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Stainless steel nodes resist earthquake damage

Words:
Stephen Cousins

Researchers develop ‘earthquake-proof’ device that limits residual drift in buildings to improve prospects for repair

Researchers at Heriot-Watt University have developed an expendable device to ‘earthquake-proof’ buildings that absorbs seismic shocks and make structures easier to repair.

The stainless steel nodes are strategically positioned at the joints between diagonal braces and horizontal beams in steel framed buildings. When a building starts to shake, they absorb the seismic loads, mitigating damage to the rest of the structure. Post-quake they are simply removed and replaced so the building can return to normal occupation quickly.

The system is intended to improve on current European ‘earthquake-proof’ buildings, which are designed to prevent collapse in the event of a strong earthquake, but do not prevent non-repairable damage or deformations caused by ‘residual drift’. Residual drift is caused when the accumulation of damage means buildings are unable to return to their original vertical orientation.

Dr George Vasdravellis, assistant professor of structural engineering at Heriot-Watt University in Edinburgh, told RIBAJ: ‘This is a major problem that makes repairs very difficult and expensive due to tolerance issues. Our system mitigates against the need for damage repair and virtually eliminates residual drift so the building remains almost vertical.’

Critical to the technology is the use of stainless steel for the nodes; its high post-yield stiffness causes them to crumple before the rest of the building structure

The system is designed to handle severe 1-in-475-year seismic events in buildings up to 10 storeys high. Experimental testing and computer simulations recorded negligible residual drift, compared to conventional building designs where drifts were four to five times larger.

Critical to the technology is the use of stainless steel for the nodes; its high post-yield stiffness causes them to crumple before the rest of the building structure.

According to Vasdravellis, the number of sacrificial devices required could range from two to six, depending on the building. He says: ‘The diameter of the devices determines the strength, so you can increase or reduce the number of devices depending on the strength required.’ The devices only work in conjunction with regular concentrically-braced steel building frames and in future it may be possible to retrofit them into existing buildings of this type.

Vasdravellis was awarded £140,000 by the European Commission for the next stage of his research into earthquake engineering. ‘The next step is to develop the technology for multi-hazard mitigation, to handle other impacts, such as progressive collapse, when a critical structural element in a building, like a column, is suddenly removed due to a bomb blast or other issues,’ he concludes.

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