Dent Fuse Plate

Fuse Plate Brochure

fuse plateWhile traveling throughout the United States, it came to my attention that there were many signs that had failed at the fuse plates from high winds. When this happens, the sign panel releases and the panel falls over at the bottom, thereby leaving the posts standing upright requiring a sign crew to take the complete structure down in order to repair it. This in turn costs the state more funds in labor to repair than if the complete sign was lying flat on the ground.

While visiting different sign crews in various states, it was also brought to my attention that although they use the fuse plates that are specified, they all seem to have the same failures in high winds.

There were six different types of fuse plates reviewed and all six had failed under similar conditions. In some of the older designs, there was a torque requirement on the side of the post facing the direction of traffic. A lot of time using this type of fuse plate opens the door for human error. If torqued to tightly, they don't come apart; consequently, torqued too loosely, they fall over when the first gust of wind hits it right.

Do they work? Yes in some cases if a vehicle travels down in the ditch and hits them straight on and the torque is set correctly.

Question: Are all of our impact hits straight on? Answer: No. I was informed by a sign supervisor in Dallas, Texas that 80% of their sign hits were considered to be in the side hit area. This causes their fuse plates to not release as they should and in most cases require the signpost to be replaced not to mention the huge force on the ground anchor thus causing it to bend over. These, in conjunction, in almost every case require the post to be replaced.


Upon impact conditions, there were different types of fuse plate failures. In some instances, on straight hits, the fuse plates did not release in the direction of the straight impact causing the complete post structure to rip away from the sign panel. This causes a completely different type of aerodynamics to occur. This pretty much demolishes the complete sign structure and can cause serious damage to the vehicle and injury to its occupants.

After working with a great many sign installers and maintenance personal, it became clear that the fuse plates in use today simply don't work all the time as they should. This is brought about by the degree or angle of impact. The type of fuse plates in use today are all designed for single or bi-directional hits. There are still a lot of states out on our highway system that use the design where the I-beam posts are cut only part of the way through with a torque slip plate located on the direction of traffic, thus causing the I-beam to bend and needing replacement or repair on every impact. Some states have gotten rid of the fuse plate torque requirement by changing the slip plate to the perforated fuse plate but still use the partly cut I-beam. In this case, you save on the torque maintenance cost however, the perforated fuse plate may cost a little more. Do you gain anything? Not much.

During the design process of the Dent Fuse Plate, it was necessary to test fuse plates currently used in the field from different states. One of the states tested uses a perforated plate on one side of a complete cut off I-Beam where they bolt a solid plate to the backside. This is still a single direction fuse plate

During our evaluation, the best design found was the design developed by the state of Texas that is currently used by many states today. This design uses a perforated fuse plate bolted to the front and backside of a complete cut off I-beam type post. However, this design also has problems. It does not always release on straight hits as designed, and rarely releases on side hits. This plate is designed with a plurality of holes horizontally across the center or break joint area. This perforated fuse plate has been made to its weakest condition so that it will perform on impact. In addition, because of its weak condition causes it to fail under high winds in some cases. It does save the I-beam in most cases where side hits are not experienced. Where side hits occur, replacement or repair of the I-beam become routine.

Conclusion: Throughout the years of highway signs, it is my belief the I-Beam type signposts have not changed since its conception in the use as a signpost. The post is still a strong piece of steel as it was during its use in the "direct burial" years with the addition of break joints added to make the beam fail and create safer highways for the driving public.

Throughout the years, vehicles became smaller and travel at greater speeds. For this reason, new designs will have to be created.

What I have tried to accomplish with my new design is a fuse plate that will not fail in strong winds, separate with a breakaway base system using less impact energy and separate from any direction. I also wanted a design that in most cases would work on all I-beams, use the same mounting holes to make retrofitting easier and no new state drawing requirements. By accomplishing this, it is possible for the states and federal government to have lower costs because of saved labor costs, and fewer lawsuits from vehicle accidents involving signs.

The Dent fuse Plate requires less energy to separate upon impact and in cases like the S-4 x 7.7 takes 69% less energy to work as designed. Because of the Web Design, the two sections of the I-Beam are tightened together, which reduces a lot of the vibration movement unlike the fuse plates that mount on the ends of the I-beam, while the web section is still fully cut off. This in turn makes the I-beam a lot closer to the strengths it had before it was cut. By adding a keyway down the fuse plate center, I was able to make the beam separate from side hits.

It was also my goal to design a plate that would work on our highway system but not be installed at its weakest conditions. To me this would allow a sign crew who experienced many hits on a structure to be able to add a simple hole and make the same fuse plates work at lower speeds if necessary. This was also tested and proved to be correct using the W8 x 18 Dent Fuse Plate.

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