Working on Human Nature Case Study: The Backlash of IS 1893:2025

 

With all the buzz moving around — PSHA, seismic demand, high-rise buildings, seismologists, earthquake academicians, practising engineers — what do you think actually happened with IS 1893:2025?

 

The code went through wide circulation for approval. The practising community read it, sat with it, and filed it away. And then, when it was formally implemented — when the numbers were actually worked into real project budgets — something shifted. The allocated funds did not fit. The cost implications hit hard. And the community backlashed — not against the logic of the code, but against the code itself.

 

This is a very human thing to do. And it is worth pausing to understand why.

 

The code was presented in a fragmented format. The seismological science arrived in one corner. The structural implication sat in another. The practising engineer — who is fundamentally an executor, not a codifier — was handed a document and expected to absorb, trust, and implement. Without a connecting narrative. Without case studies. Without a demonstration of what the new hazard levels actually meant for a real building standing on real soil in a real Indian city.

 

This is a classic instance of what Robert Greene, in his remarkable book The Laws of Human Nature, describes as the fundamental tension between those who carry knowledge and those who must receive it. Greene illustrates this through two extraordinary stories — one of patient, methodical persuasion, and one of righteous, self-defeating rage. Both are stories of people who were right. The difference in how they were received tells us everything about how knowledge actually travels.

 Two Doctors, One Truth, Two Very Different Outcomes

William Harvey and the Beating Heart

Put your hand on your chest right now. You can feel it — the steady, rhythmic thump. The heart pumping. It seems almost impossible to imagine that this was ever in dispute. And yet, in the early seventeenth century, the mechanics of blood circulation were entirely mysterious. The prevailing Galenic model, unchallenged for over a thousand years, held that blood was produced in the liver and consumed by the body — flowing outward, never returning.

 

William Harvey was an English physician who became quietly, almost obsessively, convinced that this was wrong. He had a problem: human dissection was heavily restricted in England at the time. So, he did what a man with a question and no easy answer does — he found another way. He dissected fish, frogs, snakes, and pigs. He observed the hearts of living animals at different temperatures, watching how the rhythm slowed in the cold. He counted. He calculated. He asked: if the heart pumps a certain volume of blood with each beat, and beats seventy times a minute, how much blood is the liver supposed to be manufacturing? The arithmetic was impossible. The blood had to be circulating — not being produced fresh and consumed, but moving in a closed loop.

 

He knew this for years before he said it publicly. When he finally did present his findings to the College of Physicians in London, he did it carefully, incrementally, with the humility of a man who understood that he was asking people to discard a thousand years of certainty. Greene describes how Harvey balanced — in his own words — the courtesy his profession expected with the integrity that truth required. He did not demand. He demonstrated.

 

He published his landmark work, De Motu Cordis, in 1628 — after nearly two decades of private investigation. The reception was not without resistance. But Harvey was patient. He had built his case so carefully, so empirically, that the evidence could speak without him having to shout. Within his own lifetime, his understanding of cardiac circulation was accepted. He died a recognised pioneer.

 

Ignaz Semmelweis and the Hands That Killed

Now travel forward two centuries to Vienna in 1847. Ignaz Semmelweis was a young Hungarian physician working in the maternity wards of Vienna General Hospital. What he found there disturbed him deeply.

 

The hospital had two obstetric clinics side by side. In the first clinic, staffed by medical students and doctors, the maternal mortality rate from childbed fever ran as high as 18%. In the second clinic, staffed by midwives, the rate was below 2%. Women in the first clinic begged to be moved to the second. Some gave birth in the street rather than enter the doctors' ward.

 

Semmelweis watched this, and could not rest. Then a colleague died — accidentally cut during an autopsy, developing an infection identical to childbed fever. The connection struck him like lightning. Medical students were going directly from the dissection room to the delivery ward, without washing their hands. They were carrying something — he called them cadaverous particles — from the dead to the living. The midwives did not do dissections. That was the entire difference.

 

He introduced mandatory handwashing with chlorinated lime solution. Within months, the mortality rate in his clinic fell below 2%. The data was unambiguous. He had the answer. Lives were being saved in measurable numbers.

 

And yet the medical establishment refused to accept it. Partly because accepting it meant accepting that doctors — educated, respected, well-meaning doctors — had been killing their patients. That was too much for professional pride to absorb. The criticism came from all sides. Greene describes how Semmelweis, watching women continue to die in wards where his protocol was not adopted, became increasingly unable to contain his frustration. He wrote open letters to prominent obstetricians, calling them partners in a massacre. He lost his position. He left Vienna for Budapest, where he continued his work in relative isolation.

 

He died in 1865, at 47, in a mental asylum — ironically, from a wound infection, the very thing he had spent his life fighting. It was only years later, after Louis Pasteur's germ theory had given the world the theoretical language to understand what Semmelweis had observed empirically, that his contribution was finally recognised. The mortality rates dropped. The idea was vindicated. The man was gone.

 

Two men. Both right. One received in his lifetime. One received only after his death. The difference was not in the quality of their evidence. It was in the completeness of the story they told — and in the readiness of the world to receive it.

 

Now, What Actually Happened with IS 1893:2025

India sits on some of the most seismically active ground on earth. The Himalayan arc, the northeast, the Kutch region — these are not theoretical hazard zones. The 1897 Assam earthquake, one of the largest ever recorded, ruptured the Shillong Plateau with a magnitude now estimated around M 8.7. The 2001 Bhuj earthquake, which killed nearly 20,000 people, was M 7.7 — and in earthquake engineering terms, it was actually a detailing failure as much as a hazard event. Buildings that were designed and constructed with proper ductile detailing survived. Those without it collapsed.

 

This history matters because it is the backdrop against which IS 1893:2025 arrived. The Bureau of Indian Standards issued the revised code in November 2025. It introduced a new Zone VI — the highest seismic risk category ever assigned in India — covering the entire Himalayan arc, parts of Kashmir, Assam, and the Kutch region. More than 60% of India's landmass fell under moderate to very high hazard zones. The code was built on modern Probabilistic Seismic Hazard Assessment — updated ground motion models, new tectonic mapping, international methodology.

 

By March 2026, it was withdrawn. Barely three months after release, the earlier 2016 code was restored by gazette notification. The backlash came from Metro Rail corporations, the Ministry of Housing and Urban Affairs, the National Disaster and Safety Authority. The objection was cost — projected increases of 10 to 15% for Zone V and VI structures, up to 50% for some infrastructure categories.

 

The science was not wrong. Nobody stood up and said the Himalayan belt is not seismically active. The code was withdrawn because the cost was too high — and because there was nothing in the public domain to explain why the cost was justified.

 

The Three Pillars That Never Spoke to Each Other

Earthquake engineering, at its core, rests on three pillars working together:

 

Ground acceleration — what the seismologist provides. How much the ground shakes, at what frequency, for how long, at a given location.

System response — the numerical domain. How a structure moves and deforms when subjected to that shaking. Modern finite element software handles this well.

Section capacity — the research domain. What the structural members can actually sustain before they yield, crack, or collapse. This requires nonlinear analysis — and this is where the work was missing.

 

These three pillars are not independent tasks to be handed off sequentially. They are a conversation. And that conversation, in the case of IS 1893:2025, was never held publicly.

 

The seismologists did their work. They updated the PSHA. They produced a revised hazard map. They handed it over — and, in a sense, considered their contribution complete. What was missing was the next step: someone taking those new ground motion parameters and running them through representative Indian building typologies, producing actual demand numbers, showing whether the new zone designations changed structural behaviour in ways that matter.

 

What would that have looked like? A suite of Nonlinear Time History Analyses on, say, a 10-storey RC frame in Guwahati, a 20-storey shear wall building in Dehradun, a masonry structure in Srinagar — using ground motion records disaggregated from the new PSHA — checking inter-storey drift ratios against the performance thresholds of Immediate Occupancy, Life Safety, and Collapse Prevention — and reporting: this is what Zone VI actually means for the buildings your cities are full of. This is where current detailing is sufficient. This is where it is not.

 

That work exists in fragments, scattered across research journals. It was never assembled into a coherent public argument that could stand alongside the hazard map and say: here is the complete story. Here is why the cost is justified — or here, frankly, is where it might not be.

 

A Technical Nuance Worth Pausing On

There is something deeper here that the public debate completely missed, and it is worth stating clearly for those who work in this field.

 

Higher PSHA does not automatically mean higher structural demand.

 

This is not an intuitive statement, but it is well-established in the literature. The Uniform Hazard Spectrum (UHS), which forms the basis of design spectra in IS 1893, is a statistical envelope — it represents the spectral acceleration at each period that has a given probability of exceedance, computed independently for each period. As Baker and Cornell demonstrated in their foundational work on spectral shape and record selection, the UHS conservatively implies that large-amplitude spectral values will occur simultaneously across all periods within a single ground motion event. This never actually happens. The UHS envelopes multiple earthquake scenarios, not a single physically realistic one.

 

At high hazard levels — which is precisely what Zone VI represents — the ground motions that control the hazard tend to be statistical outliers in their frequency band. They carry high values of ε (epsilon), which is the number of standard deviations by which a given ground motion intensity exceeds the median prediction of the ground motion model. A ground motion with high ε at one period tends to have lower spectral content at adjacent periods — meaning its spectral shape is peaked, not broad. If you select ground motion records that match the UHS, you are effectively selecting records that are simultaneously above average at every period — a spectral shape that does not represent any real earthquake scenario.

 

Baker and Cornell proposed the Conditional Mean Spectrum (CMS) as an alternative — a target spectrum conditioned on the occurrence of a target spectral acceleration at the period of interest, accounting for the inter-period correlation of spectral values and the ε of the controlling scenario. Studies using the CMS consistently produce lower and more realistic estimates of structural demand than studies using the UHS.

 

There is a further subtlety for tall buildings specifically. As the USGS has noted, PGA is a meaningful hazard index only for short structures — roughly up to seven storeys. For taller buildings, the relevant parameter is spectral acceleration at the building's natural period, which for a 20-storey RC frame might be 2.5 to 3.5 seconds. The ground motion characteristics that dominate at those long periods are often produced by moderate, distant earthquakes — not by the high-frequency near-fault motions that dominate PGA-based zone classifications. It is entirely possible that a building in a newly designated Zone VI city faces a lower inelastic drift demand than the zone factor alone implies — or, conversely, that the controlling scenario is a long-period far-field event that the zone map does not adequately capture.

 

And then there is the question of section capacity, where a significant body of research is still being developed. Material nonlinearity — the actual inelastic behaviour of reinforced concrete under cyclic loading, the post-yield stiffness, the ductility capacity of a section designed to IS 13920 — carries reserves that linear analysis never sees. Much of the safety that practitioners rely on is embedded in these reserves. Until those reserves are systematically quantified for Indian material specifications and detailing practices, any claim about whether a structure is "safe" or "unsafe" under the new hazard level is, at some level, incomplete.

 

The code change arrived as a hazard statement. What was needed was a structural consequence statement. The two are not the same thing, and the gap between them is where the backlash was born.

 This Is Not a Failure — This Is How It Works

It would be easy to read this story as a failure of process, or a failure of courage, or a failure of the system. I do not read it that way.

 

Robert Greene's deeper point — the one that runs beneath all the stories in The Laws of Human Nature — is that human beings are not irrational when they resist new ideas. They are behaving exactly as their nature dictates. They resist what they cannot yet absorb. They require not just evidence, but a complete story. They need the hazard and the consequence and the implication all bound together before they can move.

 

Harvey understood this. He waited. He built his case until it could not be refused. Semmelweis did not — and the tragedy is not that he was wrong, but that he could not hold on long enough for the world to catch up to him.

 

IS 1893:2025 sits somewhere between these two stories. The seismological science is Harvey — careful, evidence-based, internationally validated. The structural engineering response — the NLTHA, the fragility curves, the performance-based consequence studies — is the part that needs more time. It is being developed. It exists in research papers and doctoral theses and conference proceedings. It has not yet been assembled into the kind of clear, accessible, practitioner-facing narrative that could walk a Metro Rail engineer or a policy committee member through the story from hazard to consequence.

 

The withdrawal of IS 1893:2025 is not the end of this story. It is a pause. The science will not go away. The Himalayan belt will not become less active. The next revision will come, and when it does, the strongest argument for it will not be the hazard map alone — it will be the map plus the buildings plus the drift ratios plus the clear statement of what changes and what does not.

 

Everyone involved in this — the seismologists, the code committee, the practising engineers, the infrastructure bodies — was doing their part sincerely. The system is not broken. It is just not yet finished.

 

That is, not a failure of human nature. It is human nature doing exactly what it does — moving forward, imperfectly, in pieces, toward something more complete.

 Glossary of Key Terms

For readers less familiar with the technical language used in this piece, the following explanations may help.

 

PSHA — Probabilistic Seismic Hazard Analysis

Think of PSHA as a layered construction process. A seismologist starts with what is known — the locations of active faults in a region, their historical earthquake records, the rate at which earthquakes of different magnitudes have occurred over time. To this they add ground motion prediction equations: mathematical models that estimate how strongly the ground will shake at a given site, for an earthquake of a given magnitude, at a given distance. Then they add probability — asking not 'what is the worst possible earthquake?' but 'what ground shaking intensity has a 10% chance of being exceeded in the next 50 years?' They also factor in local geology: soft alluvial soil amplifies shaking; hard rock attenuates it. The output is a hazard curve — a relationship between ground shaking intensity (often expressed as Peak Ground Acceleration, or PGA, in units of g) and the annual probability of that intensity being exceeded. For IS 1893:2025, this process was applied across India using updated seismotectonic data, producing hazard values that were higher than the previous 2016 assessment in many regions — particularly the Himalayan belt.

 

PGA — Peak Ground Acceleration

The maximum acceleration experienced by the ground surface during an earthquake, expressed as a fraction of gravitational acceleration (g). A PGA of 0.3g means the ground accelerated horizontally at 30% of the acceleration due to gravity. PGA is a useful measure for short, stiff structures. For taller, more flexible buildings, the relevant parameter shifts to spectral acceleration at the building's natural period — the frequency at which the structure naturally wants to vibrate. A building with a natural period of 3 seconds may be barely affected by a ground motion that produces high PGA but little energy at long periods.

 

Response Spectrum and RSA — Response Spectrum Analysis

A response spectrum is a plot that describes the maximum response (acceleration, velocity, or displacement) of a Single Degree of Freedom (SDOF) oscillator — think of it as an idealised one-storey building — across a range of natural periods, for a given ground motion. It is the bridge between what the ground does and what a structure experiences. Response Spectrum Analysis (RSA) takes this spectrum and uses it to estimate the maximum forces and displacements in a multi-storey structure by combining the contributions of its vibration modes. RSA is the workhorse method of everyday structural design — computationally efficient, widely understood, and embedded in IS 1893. Its limitation is that it is linear: it assumes the structure behaves elastically and does not capture what happens when members yield and deform into the inelastic range.

 

R — The Response Reduction Factor

When IS 1893 calculates the design seismic force for a building, it takes the elastic spectral demand and divides it by R — the Response Reduction Factor. For a Special Moment Resisting Frame, R is 5. This means the building is designed to resist only one-fifth of the force it would experience if it remained elastic throughout. The implicit bargain embedded in this factor is a promise: the structure will repay the reduced design force by providing ductility — the ability to deform well beyond the elastic limit without collapsing. This ductility is supposed to be delivered through proper detailing — the requirements of IS 13920, which governs how reinforcement is placed in beams, columns, and joints. The R factor only holds its promise if the detailing is done correctly and if the actual ductility capacity of the sections has been verified. In much of India's existing building stock, this verification has never been formally done.

 

NLTHA — Nonlinear Time History Analysis

Where RSA asks 'what is the maximum force?', NLTHA asks 'what actually happens, step by step, as the ground shakes?' It feeds a recorded or synthetic ground acceleration time history directly into a detailed structural model, and integrates the equations of motion through time — typically thousands of time steps. The structural model incorporates material nonlinearity (the stress-strain behaviour of concrete and steel beyond their elastic limits, including yielding, cracking, and strength degradation) and geometric nonlinearity (second-order effects as the structure deforms). The output is the full deformation history — including inter-storey drift ratios, plastic hinge rotations, and energy dissipation — which can be checked against performance targets such as Immediate Occupancy, Life Safety, and Collapse Prevention. NLTHA is the most rigorous analytical tool available. It is also computationally expensive and requires careful ground motion selection — which is where ε (epsilon) and the UHS/CMS debate becomes practically important that the higher amplitude ground motion do they really co-relate to higher demand.

 

UHS vs CMS — Uniform Hazard Spectrum and Conditional Mean Spectrum

The Uniform Hazard Spectrum (UHS) is the design spectrum that IS 1893 is essentially derived from. It is constructed by reading off, at each structural period, the spectral acceleration that has a given probability of exceedance — computed independently for each period. The problem, identified clearly in the foundational work of Baker and Cornell (2006), is that the UHS implicitly assumes that these peak values at every period occur simultaneously in a single earthquake — which never happens in nature. Real ground motions have peaked spectral shapes: high at some periods, low at others. The UHS therefore overestimates the demand that any single realistic earthquake would impose on a structure. The Conditional Mean Spectrum (CMS) corrects for this by conditioning on the occurrence of the target spectral acceleration at the period of interest, and using inter-period correlation to compute realistic spectral values at all other periods. The ε (epsilon) parameter — the number of standard deviations by which a ground motion intensity exceeds the median prediction of the ground motion model — is central to this correction, because high-hazard ground motions typically have high ε at the conditioning period and lower ε (hence lower spectral values) at other periods. Studies using CMS-based record selection consistently produce lower and less biased estimates of structural demand than those using UHS-matched records.

 

Inter-storey Drift Ratio

The relative horizontal displacement between two adjacent floors, expressed as a fraction of the storey height. A drift ratio of 0.5% is generally associated with elastic behaviour and minimal damage. A drift ratio of 1.5% corresponds to the Life Safety performance level — significant damage but the structure does not collapse. A drift ratio exceeding 2.5% approaches Collapse Prevention. These thresholds, established through experimental testing and post-earthquake observations, are the language in which structural performance is actually measured. When an NLTHA is run on a building subjected to a ground motion from the new PSHA, the output drift ratios tell you whether the structure is within the acceptable range for a given performance objective — and this is the information that was missing from the public debate around IS 1893:2025.

 

Material and Geometric Nonlinearity

Material nonlinearity refers to the behaviour of structural materials beyond their elastic limits. Steel yields at a defined stress and then continues to carry load while deforming plastically — a property that is the entire basis for ductile seismic design. Concrete cracks, its stiffness degrades, and under cyclic loading it loses strength progressively. Capturing these behaviours in analysis requires constitutive models — mathematical descriptions of how stress relates to strain throughout the loading history. Geometric nonlinearity refers to second-order effects: as a tall structure sways laterally, gravity loads acting on the displaced configuration create additional overturning moments, potentially amplifying the deformation into instability. Both effects must be included in a rigorous NLTHA. Most routine structural analysis in practice uses linear elastic models — which are fast and sufficient for conventional design but cannot reveal the true behaviour of a structure under strong earthquake shaking.

 

References

Greene, R. (2018). The Laws of Human Nature. Profile Books.

Baker, J.W. and Cornell, C.A. (2006). Spectral shape, epsilon and record selection. Earthquake Engineering and Structural Dynamics, 35(9), 1077–1095.

Baker, J.W. (2011). Conditional Mean Spectrum: Tool for ground motion selection. Journal of Structural Engineering, ASCE, 137(3), 322–331.

Bureau of Indian Standards. (2025). IS 1893 (Part 1): 2025 — Criteria for Earthquake Resistant Design of Structures. New Delhi: BIS.

Bureau of Indian Standards. (2016). IS 1893 (Part 1): 2016 — Criteria for Earthquake Resistant Design of Structures. New Delhi: BIS.

Haselton, C.B., Baker, J.W., Liel, A.B. and Deierlein, G.G. (2011). Accounting for ground-motion spectral shape characteristics in structural collapse assessment through an adjustment for epsilon. Journal of Structural Engineering, ASCE, 137(3), 332–344.

Lin, T., Haselton, C.B. and Baker, J.W. (2013). Conditional spectrum-based ground motion selection. Part II: Intensity-based assessments and evaluation of alternative target spectra. Earthquake Engineering and Structural Dynamics, 42(12), 1867–1884.

USGS. (2006). Earthquake Hazards 201 — Technical Q&A. United States Geological Survey.

Scientific Reports. (2025). Displacement-based seismic fragility assessment of a high-rise reinforced concrete building. Nature Publishing Group.