This article by Balram Gupta, Ph.D., S.E., the West Coast Healthcare Market Leader in Walter P Moore’s Los Angeles Structures Group, originally appeared in the January/February 2024 issue of Medical Construction & Design.
Overview
In response to seismic risks, California has mandated hospitals to comply with seismic retrofit programs by 2030. While progress has been made, challenges remain for 60% of hospitals yet to meet structural requirements. Advanced seismic engineering, like the retrofit of Victor Valley Global Medical Center, showcases efforts to bolster resilience. Similarly, hospitals nationwide are implementing cost-effective seismic solutions, such as the Wonder Tower expansion in Virginia and the Shawn Jenkins Children’s Hospital in South Carolina. These initiatives underscore the importance of proactive resilience planning in mitigating seismic risks across healthcare facilities.
In the last century, several major earthquakes have amplified the risk of damage to or collapse of structures in seismically active regions. As a result, building owners have faced increasingly stringent seismic building codes.
According to the U.S. Geological Survey, California is subject to more damaging earthquakes than any other state in the country. Unsurprisingly, the state has required hospitals to comply with the California Hospital Seismic Retrofit Program by 2030. The program reduces the seismic vulnerability of hospitals by ensuring all acute care hospitals can provide services after an earthquake.
However, with the final deadline less than six years away, only 40 percent of the state’s 418 hospitals have all their buildings compliant from a structural perspective; the other 60 percent have at least one building on the campus that does not meet the structural requirements.
Seismic Engineering Solutions in Action
Recently, advanced analytical techniques were used to minimize the scope of seismic retrofit for a three-story steel moment frame building at Victor Valley Global Medical Center in Victorville, California, to justify compliance with Structural Performance Category SPC-5 criteria. It was originally designed as a welded steel moment frame building using cover-plated connections per the 1992 California Building Code.
However, construction was stopped because of concerns identified for WSMF buildings after the 1994 Northridge earthquake. As a result, the building has been exposed to the elements since 1994. The retrofit design was prepared at another firm, IMEG Corp., and construction was completed in 2020.
Acute-care services will only be allowed in VVGMC after January 1, 2030, if they meet a rating of SPC-3 or above. To ensure the structure met the new codes, nonlinear static (pushover) analyses were conducted. The model considered nonlinear load-deformation, soil-structure interaction with springs, and rotational hinges for existing grade beams.
Accidental torsion and multidirectional seismic effects were also considered. Material testing was conducted to determine the actual strengths of existing structural elements. A metallurgical investigation of structural steel, exposed to the elements for 27 years, was also conducted.
To justify compliance with the SPC-5 criteria, the scope of VVGMC’s retrofit was limited to the addition of new doubler plates at four locations, severing of top reinforcement in three grade beams, and cutting of edge-of-slab at top two levels to provide adequate seismic separation with the adjacent WSMF building.
Hospital owners must consider long-term plans when retrofitting an existing building or constructing a new one in a seismic zone and encourage engineers to design for maximum resilience.
Across the U.S.: Implementing Cost-Effective Options
While the seismic requirements for retrofitted and new hospitals in other parts of the U.S. may not be as strict as in California, several hospitals have implemented cost-effective seismic engineering options for new structures. In Richmond, Virginia, the Children’s Hospital of Richmond at Virginia Commonwealth University recently completed the 560,000-square-foot Wonder Tower, a 24-story horizontal expansion and a two-story vertical expansion of the existing outpatient pavilion. It is one of the first projects in Richmond designed to meet new seismic codes following a series of earthquakes in the area.
The expansion included an inpatient component above the existing structure that changed the risk category and increased the seismic load by 25 percent. The lateral system and foundation of the horizontal expansion were designed to support the increased seismic loads. To tie into the existing pavilion, the loads were traced through existing diaphragms, and the design augmented connections to brace frames on two exterior walls.
Integral to connecting Wonder Tower with the VCU Medical Center Hospital was a 280-foot enclosed pedestrian skybridge subject to the new seismic codes. The seismic design for the bridge included a combination of moment and brace frames to meet the higher seismic loads outlined in the new codes. “For the bridge, we weren’t able to make any direct connections to the existing building or the new section of the hospital,” says Melissa Shea, Principal and Project Manager at Walter P Moore. “We had to include expansion joints rated for seismic to get a buildable design.”
Elsewhere, the Medical University of South Carolina Shawn Jenkins Children’s Hospital and Pearl Tourville Women’s Pavilion in Charleston, South Carolina, lie in one of the most seismically active areas in the Eastern U.S. Since roughly 70 percent of the state’s earthquakes occur in the Charleston area, the building codes required strict seismic detailing.
Built to Withstand
The 625,000-SF MUSC facility includes a 10-story bed tower and a six-story diagnostic and treatment building. The 200-foot tower required special moment frames and buckling restrained braced frames. These systems were designed and detailed to provide ductility because they lower the seismic forces on the building, allowing it to move.
“MUSC is located in a high seismic and high wind zone,” says Gopi OmRaju, Senior Program Director of Planning, Design, and Construction at MUSC Health. “These factors required a very substantial structure for the occupancy type. However, a traditional approach would have resulted in budgetary pressures that could not have been absorbed otherwise.” The codes also required the critical ductwork, piping, and conduit carrying critical emergency power throughout MUSC and any supporting flammable material to be seismically braced.
Finally, the Lexington Medical Center, near Columbia, South Carolina, is also at risk of large seismic forces due to its proximity to the earthquake zone. At its core, the 12-story structural steel building was designed with concrete shear walls instead of braced or moment frames. The connections between steel beams and concrete shear walls were detailed for the structure to provide proper ductility in case of a seismic event and allow the beams and columns of the structure to remain intact. “The analysis of multiple framing methods for patient tower’s structural steel frame included different approaches to moment connections,” says Brooks Williams, Director of Construction Services at LMC. “We decided to use concrete shear walls instead of moment connections.”
Seismic building codes guide the maximum design considerations the structures must withstand regardless of location. Hospital owners must consider long-term plans when retrofitting an existing building or constructing a new one in a seismic zone and encourage engineers to design for maximum resilience.
