Robot Steel Design Query

[andrew_cross1]

Hi,

I am designing a steel truss in robot and I was reviewing the bending moments used in the design. From the attached screen shot you can see that the max bending moment is 3558 kNm but the value used in design is 2126 kNm. I assume the 2126 kNm corresponds to the point of max axial force 35169 kN and that the moment check is based on this 2126 kNm vs the reduced moment capacity MN,y,Rd. Does robot determine that this is the most critical case i.e. it may be more critical at point of max moment but with an increased MN,y,Rd value due to the lower axial force.

Additionally the MN,y,Rd value if 2695 kNm is lower than expected using the formula in 6.2.9.1; can you please outline which formula is used. 

Can you explain the concept behind characteristic points in the configuration tab; should the 'characteristic points' box be ticked, the number of points increased, 'simultaneous calculations in characteristic points and in the even-division points' be ticked or any of the points for min max values be ticked? Essentially I just want to be sure that the worst case forces are being checked in the robot design.

Zip file of model also attached.

Thanks,

Andrew 

[andrew_cross1]

Hi,

Has anyone any thoughts on my query?

Thanks,

Andrew

[Stephane.kapetanovic]

hi @andrew_cross1 

all you need to do is display the min and max elastic stresses and check the bending moment and normal force at that location. It matches the values of your check. On the other hand, you have not defined buckling or torsional buckling lengths (upper and lower flanges). Probably, you must have a floor and support points....

Look also that you exceed the elastic limit at thickeness (fy=380Mpa) and the plastic modulus favors your section, it may be difficult to justify your welded nodes.

Best regards.