Basic Principles to Design Earthquake Resistant Buildings
For a Structural Engineer, to design earthquake resistant design of any structure will require following basic principle to adopt in the design.
During earthquake, as ground moves, building deflect due to whiplash effect. That is building deflect in a direction oppsite to the eartquake waves.Hence, force is induced in the structural elements in upper floors.
- First of all, see thoroughly architectural drawings and come to the conclusion, whether the building is geometrically regular or irregular in plan or in elevation. Certain guidelines have mentioned in Indian standard code IS:2016-2016 (Part-1) to easily find out irregularity in buildings.
- Based on geometrical arrangement (Regular or irregular in plan or in elevation) and height of the building, decide which method of analysis (Static or Dyanamic).
- Read carefully geo technical investigation report and decide the type of soil (Type-I, II or III) or we can say soft soil/loose soil, medium soil or hard soil. Take N-Values from Geo technical report to decide type of soil corelating with IS:1893-2016.
- As per the location of proposed building, decide the earthquake zone and take zone factor value from the relevant code.
- As per the type of structure like residential/commercial/hospital/institutional/industrial, decide the importance factor (I) for the building. For residential building, importance factor changes as per the number of occupancies mentioned in IS:1893.
- As recommended in IS:1893-2016(Part-1), based on the plan dimensions in the direction of earthquake and height of the proposed structure, calculate the fundamental time period of the structure. You can use different empirical formulae for load bearing masonry structure and frame structure with infilled masonry wall or bare frame (Without masonry wall).
- Horizontal seismic bands will be provided through all the external and internal masonry walls at the plinth level, lintel level of doors and windows and at the ceiling level of roofs for sound earthquake resistant structure.
- Sr. No 1 to 6 Refer to feed into the software like STAAD/ETAB for analysis.
Post Analysis Checks:
- Base Shear Check: After analysis, see the result for base shear. Do scal to match base shear.
- Lateral Drift: Maximum lateral drift shall be under limit as per IS:1893-2016(Part-1)
- Mass Participation Ratio: Average mass participation ratio shall be as per IS:1893
- Soft Storey Check: For stilt floor, banquet hall or any other open area where there is no infilled wall soft storey may arise.Shear wall can help to reduce soft storey.
- Time Period: Time period for modal analysis shall be under limit as per IS:1893.
- Torsional Irregularity: Torsional irregularity shall check as per IS:1893 and torsional irregularity shall remove after changing column sizes. Shear wall will help to reome torional irrugulaity.