Faqs On Is1893

Question 1 : I want to perform a response spectrum analysis in accordance with the IS 1893 specifications. I notice in your examp14b.std that you have specified the following lines. SPECTRUM SRSS 1893 TOR X 0.04 Z 0.04 ACC SCALE 0.92 CDAMP MIS SOIL TYPE 1

What do they mean? Answer : The first line of the Spectrum command contains the term “1893”, which instructs the program to use the formula for spectra data already incorporated in the program. The formulae used are mentioned in clause 6.4 on page-16 in figure-2 of the IS:1893-2002 code, and reproduced below. The (Sa/g vs. T) values are given for three different soil sites – hard, medium and soft, for which the corresponding STAAD input for “SOIL TYPE” are 1, 2 and 3. The details of the spectra data are as shown in the aforementioned figure.

Question 2 : The block of lines which goes like this DEFINE 1893 LOAD ZONE 0.16 RF 3 I 1.5 SS 1 ST 1 DM 0.05 DT 5 SELFWEIGHT JOINT WEIGHT .. .. MEMBER WEIGHT .. ..

etc. is required only when you are using the static method of 1893 load generation, is that correct? If I am using the Response spectrum method, is it required? Answer : It is required for the response spectrum method also. The 1893 code mentions the following.

In the implementation of the above requirement, the program calculates the fundamental period Ta as per clause 7.6 of the code on the basis of the ST Parameter (1 / 2 / 3).

In case the user has not provided the pseudo-static parameters of the 1893 load, and tries to perform the response spectrum analysis as per 1893-spectra, he/she will encounter a warning message that – WARNING : IS-1893:2002 PARAMETERS ARE MISSING. DESIGN BASE SHEAR FROM RESPONSE SPECTRUM METHOD CANNOT BE COMPARED WITH BASE SHEAR CALCULATED USING EMPIRICAL FORMULA FOR FUNDAMENTAL PERIOD.

Question 3 : If I specify the spectrum command as SPECTRUM SRSS 1893 TOR X 0.04 Z 0.04 ACC SCALE 0.92 CDAMP MIS SOIL TYPE 1 can you tell me exactly what are the values of the period vs. acceleration pairs that have been coded into the program which the program will be using? Answer : The program first calculates the fundamental period (Ta) of the structure. It is obtained either defined by ST parameter (Ref. Cl. 7.6 of IS:1893-2002), or by defined PX or PZ, or calculated by STAAD itself in absence of any of the parameters mentioned before. Now, using the value of Ta and “SOIL TYPE” as hard(1) or medium(2) or soft(3), it enters the appropriate equation as mentioned below, and finds the value of Sa/g.

So, the pairs of period-acceleration value are generated using the above equations.

Question 4 : I want to do a spectrum analysis using the 1893 method, but I do not want to use the spectrum associated with soil types 1, 2 or 3. Instead, I want the program to use my own period-acceleration pairs. How do I do that? Answer : Specify your own spectra data instead of specifying SOIL TYPE, as shown in the following example. LOAD 12 SEISMIC- Z SPECTRUM CQC 1893 Z 0.01667 ACC SCALE 32.2 DAMP 0.05 0 0.34; 0.05 0.71; 0.1 0.77; 0.13 0.79; 0.2 0.79; 0.27 0.79; 0.3 0.79 0.4 0.73; 0.5 0.64; 0.6 0.57; 0.8 0.49; 1 0.43; 1.2 0.36; 1.4 0.32; 1.6 0.28 1.8 0.24; 2 0.22; 2.4 0.19; 2.8 0.17; 3 0.16