Skyline Plaza was a large complex located in Bailey's Crossroads, Virginia which included eight apartment buildings, six office buildings, a hotel, and a shopping center. In the midst of construction on March 2, 1973, one apartment building (A-4) and the parking garage adjoining it collapsed. The incident occurred at around 2:30 in the afternoon and resulted in the death of 14 construction workers and the injury of 34 others.
On March 5, 1973, three days following the collapse, the Center for Building Technology of the National Bureau of Standards (NBS) was called upon to investigate the collapse of Skyline Plaza and determined the cause of failure. A three-dimensional finite element analysis was conducted on the 22nd and 23rd floors to determine the magnitude of forces exerted on the floor slabs and whether the slabs could properly handle those forces. For completeness, an analysis of three separate cases was run in order to cover all possible conditions at the time of the collapse.
- Case I: All forms on the 22nd story were removed before the collapse. This essentially means that the 23rd floor slab carried its own weight, the weight of the 24th floor slab, and the weight of the forms underneath the 24th floor slab. The strength of the concrete on the 23rd floor slab used for this calculation was 1200 psi.
- Case II: Assumed that the concrete on the 23rd floor slab reached its design strength of 3000 psi.
- Case III: Only some of the forms on the 22nd story were removed which results in both the 22nd and 23rd floor slabs sharing the load from above. The strength of concrete on the 22nd floor slab used for this calculation was 1340 psi.
Details of the study are available in the NBS report, "Investigation of the Skyline Plaza Collapse in Fairfax County, Virginia (NBS BSS 94)."