Return to index: [Subject] [Thread] [Date] [Author]

Re: Balanced Moment vs PT Moment

[Subject Prev][Subject Next][Thread Prev][Thread Next]
In a message dated 05/31/05 5:48:33 P.M. Pacific Standard Time, gtg740p(--nospam--at) writes:
Is the "balanced moment" always equal to the moment from the post tensioning?
In other words, if I have beam with a straight tendon at a constant eccentricity of 6" and a force of 150 kips, the moment from the post tensioning is a constant 75 ft*kips. Would it be correct to also call this the "balanced moment"?  Even though this is not a parabolic profile?
Or, if the same beam has a parabolic tendon profile, but the tendon is eccentrically placed at each end. Would the balanced moment at the beam midspan be the sum of the (eccentric end moment + the moment from the drape), or would it be just the moment from the drape?
I am not sure what the definition of "balanced moment" is supposed to be for beams with tendons that are eccentrically placed at the ends.
Balanced Moment Method is the method of placing the tendon in such a way that the bending moment created by the external loads at a particular section is equal to the resisting moment contributed by the eccentricity of tendon. So for a simple beam where the end moments are zero, then the eccentricity of the tendon is also zero at the ends. The moment is maximum at midspan, then the eccentricity of tendon is also maximum at midspan.
For continuous beam, there is negative bending moment at the continuous end which is being resisted by placing the tendon above the neutral axis with eccentricity that will create an equal moment resistance to the negative bending moment.  
Hope this will help.
ASQuilala Jr.  P.E.