inwardly angled facades. Most of the facade is maintained by a window-washing rig on the bulkhead, but the lowest stories of the building are maintained by cranes, and the storefront windows are washed at street level. The girders consist of concrete poured around steel pieces of rebar. The diagrid was initially planned to be made of steel, but concrete was ultimately used because of concerns over cost, ceiling heights, weight, and collaboration with labor unions. According to WSP vice president Gustavo Oliveira, difficulties arose over how to connect the rebar within the concrete girders at each of the nodes where girders intersect. Furthermore, there were approximately three dozen nodes where at least four girders intersect; the largest node, on the north side of the sixth floor, connected six girders. Therefore, for each node, a steel core was created and rebar pieces were anchored to that core. The concrete was poured in place, except for the pinnacles, which were prefabricated. The concrete had to be poured gradually because the steel cores were almost impossible to reposition after the concrete had dried up. Structural features Foundation Langan, the geotechnical engineer, monitored the underlying bedrock and conducted seismic planning. The ground underneath the building consists of of fill, followed by of sand, of decomposed mica schist, and a hard layer of mica schist bedrock. Much of the underlying ground in Midtown Manhattan could support loads of , but the western portion of 53 West 53's site had formerly contained a stream. Groundwater was present below ground level at the site. The weathered mica on the western part of the site could only support . Furthermore, the site abutted several adjacent buildings and the New York City Subway's 53rd Street Tunnel (carrying the ). Overall, the depth of sufficiently load-bearing bedrock under 53 West 53's site varied as much as . The site was excavated using 33 reinforced concrete caissons each measuring across. The caissons descend at least deep. Where the site abutted the subway tunnel, the caissons descend deep, the same depth as the subway tunnel. Some "high-capacity" caissons were drilled at the western end of the site to shift some of the loads to below the tunnel. The floor of the sub-cellar is placed on a grade/mat foundation. The foundation is surrounded by concrete walls that are on average thick. The shear walls and columns on the eastern boundary of the site