There are a number of techniques used in the construction of bridges. These methods include Incremental launch, Mechanized bridge construction, and cast-in-place construction. Each has its own advantages and disadvantages. To understand how these techniques are used, it is helpful to know a bit about the different types of bridges.
Mechanized bridge construction
Mechanized bridge construction is a process that involves the use of large machinery. Large machinery has several advantages, including higher speed and efficiency. However, it is limited by the landscape and landform of a site. For instance, the width of a river or ravine can make the operation of such a large machinery impossible. The short-distance mechanical bridges are usually made of steel plate structures and long-span mechanical bridges are made of traditional truss structures. These bridges tend to have large weight per unit length, which requires high transport and erecting facilities.
Mechanized construction also requires a skilled workforce and a strong technical culture. The lack of technical talent can lead to poor quality and safety of work. Additionally, long subcontracting chains and human error can make it difficult to diagnose and resolve problems on-site. Many bridge construction accidents are caused by human error, which leads to a great deal of risk. Moreover, a lack of proper planning and training can lead to fatalities.
Mechanized bridge construction combines elements of traditional construction and new technologies. It is a process that is becoming the norm in bridge construction. In this e-manual, you’ll learn about the principles, methods, and equipment used to build a bridge. It also covers the different types of mechanized bridge construction machines and their impacts on the design and construction of a bridge.
Cast-in-place
Cast-in-place bridge construction involves pouring the concrete on site, rather than off-site. This type of bridge construction is often preferred when speed of construction is a priority. However, precast bridges require a higher level of expertise and can be more expensive than a cast-in-place solution. When speed isn’t as important, cast-in-place construction is justified because of the lower overall cost.
This method of bridge construction begins with the hammerhead unit, a 4-12m-long unit that is cast on temporary props, which act as temporary supports for the balanced cantilever. When the two cantilevers meet at midspan, the stitch unit is poured. This process may require additional falsework to hold the ends of each cantilever stable while the pouring occurs.
Another advantage of using this technique is that the components can be fabricated at the manufacturing facility, avoiding the need for temporary pour forms on-site. The process of connecting precast concrete columns and beams is fast and convenient, but it poses challenges in earthquake zones where reversals of large inelastic moments are likely to occur. However, this problem has been addressed in previous research, with the development of Large-Bar, Large Duct (LBLD) connections and “Socket” connections.
Despite these drawbacks, the cast-in-place method is still one of the most efficient types of bridge construction. Research conducted at the National University Transportation Center and the Missouri S&T School of Engineering has shown that it is more than 20 times faster than conventional construction methods.
Incremental launch
The incremental launch method is used to build bridges that span less than 60 meters. It is a complex process, which requires a high level of technology and detailed structural design. Moreover, it has two distinct stages, which involve the creation of two separate groups of pre-stress. It also requires careful modeling of temporary works and is not recommended for bridges with very high spans.
The incremental launch process requires that the segments be designed according to their group numbers. This will help the CSM to control the launching process. This process also requires the use of materials with low friction properties. Furthermore, the support spring stiffness must be matched to the final product. As part of the incremental launching process, the spring stiffness of the bridge needs to be adjusted.
The incremental launching sequence can be set by using the “Construction Stage Manager” command in SOFiSTiK. This command also allows you to set the direction and orientation of displacements. You can also choose the group number in which each span should be activated. This can help save time.
In 1965, the incremental launching method was used to build a PC bridge over the River Inn in Kufstein, Germany. This bridge was the first to be constructed using the incremental launching method. This method was later extended to other bridge types. During this construction process, the deck of the bridge was segmentally cast behind the abutment. Then, the segment was pushed forward until it cleared the casting cell. This process was repeated until the deck was complete. In addition to this, the bridge was also constructed with multiple temporary piers, avoiding the need for launch prestressing. After the deck was completed, the parabolic prestressing was applied.
Precast segments
Segmental bridge construction involves building a bridge in short sections, one at a time. This differs from the traditional method, which involves building a bridge in large sections. The segments of a segmental bridge are made of concrete, either precast or cast in place. They are lightweight, and can be used to span long distances.
Precast segments are constructed using a modular design, allowing them to be erected quickly, without the need for special lifting equipment. The segments are cast one span at a time, and are then transported to the erection site via a crane or traveler. Once delivered to the site, precast segments are assembled according to the proper erection techniques, using high machinery. They are then filled with epoxy glue, which provides the final strength of the bridge.
The main constraints of crane erection of precast segments include access, inaccessible terrain, and logistics. During the construction process, the erection process may require several weeks instead of hours. For a 120-meter span, a single segment can be up to 1.3 times longer than the total span. This method is suitable for smaller bridges with a few hundred meters of span, but may be too expensive for large structures.
Several challenges have prompted researchers to develop an innovative approach in bridge construction using precast segments. The new approach was initially tested in a pilot project in Austria. The prototype construction proved that the concept of casting lightweight segments directly on the construction site is feasible and can reduce the amount of falsework, formwork, and reinforcement. However, there are drawbacks to completely prefabricated segments, including the heavy weight and the problems associated with transportation and lifting them.
Double-decked bridges
A double-decked bridge is constructed with two separate levels for traffic and pedestrians. The upper level can accommodate pedestrian traffic and the lower level can accommodate vehicle and animal traffic. A double-decked bridge would be a perfect solution for Leonardo’s town planning needs.
The design of a double-decked bridge is similar to that of a conventional suspension bridge, except that there are two layers of decking. Both layers are constructed with truss-type steel. The structure consists of two separate forces – compression and tension – and is supported by main towers.
The weight of the bridge and its load are important considerations in construction. A double-decked bridge can support a lot of weight. But if there are two levels of bridges, the weight of the loads on both levels can be too much. This may lead to collapse. Fortunately, there are modern materials that help reduce the maintenance costs and increase the lifespan of a bridge.
The Brooklyn Bridge was a prime example of a double-decked structure. To repair the bridge, workers would need to remove the upper deck of the bridge. This would allow them to access the working site while repairing the existing deck. This would save 40 million pounds on the overall project and would also be safer for workers.
Cable-stayed bridges
Cable-stayed bridges are a type of suspension bridge. They are generally 100 to 1100 metres long and are a common choice for pedestrian and highway bridges. They are constructed of steel and concrete and can be constructed individually or as a composite. Cable-stayed bridges can be joined together to form multi-span structures, as seen at Lake Maracaibo in Venezuela and Millau, France.
These structures are also very economical to build. In fact, they cost approximately 30% less than other types of bridges. They also cost less to maintain than older designs. Another benefit of cable-stayed bridges is their ability to span a large distance. The Jiaxing-Shaoxing Sea Bridge is an example of a cable-stayed bridge.
Unlike cantilever bridges, cable-stayed bridges do not require two towers or anchorages. The cables, which run from the roadway up to a single tower, carry the weight of the bridge’s deck. This type of suspension bridge can be difficult to implement, especially in poor ground conditions.
Cable-stayed bridges are considered the backbone of infrastructure networks. Their reduced weight and increased seismic resistance enable them to minimize the seismic risk associated with them. In fact, they are the preferred choice for seismic mitigation.
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