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Compression Strength of Cast Iron Columns?
- Thread starter JCS613
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racookpe1978
Nuclear
What is the shape of the column? ID, OD, consistency (deviations or bad casting or flaws or holes or voids or "clobs" of extra, unbalanced metal?
Solid? Almost certainly not, but you need to actually verify EXACTLY what the interior of the old column IS .. Not what you think it is or what they "usually" are or even what the second and third and 4th one are. EVERY casting could be different because there is no checks or guarantees in the old metal. And, unlike mass-made parts, every one is hand-tamped, hand-filled, hand-cooled and broken out from the mold. Assuming they all used the same mold even. You could have 14 or 48 columns, and not know that 12 of them were near-breaking the whole time, but never quite got stressed enough to actually crack.
Also, the casting attachment needs to be checked, it will be difficult to weld to the cast metal, to drill and bolt to them, or to do much of anything but load them perfectly vertically. Metal variations from casting to casting might not change too much, but each pour could be different. 8 good metal (stronger than expected), 16 average, and 8 poor for example.
Solid? Almost certainly not, but you need to actually verify EXACTLY what the interior of the old column IS .. Not what you think it is or what they "usually" are or even what the second and third and 4th one are. EVERY casting could be different because there is no checks or guarantees in the old metal. And, unlike mass-made parts, every one is hand-tamped, hand-filled, hand-cooled and broken out from the mold. Assuming they all used the same mold even. You could have 14 or 48 columns, and not know that 12 of them were near-breaking the whole time, but never quite got stressed enough to actually crack.
Also, the casting attachment needs to be checked, it will be difficult to weld to the cast metal, to drill and bolt to them, or to do much of anything but load them perfectly vertically. Metal variations from casting to casting might not change too much, but each pour could be different. 8 good metal (stronger than expected), 16 average, and 8 poor for example.
Gray cast iron has rather remarkable compressive strength and corrosion resistance, with the former value I believe portrayed by some authorities as even many times its tensile strength. An interesting visual illustration of this perhaps non-obvious strength are the twin 48" pipe arch columns depicted in the historical photograph (image 123 of 507 this collection) at This 200 ft+ span bridge was designed by General Montgomery Meigs of the U.S. War Dept (later USACE, and I believe Meigs incidentally also designed our near equally durable U.S. capitol dome using arched cast iron). This photograph from the National Archives was taken by a gentleman named Matthew Brady around the late 1850's, who was later surrounding the Civil War to take many historical photographs, including a few of one President Abraham Lincoln. I believe these unique arches carried the structure, as well as all traffic up to street car on a little thoroughfare called Pennsylvania Avenue (and at the same time conveyed water under pressure of the Washington Aqueduct) for 50 or 60 years thereafter, at which time they were surrounded by a more modern and larger concrete bridge structure). I also believe they are still in service today, now a sesquicentury later.
I suspect many cast iron columns as you are talking about later were however perhaps designed via what was called the "New York Building Law Formula" that went through some gyrations over the years as explained in the pretty good article at This law was sometimes simplistically expressed with a form e.g. circa 1915 as:
Unit Stress = 9000 -40(L/r) (with the output I believe in psi)
In the first half of the 1900's such columns, often round shaped [for all-round (so to speak) efficiency] may have been cast either vertically in pits, or a little later on centrifugally (with the latter portrayed as stronger iron and superior to the old pit-cast, and I believe with reasonable quality producers improving on at least most issues expressed by the previous responder). The point of where possible preferring other means of attachment than welding is certainly well taken.
The development of ductile iron in the mid 20th century provided a material with several times the tensile strength of gray cast iron, but still retaining an apparent compressive yield strength up to 20% higher than its 42,000 psi minimum yield strength (that incidentally also in perhaps non-obvious fashion gives rise to a great apparent bending yield strength of approximately 72,000 psi or so for ductile iron). As structural members centrifugally cast ductile iron piles and poles are used in the present day rather widely internationally, and huge quantities of ductile iron tunnel liner plates were also used to construct the Chunnel, or world's longest undersea tunnel just a couple decades between England and France, largely as a result of these strengths along with substantial ductility. Flanged ductile iron piping is also used in the present day as single pipe, and with special gasketing even longer "long-span" pipe beams.
I guess future generations will see if some other "modern" building materials in the long run provide comparable and as cost-effective service. All have a good weekend.
I suspect many cast iron columns as you are talking about later were however perhaps designed via what was called the "New York Building Law Formula" that went through some gyrations over the years as explained in the pretty good article at This law was sometimes simplistically expressed with a form e.g. circa 1915 as:
Unit Stress = 9000 -40(L/r) (with the output I believe in psi)
In the first half of the 1900's such columns, often round shaped [for all-round (so to speak) efficiency] may have been cast either vertically in pits, or a little later on centrifugally (with the latter portrayed as stronger iron and superior to the old pit-cast, and I believe with reasonable quality producers improving on at least most issues expressed by the previous responder). The point of where possible preferring other means of attachment than welding is certainly well taken.
The development of ductile iron in the mid 20th century provided a material with several times the tensile strength of gray cast iron, but still retaining an apparent compressive yield strength up to 20% higher than its 42,000 psi minimum yield strength (that incidentally also in perhaps non-obvious fashion gives rise to a great apparent bending yield strength of approximately 72,000 psi or so for ductile iron). As structural members centrifugally cast ductile iron piles and poles are used in the present day rather widely internationally, and huge quantities of ductile iron tunnel liner plates were also used to construct the Chunnel, or world's longest undersea tunnel just a couple decades between England and France, largely as a result of these strengths along with substantial ductility. Flanged ductile iron piping is also used in the present day as single pipe, and with special gasketing even longer "long-span" pipe beams.
I guess future generations will see if some other "modern" building materials in the long run provide comparable and as cost-effective service. All have a good weekend.
I'm assuming that there is no engineering data available for these columns? If not, then it would seem to be a good idea to take some samples from the columns and do a metallurgical analysis on them. It would also be a good idea to take some dimensional data of the columns. And finally it would be helpful to survey the physical condition of the columns to account for problems like corrosion.
You will need to identify the type and grade (sample(s) for chemical analysis, metallographic examination and hardness) of the cast iron columns, and once this is completed;
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