Page 69 - ArchDC Fall 2018

ArchDC Fall 2018.qxp_Fall 2018 8/27/18 8:35 AM Page 67

The restored headhouse, with the new Pier 4 in the background. Photo © Alan Karchmer
cities but not in DC, where the famous Height of Buildings Act of upside-down pendulum effect occurs during earthquakes, as well
1910 indirectly encourages concrete structural frames, which are as in high winds. It turned out that Pier 4 had exactly this problem,
thinner and thus often allow additional floors to be squeezed in. but in the horizontal rather than the vertical dimension: one end
Divers inspected every pile and pile cap, and ultimately only a was fixed to the land, while the rest moved freely enough to create
handful required repairs or bracing. a whip-like motion. Once this was understood, it was a fairly
Another vexing structural problem was lateral forces, also simple exercise to add some shear walls, which resist lateral forces.
known as seismic forces since they become significant during These appear as blank walls along exit stairs and bathrooms.
earthquakes. In early computer models, the pier with the new Another unique contributor to the problem was the potential
building atop repeatedly failed. The architects scratched their impact force of boats pressing against the pier. Accordingly, a
heads. “It’s only three stories tall,” noted Bagnoli. “How was it “finger pier” and new pilings and moorings were added, none of
even possible to fail?” which are structurally connected to Pier 4. Unfixed gangplanks
Seismic problems generally arise because the foundation of a allow for independent movement.
building is fixed in place, but the upper floors can move freely. An

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