IS 18881:2018 is the Indian Standard (BIS) for seismic design of buildings using base isolation - code of practice. This code provides guidelines for the seismic design of buildings using base isolation systems. It covers the design principles, analysis methods, design of the isolated structure and the isolation system, and mandatory testing requirements for isolator units to ensure performance during an earthquake.
Specifies criteria for the seismic design of buildings incorporating base isolation systems.
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Damping Modification Factor (for Spectrum Reduction) | RI; Value is 1.5 for 20% effective damping (Table 2) | BD; Value is 1.5 for 20% effective damping (Table 17.5-1) | ASCE/SEI 7-16 |
| Analysis method for displacement | Total Maximum Displacement DTM = 1.5 * DD (Clause 7.5.3) | Maximum Displacement DM is calculated independently using MCE_R spectral ordinates (Sec 17.5.1.2) | ASCE/SEI 7-16 |
| Minimum Superstructure Design Shear | Vs must be at least 1.5 times the calculated base shear of the isolated structure, Vb (Clause 7.6.2) | Vs must not be less than various criteria, including the seismic force for a fixed-base building at the isolated period (Teff) (Sec 17.5.4.1) | ASCE/SEI 7-16 |
| Mandatory Time History Analysis Trigger | Required for buildings in Seismic Zone IV and V (Clause 7.2.2) | Required for buildings in Seismic Design Category D, E, or F, with some exceptions (Table 17.3-1) | ASCE/SEI 7-16 |
| Accidental Torsion Eccentricity | Total design eccentricity includes 5% of the building's plan dimension (Clause 7.4.2) | Accidental mass eccentricity shall be 5% of the building's dimension perpendicular to the direction of analysis (Sec 17.5.3.3) | ASCE/SEI 7-16 |
| Minimum Number of Ground Motion Pairs (Time History) | A minimum of 3 pairs of ground motion components (Clause 7.5.1.1) | A minimum of 3 pairs if using maximum response, or 7 pairs if using average response (Sec 16.2.2) | ASCE/SEI 7-16 |