Hello. I'm doing some research on the tower of the Montreal Olympic
Stadium and came across a specification I haven't been able to
decipher: "Freyssinet 24T/15". This is in reference to the type of
post-tensioned pre-stressing steel cable used to support the
structure. The specification was listed in the June 3, 1976 edition
of New Civil Engineer. I would like to know the diameter of the cable
in question and/or its ultimate stress.
Thanks very much! |
Request for Question Clarification by
tutuzdad-ga
on
09 May 2006 20:52 PDT
I don't believe that specification will give you the diameter or
stress of the cable. I believe "24T/15" is a Tesla forumla. If you are
not already aware, the International System (SI) unit of field
"magnetic flux density" is called the tesla (T), so named after Nikola
Tesla. One tesla (1T) is defined as the field intensity generating one
newton of force per ampere of current per meter of conductor. In other
words this is a unit used to define the intensity (density) of a
magnetic field. The term "Freyssinet" refers to Eugene Freyssinet
(1879-1962) the French engineer who was the inventor of prestressed
concrete, and while the tesla is relative to the strength of the
prestressed steel the formula is not desinged to give you the
diameter.
What do you think?
tutuzdad-ga
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Clarification of Question by
willem_oa-ga
on
09 May 2006 21:11 PDT
Hi -
I'm almost sure the "T" does not refer to Tesla - I don't see how
electromagnetics would be relevant to steel cable categorization. If
you are sure that the T in 24T/15 does indeed refer to Tesla, I would
appreciate a citation or two in defense. Could the T not refer to
tons, metric tonnes, or tension?
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Request for Question Clarification by
denco-ga
on
09 May 2006 21:53 PDT
Howdy willem_oa-ga,
Might it be a cable of 24-15mm diameter strands?
http://www.ketchum.org/Cangrejillo/Cangrejillo.html
"The four main cables carry all loads to the abutments. They are comprised
of the Freyssinet prestressing strand and anchor system developed for use
in cable-stayed bridges. Each cable consists of 37-15mm diameter strands;
each 7-wire galvanized strand is enclosed within a wax filled HDPE sheath."
Looking Forward, denco-ga - Google Answers Researcher
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Request for Question Clarification by
denco-ga
on
09 May 2006 22:04 PDT
Howdy willem_oa-ga,
There is is this as well. Perhaps the "T" stands for (as you point out)
tensioned or twisted? I am pretty well convinced it is 24-15mm strands.
http://www.senh.org/newsletters/Sept-05%20newsletter.pdf
"A value engineering proposal to use un-grouted stay cables using greased
and sheathed Freyssinet monostrand proved to be very successful. Each
strand is 0.6 inch diameter, comprised of 7 wires individually coated in
grease and wrapped by a plastic sheath. The largest stay cable was made
up of 73 ? 0.6 inch diameter strands."
Please note that .6" is close to 15mm.
Looking Forward, denco-ga - Google Answers Researcher
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Clarification of Question by
willem_oa-ga
on
09 May 2006 22:08 PDT
This sounds reasonable... however, I would like to see the "T"
accounted for. Are there additional examples of prestressed cable
referred to as "24-15mm diameter"?
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Request for Question Clarification by
denco-ga
on
09 May 2006 22:18 PDT
Howdy willem_oa-ga,
Here are some stress figures as well, from the U.K. Freyssinet site.
http://www.freyssinet.co.uk/exp/pands/construction/cablestays/tec.html
"Capacity
Freyssinet standard stay cables are designed with capacities in the
range of 1,430 - 15,144kN. These stays comprise between 12 and 127
multiple parallel strands of 15mm nominal diameter. Special units
have been designed and produced for up to 205 strands and there is
actually no limit on the theoretical number of strands which can be
accommodated in the anchorage.
Freyssinet Monostrand
The resisting element of Freyssinet stay cables is a bundle of
parallel 15mm nominal diameter seven-wire coated strands. The high
tensile strength strand (up to 1860Mpa) is hot dipped galvanized
before the last drawing operation forming the first barrier in the
corrosion control system."
Nope, I have not been able to find the "T" used anywhere else, but
considering that Freyssinet uses 15mm strands, it would almost have
to follow that the "/15" part is 15mm and the "24" is the number of
strands in the cable. With everything I have seen, I would consider
the "T" to be an anomaly, that is, some type of typographic error.
Looking Forward, denco-ga - Google Answers Researcher
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Request for Question Clarification by
denco-ga
on
09 May 2006 22:43 PDT
Howdy willem_oa-ga,
I am going to take back the "typographic error" theory.
http://www.dynamicprestress.com/products/anchorages.htm
The "T" is part of a system.
http://snsvo4.seekandsource.com/postensystems/vopage1.html
"Anchorages are manufactured in the range of 4T13 to 27T15 as per BS 4447
standards and FIP recommendation. Non standard Anchorages are available on
request."
There is this as well, which talks of (T)hreadbar.
http://www.dywidag-systems.com/download/uk/DSI-Threadbar-PT-System-uk.pdf
Looking Forward, denco-ga - Google Answers Researcher
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Request for Question Clarification by
denco-ga
on
09 May 2006 23:07 PDT
Getting closer, willem_oa-ga.
Tensile is a good candidate.
http://www.geocities.com/cedricstewart/canalbridge.html
"Each strand, of T15 type, has a section of 150mm2 and is tensed with a
force of ~22 tons, hence a tensile stress of ~1.440N/mm2.
The main prestress units used for this bridge are made up of 27T15 for
the walls cables and of 12T15 for these of the bottom flag."
Looking Forward, denco-ga - Google Answers Researcher
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Request for Question Clarification by
tutuzdad-ga
on
10 May 2006 07:53 PDT
This could also be indicative of the Stress-Energy Tensor formula
http://people.hofstra.edu/faculty/Stefan_Waner/diff_geom/Sec12.html
tutuzdad-ga
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Clarification of Question by
willem_oa-ga
on
10 May 2006 11:56 PDT
denco-ga, the 24 strand X 15 mm theory now seems quite plausible -
however, the last example you cited lists 15T as being 150 mm2, which
is at odds with the other examples (just to be sure, I checked to make
sure that a 15 mm diameter does not correspond to a 150 mm2
x-sectional area). If you can find one more example that falls in
line with the 24 strand x 15 mm theory, I will be satisfied. Thanks!
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Request for Question Clarification by
denco-ga
on
10 May 2006 13:36 PDT
Howdy willem_oa-ga,
I think the reference of "Each strand, of T15 type, has a section
of 150mm2 and is tensed with a force of ~22 tons, hence a tensile
stress of ~1.440N/mm2" might have incomplete information.
Consider this source instead.
http://www.lcpc.fr/en/presentation/moyens/bancdefatigue/index.dml
"This system was composed, depending on the stay cables, of 43 or
73 T15-type parallel strands. These strands, which feature a unit
cross-section of 150 mm˛, are composed of 7 wires and provide an
allowable stress rating of 1,770 MPa. Each cable could therefore
display a guaranteed rupture force of 11,395 kN (for the 43 T15
strands) and 19,345 kN (for the 73 T15 strands). Each strand had
been galvanized, lubricated and encased."
An earlier reference supports these general numbers.
http://www.dynamicprestress.com/products/anchorages.htm
"...
- ... 15.2 mm strand ... normal Cross Sectional Area is 140 mm˛
- ... 15.7 mm strand ... normal Cross Sectional Area is 150 mm˛
..."
Finally, we get back to the source of the "problem," Freyssinet!
http://www.freyssinet.com/intranet/internetFI.nsf/web/publications/$file/222%20GB.pdf
"...
TWO SORTS OF STRAND, SEVERAL TYPES OF ANCHOR
The two diameters of strand used are 15.70 mm (T15 strand) and
13 mm (T13). Depending on the diameter and the number of strands
they receive (1, 3, 4, 5), the anchors are given code names that
are easy to decipher: 1E15 (1 strand of 15), 3E13, 3E15, 4E13,
4E15, etc."
So, 15mm does always mean 15mm exactly, and a "strand" of ~15mm
cable is made of a number of wires, etc. The "sheath" that wraps
a strand might be included in the 150mm cross sectional measure
as well. And, no, I do not know what the "E" in 1E15 means.
Looking Forward, denco-ga - Google Answers Researcher
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Request for Question Clarification by
denco-ga
on
10 May 2006 13:52 PDT
This document strongly indicates that "T" is for "Tensile."
http://www.cclstressing.com/pdf/manual-e-range-pt-anchorage-technical-data.pdf
Check out the tables starting on page 11.
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Request for Question Clarification by
denco-ga
on
10 May 2006 13:55 PDT
Apologies, that should have read:
"So, 15mm does not always mean 15mm exactly ..."
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Clarification of Question by
willem_oa-ga
on
10 May 2006 18:45 PDT
That should do it. Thanks very much for your hard work, denco-ga.
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