When designing trails within parks or green spaces, rivers and creeks become an issue. How do you cross them? A small babbling brook might be able to be jumped across or crossed by hopping between a few rocks to continue along the natural footpath. This style of water crossing is not that accessible, nor are these natural forest footpaths. Trying to walk across this type of water crossing can be hard for a person with limited mobility, an issue of our increasingly aging population. The next option is much more expensive, a bridge must be installed to cross a little creek to a larger river.
The main materials for a bridge are wood, metal, and concrete. Each of these materials has its own design consideration; cost, longevity, maintenance, accessibility, access to the build site, just to name a few.
In 2012-2013, I was tasked with reviewing bridge repairs suggested from the structural engineer’s bridge reports. I noticed that some of the oldest bridges (around 100 years old), required less work than some of the bridges 90 years younger. Were these 10 to 15-year-old bridges designed to fail? I’m not sure but I offer these few tips to help ensure the longevity of your assets.
The first thing to know about rust on bridges is a bridge is like a very big, low voltage battery or electrical circuit. My landscape architect’s very basic understanding, as taught from an electrical engineer tasked with protecting gas lines:
One of the more common bridge types I was reviewing was made from weathering steel (Core-ten). These young weathering steel bridges (10 to 15 years old) had few structural failures and required replacement. The following Design and Maintenance tips are based on my observations and research on weathering steel (a product that was originally designed for train boxcars for use in hot and dry South-Western USA)
If the above recommendations cannot be maintained, it might be a better idea to use another material, such as wood or concrete if you don’t want to replace your bridge very 10 to 15 years at over $10,000 for a small 6-meter long bridge. In future blogs, we will look at other materials and design considerations.
If you need help designing your trails, locating your water crossings and types, creating tenders for bridge replacement or help to create maintenance procedures, please give us a call or email, we would be happy to help.
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