huangyhg

beam deflection due to temperature
i am a geotechnical engineer and need some guidance.
a 40 foot long steel beam (415) is fixed at one end and other end is simply supported. will there be any deflection (vertical) in the beam due to change in temperature. the beam is allowed to move at one end. i have a dial gauge with precision of 1000th of an inch.
i think beam will deflect under its own weight. how about deflection with temperature. will there be any deflection i should be concern about?
if it is unrestrained, then any deflection due to normal temperatures will be minimal.
if subjected to higher temperatures, then the young's modulus will diminish and the yield strength will also be reduced and deflection can increase substantially. by higher temperatures, i thinking in the magnitude of several hundred degrees.
dik
for normal changes in temp, i won't think so; 'cause the beam is free to extend axially. now if you heat it up so much that you affect e, then you'll change either the bending stiffness and it'll change the deflections (due to the weight of the beam).

what is the temperature of the beam?
under normal conditions you shouldn't get any deflection due to a change in temperature... however, the beam length will change... but as long as it is free to move at one end it should not deflect except under it's own weight.
now if the beam is at an extremely high temperature then you will get a decrease in the material properties, which would have an effect on your self-weight deflection.

if one end really can move laterally, then you shouldn't have additional deflection due to normal temperature changes. if it can't slide, however, then you will have additional deflection, even due to normal temperature changes.
based on your precision there could be effects. where are you located and what is the expected temperature differential? are all sides exposed to the sun or environment? is the beam exposed to wind? is any portion of it shaded?
thank you all for your prompt responses.
what if the temperature difference be about 25 degrees over a period of 24 hours. also, if top flange of w10 by 40 steel beam is exposed to sun and bottom flange not, is it going to make any difference. please advise
a uniform temperature fluctuation of 25° f, independent of time, should not appreciable affect the modulus (and stiffness) of the beam, but you may want to run some numbers. e = 29.5 msi and 28.8 msi, at 70° f and 200° f, respectively.
bestwench... thanks for the added info... i've been involved in a few structure fires and the beams become spaghetti that's why the comment about heat <g>
dik
5234185, can you tell us what is your application and reason for a 40 ft beam. is the 1/1000th measurement super critical or is there a different level of accuracy you are looking for....1/16 inch level or 1/4 inch level, etc...
self equilibrated thermal stresses for a differential temperature across the section appear, and cause both bending on both axis (if the temperature differential is not applied symmetrically) and stresses. i did a mathcad worksheet some years ago on this and is still freely available in the collaboratory for mathcad 2000. i followed a paper, doing it.
on the papers i was reading by then and at bridges (don't know the scale of such bridges) i think to re

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]