hi, I have made a test model for the response spectrum analysis which is attached herewith, i have two questions,1. in the Attached model,I Have Base shear difference from static to dynamic in the ratio of 4.49, can i scale up this difference thru scale factor?. or anyother way is there?. THere is a appreciable amount of Missing Mass also Listed in the output file, how to use it?
2. How to see the Value of SHear force distribution in each Floor due to Seismic by STATIC Method.
Thanks & Regards,
test_response.std
senthil
Please go trough the following.
Ans-1. The program considers the specification of Clause -7.8.2 of IS:1893 Part-1. Clause 7.8.2 requires scaling up of seismic design forces from dynamic analysis, in case base shear from Response Spectrum is lower than those from empirical T (time period). If you perform a Response Spectrum analysis using as per IS:1893, you need to provide a Seismic definition so that the program can compute base shear using empirical method. As per clause-7.8.2 of IS:1893(part-I)-2002, the program compares the base shear of Response Spectrum analysis(VB) with that of Static method(Vb). If the base shear of Static method is higher than that of Response Spectrum method, the program calculates the ratio of them and that ratio is reported as “MULTIPLYING FACTOR (Vb/VB)”. The program multiplies all the response quantities like- member forces, displacement etc. with this factor. The base shear from the Response Spectrum analysis should not be multiplied by the factor. Please look into the following picture. You don't need to do anything. If you have not reached more than 90% mass participation, you need to use CUT OFF MODE SHAPE command to increase the number of modes in the analysis. If you have rigid mode, then only use MISSING MASS correction.
Ans-2. You can add PERFORM ANALYSIS PRINT LOAD DATA command followed by CHANG command after each static load case. You can see the storey shear distribution in the output file as shown below.