On a truss bridge, the primary element of construction involves trusses. A truss is typically a structure of several connected elements that usually from the shape of a triangle. The elements, which are usually straight, can be stressed from compression or tension to support a dynamic load. It is one of the oldest construction methods for a bridge because it is simple and effective in the way it provides supports.
The key benefit of using a truss bridge to span a distance is that they are relatively lightweight, but can still be reinforced to provide strength. Many bridges of this type use small timbers or lightweight metals that are braced for tension and wind impacts. Because of the triangular design, each part of the bridge helps to support other parts, making it an effective design.
The key disadvantage of utilizing a truss bridge to span a distance is that they typically require more width than other bridges. When there is limited space for placing a bridge, a truss bridge may not be the best option since it may not fit. There are specific spatial requirements which must be met before this type of bridge could be considered.
Here are some more truss bridge pros and cons to think about as well.
More Truss Bridge Pros to Consider
1. Truss bridges can span virtually any distance.
Many truss bridges tend to be small, spanning small distances within transportation networks. The design of the truss makes it possible for this style of bridge to cover virtually any distance. As long as the necessary width of the bridge can be supported and column placements is not an issue, then a truss bridge can be installed almost anywhere.
2. It offers a superior level of strength.
The truss design of this bridge allows it to support a great deal of weight with a minimal impact on the local environment. That allows it to be useful for high population traffic areas, railroad crossings, and other spans that are necessary. A correctly designed truss bridge can support virtually any modern vehicular or transportation vehicle.
3. The road is placed on top of the span.
Most bridges are designed in a way that incorporates the road or rail supports being built into the bridge. With a truss bridge, the transportation surface is placed on top of the support structures. That makes it easier to integrate existing construction principles into the bridge while minimizing traffic delays. Modern truss bridges can even have the road sections pre-built for easy installation.
4. They are an affordable bridge design option.
Compared to other bridge types, a truss bridge requires a minimal number of materials to build it. Many of the pieces of the bridge quickly connect to one another as well, which can save on labor and engineering costs. At the same time, the amount of waste that is generated from the manufacturing and installation of a trust bridge is also reduced, adding another layer of savings for communities that need a new bridge.
5. Truss bridges are highly adaptable.
A truss bridge can be constructed under conditions that would be considered extreme by other design options. Sometimes, the truss bridge design is the only option that a span will support. It has an overall versatility that other design options cannot match, which is why it tends to be one of the first choices considered when a new bridge is required.
6. There are multiple material options available.
Most bridges today are constructed from some type of metal, usually iron or steel. A truss bridge, however, can still be constructed with wood. It can also be built with lightweight metals. Each material option offers a different weight tolerance which must be considered during the design phase. Either way, this bridge option provides several different design options so every community can complete a bridge that best suits their needs.
More Truss Bridge Cons to Consider
1. A truss bridge requires high levels of ongoing maintenance.
Truss bridges may provide high levels of support, but the additional components and connections of the bridge mean it requires high levels of maintenance as well. Every part of the bridge plays an important role in how the span functions. That means routine inspections are mandatory and repairs tend to be frequent because of the normal wear and tear the truss design tends to produce. The ongoing costs of a truss bridge can quickly eat into the installation savings that a community may experience.
2. Engineering and architectural specialists are required.
A truss bridge might seem like a simple design, but it can be quite complex. The trusses must be spaced at specific intervals to maximize the weight distribution and support features they provide. If the engineering and architectural design is not specifically followed during every step, from conception to completion, then there is a higher risk of bridge failure that will be present.
3. Truss bridges have a lower per capital weight tolerance.
The original truss bridges were designed to support early locomotives and vehicles. Although they can handle appropriate levels of traffic, there are some designs that cannot support certain modern vehicles or equipment. Drivers in a tractor-trailer or heavy vehicle must pay attention to the approved load-bearing ratings of a bridge before crossing to ensure their safety.
4. It tends to be a heavy design, even with lightweight materials.
Modern truss bridges may utilize lightweight materials, but the design tends to be somewhat heavy compared to other design options that are possible. Additional column supports are often necessary for truss bridges, even if the span is relatively short. If space is minimal and these supports are necessary to maintain the safety of the bridge, then there is a good possibility that it may not be successfully installed.
5. Truss bridges can become structurally unsound faster than other bridges.
Even with regular monitoring and maintenance, a truss bridge may experience faster wear and tear than other bridges. If that wear and tear is not addressed immediately, then the bridge tends to become unsound in a shorter time. This is especially true when a bridge design may place more pressure on certain members while having other trusses be zero-pressure members that do not provide their intended supports.
These truss bridge pros and cons show us that engineering innovations from the past can still have modern applications. If we can adapt the traditional truss design to accommodate new materials and utilize comprehensive supports, then many of the negatives of this bridge design can be limited. In return, communities can install an affordable bridge that connects them to the rest of the world.