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Progressive Collapse Mitigation: Structural Strategies to Prevent a Lethal Domino Effect

It was a typical Thursday in Newham, East London as Mrs. Ivy Hodge, a resident on the 18th floor of the 22-story Ronan Point apartment building, bustled through her usual morning routine in May of 1968. She was a tenant in a corner flat of the new building, which had opened just two months prior. She never could have anticipated the horrific sequence of events initiated by simply striking a match to light her stove. The small flame sparked a gas explosion, destroying the load-bearing precast concrete panels near the corner of the building, initiating the collapse of the floors above, and subsequently causing a chain reaction of collapse all the way to ground. While Mrs. Hodge survived, four of her neighbors were killed and 17 additional tenants were injured. The devastating accident kindled a revolution in structural engineering worldwide.

Unfortunately, the resulting improvements in structural design proved inadequate when confronted with targeted terrorist attacks. Among other disasters, the destruction of the Alfred P. Murrah Federal Building on April 19, 1995 and the horrific progressive collapse of the World Trade Center buildings on September 11, 2001 made the problem all too clear. So while building codes the world over have improved in light of such deadly structural failures, the U.S. Department of Defense (DoD) has codified even more stringent measures to reduce the potential for a progressive collapse for new and existing buildings. This Unified Facilities Criteria (UFC) – UFC 4-023-03: Design of Buildings to Resist Progressive Collapse – applies to all DoD-owned buildings of three or more stories.

Continuing our introduction to Anti-Terrorism/Force Protection, Ross Group’s Estimating Manager Scott Skidmore and Estimator Vince Adamek elaborated on the complex structural requirements laid out in UFC 4-023-03 to mitigate the potential for a progressive collapse in DoD-owned buildings.


“Let me give you an idea of just how complex UFC 4-023-03 is,” Vince said. “It is a full 245 pages long. However, we can break it down a bit for you. First and foremost, the UFC divides DoD buildings into risk categories according to the level of occupancy and building function. Based on this determination, the building must be designed and constructed according to the specified levels of resistance to progressive collapse.”

These levels of progressive collapse design employ three main strategies:

  1. Tie Forces: Prescribes a tensile force strength (the measurement of the force required to pull something until it breaks) of the floor or roof system to allow the transfer of load from the damaged portion of the structure to the undamaged portion of the structure.

  2. Alternate Path Method: Specifies strategies to ensure the building bridges across a removed element.

  3. Enhanced Local Resistance: Increases the shear and flexural strength of the perimeter columns and walls to provide additional protection by reducing the probability and extent of initial damage.

“The only risk category with no specific progressive collapse requirements is Category I,” Scott explained. “As the risk category gets higher, the requirements for design and construction increase in kind. It’s incredibly important for general contractors like Ross Group to understand these requirements for both our design-build and design-bid-build projects, as we’re ultimately responsible for constructing a safe, code-compliant building.”

Ross Group has extensive experience ensuring the intent behind UFC 4-023-03 is carried out on our projects, including both renovation and new construction.

“One memorable design-build project that applied the tie force design strategy was the renovation of two historic barracks at Fort Sam Houston, Buildings 590 and 591,” Vince mentioned, after a moment of thought. “We gutted each facility entirely, including the exterior walls. You could see straight from the front to the back once all the exterior envelope was removed.”

To mitigate a possible progressive collapse of the cast-in-place beam and column structure, Ross Group worked with our designer of record and trade partner to apply a carbon tie-force method at the perimeter of each building and within each interior. This provided adequate internal, peripheral, and vertical tie force strengths to transfer the load from a potentially damaged portion of the structure to the undamaged structure, thus avoiding additional destruction outside the initial, localized damage.

“Ross Group’s current Visiting Quarters Facility project at Little Rock AFB also includes some pretty interesting progressive collapse mitigation measures,” Scott added. “The building is huge – four stories with something like 140,000 sq. ft – and it will have around 250 units when completed. The structure is incredibly complex, but it’s more than worth it if it can prevent or minimize casualties from any catastrophic event, man-made or natural.”

Scott’s meaningful statement is even more powerful in light of the approaching 26th anniversary of the Murrah Building bombing on April 19. As the subsequent reports and UFC 4-023-03 concluded, the majority of the 168 people killed that fateful morning died because of the partial collapse of the structure, not from the initial blast.

“I’ll never forget that day,” Vince reminisced. “All of us were glued to the news as pedestrians and first responders alike rushed to the scene, absolutely horrified by the gaping hole in the side of the building. Even though progressive collapse is a relatively rare event in the U.S., you can’t help but wonder ‘Yeah, but what if it happens again?’ That’s especially true at this time of year for us Oklahomans in the construction industry.”


As the Oklahoma City National Memorial & Museum commemorates, “The best way to honor our past is by thinking forward.” To learn more about the Memorial, please visit

To learn more about progressive collapse mitigation, please visit



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