Page 348 - Forensic Structural Engineering Handbook

TEMPORARY STRUCTURES IN CONSTRUCTION 10.35

Defendant’s expert further contended that the rental agency’s young engineer, even
though a licensed professional engineer, should not be expected to have the sophistica-
tion of all these experts with doctorates to understand all the complexities arising from
the continuous, curved, interconnected, and composite beam action. Plaintiffs’ expert
contended that a licensed professional engineer must be expected to at least recognize
when there is so much complexity that he is getting in over his head and needs to seek
competent advice. Based on its verdict, the jury appears to have agreed with the
plaintiff.
An interesting question in the forensic investigation and litigation was whether the
tower was scaffolding, because it provided access for the workers, or shoring, because it
supported superimposed loads, or both a scaffolding and a shoring at different times.
Design safety factors and allowable height-to-width ratios are different for scaffolding and
shoring, as per OSHA Regulations (see Fig. 10.4).

∗
Case History 5 : West Coast Hotel Scaffolding
During the 1992 construction of a west coast hotel, three construction workers were seri-
ously injured when a scaffold collapsed, causing them to fall about 30 ft along with hundreds
of pounds of scaffold parts and building materials. The scaffold platform was erected in the
lobby of the hotel to provide access for the installation of the gypsum wallboard ceiling and
lighting fixtures. The platform was 32 ft above the lobby floor and covered a 30- by 80-ft
area. The structure included two towers constructed from pipe frame scaffolding, with a plat-
form using steel putlogs spanning between the towers. The putlogs spanned 18.5 ft and had
knee braces at their third points; 2-by-10 wood planks spanned between putlogs to form the
platform.
On the day of the collapse, 80 to 100 sheets of gypsum wallboard were stacked in four
or five piles at various locations on the platform. On the morning of the collapse, four work-
ers were on the platform. One of them approached a stack of gypsum wallboard that was
near the middle of the platform. As he got close to the stack, a sound similar to a gunshot
rang out, and the center of the platform dropped 2 to 3 in. The initial sag was followed
quickly by the total collapse of a central putlog. Within seconds, the four center sections of
the platform were on the lobby floor along with several seriously injured workers among
the pile of scaffold parts, planks, and gypsum wallboard.
The postcollapse investigation associated with the litigation initiated by the injured par-
ties included observations of hundreds of photos, hours of videotape, and samples of the
scaffold parts; metallurgical studies of the metal at the failure location; and analyses of
forces in the structure, stresses at the failure location, and progression of the collapse. The
review of the photos and videotape that were taken after the collapse immediately identi-
fied shortcomings including missing ties between the scaffold towers and the building and
missing or incorrectly installed braces between adjacent putlogs. The photos of the arrange-
ment of the fallen structure and the order of the pieces in the pile on the floor also helped
to identify the region where the collapse initiated.
The photos showed that one putlog near the center of the platform had an end sheared
off. This was the only scaffold member that broke; almost all the other collapsed members
were bent and twisted without breaking. In addition, the putlogs and towers collapsed in
toward the center of the platform, suggesting that the collapse initiated in the general area
of the putlog that sheared off during the collapse.
Visual inspection of the failed scaffold members revealed that the broken putlog had
one location on the bottom chord which had a welded repair prior to use on this job. The

*This case history was contributed by Raymond W. LaTona, Simpson Gumpertz & Hager, Inc., San Francisco, CA.