United States District Court, N.D. Georgia, Atlanta Division
OPINION AND ORDER
WILLIAM S. DUFFY, JR., UNITED STATES DISTRICT JUDGE
matter is before the Court on Defendants Terex Corporation,
Terex South Dakota, Inc., and Terex Utilities, Inc.'s
(collectively, “Defendants” or
“Terex”) Motion to Strike Rebuttal Report of
Nathan Morrill .
a products liability action stemming from the failure of a
2002 Terex Hi-Ranger XT 60/70 boom, Serial No. 2021020554
(the “Subject Boom Truck”), an aerial lift
device. Terex XT aerial devices are commonly utilized by tree
April 9, 2014, Plaintiff Jeffrey Gaddy
(“Plaintiff”) was in the bucket of the Subject
Boom Truck when the lower boom stub fractured, causing
Plaintiff to fall to the ground. Plaintiff suffered spinal
injuries resulting in paraplegia. Plaintiff claims Terex
negligently manufactured and designed the Subject Boom Truck,
and that it failed to warn him of certain dangers. Plaintiff
also claims that the steel used in the lower boom stub did
not meet Terex's design specifications.
support of his negligent design claim, Plaintiff identified
Nathan Morrill, P.E. as a design expert. Mr. Morrill issued a
report [393.1] (the “Original Report”) that
stated a variety of opinions regarding Terex's design of
the Subject Aerial Device, including his interpretation of
the standards promulgated by the American National Standards
Institute (the “ANSI Standards”), the
applicability of the ANSI Standards to Terex's design of
the Subject Aerial Device, and the feasibility of alternative
designs. Mr. Morrill's opinions included that the ANSI
Standards required, among other things, that calculated or
known stresses may not exceed 50 percent of the yield
strength of the material-a standard known as a “2.0
safety factor.” (Original Report ¶ 51). In this
case, that would mean stresses could not exceed 35, 000 psi.
(Id. ¶ 81). Mr. Morrill concluded that Terex
ignored the ANSI Standards when assessing stress concentrated
areas and that the boom had a 1.47 safety factor from a crane
testing standard. (Id. ¶¶ 66-67). Mr.
Morrill also opined that Terex failed to apply stress
concentration factors and dynamic load factors to their
preproduction calculations as required by ANSI A92.2.
(Id. ¶ 182). Mr. Morrill created Finite Element
Analysis (“FEA”) models of three lower boom stubs
in the XT series, and offered two proposed alternative
designs of the XT 60 lower boom stub. (Id.
¶¶ 108-153). Mr. Morrill concluded that the
cracking and failure of the XT boom was caused by Terex's
use of weaker steel and Terex's design of the boom, and
that, had the XT 60 been designed to meet ANSI A92.2
standards, it would not have failed in this case.
(Id. ¶ 187).
designated civil engineer Vijay K. Saraf, Ph.D. as an expert
regarding the design of the Terex XT 60 boom. On September
30, 2016, Terex produced Dr. Saraf's expert report
[393.4] (“Saraf Report”). Dr. Saraf opined that
ANSI Standards addressed only static loading conditions and
that stress concentrations could, in practice, be ignored.
(Saraf Report at 16; Saraf Dep. [393.5] at 153). Dr. Saraf
further opined that Terex's testing of the XT-60/70 boom
prototype exceeded ANSI Standards because they applied a
safety factor of 1.1 when accounting for stress
concentrations, instead of ignoring stress concentrations. In
his deposition, Dr. Saraf justified his opinion that stress
concentrations could be ignored by giving examples from
design criteria for buildings and bridges. (Saraf Dep. at 47.
Dr. Saraf also gave opinions regarding Mr. Morrill's use
of FEA models, opining that using FEA-aided measured stress
is not “good engineering practice” and would lead
to an “impossible design goal.” (Saraf Report at
16). He also opined that it was “impossible” to
design any aerial lift device that would satisfy Mr.
Morrill's interpretation of ANSI A92.2 that stresses
could not exceed 50% of yield strength based on verified
stress concentration factors and dynamic loads. (Id.
at vii, ¶ 18).
designated Mr. Morrill as a rebuttal expert to rebut Dr.
Saraf's opinions. On November 4, 2016, Plaintiff produced
Mr. Morrill's Rebuttal Report [393.3]. The Rebuttal
Report included the following opinions:
37. Based off of the new information I have reviewed, my
analyses, my professional experience design mobile equipment
including aerial lifts, and my education as a mechanical
engineer, I add to the opinions set forth in my first report
and those mentioned above.
38. Buildings and bridges are designed to different standards
and regulations than aerial lifts, the design requirements of
each are different due to the loading and operating
39. Dr. Saraf is wrong in assuming that stress concentrations
and dynamics can be ignored for aerial lift design. Stress
concentration factors when subjected to cyclic loading cannot
and should not be ignored. Doing so reduces the life of a
design and can lead to failure which will endanger the
operator of an aerial device.
40. ANSI A92.2-2001 specifically instructs designers and
manufacturers to take into account the effects of stress
concentrators and dynamic loading because they cannot be
41. Terex S.D. measured and calculated stresses in 1996 for
the XT 52 lower boom stub, and should have been put on notice
that the stress concentration factor for the area of failure
was at least 1.85. These concentration factor is [sic] a
result of Terex SD's design of this location, and is
unique to this geometry. This factor can be reduced or
removed with designs that better distribute the stresses and
42. The XT 52 lower boom stub did not meet ANSI A92.2-2001.
43. Terex S.D. should have known from 1996 forward that a
stress concentration factor of 1.1 was inappropriate for the
weld in the lower boom ...