MINUTES
From 8 July Meeting:
A.
Review of previous action items:
ART-1: Provide ART with test result data from
Vibration Tests (LAT-TD-00788) - Horn Closed
ART-2: Provide ART results of insert pull out tests
- Johnson - Open
Current Status: Tom Borden to work with
Hytec to provide data
ART-3: Provide ART the properties for the
carbon-carbon material - Johnson - Closed
ART-4: Provide a recommendation for design practice
and analysis cases for redundant load path considerations - Rodini - Closed
B.
Discussion:
- Ben
Rodini pointed out that the 8.5KSI Carbon-Carbon tensile strength seemed low
relative to other structural applications.
- Ben
Rodini reviewed concerns with tolerance variance impacting load path
design limits with inserts. A conservative approach would be to assume half the
inserts were load bearing . Discussion
with the tracker team indicated that insert location was controlled to within 2mils
on both sidewalls and base. Ben
indicated that this level of tolerance control was good and would allow the use
of something like 1.25 (TBR) load factor to account for tolerance uncertainty.
- The
ART recommended that the locking feature for the system be selected &
incorporated into the design prior to the next test
- The
flexure design was discussed and concern expressed as to the FEM complexity
impact of multiple piece flexures vs. single piece. The primary concern being whether we understood the flexure
contribution to total load at the corner interface. The tracker team indicated that design trades required multiple
piece approach due to space limitation.
Hytec also indicated that although more complex their FEM correlated
well with observed flexure behavior. The ART indicated that the tracker team
design load should also consider uncertainty due to flexure design
complexity. Ossie Millican indicated
that he may be able to conduct some special tests with spare flexures if it
would help understand this uncertainty.
- The
gasket approach and impact on dynamic response was questioned by Minh
Phan. He pointed out that frequency
instability results from the tests would not allow model correlation or ensure
dynamic response loads to be known. The
move towards a non polymeric thermal gasket should reduce this issue. It is clear that additional dynamic analysis
will be required to assess proposed corrective actions.
- Tsune
Kamae indicated that a worst case design load condition should consider the
impact of the grid distortion and resulting off-set of tower to grid
interface. The condition may adversely
impact the direct load path through the corner flexures.
- The
ART believes that there are sufficient factors that could contribute to a
greater than expected load at the corners to cause failure. An analysis of
these factors was proposed by Tom Borden to assess strength requirements. It is anticipated that this analysis will
show sufficient plausible failure modes to provide a basis for corrective
action.
- The
ART is also concerned that the design environment may be overly conservative
for this application and it may be reasonable to reduce the environment to some
extent by accounting for attenuation through the structure. Ben Rodini indicated that Swales is looking
into this. Ben and Bernie Graf to
coordinate this effort with the project office.
- Dick
Horn requested that ART members provide an email to him summarizing their view
of findings to date
C. New
actions:
ART-5:
Distribute a proposed analysis plan to the team and review it at the next ART -
Borden - ECD 9 July
ART-6:
Coordinate a review of environment requirements - Graf/Rodini - ECD 15 July
ART-7:
Consider & recommend plan for additional flexure testing - Borden/Millican
- ECD 9 July
Please
provide any corrections/clarifications of these minutes to Dick Horn prior to
the next meeting 9 July