End Length Offsets vs Insertion Points 1

[saadpervez1]

Hi all,

has anyone got a reasonable explanation of the difference between the frame end length offsets and insertions points in ETABS?

I have to model a simply supported beam resting on a corbel at the column face, this eccentricity will generate an additional moment on the column centroid, which function is better in this case?

I have used both and found that there is a moment being generated at the column centroid when I use End Length Offsets but the results are not balancing out and not comparing with a manual analysis.

 

[bgrd]

Hi there,

In this case, end length offsets is used to get the real lenght of a beam taking into account the dimension of the column. EX: Real lenght =span-0.5*Dcol#1-0.5*Dcol#2. I think Etabs do it automatically.

Insertion points move the element around his axis, but I never really took the time to try it.

Maybe you can try to model the corbel as a small cantilever beam?

Best of luck,

Ben

 

[MrHershey]

If you think of a frame element with x along its longitudinal axis and then Y and Z perpendicular to the frame member's longitudinal axis:
-End length offsets affects placement in x axis
-Insertion point affects placement in y and z axis

You would be looking for end length offsets for a corbel condition. As for moments not balancing out or meshing with your hand checks, check to see if you have any forces leaking into your slab (assuming you have one modeled). It may be helping you when you don't intend it to. Also your moments may not balance out if you have different spans and/or loadings on the different sides of the column. Really shouldn't cancel out even if you do because you should be looking at pattern live loadings. ETABS doesn't do pattern loading until the design phase for frame members.

 

[JasonMcKee71]

Be aware that if you click the "Transform stiffness" option, strange internal forces result may appear. For instance, high axial force values will be reported at beams under pure bending. You should check this especially if you perform an automatic frame design.

Jason McKee
proud R&D Manager of
Cross Section Analysis & Design
Software for the structural design of cross sections
Moment Curvature Analysis
Reifnorcement Design etc.