By Robert James Belvin, P.E.
The devastating 7.8 moment magnitude (Mw) earthquake in Turkey and northern Syria on February 6, 2023, led to the deaths of more than 55,000 people and the destruction of hundreds of thousands of buildings. The calamity displays the absolute urgency of policy-driven improvement in building designs in regions where seismic activity is moderate-to-severe in both magnitude and frequency. Reducing Pipe Repair Rubber Air Bag
Sadly, it too often requires a terrible disaster like this for good intentions to become urgent, immediate necessities.
In less than 30 seconds, the 1994 Northridge earthquake shook far more than Southern California’s San Fernando Valley. The magnitude 6.7 Mw tectonic event, followed by two 6.0 Mw aftershocks, cemented the state’s political resolve to improve building engineering and construction standards. Thirty years later, its effects are still reverberating in technological and design innovations, dramatic increases in building safety, and the mainstreaming of “resilience” as an operational design concept. Resilience is now front and center at every step of the workflow for healthcare facility design and construction. Mastering unpredictable movement must be accounted for during pre-design, in construction documents, and even beyond the ribbon cutting.
It is a common misconception that seismic risk is only a problem in California. While the risk is considered high in this state, since seismic events occur more frequently, a majority of the U.S. is subject to a seismic event, including spots in the Midwest and Southeast. Just as the construction industry uses Miami-Dade in Florida as the gold standard in hurricane resilience, California understandably sets the bar for seismic preparedness.
The Northridge earthquake had a major impact on policy changes toward seismic readiness. Two new product technologies were developed in direct response to the more stringent code requirements for healthcare buildings: structural systems and expansion joints. Bearing full witness to the impact of this stringent code evolution is the new Loma Linda University Medical Center. This healthcare facility serves as an example of how those innovations have been incorporated into a resilient design for the residents of this Southern California community.
Disasters, both natural and human-made, are often the unfortunate catalysts for necessary policy change. Following the San Fernando, Calif., earthquake in 1971, for instance, government officials, healthcare providers, and design professionals recognized the need for continuously operating hospitals during and after a natural disaster. Legislators passed The Alfred E. Alquist Hospital Seismic Safety Act (Hospital Act) to establish higher standards for new acute-care hospital design and construction. Necessary innovations then followed. For example, a “seismic moat” design was developed in 1988 for the Hoag Hospital in Newport Beach, Calif. Two of the hospitals badly damaged during the 1971 earthquake—Holy Cross Medical Center and Olive View Medical Center—were demolished and later rebuilt according to then-higher standards for seismic resilience. The work of research scientists, engineers, and architects coalesced into new design processes, more data for decision makers, and new technologies in the construction field.
Unfortunately, California’s Office of Statewide Health Planning and Development (OSHPD) was only given authority over new construction or remodeling and additions to existing hospital structures. Nonconforming buildings were not required to retrofit for seismic or service resilience and remained in use.1
Then, at 4:30 a.m. on January 17, 1994, the Northridge earthquake hit. With damage occurring as far as 130 km (85 miles) away, it earned the title of “most damage-causing earthquake since the 1906 San Francisco (Calif.) earthquake.” While the San Francisco quake was centered in an area with a lower population density and is mostly notable for the resulting fire that consumed nearly 80 percent of the city, the Northridge earthquake struck directly beneath the densely populated San Fernando Valley.2
It took a disaster such as the Northridge earthquake to prompt a range of policy responses to increase resilience to future seismic events, including a requirement to retrofit. The official death count was 57, with many more likely having died due to indirect causes such as stress-induced heart attacks and complications from broken bones. More than 8,700 suffered injuries, and medical centers faced an additional 1,600 people requiring hospitalization. At the same time, 11 area hospitals suffered structural damage or lost water and electrical services, or both. The damage was so severe in some cases that entire hospitals emptied for safety, compounding the disaster’s impact on the rest of the hospitals, clinics, and ambulance services that remained operational. Both Holy Cross Medical Center and Olive View Medical Center, two hospitals that were built to the new standards which only dealt with structural requirements, were among the buildings forced to close. Although they remained structurally sound, their water and air handling systems were not.
California legislators passed Senate Bill 1953 (Hospital Seismic Retrofit Program) later that year, mandating general acute-care hospital buildings meet stricter structural and nonstructural seismic strengthening requirements by established deadlines. Existing hospital buildings were now required to have their structural systems retrofitted to prevent collapse and provide for safe evacuation following a seismic event. The final deadline of January 1, 2030, mandates that all structural and nonstructural systems of every hospital must be reasonably capable of continued operations following a major seismic event. Utility services must be uninterrupted, supplies available, and buildings must emerge free of significant structural damage.
Following the signing of Senate Bill 1953 into law in 1994, some hospitals submitted plans to retrofit their buildings. However, retrofitting many existing hospital buildings was deemed too costly. To meet the latest standards, builders of new hospitals worked to incorporate new architectural designs, technology, materials, and construction methods.
Over the nearly 30 years since this legislation was passed, a rash of innovations have been incorporated into hospital design and construction, including advanced seismic systems (such as seismic isolation, damping, and buckling-restrained braces), nonlinear analysis techniques, comprehensive nonstructural bracing, and performance-based evaluations. There is an increasing understanding that structures and communities need to be resilient. For structures in seismically active areas, resiliency is strongly correlated with how buildings perform during, and following, an earthquake.
The Loma Linda University Health system provides crucial services to a region of Southern California known as the “Inland Empire.” With the addition of the Dennis and Carol Troesh Medical Campus in 2021, the system now treats more than 1.5 million patients every year and serves as a Level I trauma center. The 16-story adult hospital houses 320 licensed beds, while the nine-story children’s hospital holds 128 beds. The two towers share a five-story pedestal at their bases to allow critical resources to be shared.
Built by and for the community, the medical campus and hospital towers provide the highest levels of care to people in a region covering more than 25 percent of California. The 92,159.8-m2 (992,000-sf), modern medical campus rests just a half mile away from the San Jacinto fault, a branch of the notorious San Andreas Fault. This means the area is at significant risk of strong seismic activity. So, when the inevitable earthquake strikes, Loma Linda will be ground zero for an entire region of people looking for emergency services.
Architectural firm NBBJ teamed up with engineering companies Arup and Stantec, as well as construction company, McCarthy Building Co., and envisioned two healthcare buildings—a tower for children and another for adults—designed not only to withstand earthquake damage, but also to continue operations during and immediately after extreme seismic activity. Engineers from the Los Angeles, Calif., office of the Arup set out to the task of mastering movement beneath, around, and within the building so the hospital systems would remain unaffected.
“People go to hospitals when they are most vulnerable and most in need,” says Simon Rees, SE, principal at Arup. “It’s extremely important that a hospital is somewhere where people are safe. And that means all the systems have to be functional after an earthquake. It’s not just about the structure. It’s about mechanical, electrical, the plumbing systems, everything. If there’s a person on a ventilator, that ventilator has to be running before, during, and after an earthquake.”
The result is an unmatched engineering marvel. The adult hospital building is the tallest hospital building in California. The shared five-story podium that serves as the base of the two towers can move 150 mm (5.9 in.) vertically and up to 1,060 mm (41.7 in.) laterally without sustaining damage.
To accomplish this feat, Arup engineers incorporated a seismically base-isolated structural system to separate each building’s underground structure from the surrounding soil using an alternate wall system. This eliminates pressure from adjacent soil movement. Restrained brace frames and specially designed moment resting frames are buckled within the superstructure. One hundred and twenty-six individual triple friction pendulum bearings allow horizontal movement, while 104 fluid viscous dampers act as shock absorbers to reduce energy transmission from the ground to the building. A seismic moat surrounding the structure gives space for the building to remain stationary as the ground moves beneath.
This intense seismic stabilizing also introduced a new engineering problem: with Americans with Disabilities Act (ADA) guidelines firmly in place concerning safety in a hospital setting—seismic event or not—how could the buildings and ground move in relation to each other without pedestrians falling or being crushed?
“We have a moat around the building, as we call it, but you need to cover that moat with something that’s capable of recovering from an event where the ground moves 42 in. [1,066.8 mm] and the building stays stationary,” explains Rees.
Designers needed a stable walking surface that connects the buildings while also accounting for rapidly expanding and contracting joints, lateral shear, and—notably—vertical displacement.
Arup worked with engineers from an expansion joint cover manufacturer to evolve the largest expansion joint covers currently made by the company into covers that would function within the medical center’s design. The manufacturer’s engineers sought to better understand which motions can happen concurrently so they could then understand the movement of each connecting component on each axis in the chain. This engineering partnership spanned nearly four years, requiring modeling and testing to meet the stringent code requirements of multiple regulatory agencies.
The expansion joint covers provide a stable walking surface all the way up to the building’s edge. Under seismic conditions, the walking surface is stable, safe, and resilient. Once the shaking stops, the covers return to their original position. Pedestrians can safely move over the dry moat before, during, and after seismic activity. In fact, very few visitors of the hospital would know they are crossing over a large moat when entering and exiting.
Further, the new hospital connects to the existing campus with various walkways or bridges that also span the moat on multiple levels. Large-scale expansion joint systems were designed and installed on the pedestrian bridge, connecting the towers to other parts of the campus including the Schuman Addition and to the Galleria, and the “front door” of the hospital, allowing the structure to move adjacently to the building. Even if the buildings are moving, people and patients needing assistance can safely pass through the bridges and corridor.
The Loma Linda Medical Center’s monumental resilience engineering claims several notable construction records. Currently, it is the tallest hospital in California and the tallest building in San Bernardino County. In addition to reinforced concrete floors, the complex’s superstructure includes a 22,675-tonne (25,000-ton) steel frame, making it North America’s heaviest building. The facility is designed to provide 75 years of service life—essentially, the engineering of this building has been designed to withstand and remain operational under what might be considered the most catastrophic earthquake the area has ever seen.
While adherence to changing state code was the impetus to this groundbreaking facility, at the heart of the collaboration was the ability to combine new technology and a passion for resilient architecture in a project that will have a major impact on the region.
“As a designer, it’s extremely fulfilling to work on projects like that because, fundamentally, you know you are making a real difference in people’s lives,” says Rees. For communities in countless seismic activity zones, this kind of technological development, design collaboration, and concern for code compliance offers promise for a sound future.
Robert James Belvin, P.E., is the engineering manager for Construction Specialties, with 20 years of engineering experience. Belvin is licensed as a professional engineer in 17 states within the Northeast, South, and West regions of the U.S. He is a subject matter expert in seismic joint and movement disciplines.
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