Steel Design

[GalileoG]

Hello all,

I have a beam that has nodes equally spaced, creating smaller individual beams of equal lengths. When performing a steel design, I set the Ly (for the lateral torsional buckling equation) to the value of the spacing between each node. However, when performing the design, each beam (along the same line) are given different values for moment resistance and different values for the slenderness ratio. This is very strange. I am running the Canadian Code. I should also note than when inputting a Ly value that is large, all of the beams then have the same slenderness ratio and moment resistance.

Can someone please clarify?

Also, when do I use the parameters UNT UNB? Aren't Lz, Ly another name for UNT and UNB? Where is Lt used?

 

[SteveGregory]

UNT and UNB are used for the unbraced length of the Top and Bottom flanges. These come into play depending on which flange goes into compression from bending.

LZ and LY are the unbraced lengths used for axial compression (not bending) such as in a column or a brace. They are used in the kl/r slenderness.

 

[DTJ]

Even though the unbraced lengths may be the same for the different segments, the momnet in those segments is different. STAAD designs each individual member (in STAAD if there are multiple nodes, then it treats these as multiple beams, even though physically it is the same beam)for the moment in the beam and the steel parameters assigned to it. Look in the STAAD help file for a definition of the parameters. Also, if the node spacing is the same as the physical unbraced length then you do not need to specify as a parameter since the node spacing is the default.

 

[GalileoG]

Thank you.

I have one more questions,

How does Staad know to design a beam element as a BEAM (using parameters and equations for beams) or as a column (using parameters and equations of columns) or as axial tension members (using parameters and equations of tension members.) Do I have to specify the type of member it is or does Staad have its own way of finding out?

 

[SteveGregory]

STAAD does the steel design based on the default parameters and the ones you define.