There are few things that are to be noted:
1) The following IS:1893 seismic definition has been provided-
DEFINE 1893 LOAD
ZONE 0.16 RF 1 I 1 SS 1 DM 0.05
As this is a building frame model, you have the following option to compute approx. fundamental natural time period of the structure using ST 1 parameter if you have only RC Frames. If you have infill brick walls, you need to use ST 3 parameter.
ST-3 parameter:
IS:1893 Part-1 is generally meant for buildings. The empirical equations provided in the code has been considered from the recommendation of NEHRP. There are many uncertainties in the model of buildings-
• Stiffness contribution on non-structural elements
• Stiffness contribution of infills
• E value of concrete, soil
• Stiffness of RC members
Thus, a model having the above mentioned uncertainties in stiffness would not provide correct Time period if a sophisticated process of Eigen solution is performed on the model to compute Time period. IS:1893 has provided emphasis to consider the 3rd equation (T= 0.09h/sqrt(d)) for the buildings with infills. This can be incorporated in STAAD by using ST 3 parameter.
You have used Response Reduction factor (R) as 1. This doesn’t hold good as the design Seismic force would be higher. If you have an ordinary moment resisting frames, you should use R = 3.
Please read the following:
The modified seismic definition would be:
DEFINE 1893 LOAD
ZONE 0.16 RF 3 I 1 SS 1 ST 3 DM 0.05
2) There has been multiple IS:1893 Seismic load case in Load case 1 and Load case 2. You need to use only one load case in primary load cases. Please refer to the attached model.
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