Bridges are designed to provide efficient and utilitarian access from one raised bank to another across a space beneath. A short dry space should be just as simple to bridge as a short wet span. As the space beneath gets wider, however, the bridge design changes.
Required Materials
- cement
- rebar
- sand
- beams
- anchors
- nuts/bolts
- spikes
- decking
- erosion control materials
Required Tools
- level
- shovel/backhoe
- heavy hammer
- winch
- portable cement mixer
- forms
Instructions
- Placement – Your first step is assessing where you would like the bridge to go. It should be in the logical “flow” of travel and take into account the type of soil, the distance being crossed, and the condition of the space. If there happens to be a ledge on each side of the crossing, a bridge should work fine. If the soil conditions where you would like to cross are sandy or unstable, you may want to look at other options. In either case, there will be a need for a solid foundation at either side of the span.
- Foundations – There are several types of bridges. All will require a foundation at either end and possibly in the middle of the span as well. In most instances, you are likely to need permits, so ensure that you check with the proper authorities. Size and traffic type will influence the type of permit you will need. For a smaller foot bridge, you will need to dig below the frost level for a foundation. This depth is usually below four feet to keep the freeze/thaw cycle from doing harm to your structure. Pour the foundation and place rebar in it for added durability and strength. If the site offers a steeper slope, you may need forms to place the foundations properly. Depending upon the conditions, a professional may be advisable for a quicker and more complete job. At the top of the foundation, locate anchor points and place anchors.
- Placing Beams – Place a metal or wooden cross member to connect the two anchors that were placed in the cement. Notch the ends of each beam so that half of the beam covers the cross member on each side of the span. Drill and drive spikes into outer half of the beam and the cross member. Attach decking to the beams and add side walls to taste. If a longer or more complicated approach is taken, contact an engineer for specifications. In some instances, the support system and decking can be pre-built for you, guaranteeing that the measurements will be correct.
- Erosion Control – Generally, the construction of a bridge will displace soil and change drainage patterns. Regardless of the size of your project, this will be a consideration. Using an erosion control blanket along the sides of your foundation will enhance the final appearance of the bridge and will also provide assist in maintaining foundation integrity.
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