Framing of the Exploratorium's Observatory Building, the only completely new construction at at the piers, began in April 2011. Iron workers placed various sizes of steel beams in piles around the concrete base of the Observatory. Then, while a crane raised and held each beam aloft, the workers used metal spikes to line up the holes of the beams and inserted bolts, tightening them down to tie the structure together. Because the Observatory Building is less than two stories tall, the iron workers were allowed to shimmy across the beams without harnesses. Once this process was finished, the beams were plumbed and welded together.