Seismic Upgrades at La Colina and Hunter Substations Project Overview April 1, 2011
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Seismic Upgrades at La Colina
and Hunter Substations
Project Overview
April 1, 2011
Seismic Upgrades at
La Colina and Hunter Subs
Seismic analysis initiated to confirm structural
integrity due to past modifications and future
apparatus upgrades.
Seismic analysis resulted in recommended
upgrades of substation structures, foundations,
and anchor bolts.
Seismic Analysis
Methodology
Lattice Steel structures at La Colina and Hunter
Substations were modeled using a structural
computer program (STAAD Pro - V8i)
2008 U.S. Geological Survey’s Seismic Hazard
Maps
Provides levels of horizontal shaking that have a 2-in-
100 chance of being exceeded in a 50-year period.
Calculation Standards and Practices
ASCE Std. 7-05, “Minimum Design Loads for Buildings
and Other Structures”
ASCE Engineering Practice No. 113-2008, “Substation
Structure Design Guide”
IEEE Std. 693-2005, “Recommended Practice for
Seismic Design of Substations”
La Colina Substation
La Colina built in 1960’s
Steel Box-type Overhead Frame
Assembly (Lattice Structure)
Eight bays with an overall footprint of 50
ft. x 102 ft. laid out in a 4x2 pattern
Some structural modifications done
since 1960, but documentation is not
sufficient to confirm structural integrity
Future planned apparatus upgrades may
add weight to the existing structures
La Colina Substation
Original cross arms were relocated
to this position from adjacent bay at
left (just off slide to left)
La Colina - Example of Modification with Insufficient Documentation
overstressed
members in
red (typ.)
La Colina Seismic Analysis - Model
La Colina Analysis Results
Outside bay structures: analysis concluded
some structural members were overstressed
when placed under design loading conditions
Foundations and anchor bolts throughout the
structure were determined to be overstressed
under similar conditions (pull out failure)
La Colina Seismic
Recommended Upgrades
Outside bay structures: upgrade overstressed
structural cross members and add some new
cross members
Foundations and anchor bolts: reinforce
foundations to strengthen concrete around
anchor bolts (addresses pull out failure)
No anticipated customer outages, but requires
some high voltage bus outages and significant
coordination by RPU
Significant construction labor since limited
access and electrical clearances require hand
digging by construction crews
Upgraded steel
members.
New member.
La Colina Seismic Upgrades
Concrete collars will be added
to reinforce existing
structure foundations.
La Colina Seismic Upgrades
Hunter Substation
Hunter built in early 1960’s
Three bays added in late 1980’s
Some structural modifications done, but
documentation is not sufficient to confirm
structural integrity of entire structure (both
original bays and added bays)
Future planned apparatus upgrades may add
weight to the existing structures
Hunter Substation
Added 1986
Original 1960
Original location of
cross member
connection
Current location of
cross member
connection
Hunter - Example of Modification with Insufficient Documentation
Original cross
member used to be
one piece, but was
modified as shown.
Hunter - Example of Modification with Insufficient Documentation
Hunter Analysis Results
Multiple overstressed structural members in
original three bay section designed and
originally constructed in 1960s
Foundations and anchor bolts: overstressed in
both the older and newer sections of the overall
structure
Hunter Seismic Analysis Results
overstressed
members
bolded (typ.)
Hunter Seismic Upgrades
Further evaluation required to determine
appropriate modifications and the method by
which those modifications are implemented
Further evaluation will help determine cost,
schedule, and electric system impacts due to
the extent of the complex modifications at an
essential substation
Summary – La Colina Sub
La Colina Substation
Board requested to approve work order in the
amount of $266,240 for seismic upgrades at
La Colina substation
• Seismic upgrades include
– Modifications to lattice structure
– Reinforcement of foundations
Construction to begin in Summer 2011 and
complete in Fall 2011
Summary – Hunter Sub
Hunter Substation
Further evaluation is required to determine
appropriate modifications.
• To be approved separately from today’s
action and will come back to Board, if
required
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