September 3, 1999

Engineer's Research Aims at Creating Quakeproof Structures

Dr. Neven Krstulovic-Opara holds the stainless steel fiber mat used in his HPFRC concrete.

The recent earthquakes in Turkey have devastated the country. More than 14,000 people died and 27,000 were injured in the catastrophe. Images of survivors trapped in the rubble of collapsed buildings have appeared on evening newscasts and morning newspapers. But an NC State engineer believes such scenes can be prevented, and his research may save thousands of lives in the future.

"The high performance concrete we are developing can prevent this from happening," says Dr. Neven Krstulovic-Opara, assistant professor of civil engineering. "It has a great potential to revolutionize the way concrete structures are built and used."

Krstulovic-Opara and a team of researchers are testing a new generation of concrete, Slurry Infiltrated Mat Concrete (SIMCON), that will possibly save lives, buildings and bridges by changing the way concrete structures fail. The new concrete system is super strong, durable, comparatively easy to use, and economical.

SIMCON uses mats of stainless steel fibers injected with a special concrete slurry. The combination can be used to build new structures or to reinforce existing structures. Tests conducted so far have proven that traditional concrete structures retrofitted with the new concrete system are far more earthquake resistant and less likely to fail in ways that would cause injury to people.

Because failure is inevitable in all structures, engineers have to design the best and safest way for a structure to fail. In conventional concrete systems, this is achieved through proper use of steel reinforcing bars (rebars), which give the concrete tensile strength that it otherwise lacks.

For safety and design reasons, conventional concrete is designed so that the rebars fail before the concrete fails. Unfortunately, many existing structures have not been designed to sustain earthquakes. When these traditional concrete structures are stressed, such as during an earthquake, the concrete cracks, explodes and breaks away from the rebars, causing the structure to collapse. The falling pieces of concrete can also cause property damage as well as physical injury. Krstulovic-Opara's SIMCON is designed to sustain much higher loads and deformations before it fails. Furthermore even when failure does occur, the concrete does not break apart in large chunks because it is held together by the thousands of stainless steel fibers. Instead of large chunks of concrete breaking and falling from the structure, SIMCON crumbles in small, harmless flakes. In addition, the mass of fibers and concrete do not collapse in the same way that conventional structures do.

Currently Krstulovic-Opara is working with a team of NC State researchers to develop new structural systems that would best employ the advanced features of SIMCON ÿ high strength, durability, low cost and easy construction. The researchers include Dr. John Hanson, Distinguished University Professor of civil engineering, and Dr. Paul Zia, Distinguished University Professor Emeritus of civil engineering. The research project is funded by the National Science Foundation.

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