huangyhg

questions on torsion
how can i brace my beam for torsion at intermediate and end sections of my beam?
i read here that sometimes for simply supported beam the ends are not braced for torsion. how is it possible that there would be no restraint for torsion at the ends? i can't understand that.
will stiffeners help increase the capacity of my beam for torsion? i heard no but i would think yes like concrete beam stirrups.
what is the difference between torsion from eccentricity and torsion from ltb?
my understanding of torsion is weak. please recommend a journal for torsion.
aisc design guide 9 - torsional analysis of structural steel members
read all available texts, and code commentaries to gain better understanding, or confusion.
engineers hate torsion because it is not a simple, nor truely critical, in most of civil-structural works. i hear the guys are yelling with heavy dose of critism, but to me it's a fact - people tend to take things to extreme for lack of confidence, and/or to express superiority in this regard.
true torsion, as in the elemtary mechanics, is simple, and is somthing to avoid, to the best extent you can.
for localized tosion, try to look the bigger picture, the whole system, to determine its significance. maybe a detail here, a detail there, may be just enough to smooth it out without causing "un-realized" consequence down the road.
i don't mean to discourage from learning and recognize this phenonmenon, and/or any expert advices. just want you to look big, not just one beam, one connection at a time.
good luck in real world practices.
amusteit,
each of your queries in turn.
ends of a simply supported beam are generally only braced against lateral movement and nothing else.
there are 3 types of torsion, pure torsion which causes shear only and then warping torsion and st venants torsion. stiffeners on an open section do help a little with warping and st venants but not with pure torsion as there is no difference to the critical cross section. concrete beams develop compression structs in the concrete and are therefore completely different to steel beams in this regard.
fundamentally ltb torsion is the same but the calculation is completely different since ltb formulii are based on preventing lateral movement rather than twisting. this comparison will only serve to confuse you so dont go down this path.
i would suggest you look into a closed section for torsion as these are much stronger in this regard.
cant help you with any other better texts than design guide 9.

csd72:
excellent explanations.
little adds on: the torsional effect on the simple end connections is alleviated through the small rotation allowabled by the joining materials.
kslee-
that's only true for compatibility torsion, not equilibrium torsion.
structuraleit:
please explain your view point to amusteit, and wish he can gain better understanding.
i was dealing with prestressed bridge girders one time and was out at the precast plant having a word with the site manager. these deck girders are typically 4' x 2' rectangular sections with void form inserts. i notice one particular girder they were about to pour had no space between the void formers and ask the manager whether this is common practice, saying that i had always seen 6" spaces between 6' long void formers detailed. the manager told me it wasn't common and that he prefers the spaces between the voids because it makes the girders torsionally stiffer when they are transporting them to the back of the yard.
without knowing the theory behind this, i imagine it would be the same occurance for steel beams with stiffeners. that they will be more resistant to torsional deformations.
i thought i knew at least a little about torsion, but i have two questions:
csd72: what's the difference between pure torsion and st. venant torsion? i thought they were the same thing and there were only two basic types--warping and pure torsion.
strleit: what are "compatability torsion" and "equilibrium torsion"? is compatability torsion the rigid body component?
compatability torsion is what beams in indererminate frames experience, they will attract torsion but other load paths are available if cracking occurs and torsion redistributes.
equilibrium torsion is exactly what it means, equilibrium cannot be satisfied unless torsion is present and must be designed for. such as cantilevers
asixth:
well explained.

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