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>From: JStahmer@Ammann-Whitney.com
>To: Don Campbell
>Cc: JGould@Ammann-Whitney.com
>Subject: Arecibo Operational Limits
>Sender: JStahmer@Ammann-Whitney.com
>Date: Mon, 29 Mar 2010 11:01:50 -0400
>
>Don:
>
>As discussed on Friday, Jim reviewed the operational limits that we
>developed this morning and is in agreement with the information. I'm
>attaching a graph of unbalanced moment vs. safe tie down forces for your
>use. Note that this graph is not a recommendation on specific
>configurations but is a definition of the safe operational envelope for
>the telescope.
>
>We have based this graph on a review of members that we have identified as
>operating close to their allowable structural limit. I am attaching a
>copy of a matrix we developed showing member forces from the table on the
>1992 upgrade drawings and recalculated member capacities based on material
>properties specified in the 1963 AISC Code of Standard Practice. Note
>that, in addition to the U2 U2L3 members there are a number of other main
>truss elements that are designed to operate at or slightly below their
>full allowable structural capacity. The U2 U3 member demonstrates the
>highest capacity vs load ratio. I would note though that we have assumed
>a very conservative unbraced length for this member and the pipe added by
>the upgrade contractor between the upper U2 joints may allow us to
>substantially revise the capacity of this member upwards. Jim will add a
>review of the connection to his ever growing list of field inspection items.
>
>One surprise that we did have was the bottom chord of the main
>truss. This member was working at exactly it's capacity in the 1962
>design. The current configuration with the additional support point
>provided by the 1992 auxiliary cables has actually reduced the demand on
>these members.
>
>For the attached operational limits we reviewed all of the members
>identified on the attached member capacity matrix and have found that they
>are at or below the maximum allowable force for the moment/tiedown force
>envelope shown. We have also done a brief review of the forces in the
>bracing trusses and find that they are also within allowable limits.
>
>Hope this information allows the observation schedule to be extended if
>not fully met.
>
>
>
>Regards,
>
>Joel Stahmer, P.E.
>Vice President
>