Daniel Gach and Emma Cardini from the engineering and architecture firm Wiss Janney Elstner rappelled down the Washington Monument to inspect it in September. Credit: National Park Service
Following an earthquake in August, a team of engineers and architects rappelled down the Washington Monument to assess the damage, and are set to begin a similar assessment of the towers of the Washington National Cathedral.
Engineers and architects from Wiss Janney Elstner Associates, Inc. (WJE), headquartered in Northbrook, Illinois, have completed their dramatic rope-access inspection of the Washington Monument, which began in late September, concluding that the 550 ft tall icon remains structurally sound following a rare and unusually strong earthquake that struck the Washington, D.C., region on August 23. But the monument remains closed while further evaluations are conducted.
Daniel J. Lemieux, AIA, M.ASCE, the principal and unit manager of WJE’s Washington, D.C., office, says some significant cracking, spalling, and related damage was discovered, but this damage is confined primarily to the pyramidion at the top of the monument and a few additional locations at or above the 460 ft level. Less significant damage was observed below the 460 ft level, primarily loose or missing joint and repair mortar, which may be attributable either to movement that occurred during the earthquake or to normal exposure and weathering, according to Lemieux.
Engineers and architects from the same firm are continuing their efforts to evaluate, stabilize, repair, and remove or reconstruct portions of the ornamental limestone pinnacles and other architectural elements atop the Washington National Cathedral, a Gothic Revival structure located in Northwest Washington, D.C., which was also damaged by the temblor. A construction crane involved in installing netting at the cathedral collapsed in early September at the site, but was carefully disassembled and removed before work continued.
Both structures remain closed while repair work continues, although the cathedral is scheduled to reopen on November 12.
The magnitude 5.8 earthquake, which emanated from Louisa County, Virginia, was nearly the strongest ever in that part of the East Coast, and was felt as far south as Georgia, as far north as Maine, and as far west as Michigan, according to the U.S. Geological Survey.
Although most of the structures in the Washington, D.C., metropolitan region seem to have withstood the earthquake well, the temblor left a 4 ft long crack visible in the exterior of the pyramidion of the Washington Monument, and the National Park Service called for a comprehensive assessment.
A crack appeared in the Washington
Monument following the earthquake.
Credit: National Park Service
On Tuesday, September 27, members of WJE’s difficult access team (DAT)—Dave Megerle; Dan Gach; Erik Sohn, A.M.ASCE; Emma Cardini, and Katie Francis—hung ropes from the top of the Washington Monument and began rappelling down its face to conduct a stone-by-stone assessment of the marble structure; the inspections were delayed for a time by inclement weather but quickly resumed and were completed on September 28.
A report issued by WJE on September 25, titled “Washington Monument Post-Earthquake Survey and Condition Assessment,” states that the monument “remains fundamentally sound, with no visible evidence of distress observed to date that would indicate it has been structurally compromised in a way that would render it permanently unsuitable for its intended use and occupancy as a result of the earthquake.” However, the report goes on to point out that its team observed cracking and spalling of the exterior marble and underlying masonry as well as a loss of joint mortar and a debonding of cement-base patching material used in a number of locations.
The NPS hired WJE along with Tipping Mar Associates, of Berkeley, California, to inspect the Washington Monument, the Lincoln and Jefferson memorials, Wolf Trap Center for the Performing Arts, and Arlington House (also known as the Robert E. Lee Memorial) at Arlington Cemetery. The Cathedral engaged a team comprising WJE, consultant James Madison Cutts, P.E., M.ASCE, of Round Hill, Virginia; Keast and Hood Company, of Washington, D.C.; and architect Anthony J. Segreti, AIA, of Bethesda, Maryland, to investigate the Cathedral.
The DAT team responsible for the exterior survey and assessment of the Washington Monument was scheduled to begin a similar effort at the Cathedral on Monday, October 17. Inspections of the cathedral to date indicate “no visible evidence of distress that would suggest that the building was structurally compromised as a result of the earthquake,” Lemieux said in written responses to questions from Civil Engineering online. However, two slender limestone finials atop the cathedral fell to the ground, one of which hit and damaged a roof on its way down.
The Washington National Cathedral. Credit: Wiss Janney Elstner
“The aspect ratio of many of those elements, their configuration, and the manner in which they were originally constructed result in a façade that is, in many respects, uniquely vulnerable to damage as a result of this type of event,” Lemieux said, adding that “…unless and until they are appropriately stabilized, removed, and reconstructed, they remain a serious concern.”
The buttresses and flying buttresses that extend around the apse at the east end of the structure exhibit evidence of spalling due to compression and cracking, Lemieux added, and there have been lateral displacements of the limestone at the interface between the buttresses and flying buttresses. This suggests “possible differential movement between those elements as a result of the earthquake,” he said. “Additional close-range evaluation and analysis will be required in the days, weeks, and months ahead to better understand the full extent of the damage incurred at the cathedral and the steps that will be necessary to guide the restoration effort.”
A metal roof was damaged by a falling limestone cap.
Credit: Wiss Janney Elstner Associates, Inc.
The engineering team had developed a temporary overhead protection plan for the exterior as well as regions above the nave, crossing, and north and south transept spaces so that a planned service in remembrance of the terrorist attacks of September 11, 2001, could be held on September 9. The protection system consisted of a cantilevered steel and aluminum frame anchored to, and cantilevering 10 ft from, the reinforced concrete roof deck of the bell tower, and was intended to catch any debris that might fall, Lemieux said. Contractors were in the process of installing outriggers and debris netting at the bell tower when a seven-axle, 350 ft tall mobile crane collapsed.
The venue for the service was changed to the John f. Kennedy Center for the Performing Arts.
The crane supplier and operator, Crane Service Company of Upper Marlboro, Maryland, retained KCE Structural Engineers, Inc. (KCE), of Washington, D.C., to serve as its structural engineer during the stabilization, disassembly, and removal of the crane, with assistance from W.O. Grubb, which is based in Richmond, Virginia. “Planning for the stabilization and safe removal of the crane began in the hours and days immediately following the collapse,” Lemieux said.
Lateral displacements of some of the
architectural elements atop the cathedral
will be monitored for further movements.
Credit: Wiss Janney Elstner Associates,
The process required “a very carefully developed and choreographed series of steps,” he added, that were necessary “…to stabilize the up-ended truck at the base of the crane so that the winch-package, counterweights, and remaining sections of the telescoping boom, lattice boom, and components associated with the support and operation of the luffing jib could be removed and the truck lowered safely back onto its tires and removed from the property.
While the inspections and stabilization efforts at the cathedral and monuments continue, structural engineers around the region continue to evaluate other buildings as well. Most other buildings in and around the capital seem to have suffered very little damage, however. “Most of the modern buildings built or renovated after the 1960s performed exceedingly well,” says Jerome W. Rasgus, P.E., S.E., AIA, M.ASCE, the engineering principal for the National Capital Region for Weidlinger Associates, Inc., which has been hired by several building owners to conduct structural assessments throughout the region. This is true even though the magnitude of the earthquake was slightly higher than what was anticipated by the regional building codes, Rasgus says. “In the Washington, D.C., metropolitan area, technically, the earthquakes we can expect are on the lower side of moderate, and the earthquake we experienced is on the high side of moderate,” he says.
Rasgus expects that as teams of researchers begin to evaluate the strength and scope of the earthquake, they may eventually recommend changes to local codes, which are based on the International Building Code. “What we predict will happen is that on the basis of this earthquake, authorities will take the research that is being developed, and assess what the code was, and, we suspect, will revise the code to include higher acceleration levels,” he says. “This translates into higher forces on buildings.” The earthquake registered a peak acceleration of 0.09 to 0.18g near the epicenter and 0.038 to 0.09g near the district, according to the USGS.
A large construction crane was upended on September 7 while
engaging in stabliziation work at the cathedral.
AP Photo/Carolyn Kaster
Rasgus says his company has seen a 5 to 10 percent increase in business since the seismic event; many requests are being driven by residents and other occupants of privately owned structures who have asked their building operators to hire a structural engineer to investigate the structures and attest to their integrity. “The residents want assurance that someone came out and looked objectively at them, and has written a report saying there is no reason for concern,” Rasgus says. Although he expects the calls to decrease in the coming weeks, right now, he says, “We’re getting more every day.”