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Bridge construction methods
Date Uploaded:2020/3/30
Bridge construction methods

Source: wsp website

Segmental construction is one of the most important developments in construction in the last century and is a proven method for delivering durable structures that are both cost-effective and visually appealing. This construction method is used throughout the world and its versatility can be applied to most structures, including highway, rail, and even movable bridges.

Segmental construction should be considered when one or more of the following conditions exist:

  • The bridge is long and/or tall, and there is a potential for repetitive construction details.

  • Construction access is very limited and/or traffic disruptions are unacceptable.

  • Aesthetics play a significant role in the project

Segmental construction can reduce construction time, limit environmental impacts, minimize traffic disruption, improve seismic performance and reduce maintenance costs.

Precast vs Cast-in-Place

Segmental concrete construction can be implemented in two ways: using precast elements or through cast-in-place construction.

The advantages offered by precast elements are mainly related to fabrication, conducted in a plant that produces more consistency in quality products and where segments can be fabricated in parallel with early field construction activities, thus improving scheduling. The main challenges involved with precast segmental construction lie in the logistics and the setup process between the casting yard and the construction site.

Alternatively, cast-in-place construction requires that a substructure be completed prior to fabrication of the superstructure. Cast-in-place segmental construction is used when precast segments are too heavy to be shipped or access to the site is too restrictive, which can occur as spans get longer or bridges get wider.

For projects in urban areas requiring minimal lane closures, detours, and traffic interruptions, construction time is a key factor. Precast concrete segments are often optimal as they can be built and stored until needed for erection, thus reducing the on-site time of large equipment and construction activities, thus increasing the pace of construction.

The choice between precast or cast-in-place primarily depends upon project size, construction schedule, weight of segments, and site access.

Cantilever Construction

As the industry evolved, the need for a construction method requiring no falsework became obvious. The solution: a self-supporting bridge built using the cantilever construction method. When scaffolding and other temporary supports are difficult to install, this method saves all temporary work and allows bridges to be built at great heights.

The balanced cantilever construction method is used when few spans ranging from 50 to 250m exist. Bridges using this method can be either precast or cast-in-place. Once the piers are built, they are used as an erection platform for precast segments, or to support a form traveler for cast-in-place segments.

This method is easily adaptable to irregular and long span lengths, congested project sites, rough and water terrain, rail crossings, and environmentally sensitive areas.

The cantilever method is the preferred method for building cable-stayed bridges. Once segments are installed, theyre supported by new cable-stays in each erection stage. Since no auxiliary supports are required, it is both an economical and practical solution for long cable-stayed bridges.

Incremental Launching Method

The highly-mechanized Incremental Launching Method (ILM) is typically performed in a series of increments. It is used in the construction of continuous concrete bridges as well as with steel girder bridges. The ILM can also be applied to tied-arch and truss spans, if fully assembled before launching, as well as to the construction of small and medium-sized cable-stayed bridges.

Although the ILM will never qualify as the most cost-effective method for building a bridge, it offers significant other advantages when used in the proper circumstances, such as spanning inaccessible or environmentally-protected obstacles. Significant advantages of the ILM include minimal disturbance to surroundings, no falsework required, reduced area for superstructure assembly, and increased worker safety, as erection work is done from the ground.

Accelerated Bridge Construction

According to the U.S. Department of Transport, approximately 25% of the countrys bridges are in need of repair or replacement. Accelerated Bridge Construction (ABC) is ideal for congested highway networks, using innovative planning, design, material, and construction methods to reduce traffic delays, closures, and construction time.

Although ABC often requires more capital than other methods of construction, its use becomes more viable when considering the reduced impact on local businesses and the overall community.

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