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On Sun, 10 Dec 2006 20:12:03 GMT, prd <X_header@xxxxxxxxxxx> wrote:
>In sci.archaeology message news:824def924e.diggings@xxxxxxxxxxxxxxxxxx by
>Kendall K. Down <webmaster@xxxxxxxxxxxxxxxxxx> . . . :
>
>> In message <qvEeh.176874$Fi1.26072@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
>> prd <X_header@xxxxxxxxxxx> wrote:
>>
>>> What I surmise based on what F provided is that the recipe
>>> given had to little clay and it was not activated and with
>>> no aggregate for strength, it would have been too weak to
>>> be formed into load bearing arches, ceilings, or overhanging
>>> walls.
>>
>> Strong enough to support the weight of the Great Pyramid, but too weak
>for
>> load-bearing arches? Do I detect a contradiction here?
>
>In concretes stretch strengths and compression strengths are very
>different.
>
>Stren Tensile Compress Shear
>Steel 5 10E8 5 10E8 3 10E8
>Iron 2 10E8 6 10E8 2 10E8
>Brass 3 10E8 3 10E8 2 10E8
>Alum 2 10E8 2 10E8 2 10E8
>Concr 2 10E6 2 10E7 2 10E6
>Brick 4 10E7
>Marble 8 10E7
>Granit 2 10E8
>Bone 1.3 10E8 2 10E8
>
>What you should note is that while bone,steel, brass and aluminum
>have nearly equal tensile:compression:shear ratios the ratio between
>tensile:compreassion strength is nearly 1:100, this ration improves
>with reinforcement (because it takes on the properties of the reinforcing
>substances along with other additions), but decreases with the
>weakness (more looseness) of the concrete, until it reaches the
>point of an aggregate, like crushed granite that has relatively
>high compression strength once compacted, but no tensile and very little
>shear strength.
>
>This is the critical point about concrete to remember, why for instance
>a concrete and mortar arch works so well. Consider a hard brick squeezing
>a compressible mortar. To get an all concrete arch you really need
>reinforcement to replace the forces, and for a overhanging beam you really
>need good reinforcement.
Unreinforced concrete is fine providing you maintain it in
compression.
>
>http://mceer.buffalo.edu/publications/bulletin/97/11-03/jul97n2.html
>http://mceer.buffalo.edu/research/Reconnaissance/kobe1-17-95/structural.asp
>
... and the exact relevance of these to what you have just written is
- what? Both articles deal with the dynamic response of reinforced
concrete structures to to the forces of an earthquake. Any structure
of any material has the potential to fail in such circumstances. In
fact, as you quote below, steel structures failed in the earthquake
also.
>A real world test of concrete, how it fails how it compared to steel,
>and the complex relationship between reinforcement size and shear
>strength.
An explanation of the respective parts played by concrete and steel in
a structure can be found at
http://structsource.com/analysis/types/concrete.htm
>
>"
>Concrete
>
>The sixth floor of the old
>Kobe City Hall collapsed.
>(Photo courtesy of C.
>Scawthorn.)
>
>Well in excess of 100 midrise buildings constructed during the 1960's and
>1970's from reinforced concrete were observed to have failed, in many cases
>catastrophically. Most failures appear to have been shear failures of
>columns, which were observed to have very light transverse reinforcement. A
>number of mid-height single story pancake collapses were observed. An
>example was the 1960's vintage eight-story Kobe City Hall, which sustained
>a complete collapse of the sixth floor, while the neighboring 1980's
>vintage 16-story New City Hall was undamaged.
>"
>
>"
>Highways and Roads
>
>Only two limited access highways exist in the narrow transportation
>corridor. The Hanshin Expressway is carried on single large hammerhead
>reinforced concrete piers, many of the concrete sections failing in shear
>and/or flexure over a 20 kilometer length. Along the harbor shore is the
>Wangan (Harbor) Expressway, a newly elevated highway generally of steel and
>crossing a number of navigable waterways on major crossings. Many of the
>steel girders appear to have jumped from their beam seats and were askew,
>although few had collapsed.
>
>"
>Many of the steel girders appear to have jumped from their beam seats and
>were askew, although few had collapsed.
>"
>
>Rail
>
>
>A detailed view of a sheared column which supports the
>Shinkansen. (Photo courtesy of C. Scawthorn.)
>Rail facilities were particularly hard hit in this earthquake (for further
>information on damage to underground rapid transit facilities, see article
>by Thomas O'Rourke on page 6). Three main lines (JR West, Hankyu and
>Hanshin) run through the corridor, in general on elevated embankments, and
>all sustained embankment failures, overpass collapses, distorted rails and
>other severe damage. In Kobe, the Shinkansen (Bullet Train) is generally in
>a tunnel through Rokko Mountain. No information was available regarding the
>tunnel. At the east portal of the tunnel, the line is carried on an
>elevated viaduct, built in the 1960's. For a length of three kilometers,
>this viaduct was severely damaged, with a number of the longer spans
>collapsing. _In general, these collapses were due to shear failure of the
>supporting columns_.
>"
>
>[Notably the arrangment of rebar and size of columns was listed as a key
>factor, see photos]
>
>Other examples of sheer failures.
>http://whatiscivilengineering.csce.ca/structural_earthquakes.htm
>
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> -----
Eric Stevens
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