The 7.8 magnitude earthquake that hit Nepal on April 25 has killed over seven thousand people and completely or partially destroyed nearly 300,000 structures. The area’s subsequent after-shocks continued for days after causing more damage and taking more lives.
Nepal’s earthquake is a harsh reminder that Charleston and surrounding areas are in the U.S. Geological Survey’s highest earthquake hazard zone. Statistics and experts are saying we are due.
As Nepal digs itself out of the rubble, let’s ask ourselves how safe are the buildings we live and work in? Building codes first began to include explicit design requirements in the late 70s and early 80s. Locally, the International Building Code (IBC) was official adopted in 2002 and drastically improved and increased the level of seismic design and detailing required for new construction. In an effort to improve seismic performance and incorporate lessons learned, seismic design and detailing requirements are continually refined with every new version of the IBC. Charleston area structural engineers and contractors are required to follow many of the same “high-seismic zone” guidelines used in the seismic hot bed areas of California.
Despite the strict seismic building code, structures aren’t earthquake-proof. Seismic codes are in place to save people, not buildings.
In the event of a severe earthquake, structures built to seismic code will remain stable long enough for people to safely evacuate. Mark Dillon, ADC's president and principal structural engineer says, “Depending on the duration of such an earthquake, buildings designed to current code would likely see significant ‘non-structural’ damage, and although the structure would be damaged, if designed properly the structure would remain intact and protect the occupants of the building.”
But what about the many existing buildings built before 1970?
Dillon, an expert in designing structures in high-seismic zones says, “Using historic evidence, if a 7.8 earthquake were to hit Charleston, like Nepal, there would likely be significant structural damage to unreinforced masonry structures resulting in partial or even total collapse of these structures.”
During Dillon’s 32-year career he has managed hundreds of seismic evaluations, new construction, and upfits in the Charleston area. A seismic retrofit will reinforce masonry structures and prevent the roof or terrace from separating from the building during an earthquake.
In 2009 the Charleston County School District hired Dillon to perform seismic evaluations and design the structural upfits on multiple schools that were built before South Carolina adopted the IBC such as Buist Academy and James Simons Montessori. He was also the engineer that designed structural renovations for Charleston landmarks like Dock Street Theatre, Charleston City Hall,and the Grant Missroon Building.
Seismic codes don't just address the building's structure.
Seismic codes have recently addressed nonstructural and content hazards in buildings. These codes ensure heavy items like medical equipment, A/C units, bulkheads, and lighting in schools, hospitals, medical office buildings, and many retailers are properly anchored. Otherwise, during an earthquake these items can topple or fall, causing harm to people.
While the IBC exists, it is the responsibility of municipalities, owners and engineers to ensure buildings and its contents are designed to keep the public safe. The U.S. Geological Survey says an earthquake is very probable. Complete destruction doesn’t have to be.
Written by: Shelley Gibson Drulard