In seismic regions, reinforced concrete flat slabs are often valued for their architectural flexibility and construction efficiency. At the same time, their behavior under strong horizontal loading has long raised questions, especially at slab–column connections where punching failure can trigger progressive collapse.
While design models and component tests provide guidance, earthquakes rarely act on isolated details. They act on entire structures, simultaneously stressing multiple connections, load paths, and deformation mechanisms.
This gap between calculation and reality was the starting point for the SlabStress research project.
A full-scale experiment, not a laboratory abstraction
The SlabStress project was financed by the European Commission and carried out at the Joint Research Centre in Italy. What made it exceptional was its scale and ambition: instead of testing individual connections, researchers constructed and tested a full-scale reinforced concrete flat-slab building.
“One of the unique aspects of this project is that it was the first full-scale test,” explains Lorenzo Bianco, Managing Director of Peikko Italy. “Typically, tests focus on single connections or very specific joints. Here, the whole structure was pushed and pulled to simulate seismic behavior.”
Two structural configurations were examined. One two-story building was constructed, one story without punching reinforcement, while the other incorporated Peikko’s PSB® Punching Reinforcement at the slab–column connections. Vertical loads were applied to the slabs, and horizontal displacements were imposed using actuators to reproduce earthquake-type actions.
Throughout the test, researchers monitored force–displacement relationships at each story and carefully recorded damage development around the columns.
Observing behavior, not just resistance
Rather than stopping at ultimate strength, the SlabStress tests focused on deformation capacity and overall robustness.
“The structure was moving horizontally while the actuators applied the loads, and the behavior was recorded throughout,” Bianco says. “What emerged clearly was how the connections behaved as part of the whole system.”
The results showed that punching reinforcement influenced more than just punching resistance. Even in cases where punching failure was not governing, the reinforced connections exhibited a more ductile response under seismic loading.
“It showed that punching reinforcement helps achieve a more ductile behavior at the slab–column connection,” Bianco notes. “This is a very important result, because ductility is what allows a structure to dissipate energy and avoid sudden failure during an earthquake.”
From local detail to global robustness
In flat-slab buildings, slab–column connections play a disproportionate role in seismic performance. If one connection fails in a brittle manner, the consequences can propagate quickly.
The SlabStress project demonstrated how local reinforcement measures can influence global structural behavior. By confining the critical zone around columns, punching reinforcement contributed to a more controlled damage pattern and improved the deformation capacity of the structure as a whole.
“In Italy, punching reinforcement is traditionally used when punching resistance is required,” Bianco explains. “But this research supports the idea that even when punching is not critical, reinforcement can improve the overall seismic behavior by confining the area around the column.”
A changing seismic landscape in Italy
The relevance of these findings extends beyond a single test program. Italy’s approach to seismic design has evolved significantly over recent decades.
“In the past, seismic areas were often identified after earthquakes had already occurred,” Bianco says. “Today, the whole country is considered seismic, with different levels of seismicity. Horizontal loads must be taken into account in every project.”
This shift places greater emphasis on predictable behavior, verified performance, and structural robustness. Full-scale testing provides evidence that complements analytical models and supports more informed design decisions.
Research as part of engineering practice
The SlabStress project brought together universities, research institutions, and industry partners from across Europe. According to Bianco, this collaboration was essential.
“Being part of this kind of research is very important,” he says. “It allows us to verify assumptions, learn from observed behavior, and contribute to the development of better design practices.”
Rather than producing abstract conclusions, the project generated data that designers can relate directly to real buildings, real displacements, and real damage mechanisms.
Why testing still matters
As seismic design continues to evolve, the SlabStress project highlights a simple but often overlooked point: calculations describe expected behavior, but testing reveals actual behavior.
Full-scale experiments are demanding in time and resources, yet they offer insights that smaller tests cannot. By observing how an entire structure responds under seismic loading, engineers gain a clearer understanding of robustness, ductility, and failure modes.
In seismic regions, that understanding can make the difference between a structure that merely meets requirements on paper and one that performs as intended when it matters most.
The experimental campaign was part of the Transnational Access activities of the SERA (Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe) project. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No.730900. The partners involved are:
- École Polytechnique Fédérale de Lausanne
- Politecnico di Milano
- European Commission
- Joint Research Centre (JRC)
- Universitatea Tehnică de Construcţii Bucureşti
- Universidade Nova de Lisboa.
Further open access papers are freely available:
- Testing of a full-scale flat slab building for gravity and lateral loads
- Deformation capacity evaluation for flat slab seismic design
- Seismic Performance of Strengthened Slab-Column Connections in a Full-Scale Test