Problem definition : Four identical (in all aspects loading, span, section etc.) portal frames as shown below is analyzed and deflection check has been performed as per AISC 360-10 ASD. First and third frame beams are single member whereas the remaining frame beams are with node at mid point. "CAN 0" Parameter defined for beams in the first two frames and "CAN1" for the beams in the remaining frames.
Clarification : Does introducing nodes in the member, results increase in beams displacement and reduction in section displacement ? see the snap below Why the design ratios and displacements are not comparable? Higher displacement is having lesser ratio.Which design parameter yields accurate results "CAN 0" or "CAN 1" parameters ? Are these DFF/dff ratios ? Because the values are not matching w.r.t displacement values.
Hello,
CAN 1 should be used for cantilever type of member and CAN 0 for a span between 2 nodes defined by DJ1 and DJ2. you may find details in the help file. I am providing a snap for ready reference.
In STAAD all members are treated as analytical member and whenever a node is introduced the member splits in 2 different members. By default the length changes and the design capacities, deflection length etc. get changed. To cater this some parameters are used in the design part to take care of this and define the member as a physical one. I will recommend to refer the design parameters in help file and to use them so that the required physical length can be input in the design part.
Once done, the results should be matched with your manual calculation. However, if you still have doubt please upload the file with your queries so that we can investigate and get back to you.
Even if you have a middle node inserted on the beam, there is no need to assign the CAN 1 parameter if the beam has 2 supports. CAN 1 needs to be applied to the cantilever members only.The difference between the displacements when a node is inserted occurs due to a shear deformation calculated at the node. This Wiki provides some more details on this topic: My hand calculations do not match the displacements being reported by STAAD.Pro - RAM | STAAD | ADINA Wiki - RAM | STAAD | ADINA - Bentley Communities
Thanks for your Prompt reply. why the design check ratios are not propionate with displacement ?.
Please attach the model.