NBC105: 2019 Seismic design of buildings in Nepal: New provisions in the code (2020)
The NBC 105: 2019 Seismic Design of Buildings in Nepal is the revised version of the original code for seismic design first published in 1994. The code has never been reviewed and updated since then till the moment. Recognizing the development in research and technology and new knowledge learnt from various large earthquakes in last 25 years, the Government of Nepal decided to initiate the first revision of the seismic design code. The objective of this revised standard is to provide designers with general procedures and criteria for the structural design of buildings prevalent in Nepal. This paper presents the basic features of the revision and the principles adopted in the standard. A new seismic hazard map of Nepal was proposed at the outset based on probabilistic format. Accordingly the PGA values for various locations of Nepal were revised. The performance requirements have been introduced precisely in terms of collapse prevention and damage limitation; there is a further recommendation to verify the performance requirements checking the ultimate limit state and serviceability limit state. It is proposed to check life safety and damage limitation performance requirements. Two different spectra are proposed for seismic coefficient method and modal response spectrum method. Four types of sub soil category are proposed. Very soft soil category is added in addition to previous three categories. This new soil category represents a very deep soft soil found in Kathmandu valley. Research has indicated that hard soil should have greater acceleration demand at smaller periods. This issue is rarely addressed in design codes internationally and the revised version of the NBC 105 is one of the first codes to accommodate this in practice. The revised code, retaining the linear analysis, introduces the non-linear methods of analysis. The empirical formulae for determination of fundamental translation period have been revised. Other principal changes include the importance classes and importance factors, load combinations and load factors. The Performance factor (K), which was used in the earlier version to obtain seismic coefficient, does not reflect the modern seismic design philosophy of reducing the elastic seismic forces. The response reduction factors (Ductility factor, R and Overstrength factor, ) are introduced. The horizontal base shear coefficient will be determined separately for ultimate limit state and serviceability limit state. The horizontal design spectrum for the modal response spectrum method has been given different for ultimate limit state and for serviceability limit state. A separate section on structural irregularity has been added. The revised code now requires checking the inter-story drift for both serviceability limit state and ultimate limit state. The standard has been developed in a new format considering the recent development in the research and technology as well as the lessons from the recent earthquakes. The whole document has been spread over 10 sections with 2 annexes separately for ductile detailing of structural concrete and structural steel.
CitationMaskey PN, Dhakal R, Tamrakar MR, Bista MK, Ojha S, Gautam BK, Acharya I, Chamlagain D (2020). NBC105:2019 Seismic design of buildings in Nepal: New provisions in the code. Sendai, Japan: 17th World Conference on Earthquake Engineering (17WCEE). 27/09/2021-02/10/2021.
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KeywordsNBC 105, ultimate limit state; serviceability limit state; ductility factor; overstrength factor; building code; parts/ components
ANZSRC Fields of Research40 - Engineering::4005 - Civil engineering::400506 - Earthquake engineering
40 - Engineering::4010 - Engineering practice and education::401001 - Engineering design
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