NBC 105:2020 is Nepal’s code for seismic design of buildings. It sets out how to analyze and design building structures to resist earthquake forces across the Federal Republic of Nepal. The code applies to new buildings and provides the basis for determining seismic design forces, detailing requirements, and configuration rules.
Seismic Zones of Nepal
Nepal is divided into five seismic zones based on seismic hazard. The central zone — which includes Kathmandu Valley — falls in a high seismic hazard region. The zone factor (Z) reflects the peak ground acceleration expected in each zone and is a key input to the design base shear.
Design Base Shear
The code defines the lateral seismic design force (base shear) as V = Z × I × C × W, where Z is the seismic zone factor, I is the importance factor (higher for hospitals, schools, and emergency facilities), C is a coefficient depending on the structural system and soil, and W is the seismic weight of the building. This base shear is distributed vertically as lateral forces at each floor level.
Key Requirements for Engineers
- Use regular, symmetric building configurations; avoid soft storeys, large overhangs, and abrupt stiffness changes.
- Provide ductile detailing of reinforced concrete and steel members so the structure can absorb seismic energy without collapse.
- Design foundations for seismic overturning and sliding, considering local soil conditions.
- Separate adjacent buildings with adequate seismic gaps to prevent pounding.
- Apply the importance factor: critical facilities (hospitals, fire stations) are designed for higher forces than ordinary buildings.
Summary for working engineers. For the full legal requirements, always refer to the official NBC 105:2020 document (106 pages) published by the Government of Nepal.
Hosted copy of the DUDBC publication.
Published by the Government of Nepal (DUDBC).