Seismic design codes form the backbone of structural safety in earthquake-prone regions. In India, IS 1893 has long served as the primary reference for earthquake-resistant design of buildings and earthquake resistant house design. With the publication of IS 1893:2025 (Part 1), the Bureau of Indian Standards has taken an important step toward improving clarity, consistency, and reliability in seismic design practices under updated structural design codes.
This revision is not merely a routine update; it reflects the evolving understanding of earthquake behaviour, structural response, and the need for more rational and performance-oriented design approaches supported by modern seismic analysis methods within current structural design codes.
Why Revision of IS 1893 Was Essential
Over the last two decades, India has witnessed multiple moderate to strong earthquakes, along with extensive post-earthquake damage studies. These events revealed that while many structures complied with earlier versions of the code, their actual seismic performance often fell short of expectations, particularly due to limitations in seismic load calculation procedures defined earlier in structural design codes.
At the same time, the profession has evolved:
- Better seismic hazard assessment
- Advanced analysis software
- Increased use of irregular architectural forms
- A growing number of mid-rise and high-rise buildings
The revision of IS 1893:2025 (Part 1) attempts to bridge the gap between code-based design and real structural behaviour during earthquakes.
Scope of IS 1893:2025 (Part 1)
Part 1 deals specifically with:
- General seismic design principles
- Earthquake-resistant design of buildings
- Seismic loads, analysis methods, and basic design criteria related to seismic analysis of buildings
It acts as the foundation document, on which material-specific codes (RCC, steel, masonry) and ductile detailing codes depend within the overall framework of structural design codes.
Key Improvements in IS 1893:2025 (Part 1)
1. Clearer Seismic Design Parameters
One of the major strengths of the 2025 revision is improved clarity in defining seismic parameters, such as:
- Seismic zone factor
- Importance factor
- Response reduction factor
- Damping considerations
By clearly explaining the intent behind these parameters, the code reduces ambiguity and promotes uniform application across projects governed by updated structural design codes.
2. Refined Design Response Spectrum
The response spectrum is central to seismic analysis. The revised provisions aim to better represent:
- Realistic ground motion behaviour
- Influence of soil conditions
- Expected structural response under design-level earthquakes
This refinement helps avoid both over-conservatism and unsafe under-design, leading to more balanced and economical structures.
3. Better Definition of Structural Irregularities
Architectural demands often result in plan and vertical irregularities. Earlier, interpretation of these irregularities was sometimes subjective, especially concerning structural irregularities in buildings.
IS 1893:2025 (Part 1) provides:
- Clearer classification of irregular buildings
- Better guidance on when advanced analysis is mandatory
- Reduced scope for misinterpretation
This ensures that irregular structures receive the level of analysis they truly require.
4. Rationalized Analysis Procedures
The revised code streamlines and clarifies the applicability of:
- Equivalent static method
- Response spectrum analysis
- Dynamic analysis procedures
The emphasis is on choosing the right method for the right structure, rather than applying simplified methods indiscriminately.
5. Emphasis on Structural Behaviour and Load Path
A notable shift in the 2025 revision is the focus on:
- Load transfer mechanisms
- Stiffness and mass distribution
- Torsional behaviour
- Ductility and redundancy
The code implicitly encourages engineers to think beyond numbers and understand how forces actually flow through the structure during an earthquake.
Practical Implications for Structural Engineers
The revised IS 1893 (Part 1) directly impacts day-to-day practice:
- Existing design templates and spreadsheets must be reviewed
- Software models need careful input verification for updated parameters
- Engineers must exercise greater professional judgement
- Early coordination with architects becomes even more critical to control irregularities
In short, the revision demands better engineering, not just faster calculations.
Challenges and Opportunities
While the transition to the revised code may initially seem demanding, it also presents opportunities:
- To improve design quality
- To educate clients about the importance of seismic safety
- To enhance professional credibility
- To reduce long-term structural risk and liability
Conclusion
IS 1893:2025 (Part 1) marks a meaningful evolution in India’s seismic design philosophy. It moves the profession closer to performance-based thinking, without losing the simplicity needed for practical application within India’s structural design codes framework.
For structural engineers, the message is clear:
Code compliance is mandatory, but true safety comes from understanding the intent behind the code.
Adopting IS 1893:2025 (Part 1) with seriousness and technical depth will play a crucial role in creating safer, more resilient buildings across seismic regions of India.