A structural engineer with the U.S. Army Corps of Engineers Caribbean District recently reshaped the way engineers design concrete buildings thanks to groundbreaking research he did for his PhD in Structural Engineering at the University of Massachusetts Amherst.
Dr. Jorge A. Rivera-Cruz’s study involved testing three full-sized concrete frame structures in a lab. He simulated what happens when a key column inside a building suddenly fails; something that can lead to a dangerous chain reaction known as “progressive collapse.”
His research revealed a flaw in the current building code: even though beams had enough strength to bend or reach flexural capacity, they failed because they couldn’t handle sudden shear forces. This shortfall meant the beams couldn’t shift into a backup mode called catenary action.
How it works
Catenary action is the way a beam holds itself together at large displacement when its usual supports (like a column) suddenly fails. Normally, beams resist loads by bending (flexural action). If a column is removed (say, in an explosion or collapse), the beam starts to rotate and displace. Once it stretches far enough, it switches to catenary action, where it resists loads through tension, like a cable. This tension helps redistribute forces and can prevent a full progressive collapse. In simpler terms, imagine a clothesline between two poles. If one pole falls, the line sags but still holds the clothes—thanks to tension. That’s catenary action in action.
Why It Matters
Rivera-Cruz found that in low-seismic zones, concrete beams designed under previous standards couldn’t develop strong catenary action. They failed in shear before they could stretch enough to activate this backup mechanism. But even he was surprised by the changes made to ACI 318 based on his findings.
“We [engineers] thought the existing detailing met code requirements, but testing proved otherwise. Wider stirrup spacing led to early failure, stopping the beams from activating catenary action,” he said.
Safer Building Design in Low-Seismic Zones
The American Concrete Institute (ACI) revised its 2025 ACI 318 code based on Rivera-Cruz’s findings. This update, which guides engineers across the U.S. and internationally, now requires designers to space stirrups (steel loops that resist shear) more closely in perimeter concrete beams, even in areas with low earthquake risk. The change helps prevent shear failure and allows beams to activate catenary action and keeps buildings standing even if a column fails.
His research even suggests that critical infrastructure already built under older standards -- like hospitals, bridges, and government buildings -- could benefit from retrofitting to improve collapse resistance. Asked whether his findings could have prevented past disasters, Jorge explained, “While I can’t name specific cases, my work mirrors real collapses tied to sudden loss of support columns. Better reinforcement detailing could’ve redirected loads and prevented those failures.”
The Army Corps of Engineers is now applying enhanced structural safety measures inspired by Rivera-Cruz’s research, most notably in Caribbean District projects across Puerto Rico and the U.S. Virgin Islands.
His work has also gained widespread attention in the engineering community. He’s presented at leading industry conferences and has collaborated with government agencies rethinking their design strategies considering his findings. International organizations continue to seek his expertise to help shape future building standards and guide ongoing structural research.
With degrees in Surveying and Civil Engineering and a Professional Engineer license in Puerto Rico, Rivera-Cruz brings deep expertise and heart to his mission. He’s committed to mentoring students in STEM and advocating for equity in engineering. His story proves how full-scale testing doesn’t just change building codes; it can save lives.