Progressive Collapse: Surrey Engineers Make It Easier to Check a Floor Can Survive a Lost Column

If you walk through a multi-storey car park, you'll find yourself under a concrete slab supported by many columns. Each column holds up part of the floor above and all the cars parked there. But what if one column suddenly fails? Would the floor just dip, or could it trigger a bigger problem? Engineers at the University of Surrey have found a simpler way to answer this and help make sure nothing dramatic happens.

This research, led by Surrey and published in Structural Concrete, offers engineers an easier way to check how reinforced concrete floors react if a support column suddenly fails.^[1] The focus is on a failure called punching shear, where a column pushes through the slab above.^[2] If one column goes, its weight shifts to the nearby columns, which can sometimes set off a chain reaction called progressive collapse.^[3]

Progressive collapse without the heavy maths

Usually, checking for this kind of failure involves long, complicated calculations. The Surrey team has created a set of equations that make things simpler. With these, engineers can figure out how much steel reinforcement a floor needs to prevent one failure from causing more.^[4] The method also works with the upcoming version of Eurocode 2, the European standard for concrete design, so it matches the rules designers will use.

Engineers call a building that can handle this kind of damage and stay standing robust. That's even in the job title of Professor Juan Sagaseta, Surrey's Professor of Structural Robustness. “The loss of a single column should not mean the loss of an entire building,” he said^[5].

Tested against a real car park

Equations only matter if they work in real life. The team tested theirs with past experiments and new data from the 2020 collapse of the Nueva Montaña car park in Santander, Spain.^[6] On January 13, 2020, a children's play area with a sports court, built above an underground car park, sank onto the parking below early in the morning.^[7] Spanish engineers later published their own analysis of why the concrete slab failed.^[8]

The new equations correctly predicted the kind of failure seen at the site, where damage spread from a failed column to its neighbor. The researchers also found their method works even if more than one column suddenly fails.

Lead author Dr Maria Liapopoulou did this research while she was a Research Fellow at Surrey and is now a Brunel Fellow at the University of Cambridge^[9]. “It’s one thing to develop a mathematical model, but being able to test it against a real case study gives us greater confidence that it could make a difference in practice,” she said^[10].

The team worked with Universidad Politécnica de Madrid, Universidad de Extremadura, and the design firm Skidmore, Owings & Merrill (SOM).^[11] Having a design firm involved is important because the goal is a check that engineers can use on real projects, not just a result for a journal. And if you're curious why a UK university studied a Spanish car park, it's because concrete acts the same way in Santander as it does in Surrey.

These equations address one major way a concrete floor can fail, but they still need to become part of everyday design practice. Steel frames, timber buildings, and floors with big openings behave differently. The next step is to see if design engineers start using this method as the new Eurocode 2 comes into effect.

What this means for you

Structural engineers design concrete frames to survive damage, and forensic engineers study failures like the one in Santander to make future buildings safer. Most structural engineers begin with a civil or structural engineering degree or a degree apprenticeship - our guide explains the difference. The maths here comes straight from A-level, so it's worth reading how a Maths A-level prepares you for engineering.

Image: Claudio Schwarz on Unsplash