Page 329 - Forensic Structural Engineering Handbook

10.18 CAUSES OF FAILURES

• The tops of the shoring towers were not adequately stabilized against the longitudinal
movement which occurred when the concrete pads cracked and the tower frames dropped
slightly.
• The quality of welds in the U-shaped supports for the falsework’s crossbeams at the top
of the towers was poor, thus making them unable to resist the forces resulting from the
longitudinal movement.
“Had any one of these deficiencies not existed, it is unlikely that the collapse would have
occurred,” the NBS report concludes.
Additional deficiencies contributed to the collapse of an adjacent ramp unit, which
failed about 5 minutes after the first unit:
• Specified 1-in bolts to connect certain stringer beams to crossbeams were not used; fric-
tional clips were used instead.
• Special overlap beams at the ramp’s supporting piers were not constructed as specified.
• The construction sequence deviated from that specified in the construction drawings, so
that concrete for one span was placed before it should have been (see Fig. 10.1).

(a)
FIGURE 10.1 Riley Road Interchange (a) Shoring towers before
failure. (From John Duntemann, Wiss, Janney, Elstner Associates,
Inc., Northbrook, IL.)