Two-Year Frangible Pin Study Continues

Frangible devices must be able to sustain high-intensity hits, but still activate under a specific weight and angle to reduce the risk of rotational falls.

Photo: Taylor Pence Photography

As 2016 came to a close, so did the first half of a two-year study being conducted by the University of Kentucky’s (UK) College of Engineering in partnership with the United States Eventing Association (USEA) examining the physics behind rotational falls in the sport of eventing.

The study is led by Suzanne Weaver Smith, PhD, director of the Kentucky Space Grant Consortium and NASA EPSCoR and Donald and Gertrude Lester professor of mechanical engineering at UK, who is the dynamics and motion principal investigator. Smith’s team includes Gregorio Robles Vega, a mechanical engineering graduate student at UK, Lange Ledbetter, a senior mechanical engineering student at UK, and Shannon Wood, an equestrian and engineering physics student at Murray State University.

The study builds on previous research Smith conducted and aims to fill in the missing information regarding what happens between the fence, horse, and rider during a rotational fall. This information can be further translated into recommendations and requirements for new designs of frangible (easily broken) fences. Smith recently presented the first half of the study to the USEA Board of Governor’s to highlight the progress the team has made and what is left moving forward with the data that has been acquired.

The study is separated into three different areas of research aimed at answering three questions—how far, how fast, and in what direction—frangible fences need to react in the case of a rotational fall. This is not an easy task considering there are many gaps in the existing data due to the rarity of rotational falls.

Smith said one in 536 starters had a rotational fall in 2015, based off of data collected by the Fédération Equestre Internationale. If, on average, each rider jumps 30 cross-country obstacles per start, that translates into one rotational fall per 16,080 jump attempts.

A large part of the study revolves around understanding how the horse’s and rider’s masses and inertia affect the outcome of a fall. Even with a strong base knowledge of the current practices in place, “we still don’t understand what is going on between the horse and the fence, regardless of fence design,” Smith said.

There are only four published papers that reference horse inertia, Smith said, and only seven horses are represented (six Dutch Warmbloods and one Thoroughbred) in those studies.

Due to the lack of knowledge on horse and rider orientation, USEA and UK’s College of Engineering launched a citizen survey to obtain this information from owners and riders of event horses. So far, the survey has 74 responses and researchers are continuing to process submissions from around the world.

The second variable the team is studying is the speed and force involved with jump contact. Despite there being no data available on the contact forces that occur during a rotational fall, the team does have access to previous data from a British Eventing study measuring non-rotational fall contact on course.

Those results showed that horses made contact with fences almost 40% of the time, illustrating the complex job of the frangible pin. Frangible devices must be able to sustain high-intensity hits and still activate under the specific weight and angle requirements.

This past year, data was revisited and sorted by front leg hits and rear leg hits and the respective rail those hits struck, based on the type of jump. This gives Smith’s team an idea of the force amplitudes and angles of each specific case.

“The reason that this is relevant is because the original pins assumed that the force was straight down and that’s what they were designed to activate, but what we’ve learned through this is sometimes the force is up,” she said.

Using the videos that exist from the correct perspective, the team can better understand the contact speed of the horses upon impact and the duration and rate of angular rotation. The angles of the horses’ trunk, neck, head, and rider will also be analyzed.

As the team moves forward with the analysis it will utilize a Monte Carlo simulation, which performs risk analysis by building models of possible results. This process has been used in the past to solve complex problems that scientist have little information about. For instance, NASA utilized this method before the first moon landing to evaluate the risks associated with overturning of a lunar landing.

“From the Monte Carlo simulations, we will have a better understanding of the physics,” Smith said. “With that understanding, the builders and course designers will be able to come up with new solutions.”

There are multiple other safety initiatives in place to promote rider safety, such as leading organizations ensuring that riders are riding at the appropriate level, she added. Risk is high in eventing, and even when the circumstances are just right, horses and riders can find themselves in trouble.

“This research is focused on what happens when a rider is in trouble and what can be done to mitigate the consequences,” Smith said.

The team is still accepting survey submissions survey, mainly from eventers and especially those who have competed at the advanced level. To complete the survey, visit

Taylor Pence is a marketing and communications intern at the UK Gluck Equine Research Center, a senior marketing major at UK, and president of the UK Dressage and Eventing Team.

Want more articles like this? Sign up for the Bluegrass Equine Digest e-Newsletter.

More information on Gluck Equine Research Center and UK Ag Equine Programs.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from Learn More