|
 Wood Frame Structures Exponent investigated a four-story engineered structure with
three stories of wood-frame construction over a one-story parking garage. Constructed
in circa 1978, the building sustained serious damage in the first story of wood-frame
construction during the January 17, 1994, Northridge earthquake, was red tagged (unsafe)
by the City of Los Angeles Department of Building and Safety, and
evacuated. An important observation from the investigation was on
the mode of failure—the level of damage was significantly exacerbated
by horizontal shear failure of the 3-ply, 3/8-inch thick plywood. The
observed failure of 3/8-inch plywood indicated that, for closely nailed
plywood, the expected ductility capacity of the plywood shearwalls
would not be achieved. This indicated a clear defect in the building
code—panels nailed so heavily that the failure mode was rupture of
the plywood (a brittle, undesirable failure mode), a condition that
should not be used in seismic applications.
 Concrete and Tilt-Up Structures Exponent was retained by a high-tech company
with facilities in Silicon Valley to conduct a seismic vulnerability study of two of its
facilities that operated on a 24-hour-a-day, 7-day-a-week schedule. State-of-the-art
deterministic and probabilistic seismic hazard/risk analysis, extensive field inspections,
and structural analysis were used to determine the vulnerability of the buildings and
contents. We found that the facilities missed the immediate occupancy/operational
performance levels in many areas and did not satisfy the life-safety criterion in some
areas for the seismic hazard considered. We worked
with the client to provide solutions for seismic
performance upgrades, within the facilities’ continued operation constraint, that would reduce
the damage under severe ground shaking, minimize
the chances of catastrophic failure, strengthen critical
areas, and reduce the chance of extended downtime,
while providing a cost-effective solution. Exponent
has provided similar services for other commercial
and industrial facilities, as well as historic buildings.
 Steel Moment Frame Buildings Exponent was retained to investigate the extent of
damage from the Northridge earthquake to particular steel buildings in Los Angeles,
and to determine the causes leading to the unexpected damage. The investigation
consisted of extensive field inspections, removal of samples, metallurgical analysis,
detailed finite element analysis of connections, and extensive
global structural analysis. In addition, we were asked to
develop a new moment resisting connection that could
reliably improve the performance of a particular SMRF
building. Exponent assembled a cross-disciplinary team
of in-house experts in structural engineering, earthquake
engineering, fracture mechanics, metallurgical engineering,
construction management, and economic systems coupled with experts from academia
to fully address the issues posed and to develop an optimal strategy for repair.
 Industrial Facilities Exponent was retained to
assess the overall seismic risk for the three largest
oil refineries in Turkey for TUPRAS (Turkish
Petroleum Refinery) following the 1999 earthquake
that struck western Turkey. The assessment included
a detailed and extensive field investigation coupled
with structural analysis for the various components
and structures, especially storage tanks, stacks and
chimneys, and frame structures. Our investigation
helped identify hierarchically the seismically vulnerable components within each refinery
and provided a foundation for staging proactive seismic upgrades, thereby reducing the
seismic risk to the refineries.
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