated this into their overall master improvement plan. As funding becomes available, seismic considerations are now included in design, and repairs and upgrades are completed in a manner that will create large resilient sections of their systems. Further, with their seismic evaluation and agency resilience plan in place, they are in a good position to apply for funding to continue needed upgrades. This model is a good example for other public and private organizations in making resiliency an affordable and attainable goal.

Another idea to consider is how resiliency relates to sustainability. Sustainability has been ingrained in our society and almost every public and private entity generally has a person or position that is responsible for facilitating sustainability. Private and public entities put money into sustainability and it is valued by consumers. But the real question is: Can we be sustainable without being resilient? If a new sustainable building is constructed with the intention of saving additional costs over a 20- to 50-year period (we anticipate the Cascadia earthquake within that time frame) and the structure is not designed to be usable after the quake, can it really be considered sustainable?

The cost of not being resilient deserves serious consideration. If seismic resiliency is not addressed in our long-term planning, our region will not recover from the Cascadia event. Businesses will fail or leave; many residents will also choose to move instead of rebuild; and without the tax base, local agencies will be hard hit and will have trouble rebuilding. The currently booming towns of Seattle and Portland will no longer be destinations for travel or for business.

The path forward—what can we do?

As engineers and scientists who are well educated in the failings of our current infrastructure and our seismic hazard, it is our responsibility to educate the public so that resilience—especially seismic resiliency—becomes a priority. In looking at ways to make resiliency a priority, it is valuable to consider what the resiliency movement can learn from the success of the sustainability push. Engineers, architects, and planners need to find a way to educate the public about seismic risks and to make resiliency something that people understand and are willing to spend money to achieve. When projects are in the planning stages, the additional cost to design the structure for resilience should be factored into the cost analysis. Further, creating a LEED-type rating system for resiliency and seismic safety should be considered. If office buildings, homes, and apartment buildings have resilience or seismic safety ratings, consumers and business owners would start to demand and be willing to pay for the real estate with higher ratings. If a business rents a space that can be used within a week after the expected earthquake, even on emergency systems, it would be significantly more valuable and allow commerce to continue after an emergency.

Statewide resiliency plans, as well as the national push for resiliency after Hurricane Sandy, have brought attention to our lack of resilience as a society. In Oregon and Washington, where the Cascadia event is imminent, resiliency is becoming a more focused goal. Hart Crowser has put together a team to help agencies and private organizations evaluate their resiliency with regard to the Cascadia subduction zone earthquake and tsunami. The team includes an architect, structural engineers, planners, emergency managers, public involvement specialists, and experts in finding funding for projects such as these. We are working with private and public organizations to put proposals together to help evaluate and develop resilience plans on a smaller scale. These plans can be used to apply for funding and be incorporated into master planning initiatives so that resilience becomes a reality.

In addition to this planning, as professionals who are responsible for the design in infrastructure, it is our responsibility to educate the public, as well as our clients, on the risks of not being resilient. A few ways this can be accomplished are:

  • Discussions with public and private clients on the additional cost and benefits of designing new and rehabilitated structures to be resilient beyond code requirements, so that they are resilient beyond the standard life safety requirements of the building codes;
  • Support for legislation and laws that require seismic upgrades and provide funding for resiliency;
  • Support for development of a LEED-like rating system for resiliency of structures and other measures to make “resiliency” the new buzz word in real estate and infrastructure spending; and
  • Education of the public about infrastructure risks and the need to become resilient.