We got a tour of the two-year-old U.S. Embassy in Port-au-Prince, including its mechanical spaces, to see how its seismic mitigation measures play out, and how they performed. We found the building’s systems came through Jan. 12’s 7.0 earthquake with flying colors for a lot of good, specific reasons.
The $109-million, 134,000-sq-ft building was completed as a design-build project by Fluor Corp. in 2008. The U.S. Dept. of State's Bureau of Overseas Building Operations specifies compliance with the International Building Code and the OBO site-specific code supplements, including seismic loading. The preferred earthquake resistant structural design system, including the one used here, is reinforced concrete shear walls.
Doug DeMagio, the facilities manager, and Alain Brun, the operating engineer, showed us some of the building systems' seismic mitigation features, which weathered the quake without a burp, even though DeMagio said the massive structure was rolling around like a ship at sea.
“I could have sworn I saw the floor undulating,” he says, but in thinking about that further, he is beginning to suspect that undulating sensation was in his head, and not in the un-cracked floor tiles and myriad un-started joints and connections throughout the structure. It seems clear that the whole building moved as one.
The motion was enough to throw file cabinets down and monitors to the floor and send people sprawling, says DeMagio. He says he has been through a number of quakes in various parts of the world and he knew what was happening immediately. “This is an earthquake,” he remembers telling a woman he was standing with when it began. They held onto a door, although she lost her grip and fell a couple of times, he says. He was thinking it wasn’t too bad, “and then it got worse. I was thinking, ‘Wow. This is it. If it feels like this, we’ve had it.’ ”
Throughout the main building and in its associated backup power generation and mechanical systems building, equipment such as chillers, HVAC fan units and pumps are not hard-mounted, but are trapped by keys on rails so they can slide.
There is evidence that some pieces of equipment came to rest as much as two inches from their pre-quake positions. Pipes connected to the water pumps pass through lengths of flexible, braided stainless steel couplings and are isolated from cutouts in foundation walls with rubber braces and gaskets. Everything is cross-braced with steel struts, the same way you would moor a vessel with bow, stern, and forward and aft-run spring lines to restrain lateral movement.
The embassy takes power from the grid when it is avalilable, but backs that up with five, 600-kw diesel generators. It runs one pair at a time while keeping the others for backup and standby. They are hard-mounted on base isolators, but connect with rubber couplings at the first opportunity.
The damage the building suffered was limited to a very few isolated locations and seem to be related to a couple of common causes.
In a a few instances, mounting bolts and brackets run-in too near and parallel to surfaces spalled off small patches of tile or concrete. There is a chip of tile about the size of a playing card that popped out just to the upper right of the front door.
One air handler on the roof came adrift when concrete below a rail key popped off and allowed the unit to twist just far enough out of alignment that its ductwork requires repair. Several other rail keys popped concrete or showed similar signs of stress, but the operational functionality was not interrupted.
Some ceiling tile hangers in the offices of the USDA on the east end of the second floor, which look to have been installed with insufficient diagonal wire stays for bracing, fell down; but the big stuff like seismic bracing and flexible joints between fixed equipment and pipe runs performed well.
A lot of the survivability of the building’s systems looks to be attributable to attention to small details, a few rather simple considerations—like flexible joints between fixed systems and runs and isolators where they pass through foundation walls—and thoughtful construction execution mindful of the need to mitigate for lateral loads.
None of it looked like a budget buster.
It’s all in the details.