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While checking the allowable deflection in member in ETABS, which deflection is to be considered, absolute or relative? Which one represents the actual deflection of the member?

I am analyzing a regular structure 120 feet high in seismic zone 4. Will it come under the static lateral force procedure or dynamic analysis? How can we relate p-delta analysis and lateral force procedure?

It should be relative deflection. For example a beam in X supporting on girders in Y direction. You need to take the net deflection of supports and mid-span (for s.s. case) to compute deflections.

ASCE 7-10 Table 12.6-1 provides criteria for selection of Permitted Analytical Procedures for various Structural Design Categories, building heights and conditions. See Section 12.8 of ASCE 7-10 in general, and Section 12.8.7 in particular. Regards.

Your understanding is correct. The higher mass participation, the important the mode. Once you have figured out which modes have the greatest mass participation, take time to see the mode/ demformed shape and think about how can you improve your structural framing. Thanks.

Correct I am wrong. As per UBC # of modes shall be such that it incorporates 90% of participating mass. If participating mass is 90% in first two modes then no need of other modes. If 90% is acheiving in first 6 modes then first 6 modes are sufficient. If 90% is not acheiving then you have to scale your spectrum. In STAAD add missing mass value. Also, I have worked on STAAD mostly. If you require STAAD model then i can attach it as well.

Following are some lines from my ms thesis; Ritz modes are more efficient specially for a tall building with higher modes and it captures the most "optimum" modes (CSI, 2011). In non-linear analysis, use of Ritz modes become essential (CSI, 2011). If the building has some flexibly elements like antena etc, use Ritz modes, it will discard the modes associated to antena. There is also a youtube video about this from Ashraf HabibUllah delivered at AIT, Thailand. Search this on youtube; Ashraf HabibUllah Eigen vs Ritz Modes Lecture

Dear Waseem, This is the minimum brief which I can write, otherwise if you start elaborating this you could end up with 20 or 30 pages. Anyways thanks for your appreciation......

You can find solved examples in the books such as Dynamics of Structures by Anil k Chopra, and Seismic and wind design of concrete buildings by S.K. Gosh and David Fanella.