Page 363 - Forensic Structural Engineering Handbook

10.50 CAUSES OF FAILURES

(b)
FIGURE 10.11 Column reinforcing steel. (Continued) (b)
Column rebar cage bent over at top of previously poured concrete.
(From Jozef Jakubowski, Workers’ Compensation Board of British
Columbia, Vancouver, BC, Canada.)

“The contractor is required to address the support and stability of reinforcing steel in concrete
structures . . .” and suggested to “consider retaining an engineer to design the temporary sup-
port and stability of rebar column cages, wall panels and [elevated] reinforcing steel mats in
[thick] foundation slabs.” (see Fig. 10.11).

Case History 12: Bridge Demolition

The project: The State of Connecticut contracted to demolish the old Sikorsky Bridge
on State Route 15 over the Housatonic River, and construct a new bridge. The demo-
lition work was done with the use of cranes on barges anchored in the river below.
The structure: The bridge to be removed was a 61-ft-wide, 1824-ft-long, 12-span
carbon steel highway bridge on reinforced concrete piers constructed in 1939. It con-
sisted of an open-grid steel roadway deck on longitudinal stringers which were sup-
ported on transverse floor beams at 32-ft spacing. The floor beams framed into three
longitudinal plate girders, along the center and along the two edges of the bridge
spanning pier-to-pier.
The incident: A catastrophic failure occurred on February 17, 2004 during the demolition
of Span 8. During its removal, the north girder buckled, dragging and toppling one of the
cranes off the barge into the water, killing the crane operator who was entrapped in the cab.