Kanazawa Institute of Technology develops low-cost base-isolation-level warehouses using spherical artificial aggregates

Amid a series of earthquakes occurring across various regions in Japan, including the 2026 Kumamoto Earthquake, Kanazawa Institute of Technology has succeeded through industry-academia collaboration in developing a seismic mitigation construction method to prevent cargo in logistics warehouses from suffering damage. It is said that after scattering spherical artificial aggregates on the floor and placing bottom boards on top, one simply needs to place palletized cargo. Due to optimal sizes and frictional forces of the spheres, bottom boards slide at appropriate timing during an earthquake, preventing cargo collapse. While earthquake resistance and base isolation of buildings have been advanced in warehouses, this construction method yields effects of securing cargo safety and reducing building damage at low cost. Going forward, they intend to advance their research toward demonstration with business operators.

Professor Kuniaki Yamagishi (Earthquake Engineering) of the Department of Architecture, College of Architecture at Kanazawa Institute of Technology, has been working on research regarding the state of architectural structures from the viewpoints of economic rationality and business continuity. If logistics operations are disrupted by an earthquake, the effects can ripple across many sectors. Therefore, it is essential that logistics warehouses remain operational even during major earthquakes.

However, because logistics warehouses are not places where people reside, low-cost measures are usually implemented. Because introducing expensive base isolation devices affects business profitability, discussions on earthquake resistance of logistics warehouses tend to be relegated to the background. In recent years, while base isolation is adopted in many cases for large warehouses, general earthquake-resistant structures are common in medium-sized and smaller warehouses. Furthermore, in the 2026 Kumamoto Earthquake, base isolation devices of city halls deformed significantly, making it clear that even base isolation is not a cure-all.

In 2014, Yamagishi commenced research toward realizing logistics warehouses with functions on par with base isolation at lower costs. He devised a "sliding effect" that addresses shaking measures for both goods and buildings in one stroke, reducing the risk of goods shifting, collapsing, or overturning. To reflect the effect in design, he considered logistics warehouses with large live loads to be appropriate.

However, creating devices and materials to realize the sliding effect was a challenge. While searching for substances that slide appropriately against earthquakes, in 2018 a product of a manufacturer selling artificial aggregates used as molding materials when making castings caught his eye, and he made an inquiry. Receiving samples of spherical artificial aggregates called by the product name "ESPEARL" free of charge from that company, Yamakawa Sangyo Co., Ltd. (Amagasaki City, Hyogo Prefecture), his research began. The material of ESPEARL is sapphire. Because purity is low, it can be obtained relatively cheaply.

Yamagishi repeated experiments combining ESPEARL with various bottom boards and floor finishing materials to understand the timing when bottom boards slide. As a result, it was found that a combination of particle sizes of 50 to 425 micrometers scattered on the floor and bottom boards exhibited a sliding effect.

When the system was subjected to earthquake-like shaking, the goods barely moved at a seismic intensity of around 5 on the Japanese seismic intensity scale. Even at a seismic intensity of lower 6, goods moved only a few millimeters to a few centimeters, and collapsing did not occur. In terms of cost, it fell within a few hundred yen per square meter, and Yamagishi smiles wryly stating, "The bottom boards are more expensive."

A merit of ESPEARL is that changing sphere sizes can alter sliding timing. By scattering optimal sizes for each floor, the sliding effect can be enhanced further, or sliding widths of bottom boards can be adjusted. By using artificial aggregates optimally adjusted in this way, construction costs of newly built logistics warehouses can be lowered, and earthquake resistance of existing logistics warehouses can be enhanced to reduce the risk of cargo overturning.

However, there are also points to note, such as the sliding effect occurring only in two-story or higher logistics warehouses. Going forward, he wants to make better solutions by repeating demonstration experiments together with the logistics industry. Yamagishi stated: "While introduction costs are low, effects are on par with base isolation. One might hesitate toward a new construction method, but the effects are guaranteed."