Moment Connection 1

[vintage70]

How does a moment connection differ from a fixed connection for a cantilever beam, and how does the calculations differ when analyzing the bending moment?

 

[ishvaaag]

Well, this is an issue of structural analysis tha upon ordered study you won't have important doubt about. A cantilever is statically determined and the evaluation takes less, and can be made easily by hand. Fixity moments in inner members use to need a somewhat more complicated evaluation, yet in any case the methods to evaluate moments are well exposed in the texts.

 

[obviousguy]

A fixed connection is a SUPPORT, in which you attach a member to the earth, with no degrees of freedom. The moment connection, on the other hand fixes two members together, such that no movement is possible relative to the other member. Different softwares allow you to create supports or moment connections in which you can limit which degrees of freedom are fixed, and to what extent.

For a cantilever situation, so long as there is no stability problem in the member to which it is connected, a cantilever that is analysed as a fixed member versus one that is moment connected should be identical, since the stiffness of the member to which it connects has no impact on load distributions to the cantilever.

 

[dougantholz]

Here's my 2 pennies worth.
A cantilevered beam can be a through-beam cantilever or an over-beam cantilever. Both types of connections are designed to transfer 100% of the cantilevered stress back to the backspan beam, without adding a moment to the supporting member. The supporting member should only see the shear reaction.
A moment connection is a connection that is typically designed to transfer the rotational force between perpendicular members.
From a desgin standpoint, I would typically design a cantilevered beam connection to withstand the full moment capacity of the cantilevered element. For a moment connection of beam to column, then I design for varying levels of performance.
I am in a moderate seismic zone, and due to costs, do not want to reinforce my columns with web stiffner plates. I would therefore design the connection for 200% of the calculated load, and size the members accordingly. In regions of high seismicity, the connection is typically designed for the full capacity of the weaker member (beam)
HTH

 

[aun]

I have a question regarding to a beam-girder connection.
Assume a rc beam supported by a rc girder, should the end of beam be fix or pin support? and why?? I know that if the beam end is a fix support the moment will be less than the pin support but the girder have to consider torsinal moment from the beam...Any comment would be appreciate.

 

[ishvaaag]

For RC you model the connection with NO releases. The software for analysis will deliver what torsion is induced in the supporting beam, and how much bending moment is then relieved of the supported beam.

Of course you can also put a pin at the end and the supported beam and it may still function within ordinary ways of construction but it will be less truer to the expected behaviour.