November 11, 2014

How Much Does a Pedestrian Bridge Cost? Part III: Size

This is the third blog in our series to answer the question GatorBridge hears most often: "What is the cost of a pedestrian bridge?" Our answer has three main components: Decking, design and size of your structure. You can read our decking discussion here; and here is the blog on design

The last component of the question -- how much does a pedestrian bridge cost? -- is the bridge’s size. (Be aware that GatorBridge has a friendly, knowledgeable staff that can help you determine the most economical size combination for your project. Reach us anytime through our contact page.)

We will start with length and width considerations, and then move to other important considerations, number of sections and loading requirements.


Determining your project’s bridge length

The sub-heading may raise an eyebrow.  You may be thinking: Doesn’t the width of what the bridge is traversing – say, a creek, road, trail, or canyon – determine the length of the proposed bridge? Yes, your project environment will determine the approximate length of your bridge. However, if your project needs a bridge that spans 52.5 feet, you may be better off choosing a bridge length of 55 feet or even 60 feet to achieve the most efficient cost per-square-foot of a bridge. Only our family of talented, handsome, and sage Gator representatives can determine if this is a factor in your specific bridge project, so contact us after reading this blog. 


Determining the number of sections

Adding additional bridge supports for long spans may be a way to minimize the cost of your bridge. For many projects, however, the cost of installing additional supports is more than the savings of increasing the number of bridge sections.  

Also, shipping costs could determine whether your bridge should be fabricated in a single long section or several sections. Longer or wider bridges may need special shipping arrangements. Even if your project must have a single-span bridge with no additional supports, your bridge can be shipped in multiple sections and spliced together on site. In fact, this is the approach some of our Parks and Recreation clients use to install pedestrian or pipe support bridges in hard-to-get-to areas. These smaller sections weigh less, allowing more installation options, including the man-power option: carrying the bridge to the site or even helicopter delivery. Ask you Gator rep about splicing your bridge into multiple sections to reduce bridge cost.


Determining your project’s bridge width

Gator clients often have a small range of bridge widths which will work for their project. Narrower bridges often cost less for three reasons: 1) more efficient load support; 2) less material; 3) minimizes the risk of unintended use (like vehicular traffic).

Keep in mind that when discussing the width of a bridge, we measure inside-clear width. Meaning, if a client chooses 4 foot wide (the ADA compliant minimum width) bridge, the inside clear width will be four feet, but the actual width of the bridge will be 5 to 6 feet.

As a rule of thumb, if your bridge is 40 feet to 80 feet long, the most economical price per square foot is achieved when you choose a bridge width between 4 and 10 feet be. If your bridge is longer than 80 feet, narrower widths will help you stay within budget. 


The most important consideration: Loading

Loading is the most important criteria in a bridge project for public use. At Gator, we always caution on the side of safety. If a client does not specifically request a loading requirement, we build our bridges to the high standards of AASHTO requirements. Pedestrian bridges meeting this industry standard must be built to withstand 90 pounds per square foot (psf) loading as well as other environmental loading requirements. Be aware that some bridge suppliers quote all their bridges at only 60 psf, a third less than the structure strength of our standard.

In some cases, projects may only need 50-60 psf loading requirements, such as maintenance walkways or catwalks. We are happy to design our products to this structure strength and pass on the savings – be sure to mention your strength needs when talking to Gator staff.

Loading requirements also affect the truss style and design options for your bridge (learn more in the design blog).

If you have questions about pedestrian, vehicular or environmental loading, our in-house engineering staff would be happy to answer your questions.  


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