Baja Earthquake Reconnaissance – El Centro Hospital and McCabe School
Our second stop was a hospital in El Centro. From the main entrance it appeared to be business as usual. This site was of interest to use because USGS Station 0412 recorded a peak ground acceleration of 0.38g. A few spots in the corridors had ceilings that cracked but had not come down. So the facility was able to maintain operation with a minimum of clean up. There are also a few other buildings on the site. The Physical Therapy building is the equivalent of a manufactured home. It had no foundation. Instead it sat on steel jacks that were not positively connected to the structure or the ground. As a result the structure was red tagged by the city.
Another building on the site housed administrative offices and had received a yellow tag from the city due to the ceilings being a falling hazard. The structure is a Butler Building consisting moment frames in the transverse direction and we assume rod bracing in the longitudinal direction. I say we assume because we were not able to see any rod bracing but that is typical of these types of buildings. The flexible nature of the system allowed for quite a bit of movement resulting in the cladding, partitions, and ceilings being damaged but the structure appeared to be undamaged. The performance was not limited by strength but by drift and the ability of the non-structural items to accommodate the drift of the flexible structure.
All three buildings achieved a life safe performance and the main hospital achieved an immediate occupancy performance level as the building code intends. But in talking to facilities people on the site, the fact that all the administration offices had to be relocated during repairs was not what they were expecting from the building performance. So the structural engineering community still has work to do in educating the public and working toward resilience in structures other than just the critical care facilities.
Next we headed farther south to McCabe School. This site also has a strong motion sensor, USGS Station 5058. We were able to look at the sensor and verify that it is attached to the slab on grade and undisturbed such that we are confident in the record from this station. The record indicates a peak ground acceleration of 0.58g. This site saw even more shaking than the hospital. There are several buildings of different ages on the campus and all performed pretty well. Most of the clean up was done before we arrived but there was essentially no structural damage. A few roof tiles came off and there was some cracking in the sheet rock but that was about it.
All of the school buildings are short single story wood or masonry shear wall buildings. The building periods were likely shorter than the period corresponding to the peak in the spectral response so that probably helped but the lack of non-structural damage seems to indicate that the low drift demand of the stiff buildings was a benefit. And at least in this case, the contents did not suffer too much from high accelerations.
Both of these sites experienced significant ground shaking but performed pretty well. All of the buildings were life safe and appear repairable. These facilities were functioning with relatively little disruption and I think that is the goal as we work toward resilient communities.
