INFRASTRUCTURE ROTECTIONCreating Buildings That Can Withstand the Most Extreme Stress Loads

By Sølvi Normannsen

Published 2 February 2023

Combined ballistic impacts pose a major challenge for engineers who build structures that must withstand extreme stresses. An explosion can hurtle fragments and debris at enormous velocities so they strike the surroundings. Then comes the shock wave. It’s a scary combination.

Combined ballistic impacts pose a major challenge for engineers who build structures that must withstand extreme stresses. The combination of blast pressure and impact at high speed increases the chances of greater damage. Ph.D. candidate Benjamin Stavnar Elveli describes it as the scariest stress there is.

“These combined impacts work in the same way as shrapnel bombs,” he says.

Infrastructure Shift from Massive and Military to Light and Civilian
In the past, massive concrete military buildings formed the bulk of structures that were built to be protective against blasts. In recent decades, new threats have emerged, and the need to protect civilian buildings and structures in urban areas has increased.

This has fueled interest in lighter, thin-walled solutions that can withstand a great deal of deformation without cracking and collapsing.

Regulations don’t yet reflect these changed needs. There are no standards for this type of load yet, and research in the field is very limited.

Elveli has investigated how different types of thin steel plates behave when exposed to extreme stress loads. His work can help to establish guidelines for how resistant, lightweight structures should be designed.

Initial Projectiles Do the Most Damage
Whether they occur in accidents or on purpose, explosions can cause massive damage. Debris and fragments can be torn loose from parts of buildings, cars, gravel or stones. When they hit, they can act like projectiles.

Elveli says that any buildings, cars or other objects in the vicinity would be exposed to a load that is more serious than if either stress load occurred alone. The damage is believed to be greatest when fragments hit first.

“That’s because the structure already has a defect or weakness from the projectile and then has to withstand the shock wave itself,” he says. “Most often, cracking and destruction start in the weak spots.”

Safer Structures, Safer Society
Elveli’s Ph.D. is based on more than 80 small-scale explosion tests on three different types of steel. By combining physical experiments with theory and mathematical modelling, he has recreated the explosive loads in computer simulations. The aim is to gain as much control as possible over how structures react to such loads.

The more scientists understand about the actual physics of these loads, the more accurate, safe and sustainable solutions the construction engineers of the future can deliver.