You have to use REPEAT loads for this analysis in lieu of LOAD COMBINATION. For example if you have a wind only load case then it would not converge since there is no dead load within that case to resist.
For most single story structures you probably will be rigid, but on process towers, open structures etc. you need to look at these individually. I have had braced frame structures because of their height be classified as flexible and end up with Gust factors approaching 1.
Even though the unbraced lengths may be the same for the different segments, the momnet in those segments is different. STAAD designs each individual member (in STAAD if there are multiple nodes, then it treats these as multiple beams, even though physically it is the same beam)for the moment...
To me the question is if the Site Class is a "D" than what is the Seismic Design Category? If going from a Site Class D to a C does not change the Seismic design category, than there is no reason to perform any additional testing. If going from a Site Class D to a C does enable you to lower...
Be careful with your P-Delta, as Chapter C in the new code requires not only a big P-Delta (Frame Stability) but also a small p-delta (member stability) analysis. While STAAD performs a standard frame stability P-Delta anlayis I am not sure it does the small p-delta.
A pin supported node will wxperience zero translation in the X,Y and Z directions. you would have to use the fixed-but support to release the translation.
You don't indiate any load combinations in your input file. D+L? Also note that the DFF command will check deflection for all load cases unless a LOAD LIST command is used to specify only the Live Load Case.
In the September 2003 issue of Structural Engineer, there is an article on Seismic design usig structural dynamics.
RAM will do a respose spectra analysis, you may want to check out the help file for that.
Example 7 of the 2000 IBC Structural/Seismic Design Manual Volume 1 has a similar example. In this particular example they design the columns below the discontinuity for Omega and the collector beams along that line for omega as well.
There is a 2004 supplement to the 2003 IBC that allows the use of the 0.75 in conjunction with the 0.7 factor. The supplement can be ordered from the ICC website.
In certain situations, in the case of chevron bracing, I design the beam to take the full gravity load. There are some situations where this is a code requirement. (i.e Special Concentrically Braced Frames)
Thats what I was getting at. The only problem I have with this is that if the client came back and wanted to relocate the brace later on, the column would not be sufficient to carry all of the gravity loads. In my mind, I always want the columns to have the ability to take the full gravity...
I should also clarify, that this only occurs when there are for example, three bays and the bracing works up from the outside to the middle column. The opposing braces prevent rotation from occuring and therefore the result is force in the bracing and the resulting vertical load in the middle...
The column is shortening due to the axial load present (Delta=PL/AE). For tall structures, this cumulative shortening from floor to floor could be significant.
