Lab-Simulated Earthquakes Test the Mettle of 'High-Performance' Building Materials

*"Lab-Simulated Earthquakes Test the Mettle of 'High-Performance' Building Materials" is part of NJIT's 2023 Research Magazine*

Despite advances in construction design and materials, a powerful 7.8 magnitude tremor on the San Andreas fault could kill a projected 1,800 people, injure an additional 50,000 and demolish 200 million square feet of commercial, public and residential buildings, according to a recent study. Even the newest, most up-to-date structures would be toppled at a rate of up to 1 in 10.

“Ten percent is not a random figure – it’s the accepted failure rate in today’s building code when weighing the economics of improving construction with the risk of such large events,” says Matthew Bandelt, associate professor of civil engineering and co-director of NJIT’s Materials and Structures Laboratory. “The risk is rising, however, as more people move into urban areas. As a result, we now have very concentrated losses when a natural disaster, in any form, hits a major metropolitan area.”

According to FEMA, about half of the continental U.S. population is at risk of damage from earthquakes.

Engineers increasingly use a new class of high-performance concrete to bolster new and existing bridges against harsh conditions, but there has been little push to incorporate them in the construction of buildings.

“We don’t know how buildings would behave with these new materials, including during earthquakes, so it’s difficult to quantify the benefits,” notes Bandelt, who secured a CAREER award from the National Science Foundation to assess the seismic response of materials known as high-performance fiber-reinforced cementitious composites (HPFRCCs) in structures of various configurations and to develop design criteria for using them.

The HPFRCC materials that Bandelt and his team study have small fibers made of steel or polymers that are one-half to 1 inch in length and range in thickness from that of a human hair to the tip of a pen. When building components made with HPFRCC materials are subjected to seismic shaking, the fibers help keep the concrete together, potentially making it stronger and more able to deform or bend.

Buildings designed with high-performance fiber-reinforced concrete are also potentially more sustainable, meaning they would require less steel, for example, because the concrete itself bears more of the load. “The beams and columns could be smaller,” Bandelt says, “because less material carries the same amount of weight.” He hopes that his research will contribute to the establishment of LEED-like standards for building resilience.

Earthquake forces push and pull the beams and columns that make up a building. Bandelt uses hydraulic machines that apply up to 220,000 pounds of force to simulate these impacts on individual building components, and to better understand their behavior under the combined effects of axial load and bending. Their studies have shown that HPFRCC dramatically improved the seismic response: increases in strength of 30% to 40%, or even more, are common in comparison to traditional reinforced concrete. But the deformation capacity – the amount a structural component can bend before breaking – requires further consideration.

When building components made with HPFRCC materials are subjected to seismic shaking, the fibers help keep the concrete together, potentially making it stronger and more able to deform or bend.

The team is now building mathematical representations of buildings with different frame configurations, story heights, building layouts, structural element geometries and HPFRCC mechanical properties to test the materials’ performance at the system-level. They apply nonlinear dynamic structural analysis, a technique to computationally simulate structural response under loading, to see how much shaking would make the buildings collapse.

“We have component-level information, but not for an entire building, and without it, we’ll never get buy-in,” Bandelt said, adding that part of their research is to perform risk assessments to understand how rates of damage change with these new materials and to analyze cost-benefit scenarios for HPFRCC systems.

They’re investigating methods to engineer and place HPFRCC in key regions of buildings, while quantifying their impact on performance, safety and life-cycle costs. Specifically, Bandelt and his team will study how HPFRCCs can be placed in “plastic hinge regions” where damage is expected to occur during an earthquake, with the expectation of reducing damage while also increasing strength and elasticity by using HPFRCCs. Their goal is to help people understand the relative benefit of using the new composites under different risk scenarios. 

“If a building owner asked for their structure to be immediately occupiable after a specific earthquake magnitude, for example, we would tell them how to meet that standard,” he said. “We do this by using our computational models to simulate performance under various earthquake magnitudes and integrating those results with the risk of different earthquake hazards based on how likely they are to occur and how much shaking they cause.”

According to the Federal Emergency Management Agency (FEMA), about half of the U.S. population, not including residents of Hawaii and Alaska, are at risk of damage from earthquakes. Regions that are most vulnerable to earthquakes are largely uninsured or underinsured against them, Bandelt notes. As of now, the federal government through government agencies such as FEMA covers the lion’s share of damage repairs. 

“There is a lot of loss in natural disasters, not just in terms of lives and revenues, but also in community,” he says. “Buildings are places people gather.”