large rotational displacement

When running the STAAD, the result shows everything is right,. Structure is stable, no warning. Displacements are limited. BUT, I get some funny numbers for rotational displacement e.g. 533 degree & sometimes more.

I checked releases. I believe they are correct.

any body can help me out kindly ?? 

  • Gentlemen,

    I'd like to have braced frame with hinge connections and cause I have to consider accidental torsion produced by IBC, I tried to find a trick.

    Basically STAAD puts torsions on nodes (because of defined mass) but in real world, torsion would be generated by horizontal seismic loads. This torsion acts on the entire building, NOT concentrated on node by node. Although the total magnitude will be the same.

    So I thought I have to add up all nodes stiffness against the torsion. Hence I tied all nodes together by master/slave option just around vertical axis MY.

    I suppose I got a reasonable answer. My only concern is maybe in reality the structure is not that stable and integrated as I modeled.

    Could you please comment on that?

    I apprriciate your time

    Hajir

  • Thank you ver much sureshprsharma & Kris, problem solved

    Hajir

  • Along the ridge (where the 2 sloping sides of the roof meet at the top), all the members except the columns have MY and MZ released, or have been declared TRUSSes.

    Since you have asked for the ACCIDENTAL torsion to be considered for the IBC loading, the torsional moments are generated along MY at those joints. Due to the MY release and TRUSS specification, those moments will not enter those beams. So, the columns by themselves have to transmit the moment to the supports. Since these columns are over 12.6m tall, and have been assigned open sections that aren't torsionally strong, there is a large MY rotation at the top of those columns.

    You need to change the manner of the connection between the column and other members so there is a better arrangement for resisting the torsion. Perhaps the trusses should be changed to resist the MY rotation while being released only at the other end.



  • Remove "Accidental" from the definition of IBC 2006. You will not get any abnormal node displacement.

  • really sorry ...........I am working on two models at the same time.

    here are correct numbers:

    Laod case 3 >> node 28, rY 293 deg

                           &     node 20, rY 288 deg

    Load case 175 >>  node 28

    Lad case 173 >> node 10

    Hajir