Is there any provision in Staad pro to know the story drift for each mode in dynamic analysis of the model. If yes, then how?
The easiest would possibly be to use the IMR command in your spectrum case. Here is an example
LOAD 4 LOADTYPE None TITLE LOAD CASE 4 SELFWEIGHT Y 1 SELFWEIGHT X 1 SELFWEIGHT Z 1 SPECTRUM SRSS IBC 2006 X 1 ACC DAMP 0.05 LIN IMR 10 STARTCASE 101 ZIP 92887 SITE CLASS A FA 0.800 FV 0.800 TL 8.000 PERFORM ANALYSIS CHANGE PRINT STORY DRIFT
The above IMR command would instruct the program to include 10 additional load cases each corresponding to the first 10 modes of the spectrum case and you can get story drift printed for these cases using the PRINT STORY DRIFT, as you would normally do for any other load case. You can change the value after the IMR to include as many modes you need.
For details on the IMR option, you may refer to the section 5.32.10.1.1 of the Technical Reference manual titled Response Spectrum Specification - Generic Method
If your are using Response Spectrum Analysis as per IS:1893, you can try the following :
For dynamic IS 1893: 2002 Response Spectrum analysis the process used for inter-story drift check does not hold true. The reason is that in response spectrum analysis the joint displacements represents the maximum magnitude of the response quantity that is likely to occur during seismic loading. Any response quantity like story drift should be calculated from actual displacements of each mode considered during analysis. The inter-story drift from each mode is combined using modal combination to get the maximum magnitude of this response quantity. In order to compute story drift for IS 1893 response spectrum load case following command needs to be defined . General Format: LOAD ld ............ SPECTRUM {Method} 1893 ........................ ................... CHECK STORY DRIFT (RF <factor>) where ld = the primary load number for 1893 response spectrum factor = response reduction factor. If not defined the program will look for the factor defined under DEFINE 1893 LOAD. If none provided a factor of 1.0 is assumed. (Response reduction factor represents ratio of maximum seismic force on a structure during specified ground motion if it were to remain elastic to the design seismic force. Actual seismic force is reduced by a factor RF to obtain design force.)
One of the sample model has been attached in this regard. On opening the model, you can get some errors from GUI. You can just ignore them. Please note that in this model, Rigid Floor Diaphragm command has been used.
So Let me have this clear out.
Please see file below
The L/40 would be the allowable drift. As defined by the code, it is the maximum inelastic diplacement. And the items tabulated are the elastic displacements.
Since I need Cd/I to be incorporated in the elastic displacement to become inelastic and thereby we can compare directly the values and the ratio given in the tabulation, we are to divide the inelastic (allowable) factor of L/40 by I/Cd or just simply by multiplying the same L/40 by Cd/I... Am I correct on my understanding to your reply awhile ago?
Also, a couple of observations and needed more clarification and direction
1. Why does the tabulated ratio had different denominators? How do STAAD compute this ratio in terms of a factor?
2. What is the difference between the average displacement and the drift? What values to use and what would I be needing to understand with these infromation aside from check the lateral displacement (in which STAAD provided two distinct values)? My understanding on this was that the first was the average of the relative movement of the nodes in that storey while the later was the external or edge displacement of the outer frame of the building to that of a plumb line or column line.
I stay attentive to your response on this