[asapmembers] ASAP Member Newsletter: Earthquake Damage and Planned Repair
secretary at areciboscience.org
secretary at areciboscience.org
Wed Feb 12 01:17:00 UTC 2014
A non-text attachment was scrubbed...
Name: ASAP_banner.jpg
Type: image/jpeg
Size: 47196 bytes
Desc: not available
URL: <http://areciboscience.org/pipermail/asapmembers_areciboscience.org/attachments/20140211/33c1f4f7/attachment.jpg>
-------------- next part --------------
Dear ASAP Member,
As many of you may have heard, the Arecibo Observatory suffered
serious damage to one of its
main support cables during the January 13 magnitude 6 earthquake. The
damaged cable was the
"short" cable delivered 12 feet too short by Bethlehem Steel in 1962
and then spliced so it could go into
service at that time. The other cables retain sufficient strength to
support the platform; however, should
the damaged one give way, it would fall in a manner that would do
severe damage to the reflector and
its precise alignment.
Observatory engineers identified the breakage the morning after the
earthquake. Then consulting
structural engineers from Ammann & Whitney in NYC flew in promptly to
assist in assessing the scope
of the damage and strategizing about its repair. Head Maintenance
Engineer Filipe Soberal has now
designed a temporary repair to the damaged cable, and most telescope
motion and access to the bowl
and platform are mostly curtailed pending completion of the repair.
Several science programs that do
not require telescope motion, however, remain in progress. The heavy
steel materials for the repair
have been ordered, and the detailed machining of the various parts is
underway. Under current plans
the repair will be completed by March 11.
A more detailed series of photographs and explanation of the damage
and repair prepared by NAIC
Director Bob Kerr is attached below. We will keep you informed about
how the work continues and is
completed.
We salute the platform maintenance staff at the Observatory for their
extraordinary skill and ingenuity
at this critical time. It is remarkable and highly admirable that a
repair of this magnitude and complexity
can be carried out by the Observatory engineers and platform staff
internally.
With sincere thanks and regards,
The ASAP Board
Hello ASAP Members
During original AO construction, in 1962, one of the original 12
platform suspension cables was delivered
too short, and a short cable section (12') was "spliced" to a 568'
cable section running from tower T8 to the
triangle corner — to provide sufficient reach to the platform. That
cable segment and splice, near the top of
one of the telescope towers, was consequently more rigid than the
balance of the suspension system. When
the earthquake shook the site, just after midnight on January 13,
2014, it is that short cable, and splice "box",
that suffered damage. You might say that our structural Achilles heel
was exposed.
The photo "Tower 8 Top.jpg" shows the top of tower 8, post-quake. In
this photo you can see the rectangular
cuboid that is the "splice box".
A protocol structural survey following the January 13 earthquake
revealed serious damage to that short
cable section, with apparent breach of several cable strands. An
experienced structural engineering firm,
Ammann & Whitney in New York, was brought to assess the damage, and to
consider repair options.
The photos "OVERALL EXTENSION CABLE 20110302.jpg" and " OVERALL
EXTENSION CABLE 20140117.jpg"
show the 12' extension cable pre-quake (03/02/11) and post-quake
(01/17/14), respectively. (We had a
structural survey performed in 2011 as a matter of structural
stewardship.) Note the additional paint that
was wrenched from the cable section, by quake motion — near the
"saddle block" end of the cable.
The photo "UPHILL Splice Box.jpg" shows the end of the 12' extension
cable going into the splice box,
post quake. Note loose cable strands, likely broken.
The two photos "DOWNHILL SPLICE BOX 1.jpg" and "DOWNHILL SPLICE BOX
2.jpg" show the splice
box at the side where the 568' cable runs from the box on out to the
platform - from two perspectives.
No damage to cable strands on this side of the splice box, the
platform side, is evident. Ammann &
Whitney conclude that swaying motion in the long cable absorbed the
energy of the quake motion, but
that the shorter side of the cable arrangement, the extension cable,
was more rigid, and more brittle, and
thus the damage to the shorter, extension cable component.
The photo "EXTENSION CABLEIN SADDLE.JPG" shows the end of the short,
extension cable, within
the saddle block atop the tower. At this end too, A&W believe there
may be extensive damage to the
cable strands, including internally, that cannot easily be assessed.
A&W believe there was a significant "friction override" within the
splice box, as the entire box was
pivoted 15 degrees by consequence of quake motion. No one really
knows what is inside that box,
but A&W surmise it is arranged as in the drawing "SPLICE BOX.pdf" —
with two "button sockets" on
the end of each cable, fitted into the steel box. These button
sockets are similar to those you can see
at the end of cables in the saddle block. The photo "OVERALL
EXTENSION CABLE 20110302.jpg"
shows the button socket ends of the back-stay cables fitted into
saddle block, as examples.
A relatively low-cost ($80,000) repair option has been designed, and
materials are being procured
to complete a repair that we expect will bring the telescope back into
full service. While the project
awaits full review by the National Science Foundation, necessary steel
materials for the repair are
being shipped to the Observatory at this writing. Our estimated
completion date for this repair project
is March 11, 2014.
A rough drawing of the A&W repair design appears in the file "Short
term repair.pdf" - courtesy of
Tony van Eyken. (Of course, we now have very detailed CAD drawings of
the repair design detail.)
Basically, the saddle block has two empty slots - by design. These
extra slots were used for cables
that originally hoisted the platform, as the final suspension cables
were tensioned and attached. Once
erected, these cables were removed, and the empty slots could be used
for necessary strengthening,
additional cables, or possible repairs. (Brilliant!). The photo
"OVERALL EXTENSION CABLE 20110302.jpg"
shows one empty slot in the saddle block, and there is another,
eclipsed in the photo, on the other
side of the saddle block. Basically, we will connect two long (15')
"lead screws" into these slots, and
attach a large steel "C" channel to their other end — grabbing the
entire splice box on the undamaged,
platform side. (There is a lot more detail - but this is the basic
idea.)
In the meantime, in an abundance of caution, telescope motion has been
very limited. Despite that, the
telescope has continued its science mission by participation in a ten-
day global ionospheric study in late
January, by a continuing a productive search for pulsars in the sky
above Arecibo, and by a search for
fast radio bursts (FRBs).
Arecibo Observatory proceeds on schedule to complete this emergency
repair as expeditiously and
safely as possible. We do consider the repair to be temporary, and a
more comprehensive long-term
cable repair design is being developed. Nevertheless, we do expect
the Gordon telescope to return in
full service to the Astronomy, Atmospheric Science, and Planetary
communities in March. The nature
of the repair is also "rigid", like the 12' cable extension kluge,
itself. And so the structure will remain
susceptible to quake damage, at this location, until a more
comprehensive cable replacement effort
might be made....
It is testimony to the remarkable expertise, capability, and bravery
of the Arecibo Observatory staff
that they will be able to effect this repair themselves, working 365
feet above the ground on a 900-ton
steel suspension bridge system. I am doubtful that a comparable
capability exists at any other U.S.
science facility.
Sincerely,
Bob Kerr
Director, Arecibo Observatory
978-314-9760
-------------- next part --------------
A non-text attachment was scrubbed...
Name: DOWNHILL SPLICE BOX 1.jpg
Type: image/jpeg
Size: 503728 bytes
Desc: not available
URL: <http://areciboscience.org/pipermail/asapmembers_areciboscience.org/attachments/20140211/33c1f4f7/attachment-0001.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: DOWNHILL SPLICE BOX 2..jpg
Type: image/jpeg
Size: 660806 bytes
Desc: not available
URL: <http://areciboscience.org/pipermail/asapmembers_areciboscience.org/attachments/20140211/33c1f4f7/attachment-0002.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: EXTENSION CABLE IN SADDLE.jpg
Type: image/jpeg
Size: 354712 bytes
Desc: not available
URL: <http://areciboscience.org/pipermail/asapmembers_areciboscience.org/attachments/20140211/33c1f4f7/attachment-0003.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OVERALL EXTENSION CABLE 20110302.jpg
Type: image/jpeg
Size: 397441 bytes
Desc: not available
URL: <http://areciboscience.org/pipermail/asapmembers_areciboscience.org/attachments/20140211/33c1f4f7/attachment-0004.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OVERALL EXTENSION CABLE 20140117.jpg
Type: image/jpeg
Size: 448881 bytes
Desc: not available
URL: <http://areciboscience.org/pipermail/asapmembers_areciboscience.org/attachments/20140211/33c1f4f7/attachment-0005.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Short_term_repair.pdf
Type: application/pdf
Size: 1271562 bytes
Desc: not available
URL: <http://areciboscience.org/pipermail/asapmembers_areciboscience.org/attachments/20140211/33c1f4f7/attachment.pdf>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: SPLICE BOX.pdf
Type: application/pdf
Size: 32868 bytes
Desc: not available
URL: <http://areciboscience.org/pipermail/asapmembers_areciboscience.org/attachments/20140211/33c1f4f7/attachment-0001.pdf>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Tower 8 Top.jpg
Type: image/jpeg
Size: 93447 bytes
Desc: not available
URL: <http://areciboscience.org/pipermail/asapmembers_areciboscience.org/attachments/20140211/33c1f4f7/attachment-0006.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: UPHILL Splice Box.jpg
Type: image/jpeg
Size: 1438846 bytes
Desc: not available
URL: <http://areciboscience.org/pipermail/asapmembers_areciboscience.org/attachments/20140211/33c1f4f7/attachment-0007.jpg>
More information about the asapmembers
mailing list