Redistribution of forces
Redistribution of forces
(OP)
Pardon me if this comes across as a naive question.
Assume I have a 3 span continuous beam (each span say 40') in which the sequence of construction is such that the two end spans are built first and then cantilever towards each other in the mid span. Assume the final piece that gets put is rather short (say 4') so as to maximize cantilever moment. The final piece is a full moment connection.
What happens to the negative moment (and stresses) at the supports after this piece is put in? The cantilevered moment is more than the continuous beam moment. Does the system compensate for the addition of the middle member? I presume it will if the system is elastic. Are there any locked-in stresses?
Thoughts?
Assume I have a 3 span continuous beam (each span say 40') in which the sequence of construction is such that the two end spans are built first and then cantilever towards each other in the mid span. Assume the final piece that gets put is rather short (say 4') so as to maximize cantilever moment. The final piece is a full moment connection.
What happens to the negative moment (and stresses) at the supports after this piece is put in? The cantilevered moment is more than the continuous beam moment. Does the system compensate for the addition of the middle member? I presume it will if the system is elastic. Are there any locked-in stresses?
Thoughts?






RE: Redistribution of forces
Regarding the "locked in" stresses - if you have a fixed end beam that is installed unshored with the shear connection first it's going to behave pinned-pinned for self weight, but that doesn't impact the final design.
RE: Redistribution of forces
If the beam is adequately propped during construction than it will behave as a continuous beam.
If it is built as a cantilevered system before a moment splice is installed, the selfweight moment distribution (two cantilevers) will be built-in and any additional loading after the installation of the moment-splice will be based on a continuous beam moment distribution.
RE: Redistribution of forces
Will the residual stresses go away with redistribution? Only if you jack up the cantilevers to remove the deflection prior to installing the last section with moment connections.
RE: Redistribution of forces
How does that affect behavior?
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Deflections will be the same amounts from the installed position of the steel.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Redistribution of forces
No, you are not missing anything. This was a hypothetical question. I was trying to maximize the negative moment due to the cantilever and compare it to a monolithic continuous beam.
RE: Redistribution of forces