Page 333 - Forensic Structural Engineering Handbook

10.22 CAUSES OF FAILURES

Case History 2: Baltimore-Washington Expressway Shoring Towers
A highway bridge built to carry Maryland Route 198 over the Baltimore-Washington
Expressway collapsed during construction on August 31, 1989, injuring 5 workers and 9
motorists. The structure was designed as five contiguous posttensioned box girders spanning
100 ft between simple-support abutments. The bottom slab was cast in July, and the box
girder webs were cast between July 21 and August 4. On the day of the collapse, workers were
pouring the 8-in deck slab. The collapse occurred 5 hours into the pour, when 120 of the 160
3
ft were in place. The shoring collapsed “in a flash” without warning, landing all the form-
work and concrete on the roadway below. The formwork had been used earlier to cast the
westbound structure.
FHWA and private investigators found that the most likely factor causing the failure of one
of the shoring towers was the use of 10-kip rather than the 25-kip screw jacks, shown on the
approved drawings, on the tops of the shoring towers supporting the bridge. A review board
found no evidence that the FHWA (the owner) had not lived up to its contract responsibilities,

(a)

(b)
FIGURE 10.2 Baltimore-Washington Parkway. (a) Aerial view of collapse. (From The New
York Times, September 1, 1989.) (b) Collapsed falsework previously supported construction of
bridge’s twin. (From Kate Patterson, Springfield, VA, and ENR, September 7, 1989.)