Building a bridge is an inherently risky endeavor. Some statistics show that one in three bridges will need to be repaired or replaced before the end of its intended life span. Building bridges is also an expensive undertaking, with construction costs averaging around $8 million per mile of bridge. And as any driver knows, traffic slows when crossing a bridge during rush hour, which can be inconvenient and costly to drivers while increasing the risk of accidents.
Fortunately, there are things we can do to make our bridges safer and more efficient. In addition, we can look to bridge structures developed in other parts of the world that may be effective here in the United States.
1- Use of Gabion Bases
Gabion bases are used as support for long-span bridges and are increasingly used in the United States. Gabions are made of recycled metallic wire mesh baskets filled with rocks to create a retaining wall or fence. In bridge applications, they provide stability for foundations and lower the total dead load on the supporting soil.
They serve as an aesthetic alternative to concrete walls, which can be unsightly or intrusive in some locations. Also, using gabion baskets can reduce construction time and costs by up to 40 percent. On long-span bridges, gabions eliminate mid-span compression zones, leading to cracks and bridge failure.
2- Accelerated Bridge Construction
As the name implies, accelerated bridge construction is an alternate way of building bridges that results in a shorter project schedule than standard bridgework. While the concept was developed for the United States military bases, it can also be used for other applications.
In accelerated bridge construction, the bridge’s foundation piers are formed from prefabricated units. This reduces the time required to pour concrete and set reinforcing steel while also reducing long-term maintenance costs due to fewer joints and more precise placement of reinforcement. The piers are joined together with temporary struts to build the bridge superstructure. The entire process allows bridge construction to be completed in as few months.
3- Strengthening the Columns
The columns that support a bridge are often the weakest link in the system, as they carry most of the load. Piling columns with steel can make them stronger, increasing their size and weight. This increases the cost of construction and can also affect aesthetics.
A new method for strengthening columns uses a concrete pre-compression technique that eliminates additional weight on bridges by making the column’s cross-sections smaller and lighter. Pre-compression of column sections, done before the concrete is poured, provides the strength required to carry weight without the weight penalty.
It also allows for an increase in the number of columns. The pre-compression technique is similar to a technique in shipbuilding called light-ship or ship arch construction. Here columns are built with smaller cross-sections but larger diameters than normal construction.
In conclusion, there are several ways to improve a bridge’s safety while cutting construction costs and reducing traffic delays. This will make bridges an even more attractive means of crossing a body of water.