# Torsion of continuous vs simply supported beam [closed]

Say that I have a 2 span of continuous beam subjected to torsion, is the torsion value smaller than those 2 single span beam subjected to torsion of same value ??

I think the torsion of continuous beam shall be lower, correct me if I am wrong...

Anyone can correct and explain the situation???

The length and loading of both span are the same. If i analyse 2 beams with simply supported condition, vs continuous condition, which one gives the greater torsion value ? (both span length are same and subjected to same UDL value)..... I am not sure whether my result is correct or not

Edited with diagram for easy reference....

• do the beams have the same length L? Does the middle support allow rotation? Please edit and update the question to make clear what you are asking.
– NMech
Jun 7, 2021 at 9:21
• just assume both beam have same L, same load applied.... If they are separated (both simply suppprted condiition) and continuous condition, which will have higher torsion value ? Assuming in simply suppported condition, both torsion value of beam are the same.. Jun 7, 2021 at 9:30
• Have you checked other questions on here? Jun 7, 2021 at 10:11
• ya, it seems none of them is similar to my question Jun 7, 2021 at 10:34
• For a curved beam, torsion and bending are not independent like they are for a straight beam. I don't think the question is answerable, aside from the fact that IMO it is very unclear what loading the OP is actually applying to the beams. Jun 8, 2021 at 13:28

If your middle support does restrict rotation it will help diminish the torque on the second span. But even if the middle support does not restrict rotation the geometry of the beam will cause some overturning moment resistance hence absorbing some of the torque.

Consider a continuous two-span beam W 12x136 beam with a depth of 13.41" and width of 12.4" with a torque, T applied at one end. Let's call the mid-support reaction Pkips.

This reaction,P,will have a torsion resistance capacity of $$\text{over turning moment} =torque = P*12.4/2= P*6.2kips.inch$$

So the torque of the second span of the continuous beam is

$$T_{2nd.span}= T-P*6.2$$

• for continuous beam, one of the midspan of beam subjected to torsion only, The support reaction will be much higher than those simply supported beam, does it mean that the torsion of the continuous beam will be much higher in this case?? I knew that the torsion reaction of support will be greatest (torsion reaction= support reaction * ecc) Jun 8, 2021 at 0:43

From the structural engineering perspective, for geometry and compatibility concerns, an idealized beam end support MUST NOT have rotational freedom about the beam's longitudinal axis. Thus, a continuous beam is treated as consisted of multiple-single span fixed end beams for the concern of torsion.