IS:1893 (Part-I)- 2002 code has a specific guideline for the buildings. The code has a special guideline on using lower bound Time Period to be used in the design. Based on HEHRP documentation on the research on the building, the code has specified some of the empirical formula to calculate the fundamental time period of the buildings. With the advent of high speed computers and structural software, the building models are prepared in software. While modelling a building, the designers do not consider the stiffness of the non-structural elements. The so called non-structural elements like brick walls do provide a load path for a lateral load like earthquake load. Thus, they should have a proper way to consider the stiffness in the model while calculating the fundamental time period of buildings. The model prepared in the software do not contain the contribution of non-structural elements like brick walls. The code has proposed empirical formula to calculate the fundamental time period of the buildings- the time period calculated using these equation would generally give lower time period than the time period calculated from the model prepared in the software, which would indicate that the stiffness of the non-structural elements have been considered. On using this time period, the value of spectral acceleration (Sa/g) computed from the generalised Response Spectrum data provided in the code would give higher value and it would generally provide higher base shear compared to the other method of seismic analysis.
As per clause-7.8.2 of IS:1893(part-I)-2002, one has to compare 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, one need to calculate 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. This is an indication that the Static Method proposed by the code would generally provide higher responses and the code demands a scaling up of the Response quantities obtained from Response Spectrum method.
Observation:
Max X deflection from Static method= 235.803 mm at node # 88
Max X deflection from Response Spectrum method= 200.46 mm at node # 93