Earthquake proof: UBC engineers develop 'unbreakable walls'

Engineers at UBC have developed a type of seismic-resistant concrete that can withstand earthquakes with magnitudes as high as 9.1, like the earthquake that struck Tohoku, Japan in 2011.

The material is called an eco-friendly ductile cementitious composite (EDCC) and is so strong and flexible that it acts like steel, bending during an earthquake instead of crumbling like concrete.

Walls that are sprayed on both sides with the material performed so well in seismic tests that UBC engineers dubbed it the ‘unbreakable wall.’

Soleimani-Dashtaki had to turn the dial to three-times the magnitude of the strongest earthquake ever recorded in order to break down a two-meter wall of EDCC in seismic tests.

The technology developed at UBC will cut retrofit costs in half, added UBC civil engineering professor Nemy Banthia, who supervised the EDCC project.

An unreinforced wall collapsed at about 65 percent intensity (magnitude 9 quake). In contrast, the reinforced wall withstood full intensity shaking and flexing. “A 10 millimeter-thick layer of EDCC … is sufficient to reinforce most interior walls against seismic shocks,” said Soleimani-Dashtaki.

EDCC is already on the market – in British Columbia, Canada, the product has been designated as “an official retrofit option.” The product is growing in popularity, as it is more cost-effective than major structural renovations or the steel bracings often required for earthquake protection.

Effects of eco-friendly ductile cementitious composites (EDCC) on dynamic characteristics of hollow concrete masonry walls.

Walls are the main structural elements used to resist lateral forces in masonry structures. Masonry walls dissipate energy input from an earthquake dominantly through three damping mechanisms; hysteretic damping, viscous damping and Coulomb friction. This study was aimed at assessing the effectiveness of an Eco-friendly Ductile Cementitious Composite (EDCC) repair material in improving the dynamic behaviour of hollow concrete blockwork walls. The material will be used to retrofit unreinforced concrete blockwork walls in seismic-prone areas of British Columbia to reduce the risk of collapse of such walls in a future earthquake. The walls used in the experimental program were 1.8 m high by 1.8¬¬¬ m wide by 0.19 m thick, constructed with hollow concrete masonry units of actual size 390 × 190 × 190 mm and type S mortar. The thickness of the EDCC repair material applied to the wall surfaces was about 20 mm. The dynamic characteristics of the walls were evaluated through in-plane free vibration tests at two levels of damage before and after strengthening: the first level was the uncracked condition and the second was after cracking resulting from in-plane quasi-static loading to the same level of drift. The natural frequencies, damping mechanisms and ratios have been investigated from the free vibration response data. The natural frequency of vibration increased in the strengthened walls as a result of the application of the EDCC material.