Several years ago, I made the decision to move to the South-Eastern United States. The house I lived in was very old, and the only way to access it was to cross a 30 year old foot bridge over a small creek. Though the creek was small, it had the potential to rise up above the bridge, washing it downstream at least three times. On a tight budget, I would generally just hunt it down and drag it back to its former location. In addition to the burden of flash floods, it was also dangerous, with several weak spots and no handrail. It was basically two extremely old logs with planks nailed across it. In addition to the number of times that I’ve watched this relic float away, I can only assume there were several other occasions in which this occurred. Evidence that lead me to this conclusion was that there was a chain connected from the bridge to a nearby tree. Obviously this was intended to prevent it from washing too far downstream in event the waters would rise. Note that despite my research, this was my first time building a bridge. For this reason, you may wish to contribute your own ideas to this project based on your personal experience and building location. Once the project began, I had it completed over a weekend.
One day, the waters would rise yet again, but this time the bridge was found in pieces beyond repair. It’s obvious that the bridge had was long overdue for replacing, but I did not get around to this until I decided to put a new home right next to the old one. Even before it washed away, I had planned putting another bridge closer to my new home. I procrastinated for several months until the old bridge finally washed away, which encouraged me to begin plans on a replacement.
Several factors came into play as to why the old bridge didn’t last. But instead of dwelling on the fact that I now had no way to cross the creek, I decided to learn from the faults of the previous bridge’s design. Note that I did not build the original foot bridge, I am not completely clear on who did.
I decided that if I’m going to invest the time and money in building a new foot bridge, then it needed to have the following features:
- Strong, durable and built to last.
- It would have to be above the water line, to prevent water damage.
- The bridge would have to be secured to the ground in event waters from a flash flood should happen to hit it.
- Safe for my family to cross.
- Within the budget of about $500.
- Built from locally accessible materials.
I started out doing research. I needed the bridge to not only support the weight of people, but any items they may be carrying across with them. Many of the designs that I came across were arched bridges, but these looked not only expensive to build, but I also had no idea on how to do it, especially since I had to build this thing all by myself. I found some very useful designs that were used by the United States Forest Service.
Based on these designs, I started out by using a program called 3D Max, which is a software used for creating computer models. In doing this, I was able to create a visual aid to give me an idea of what I wanted my bridge to look like. I did stray a bit from the actual design at times for one reason or another, but this is to be expected on a first time project.
In addition to structure and stability, I also had to think about the weather. I knew that Pressure treated lumber would need to be used, but what I didn’t consider until just a couple days before starting the project, was that it wouldn’t take long for the hardware used to hold the thing together, would eventually start to rust. After an evening of internet research, and a trip to the local hardware, I learned that Galvanize would stand up to the weather, though it would raise the cost of the project by about $100.
In regards to the actual design, the bridge needed to be 24 foot long. Note that the previous one wasn’t near this long, but it was also located at a low point where the water could easily reach it. Since I wanted the bridge to be closer to my new home, and high above the water, the spot I picked out happened to be a much longer crossing point. This was of course a small problem, the local lumber store’s max length on lumber was 16 foot. After a little more research, and with the help of my 3D software, I decided to butt two 12-foot pieces of lumber together in order to make the distance. Reasons I stayed away from the 16-foot boards was due to the fact that there were problems getting the lumber from the store to the site. This called for more galvanize bolts of course, which were not cheap compared to the other alternatives. Nevertheless, it had to be done.
Here’s the list of Materials that I needed to begin this project. Keep in mind that I no longer have my initial list so this is off the top of my head. You may need to make adjustments here and there for your own personal design.
6 2x10x12 Pressure Treated Lumber (Runners)
6 2x4x12 Pressure Treated Lumber (Rails)
2 2x8x12 Pressure Treated Lumber (Cross Braces)
4 1x6x12 Decking (Treated)
1 4x6x12 Post (Foundation)
4 4x4x8 Posts (Rails)
1 Box Galvanize Screws
16 8 x 3/4 Galvanize bolts
16 3/4 Galvanize nuts
32 3/4 Galvanize washers
1 Bag quick setting concrete
16 8 x 3/8 Galvanize bolts
16 3/8 Galvanize nuts
32 3/8 Galvanize washers
Time to Build
Since I was building this thing myself without any heavy machines (a crane would have been nice), I decided to begin next to the spot I would place it, but on the ground as oppose to working in the water. I began building the frame by screwing together the runners and braces. Note that I joined the runners using two 6 foot long 2×10’s on each side, so that the center of the rails were sandwiched between with a 3 foot span on both sides. I then secured with galvanized screws while I drilled the holes for the 4 3/4 bolts that would be used on each runner. There are alternative methods of butting the two boards together if you wish to do so.
Once the frame was completed, using nothing more than my hands, feet and a set of rubber boots, I dragged the frame over the creek, and positioned it where I wanted the bridge to cross. Next, I got my post hole diggers and dug out holes going down about 2 feet into the ground on the inner rails (2×10’s). I cut the 4×16 posts so that they’d go into the ground, but rise up flush with the top of the runners. After this, I mixed the concrete and poured around the 4×6 posts, and installed rebar for added security. This was my insurance policy to prevent the bridge from washing away in event the water should happen to get that high. Next, using the 3/4 bolts, nuts and washers, bolt (or you can use lag bolts) the runners to the posts with 2 bolts per runner on each end.
Once the bridge is secure where you want it, you can begin nailing or screwing down the deck boards. I spaced mine about ½ apart and spanned 3 foot, which was the width of the bridge. The decking was flush with the sides of the runners from end to end. Looking back at the images, I believe I anchored after this step but wish I hadn’t of. I left off the deck boards (Screws anyway) where I needed access for bolting on the 4×4 posts to support the 2×4 rails. I then went back and screwed those deck boards down like the others.
At this point, you can attach the 4×4 posts using the 3/8 bolts, nuts and washers. Following this, you can attach the 2×4 railing. I got tired towards the end, so got sloppy at this point.
If I was to go back and do this again, I’d make a few changes, such as zig-zagging the center bolts that butt the runners together. I may have also used 2×12’s in place of the ten inch boards just to make it a little sturdier, though it seems to do okay. There is a little bit of wobble, which may lead me to anchoring a couple posts towards the center at an angle. Then again the wood has probably cured out a bit, so shrinking may involve my going back and tightening the bolts up some more. This alone may solve this small problem.
Nevertheless, my family and guests feel comfortable crossing this foot bridge, and the rails are built at a height to prevent both short and tall from falling into the creek. There have also been a couple times the water came up, it never reaches the bridge, those it did once reach where it is anchored into the ground. Of course because of the concrete and rebar, it failed to move so much as an inch. I also have yet to see any rust on any of the hardware.
Overall, I’m satisfied with the results of this project. It’s a strong, sturdy and safe foot bridge that I hope will last for years to come. I hope this article has helped you in designing a bridge to suit your own individual needs.