Question Corner: Are buildings with stilt parking at greater risk of collapsing due to earthquake?


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Are buildings with stilt parking (without a wall joining the stilts) at greater risk of collapsing due to earthquake?


Prof. Devdas Menon,

IIT Madras In general, yes — unless the buildings have been designed structurally to mitigate the risk. Typically, in multi-storey, reinforced concrete framed buildings on stilts, masonry infill walls (between columns) are present in all upper storeys, except in the ground storey. This introduces a sudden reduction in lateral stiffness in the building in the open ground storey, relative to the upper storeys, under the action of lateral loads during earthquake.

The lateral inter-storey movement (‘drift’) in the ground storey is likely to be very high, compared with the upper storeys, inducing local high stresses in the ground storey columns. In an extreme seismic event, the vertical steel reinforcement can yield at the top and bottom locations of the ground storey columns, making the building vulnerable to a ‘soft storey mechanism’ collapse: the building can simply ‘cave in’, with the upper storeys coming down. (flattening the cars parked in the ground storey — as witnessed during the 2001 Gujarat earthquake).

Such sudden failure can be avoided by proper structural design such as providing reinforced concrete shear walls at appropriate locations, or at the very least, adequately stiffening and strengthening the ground floor columns. Existing open ground storey buildings most at risk can be retrofitted to make them safe.

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Printable version | Jan 24, 2020 7:25:35 AM |

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