Cable Ties for Buildings

What if a building could sway back and forth in an earthquake and return to its upright position with no help, and without damaging the connections between the building and its foundation? Greg MacRae of the University of Canterbury has thought of this already. He conceived of a device he calls the “GribNGrab” that’s a bit like a giant cable tie for holding buildings in place.  

GribNGrab devices are installed at the base of rocking buildings to tie the frame to the foundation. When an earthquake strikes and ground shaking causes the building to sway, the GripNGrab device on one side of the building allows the structure to uplift while seismic energy is dissipated via friction. When the building sways back in the other direction, a ratchet component operates preventing the GripNGrab from buckling in compression. The building self-centres and the device survives undamaged.

These clever mechanisms are undergoing refinement in a Te Hiranga Rū QuakeCoRE project entitled, “Improving building system performance considering GripNGrab tension-only friction devices in rocking frames.”

University of Canterbury PhD student Kiran Rangwani has been working with Geoff Rodgers to test the GripNGrab device. They found that the ratchet part worked as anticipated but performance of the frictional part was surprisingly unpredictable. Changes to the set-up of nuts and bolts have indicated how improvements may be made. Kiran’s work highlights the importance of proof-of-concept component testing prior to larger-scale experiments. 

The GripNGrab device with a rocking steel frame will be one of nine structural configurations to be tested in a full-scale, three-storey building on a massive shake table at a QuakeCoRE Affiliate Organisation in China. This is a crucial part of QuakeCoRE’s Disciplinary Theme 2: “Whole-of-Building seismic performance.” Known as the Robust Building System (ROBUST) project, it aims to demonstrate how economic energy-dissipating technology can ensure buildings are not only safe after earthquakes but also easy to fix, enabling rapid reoccupation.