Although a cable-stayed bridge may look like a suspension bridge at first glance, it carries the load of the roadway in a different way. While the cables of a suspension bridge carry its load, the pillars carry the load in a cable-stayed bridge. The cables are merely a redirection of that load bearing. Here is how to build a cable-stayed bridge.
Design and Placement
Study the area. You may need to do a traffic study to determine the best place to build your bridge. In most cases you will be crossing a wide area such as a large river or small bay. Bore holes to determine the makeup of the soil under the waterway.
Determine the materials you will use for construction. Steel cables and pillars with poured concrete bases are most commonly used.
Obtain survey data and draw construction drawings of the bridge. This will require a team of drafters, designers and structural engineers. The structural engineer will need to stamp the drawings to be approved by your local governing body.
Estimation and Bidding
Estimate the cost of the bridge building project. Obtain a copy of the construction drawings from the designing engineer and determine how much each item will cost in labor as well as materials.
Complete your itemized bid to build the bridge. Make sure you take into account all specifications and details, including typical section details and utility restoration.
Submit your bid to your governing authority. Most of the time, these are closed bids and the lowest bidder with the most complete itemization will win the bid.
Building a bridge is a long, complicated and dangerous process. A building company experienced in the bridge building process should do this type of work.
Build the concrete forms for the pillars. These are placed in the waterway, connected and sealed to make a watertight form. Pump out the water and excavate to a solid base.
Pour the pillars and place anchor-bolts or other steel connectors into the concrete. This is where the tall steel poles will be placed.
Set your pre-cast towers on your concrete base and secure by the method detailed by the engineer. This will require a large crane and some other heavy construction equipment.
Thread cables through the pillars according to the engineer's specifications. Attach these to the decking as each bridge section is built, cantilever style. Many cable-stayed bridge designs allow for an adjustment to the tension on the cables, so one section is not supporting more weight than its neighboring cables, thereby weakening that cable and possibly causing catastrophic failure.
Prepare the terminal ends of the bridge. In building a cable-stayed bridge, the terminal ends are where the roadway meets the land. These ends are where the greatest tension on the cables are and don't need as much reinforcement as a beam bridge, for example. In fact, depending on the stresses, you might be "pulling down" the roadway, instead of "holding it up."
Pave the decking and enjoy your new cable-stayed bridge.
- Greenwood Photography: Flickr.com