Accelerated Bridge Construction -Features, Advantages and Sequence of Construction

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Accelerated bridge construction (ABC) uses innovative planning, design, resources and techniques to accelerate the bridge construction without compromising safety. This method also focuses on bringing down traffic disruption to the maximum. This approach is applied to new projects or to replace or rehabilitate existing bridges. Over years, the bridge construction has been using the same theories without any change in the design concepts. Accelerated bridge construction design would affect the design, hence the geometry as well as the configuration of the bridge deck slabs and girders. Accelerated bridge construction is quite a new subject as it is more into art than to science. It is the construction management system of accelerated bridge construction that makes a conventional bridge construction and accelerated bridge construction differ from each other. The research on this area and its aspects are still in progress.

Drawbacks of Conventional Bridge Construction

Bridge construction or rehabilitation surely end up as a burden till its completion. Huge traffic problems, gasoline wastage and loss of labor hours are a great problem with the public and the society. These are all bought by conventional bridge construction. Maintenance of bridges to the required standards demands large funds. The bridges undergoing simple defects and damages require to shut down the highway for long, for its maintenance. Hence in the transportation system, the bridge behaves as bottle necks. The accelerated bridge construction management system brings innovative planning that brings durable bridges that perform longer compared to those constructed by conventional methods.

Need and Promotion of Accelerated Bridge Construction

It can be observed that one-fourth of nation's bridges demands rehabilitation or repair or complete replacement. This is possible only through on-site construction, that results in huge social impacts both for safety and mobility. It has been observed in many cases that the direct and the indirect cost due to detours (due to loss of bridge transportation) exceeds the cost of the bridge structure. For example, heavy traffic in large urban areas brings huge economic impact on the industrial and commercial activities of that region. So, traffic disruption must be minimized for maintaining the economy and safety. This is of higher priority in accelerated bridge construction. We can altogether summarize as:

• ABC helps in improving the constructability of the site, project duration, and safety of work zone for the public traveling.
• ABC helps in reducing the impact of huge traffic, the onsite construction time and the delays due to weather.

Accelerated Bridge Construction composes the following features for its promotion

• Design - Build engineering teams are introduced and the best is selected
• Factories are used to carry out conventional works
• Prefabrication methods are improved
• Use of long vehicles and SPMTs; for transporting components
• Cranes and equipment of high capacity are used
• Co-ordination between the stake holders and the highway agencies for design approval, in a well systematic way
• Construction management is handled by contractors and the consultants. Special contractors and product suppliers are also employed.
• Skilled labor is made available and training are provided if necessary
• Cost-benefit analysis is carried out by planning
• Construction faces modified inspection throughout its course

Distinct Structural and Material Aspects in Accelerated Bridge Construction

Certain features that are employed in accelerated bridge construction make them unique. Some of the main elements are:

• Using light weight material for transporting and erecting. This will help in reducing the overall dead loads.
• Employing Precast abutment walls are a means for quick construction and backfill. This system is not required for conventional construction system.
• Precast Pier Columns is a quick construction remedy, that is not used in conventional construction.
• High-performance concrete and high strength steel girders, facilitate in having light girder sections that are highly durable in nature. This help in reducing the life cycle costs of the material.
• Prefabricated Deck Panels is a quick construction technique that does not employ expensive formwork. This method is not employed in conventional bridge construction.
• For small and medium spans, precast prestressed girders can be employed.
• The provision for six degrees of freedoms at the girder ends can be given by using elastomeric bearing pads.
• Easy lowering of partial site assembled components of the bridge, make the construction move faster. This method is not employed in conventional bridge construction.
• Unlike conventional construction methods, the robotic feature can be used for pouring concrete into multiple joints, nuts, and bolts.
• Use of high early strength grout in joints will let the casted concrete ready for live loads
• High capacity cranes and SPMT lets transportation and erection in ABC, which is not employed in conventional construction.
• Provision of bridge lighting and signage are quickly carried out by having the proper coordination of speedy utilities.
• The prefabricated approach slabs let subgrade preparation, unlike conventional construction.

Classification of span lengths in Accelerated Bridge Construction

As discussed, the ABC method takes less time for construction. This is through bringing variation in the construction materials and the configurations. For ABC, these features vary for different span lengths of the bridge. The type of girder, whether concrete or steel; the erection method; all are based on the span length in accelerated bridge construction method. Such classification is:

1. Small Spans: This ought to have a length less than 60 feet. Based on ABC, a timber reinforced concrete, steel, and prestressed concrete girders can be suggested.
2. Medium spans: The span length greater than 60 feet and less than 120 feet can be regarded as medium spans. Girders either steel or prestressed can be preferred.
3. Long Spans: These have span length ranging from 120 feet to 300 feet. Hybrid girders, steel trusses and high-performance steel (HPS) are the best options, as per ABC.
4. Very Long Spans: These have a length from 300 to 600 feet. We make use of segmental construction and cable-stayed bridges based on ABC method.

Categories of Bridge as per Accelerated Bridge Construction

Table-1 shows categories of modern bridges as per ABC theory and span classification. When employing ABC methods, some of them tend to demand special design both in sub and superstructures. Based on the geometry; whether straight, skew or curved decks; the analysis process will vary, hence the final design. Table-1: Categories of Modern Bridges as per Accelerated Bridge Construction and Span Classification

Accelerated Bridge Construction with Multiple Structural Designs

When looking to all criterion of ABC, it possesses large variations in the structural designs. Even the conventional bridge construction take more time, they use to employ prefabricated elements and components. Hence the ABC construction method can be classified briefly as:

• Partial ABC: Here No formwork is required for the construction
• Fully ABC: Here the elements are prefabricated and are assembled partially in the factory
• Super ABC: Here the whole system components of the structures are fully assembled on site.

Accelerated Bridge Construction Sequence

The flowchart below shows the construction sequence of an accelerated bridge construction. Read More: Types of Bridges Based on Span, Materials, Structures, Functions, Utility etc. Methods of Bridge Construction Balanced Cantilever Method of Bridge Construction Planning for Bridge Construction including Sequence and Steps of Planning Types of Prefabricated Bridge Elements and Systems for Bridge Construction