Howrah Bridge, standing tall over the Hooghly River, silently connects the bustling cities of Kolkata and Howrah. An emblem of architectural resilience, it recently marked its 75th year of service, portraying an enduring legacy in the hearts of the locals. Let’s delve into the remarkable tale of its construction, revealing the careful planning and ingenious engineering that went into this iconic structure.
In a region plagued by humid weather and environmental pollution, steel structures often succumb to corrosion. However, Howrah Bridge emerges as an exception. With minimal repair needs, it stands strong, a testament to the meticulous construction practices and consistent maintenance protocols implemented since its inception.
The saga began with the strategic selection of the bridge site. The existing pontoon bridge facilitated uninterrupted traffic flow, and the new location, wisely chosen 500 meters away from religious structures, prevented any hindrance to construction. Careful alignment and foundation planning steered clear of potential scour issues, ensuring a robust base for the bridge.
In 1922, a dedicated commission kickstarted the planning phase, evaluating various bridge designs. The journey involved rejecting unsuitable options like single-span arch and suspension bridges. The balanced cantilever bridge emerged victorious, offering a solution that allowed the construction of the main girder away from the river, ensuring uninterrupted river traffic.
To counteract the challenges posed by the region’s conditions, specific steel members were meticulously chosen, as illustrated in Table-1. Tata Steel played a significant role, supplying 23,000 tons of the total 26,500 tons of steel used. The infusion of copper and chromium enhanced corrosion resistance, preserving the bridge in the face of high humidity and soaring temperatures.
| Steel Items | Yield Strength (MPa) | Ultimate Strength (MPa) |
|---|---|---|
| Plate and Sections | 355 | 664 |
| Plain Manganese Steel | 380 | 580 |
| Manganese Chromium Steel (Imported) | 375 | 575 |
| Manganese Chromium Steel (India) | 395 | 614 |
Detailed soil analysis revealed a clayey layer beneath the riverbed, presenting both challenges and insights. Stiff clay at varying depths and the presence of sandy silt posed construction difficulties. The knowledge gained informed subsequent construction decisions.
In the absence of standardized codes during construction, loading standards were developed to accommodate existing traffic and allow for future expansion. High-strength steel, a hallmark of the design, reduced weight while maintaining structural integrity. A meticulous focus on design ensured the bridge’s longevity as an iconic structure.
The balanced cantilever design, with a central span of 457 m, showcased intricate details. The deck, 21 m wide, accommodates six lanes with provision for vehicular movement. The grillage system, articulation joints, and expansion joints attest to the engineering precision embedded in the structure.
The towers, main bearings, and wind frames, carefully designed to withstand lateral forces, contribute to the bridge’s stability. The K-type truss formation reduces slenderness effects, emphasizing both functionality and aesthetics.
The absence of modern soil tests led to innovative approaches in understanding the soil’s strength. Cast-iron cylinder tests and load simulations provided crucial insights into the foundation’s resilience, laying the groundwork for a robust structure.
The pier foundation, accommodating 30,000 tons downward compression and 13,500 tons upward tension, showcases a monolith design, ensuring stability. Anchorage blocks, strategically designed to counter uplift during construction, exemplify economical yet effective engineering.
As we unravel the story behind Howrah Bridge, it becomes clear that this engineering marvel is not just a structure but a testament to human ingenuity. Through meticulous planning, innovative materials, and careful execution, it has stood the test of time, connecting two cities and embodying the spirit of resilience.