How a high-rise stands up: shear walls, Mivan formwork and a raft foundation

Height changes the problem

For a house, the main structural job is carrying weight down to the ground. As a building gets taller, a second force takes over: the sideways push of wind and earthquakes. Wind pressure grows with height and acts on a bigger face, and the taller the building, the larger the overturning effect at its base. Ching, Onouye and Zuberbuhler make this the central theme of high-rise structure: lateral stability, not gravity, drives the design.

At 84 metres, the tower falls under India’s tall-building code, IS 16700, which sets extra criteria for concrete buildings taller than 50 metres. Kanpur is also in seismic Zone III under IS 1893, so earthquake forces had to be designed for alongside wind.

Shear walls: stiff planes in both directions

The tower resists those sideways loads with reinforced concrete (RCC) shear walls. A shear wall is a deep concrete plane running from the foundation to the roof. Under load it behaves like a giant vertical cantilever fixed at the base, and because it is so deep in its own plane it is very stiff, which keeps the sway of the building small.

Walls only resist load along their length, so they are set in both directions on plan. Floor slabs tie them together at every level, so the whole building moves as one stiff box rather than as separate parts.

Mivan: walls and slab in one pour

If the structure is mostly concrete walls, the walls themselves can be cast in place along with the slabs. That is what Mivan aluminium formwork does. Lightweight aluminium panels are set up for the walls and the slab of a whole floor, and the concrete is poured in one go, so walls and slab are monolithic, with no joint between them.

Once the concrete has gained strength, the panels are stripped, lifted to the next floor and reused. A tower of repeating floors suits this well: the same set of panels is used again and again, which gives speed, consistent dimensions and a smooth finish that needs little plastering.

A raft spreads the load

All that weight, plus the overturning effect of wind and earthquake, has to go into the ground. Kanpur sits on the soft alluvial soils of the Ganga plain, and the tower stands close to the river. Instead of resting each column or wall on its own footing, the tower stands on a raft: one thick reinforced slab under the whole footprint.

Ching describes this mat (or raft) foundation as the answer when loads are heavy or the soil is weak: spreading the load over a large area keeps the pressure on the soil low and helps the building settle evenly, avoiding the uneven settlement that separate footings can cause.

And at the top, the crown

With the structure solved below, the crown could be expressive: sweeping arched fins rise above the top floors and are lit at night. How the elevation leads the eye up to them is the subject of a separate article on the tower’s horizontal and vertical lines.