According to United States Geological Survey (USGS) long-term records (since about 1900), 16 major earthquakes are expected in any given year. That includes an estimated 15 earthquakes in the magnitude 7 range and one earthquake magnitude 8.0 or greater, but many buildings within seismic zones are not built to withstand the impacts of earthquakes. Legislators in seismic regions across the U.S. have updated building codes and regulations to better handle seismic events for new construction and have put legislation in place to bring older buildings into compliance. Seismic retrofitting – reinforcing or modifying an existing structure against anticipated seismic activity – was first formed following the 6.5-magnitude Sylmar Earthquake that shook the San Fernando Valley in 1971. This earthquake caused more than $500 million in property damage and dozens of lives were lost.
PCL Construction has been a leader in the seismic retrofit field for more than two decades working on nearly 100 seismic projects across California and the Pacific Northwest. Since PCL’s first-ever U.S. seismic retrofit project at the University of California, Los Angeles’ (UCLA) Kinsey Hall in 2006, the company has constructed approximately $350 million dollars’ worth in seismic retrofits at UCLA alone.
While progress is being made to seismically retrofit buildings on college campuses, acute care facilities, schools and government buildings, tens of thousands of buildings of all kinds are still in need of retrofit across the country to keep their occupants safe.
Let’s say you were given a truck made from an old box of Legos and asked to rebuild it into a Hummer with no instructions. As you start to deconstruct the truck, you may realize you’re missing the right colors, shapes and sizes to complete the Hummer.
Similarly, there are no instructions to retrofitting. These buildings are old and until you start investigative work to see what is behind walls, under flooring and above ceilings, you don’t really know the true extent of the work and what “Lego” pieces you might need to get the job done. There is more risk and unforeseen circumstances behind seismic retrofit but a lot of that can be avoided through early investigative work during the design process.
As with many older buildings in need of seismic retrofit, contractors often discover asbestos and lead-based paint once they start accessing beams and concrete. Abatement poses challenges, especially in active buildings that must remain open and functioning throughout the retrofit. Similarly, rerouting of mechanical, electrical and plumbing (MEP) systems is almost always encountered in some quantity during a seismic retrofit. Identifying MEP lines during design and incorporating that scope duration and cost upfront helps ensure the project is successfully on schedule and budget.
“Safety is the number one priority for PCL,” says Sam Wen, a construction manager with PCL’s California Buildings office. “It’s imperative to make sure the abatement area is isolated properly to ensure workers and building users are not exposed. Communication is also critical throughout the abatement process so there are no surprises.”
PCL is well-versed in keeping an occupied building functioning during a seismic retrofit such as the UCLA Center for Health Sciences (CHS). CHS is the second largest U.S. public building (next to the Pentagon) and conducts $2 billion in research annually. PCL has constructed $250 million dollars of seismic work in the building while maintaining building operations. Crews had to navigate the installation of shear walls at a CHS laboratory amidst a nine-month experiment. Halting the experiment to complete seismic work was not an option. The team worked with the University to create a solution. Jeffrey Hoese, general superintendent explains that the team installed a beam above the laboratory to support the weight of seven stories of installed shear walls. Once the experiment was complete, PCL came back to install the remaining shear wall in the laboratory.
“I am proud to work with a group of innovative solution providers day in and day out,” Hoese says. “This project was the epitome of a true collaborative effort to overcome challenges, minimize impacts to users and ultimately provide a safer structure for years to come.”
Lateral movement, which is when an earthquake causes the land beneath a building to crack or shift, is often what brings structures down during a seismic event.
That’s why almost all seismic retrofit techniques share the same goal, according to Larry Karlson, a structural engineer with PCL’s Integrated Construction Services team. Seismic retrofitting either aims to boost a building’s ability to resist lateral forces (which often cause structural collapse), lower the lateral forces a building will experience during an earthquake, or both. Despite these shared ends, seismic retrofit techniques vary widely in their approach and complexity.
- Fiber reinforced polymer (FRP): This material is similar to an epoxy wallpaper used vertically to wrap columns or shear walls. FRP is used in lateral forces but more commonly in compression mode so the column does not crack or break apart. Typically, inside of these older columns is a cage of steel not strong enough to withstand a seismic event so the FRP is added to strengthen it so the column does not split apart. This technique is less invasive as it requires less demolition to install. Plaster or paint can be applied directly over FRP and can often be quite a bit cheaper while just as safe and effective.
- Viscous dampers: Acts as shock absorber, similar to those on your car. These dampers minimize lateral movement and stress on the structure and allow buildings to move separately in the event of an earthquake.
- Seismic bolting: Bolt two buildings together at a seismic joint using large bolts (approximately four to five feet long and two inches in diameter) to make the buildings more ridged and heavier so they can move together during seismic events.
- Internal and external concrete shear walls or steel bracing: Offer back up support to keep a wall from collapsing on itself under pressure.
Unlike new-build construction, seismic retrofits don’t start with a fresh box of Legos so it’s critical the owner works with the contractor as early as possible to allow for extensive investigative work. This allows for more certainty in schedule and cost because unforeseen aspects and risks have been accounted for.
Contractors can’t just rely on as-built drawings to determine exactly what is behind the walls and under the ceilings and floors. They need time to investigate and then provide feedback to architects and engineers so the drawings can be adjusted.
“For many of our seismic projects, we advise the owner to allow us to spend a small amount of money upfront to investigative the building during the design process,” says Nicholas Rigali, PCL superintendent for seismic retrofit project, York Hall at the University of California San Diego. “This helps provide price and schedule certainty.”
Involving the contractor early on allows for collaboration with the client around finding innovative solutions to project challenges, such as utility shutdowns. Relocating and replacing MEP lines throughout a building poses an additional challenge when it comes to temporary shut offs. Water and power shut offs need to be coordinated closely with the client to minimize impacts to users. PCL works closely with the owner to determine the best schedule for these activities with the least potential to impact building users.
Despite the many challenges and unknowns associated with a seismic retrofit project, PCL’s team of experts share a sense of passion and pride when it comes to their work. “It’s more than just updating buildings, it’s about saving lives,” says Wen.