Guwahati's soft storey buildings and seismic vulnerability demand urgent action

Guwahati, May 10: The Earth continues to remind us of its immense power. In early 2025, a devastating earthquake in Myanmar caused widespread destruction and loss of life, sending shockwaves - both literal and figurative-across the region. For Guwahati, Assam's rapidly expanding urban centre, this disaster should serve as a wake-up call. Located in India's highest-risk earthquake zone (Seismic Zone V), Guwahati's vulnerability lies not only in geography but in the structural weaknesses of its buildings.

A key concern is the widespread presence of soft storey buildings-multi-storey structures where the ground floor is significantly weaker than the upper floors, often due to open parking or retail spaces supported only by slender columns. While space-efficient and cost-effective, these designs are highly unstable during seismic events.

When an earthquake strikes, the lateral forces that act on a building are supposed to be evenly distributed through the structure. But in soft storey buildings, the ground floor absorbs a disproportionate share due to its lack of stiffness, leading to a sudden "pancake" collapse. This was tragically demonstrated in the 2001 Bhuj earthquake and, more recently, in the Turkey-Syria disaster.

In Guwahati, soft storey designs are prevalent, including in new constructions. Many older buildings predate modern seismic codes, and some newer ones bypass or inadequately implement those standards. Developers often prioritize usable space and cost savings, while residents remain unaware of the invisible danger posed by weak ground floors.

India's seismic design code, 15 1893 (Part 1): 2016, identifies soft storeys as a structural irregularity. While not banned, these buildings are flagged as high-risk. To offset their vulnerability, the code mandates that structural elements at the soft storey level be designed for 2.5 times the standard lateral seismic forces. This significant increase is meant to promote the use of shear walls. bracing systems, or other reinforcements.

The code also emphasizes uniform stiffness and mass distribution throughout a building's height, discouraging abrupt changes in structural behaviour that can lead to failure. However, unless enforced rigorously during planning and construction, these provisions offer little real protection.

A major driver of soft storey construction is the demand for ground-level parking. A safer alternative is underground parking, which provides structural benefits due to reinforced concrete retaining walls and soil confinement that enhances lateral stability during earth-quakes. Updating building regulations to favour basement parking could reduce the reliance on dangerous open ground floor designs.

For existing soft storey buildings, retrofitting is essential. One effective method involves installing seismic dampers, which absorb and dissipate earthquake energy. These devices, used in tandem with steel cross bracing systems, greatly improve seismic resistance. Among them, 'friction dampers', which use sliding steel plates to absorb energy, are ideal for integration with braced frames in open ground floors, Metallic yield dampers', which deform under stress, are well-suited to bracing systems. "Viscous dampers', often used in high-rise buildings, can also be adapted for low-rise structures requiring higher energy dissipation.

Each building must be assessed individually based on factors such as height, materials, age, and soil conditions. Retrofitting plans should be developed and overseen by qualified structural engineers, not general contractors or unspecialized designers.

This brings us to a critical issue: the building approval process. In Guwahati, like in many Indian cities, structural plans are often reviewed by Registered Technical Per-sons (RTPs)-a category that includes architects and civil engineers who may lack deep expertise in seismic design. In a high-risk zone, this is an unacceptable risk.

Structural drawings and safety assessments must be reviewed and approved only by licensed structural engineers. Municipal bodies need to implement and enforce this requirement without exception. Equally vital are construction site inspections. Regular checks by qualified engineers can detect deviations from approved plans and substandard practices early, preventing catastrophic failures later.

Global precedents offer important lessons. After the 1994 Northridge earthquake, cities like Los Angeles and San Francisco mandated the retrofitting of soft storey buildings. Japan, which experiences frequent and intense quakes, imposes even stricter regulations. New soft storey constructions must include steel bracing, shear walls, or seismic isolation systems, and older buildings must be retrofitted.

Japan's building approval system is far more robust than Guwahati's. Every project undergoes multiple layers of vet-ting, including zoning, fire, accessibility, and, most crucially, rigorous seismic evaluation. Structural calculations - such as base shear, inter-storey drift, and seismic response-must comply with the Building Standards Act and are tested using advanced simulations. Designs that do not meet strict criteria are rejected or revised.

In contrast, Guwahati's enforcement of IS 1893:2016 is uneven, especially for mid-and low-rise buildings. Mandatory review of detailed structural calculations is rare. This leaves the city exposed to the very dangers these regulations are designed to prevent.

Guwahati is on a path to modernization and growth. But without seismic resilience, this growth could come at a devastating cost. Earthquakes are inevitable; building failures are not. Through stronger codes, better enforcement, public awareness, and investment in retrofitting, the city can turn vulnerability into preparedness.

Ultimately, it's not the earthquake that kills-it's the building. Guwahati must act now to ensure its structures are part of the solution, not the problem.

(The author is a structural engineer and currently working as an Assistant Professor in a private university.)