Actual temperature in steel exposed to summer/winter? 2

[IJR]

Pals

Usually there is a minus and plus temperature values associated with a region. Example in my region is

Winter -30Celsius(-22Fahrenheit)
summer +40Celsius(+104Fahrenheit)

So far so good.

Someone recommended that I check the structure for almost 2.5 times those values, mentioning that steel is a conductor and will reach +100Celsius(+212Fahrenheit).

Anyone wants to share an experience on this issue?

Respects
IJr

 

[civilperson]

Steel exposed to the direct solar radiation will experience temperatures much higher than ambiant air temperatures. (Pick up a rebar lying out in July afternoon only with gloves on.) If shaded by a bridge, cladding or a roof then no extra temperature gain above air temperature will occur.

 

[SlideRuleEra]

Here is a round-about story. There are photos of World War II soldiers frying eggs on the surface of solar-heated steel tanks (Panzers) in the Sahara Desert. According to the Egg Nutrition Center

http://www.enc-online.org/f_a_q.htm

this requires a temperature of 145 Degrees F., or more.

http://www.SlideRuleEra.net

 

[IJR]

SlideRuleEra

So what is the industry standard. I mean what would a structural engineer has to assume?

respects
ijr

 

[SlideRuleEra]

IJR - I don't think that there is an industry standard... but there are analogies that may help use engineering judgment to pick a reasonable maximum temperature.

Back in the 1970's I designed a few prototype passive solar collectors. It is very hard to get direct sunlight to boil water - it takes optimum solar exposure, quality glazing, collector insulation, stagnant cooling conditions, high ambient air temperature, etc. Therefore the 212 degree F. temperature suggested to you, while conservative, is probably higher than necessary.

A more obtainable maximum temperature for a properly designed solar collector is 150 degrees F.

IMHO, I would still "hedge my bets" a little and suggest 180 degrees F. as a reasonable (first approximation) for a maximum design temperature for solar heating of steel used in typical construction.

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[civilperson]

A focused array of reflectors can multiply the solar radiation to many times a flat plate collector; a glass partition to isolate the steel from air convection cooling and to keep long length waves reflected, (green house effect), can easily produce concentrated temperatures in the focal point of the array above the melting temperature of metal. No single temperature can be used. A study of the various factors should be made. A simple solar oven for baking a turkey can be made out of aluminum foil.

 

[SlideRuleEra]

IJR - Turns out there is an industry standard... in the Railroad Industry. It is:
Maximum Ambient Temperature (Deg F) + 30 Deg F

The concern has to do with buckling of tracks due to thermal expansion. See this article from the February 2005, issue of Railway Track & Structures Magazine

http://findarticles.com/p/articles/mi_m0BFW/is_2_101/ai_n12416922/pg_1

Discussion begins near the bottom of page 1.

http://www.SlideRuleEra.net

 

[flamby]

What really matters is the teperature difference in the maximum and minimum temeprature. In India there are many places where steel temperature can reach 60 C but minimum temperature in the winter are no less than 10 C in such places. Again there are places where the max and min temperatures are of the order of 30 and -20 C. As structural engineer both of them mean same to me.

Ciao.