This is my 3rd thread and seems that no one from Bently staff seems to bother to give me a reply. I am still writing to try my luck once more.
I am applying a pushover analysis on a steel structure. But I am stuck at the application of hinge properties. Apparently FEMA has a default linear Moment-rotation curve, hence I want to add a new curve. But I do not know how to define the Yield Moment and Yield Rotation. Also when it comes to apply the hinge properties for braces how do I do it because braces need another type of hinge but StaadPro appears to have only Moment-Rotation type of hinge.
Can anyone help (is Benltly Forum still operating?)
Answer Verified By: Andi
While it may seem like a shortcoming of the program, an examination of the method used in member selection will enable us to realize that it is not easy to arrive at a final set of sections without several iterations, especially for large structures. The steps involved in member selection are described at the following link
Procedure used in STAAD for Member Selection
Note that the selected section is optimum only from the standpoint of the recent analysis. Since a new analysis has to be done following the selection, the new stiffness distribution in the structure will determine the extent to which the forces change in the members. Also, a new section also means a new weight, which too will affect the forces in the members.
Another layer of complexity is added when a GROUPing operation is done following the MEMBER SELECTION. Grouping can inadvertantly cause a safe section to be replaced by an unsafe section. For example, consider a physical member made up of members 1 and 2. Let us assume that during member selection, a W14X61 (AX = 17.9, IZ = 640) was selected for member 1, a W12X65 for member 2 (AX = 19.1, IZ = 533). Observe that the area and hence the weight of the W12X65 is larger than that of the W14X61. But the W14X61 has a larger IZ and hence a larger section modulus than the W12X65. When a grouping is performed, both members will receive a W12X65 since it is the heavier one. But if bending about Z is the critical condition for member 1, by replacing the W14X61 with a W12X65, an unsafe section is being chosen for it.
The method I suggested earlier, which is use the RATIO parameter is the most effective method I have seen to minimize the number of iterations. Something similar is automatically done by the program if the command SELECT OPTIMIZED is specified. But I am not sure if it is any superior to the one I suggested earlier.