10 minute read
BEFORE DISASTER STRIKES
ARCHITECTURE & ENGINEERING Before Disaster Strikes
How engineers prepare for the unknown
By Brad Joyal
Earthquakes, floods, volcanoes, tsunamis, wildfires, and landslides: Alaskans endure a volatile landscape of natural disasters. Whenever these catastrophic events occur, engineers have already prepared for the worst. Whether it’s a dam, a road, an office building, or a hospital, all of the state’s infrastructure is designed to anticipate 10-year, 50-year, or even 100-year disasters in addition to humancaused damage that may occur during its lifetime.
Planning for the Long Term
Beyond the minimum standards for any type of project, engineers implement more vigilant requirements and practices depending on a structure’s location and function.
“The first thing that engineers typically start looking at is to find the design criteria the engineer will base the entire project on,” says Mark Sams, senior engineer at PND Engineers. “That’s a process the engineer needs to work out with the owner of the project at the beginning to kind of decide, ‘What is the design life of the project? What is the design life of the infrastructure? Is this project a 10-year design life? Are we looking at some sort of mining infrastructure with a design life of 10 years that the project is only there for 10 years and then the mine is going to close up and shut down, or is this a big, long-term infrastructure project that has a 100-year design life?’ That’s a big concern at the beginning of a project that really dictates the environmental loading on a facility.”
Once the owner and engineer identify the purpose and longevity of the structure, the next step is recognizing hazards that could complicate construction or present long-term challenges. The most common tool engineers turn to during this process is ASCE 7, the American Society of Civil Engineers’ publication that is released every six years and includes ASCE’s most widely used professional standards.
“Every time the ASCE is updated, it gets a lot thicker, and that’s because every so often there’s a major earthquake—as was the case when we had our [2018] Anchorage earthquake— that will affect earthquake design and seismic designs nationally,” says Sams. “Every time there is a national disaster, there are commissions set up to study what happened, what lessons were learned from damage that occurred, both for big infrastructure and small infrastructure.”
Codes Present the Framework
While ASCE-7 is the standard for proper techniques, engineers operate in a framework defined by codes, specifically the International Building Code, the model formulated by the International Code Council and commonly used as the standard in most US jurisdictions.
“There are code requirements for ports and harbors, separate code requirements for fuel terminals and facilities, and separate code requirements for infrastructure,” says Kyle Brennan, vice president and Anchorage office manager for Shannon & Wilson. “Depending on what type of work we’re doing, they all have governing codes that determine how we look at hazards.”
The scope of a project determines the severity of the codes that must be implemented, but some aspects— especially safety—are non-negotiable.
“At a very basic level, the codes are mostly about protecting life safety,”
explains John Daley, a senior engineer at R&M Consultants. “If you just follow the code and you walk through it in kind of a stepwise manner, you’ll get a design that meets modern standards and all it’s really doing is trying to protect your life. If the building you’re in was designed to a basic code, it shouldn’t fall over but it may be totaled in a major event. In an extreme seismic event, it may be sitting there leaned over 20 degrees and you can’t open the doors and the windows are all blown out, the foundation is cracked, everything on every shelf is gone, water mains are broken… The building may not be serviceable, but it protected your life.”
So codes are designed to ensure safety, but who makes sure the codes are followed?
“There’s this idea of the authority having jurisdiction. If you’re in the Municipality of Anchorage, it’s the building department and the municipality has code overview. And you’ll have to submit building plans and then they’ll review them and they’ll check all of these standards and see what you did and make you prove that you did them,” says Daley. “There are remote communities where there isn’t really [that process], but you’re still held to some standard. You’d want to identify the authority that has the jurisdiction, which could be the local building official or the state or somebody else.”
Not Just Natural Hazards
Thanks to design codes and requirements, infrastructure commonly withstands most natural disasters. But not all damage is caused by earthquakes or tornados; what happens when structures clash with humans? For example, the Glenn Highway overpass at Eagle River survived decades of blizzards and earthquakes until March 2018, when an oversized semi failed to fit underneath the support beams. A concrete girder that weathered every stress engineers had anticipated was, in the end, brought down by mismeasured cargo.
Engineers do consider human factors, but those rank low in terms of importance.
“It’s very project-specific,” explains Sams. “You have to look at it and say, ‘In the life of the structure, can you see somebody running a vehicle into this?’ www.akbizmag.com
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DESIGNING INFRASTRUCTURE THAT MAKES
A POSITIVE DIFFERENCE
IN THE DAY-TO-DAY LIVES OF ALASKANS
If we check that box and it can happen, what’s the economic cost to design to withstand it and what’s the economic cost to design this so it meets code and it’s safe in the sense there’s no loss of life?”
Sams points out that designing structures to be literally foolproof can send engineers and property owners down an expensive rabbit hole— especially considering that humaninflicted damage is usually insignificant for structures built to withstand catastrophic events.
“A lot of times, the environmental loads that we look at on these big infrastructure projects—when we’re designing for these really big 50-year or 100-year design events—are so large that when you look at somebody running into the side of something at full speed, it’s not nearly as big as some of these major environmental loads,” says Sams. “When you’re designing a tsunami shelter, the load on something like that is so immense that a pick-up truck running down the road and smashing into it is smaller than a major tsunami.”
Experience Points the Way
As much as design standards guide engineers to prepare for natural disasters, they also view real-life events as benchmarks. The November 2018 Anchorage magnitude 7.1 earthquake shook plenty of buildings and cracked multiple roadways, but it also indicated that the policies and standards practiced across the region can withstand major events when they do occur.
“I think the overall performance of buildings and whatnot in the Anchorage area during that earthquake—yes, there was damage; yes, there was settlement—but there were very few wholesale failures of houses,” says Brennan. “The infrastructure, by all intents and purposes, held up pretty well. I think the performance we had in general was a really great testament to the ability of codes to protect life, health and safety because we didn’t have any major injuries and we didn’t have any death as a result of the earthquake.”
Brennan and his colleagues at Shannon & Wilson weren’t the only ones that were pleased with how the state’s infrastructure held up.
“We had just finished the installation of the bridges on the Glenn/Muldoon Interchange right before that earthquake hit,” says DOWL Transportation Practice Area Leader Steve Noble. “When the bridge did get hit, it failed in the mechanisms it was supposed to fail and it stayed in service—it didn’t collapse down to the Glenn Highway. That always feels good and it reaffirms that the design standards we’re using are rigid enough and appropriate for the location we’re in.”
Noble has noticed some concerning trends, however, related to hydrology, such as large rainstorms or snow melting.
“You get these combinations of events where it can cause the slide that occurred across the highway in Cooper Landing… or the ones in Haines,” Noble says. “It’s usually water causing most of the disasters we face. We get the big earthquakes now and then, and those are an expensive event, but upgrading our bridges and our culverts and our drainage systems to accommodate the design storms is where we see most of our more significant reconstruction needs for infrastructure.”
Another recent large water event that concerned Noble was the record washouts Girdwood experienced at the end of October and beginning of November. Noble believes that event should alter the way engineers and builders view data and plan for the future.
“Some of those culverts were designed for a 30- or 50-year storm and we had a 100-year storm, or maybe we even raised the bar for what we think is a 100-year storm,” he says. “When it comes to hydrology, climate change is affecting and raising the bar on what we think are storm events across Alaska. It affects not only coastal areas where erosion is impacting communities, but it affects areas where we get very large rain events that previously were thought to be beyond a 100-year storm event. And if we get two of those in 25 years, then clearly we have to reassess what we think is a 100-year storm event. That was probably a 100-year-plus storm event in Girdwood that caused those washouts; they got 10 inches of rain in a very small amount of time.”
When considering past events and preparing for the future, Sams points out the importance of acknowledging Alaska’s historical data isn’t very old— which requires the state to consider other states’ history when mapping its own future.
“What we have, in a lot of places, is maybe 50 years [of data]. In some spots, maybe 100,” Sams says. “We’ve statistically projected what a 100year event is, and we’ve statistically projected what a 50-year event is, but we don’t have the historical data to see what 100 years might actually be, just because we haven’t had the time. What we’ve done is develop the bestcase scenario with the data we’ve got, and it’s all based on statistical analysis and stuff that we’ve developed elsewhere in the United States based on the large pools of data we’ve got elsewhere.”
Faced with the unknown, engineers tend to design conservatively, with large margins for error. That way, they can be reasonably certain their structures will pass the inevitable test. “It’s nice,” Noble says, “to get those [magnitude] 6 and 7 earthquakes once in a while so, God forbid, if we ever get something larger, we’re confident that the structures and network we have in place are going to hold up.”
John Daley, Senior Engineer, R&M Consultants
