Rutgers Engineering Expert Explains How Earthquake-Resistant Construction Can Curb Catastrophe
Husam Najm, a professor of civil and environmental engineering, specializes in bridge design and the study of advanced concrete materials
A rare 7.8 magnitude earthquake that struck south-central Turkey near the Syrian border has claimed more than 36,000 lives and raised questions about whether the death toll could have been mitigated.
Within 11 minutes, a magnitude 6.7 aftershock convulsed a region 60 miles north. Scientists at the U.S. Geological Survey (USGS) said an earthquake of this magnitude is unusual anywhere in the world.
Husam Najm, a professor of civil and environmental engineering in the Rutgers School of Engineering who specializes in the study of various advanced concrete materials and the design of novel forms of concrete bridges, discusses the unfolding tragedy, its causes and efforts to design earthquake-resistant structures to stave off such catastrophic losses in the future.
USGS scientist David Wald said, “an earthquake this size has the potential to be damaging anywhere in the world, but many structures in this region are particularly vulnerable.” What is it about buildings with older types of concrete frames that makes them prone to collapse in a strong earthquake?
Although the Turkish building code includes seismic design and retrofit requirements to make structures like buildings and bridges resistant to earthquake damage, many of the buildings in Southeast Turkey were older buildings and were designed and built prior to the implementation of the seismic code requirements. Most likely many of these buildings are built from reinforced concrete frames or unreinforced masonry that do not have sufficient ductility capacity and energy dissipation ability – especially at joint locations – that they can sustain the ductility demand imposed on them from a large magnitude earthquake.
Reports indicate the two largest earthquakes in the recent series were relatively shallow, with the main earthquake 11 miles deep and the aftershock about 6 miles deep, leading to intense shaking on the surface. Can you describe what excessive ground motion does to a building? Why can’t buildings simply absorb the motion?
Excessive ground motion can cause large forces on buildings because of the acceleration of the ground motion. These forces will be amplified if the building weight is large and the soil on which the foundations are built is soft. These forces will produce large horizontal movements, shaking, of the building. If the building is not designed to accommodate these movements or absorb the energy generated by the ground motion, collapse can happen.
Current seismic codes in countries with high seismic activities like the U.S, New Zealand, Japan, Turkey, Iran, Greece, South America and China have seismic design and retrofit requirements that allow buildings to absorb the energy generated by the ground motion and accommodate the movements.
What is it about the design of some buildings that makes them resistant to earthquakes? Are more such buildings being constructed? Are most people now living in buildings designed to withstand earthquakes?
A building designed with enough ductility capacity to accommodate the demand put on it from an earthquake should be able to resist earthquake ground motion and only suffer minor damage – mostly nonstructural damage. This is achieved by designing building columns, walls, braces and joints to resist the ground motion forces. Proper detailing is also essential to provide the needed ductility. Detailing in concrete building means how the steel and the concrete are connected and the type of concrete used, such that the concrete is always confined so that it can provide the needed ductility. For steel buildings, detailing means how the bolts and welds are made and what type of steel material is used to ensure the needed ductility of steel.
More buildings in high seismic zones are designed and constructed to withstand large ground motions. There are many people living in buildings designed to meet seismic code requirements. But unfortunately, older buildings – if not retrofitted to meet current seismic code requirements – may not withstand large earthquakes and there are many people around the world still living in those buildings.
What is the potential for new science and engineering approaches to protect people during earthquakes in the future?
It is still difficult to predict when an earthquake will happen and how big it will be. There is a lot of current research on this topic. Hopefully, we can get there soon – even if we can get an early warning of a few minutes, it will make a big difference.
We learn a lot from every earthquake that happens, and we update our seismic design requirements. There have been a lot of advances in seismic design and ductile materials.
The other thing that needs to be done is to retrofit older buildings and historic buildings. That is not an easy thing because it is very expensive and disruptive to people and businesses.