Span by Span Erection of Precast Segmental Bridges: A Comprehensive Guide

Precast segmental bridges have become increasingly popular due to their numerous advantages, including faster construction times, reduced labor costs, and improved quality control. Span by span erection is a specialized technique used to construct these bridges, offering further benefits in terms of efficiency and safety.

Span-by-Span Erection of Precast Segmental Bridges: Introduction

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Advantages of Span by Span Erection

• Reduced Construction Time: By constructing the bridge segment by segment, the overall construction time can be significantly reduced compared to traditional methods.
• Enhanced Safety: The controlled and sequential nature of span by span erection minimizes risks to workers and the public.
• Improved Quality Control: Each segment is precast in a controlled environment, ensuring high-quality construction and consistent results.
• Reduced Labor Costs: The use of precast segments eliminates the need for extensive formwork and on-site casting, resulting in lower labor requirements.

Erection Techniques

There are two main span by span erection techniques:

1. Cantilever Erection: In this method, each segment is cantilevered from the previously erected segment, gradually extending the bridge span.
2. Balanced Cantilever Erection: Two cantilevers are erected simultaneously from opposite sides of the bridge, meeting in the middle to form a continuous span.

Cantilever Erection

Cantilever erection is particularly suitable for bridges with short to medium spans. The process involves:

1. Erecting the first segment on the pier or abutment.
2. Prestressing the first segment.
3. Erecting the next segment on top of the first, ensuring proper alignment.
4. Prestressing the second segment, connecting it to the first.
5. Repeating steps 3-4 until the desired span is reached.

Balanced Cantilever Erection

Balanced cantilever erection is ideal for bridges with longer spans. The process involves:

1. Erecting the first segments on both sides of the bridge.
2. Prestressing the first segments on both sides.
3. Erecting additional segments on both sides, prestressing each segment as it is erected.
4. Gradually extending the cantilevers towards the center until they meet.
5. Connecting the cantilevers using a closure segment or a temporary support.

Design Considerations

Span by span erection requires careful design considerations, including:

• Segment Geometry: The shape and dimensions of the segments must ensure stability during erection and provide the desired structural performance.
• Prestressing System: The prestressing system must be designed to control deflections, minimize cracking, and ensure the integrity of the bridge.
• Erection Sequence: The erection sequence must be carefully planned to minimize stresses and ensure the stability of the structure at all stages of erection.

Construction Equipment

Specialized construction equipment is required for span by span erection, including:

• Erection Cranes: High-capacity cranes are used to lift and position the precast segments.
• Segment Transporters: Vehicles specifically designed to transport the precast segments from the casting yard to the erection site.
• Prestressing Equipment: Hydraulic jacks and other equipment are used to apply the prestressing force to the segments.

Case Studies

Numerous successful precast segmental bridges have been constructed using span by span erection techniques. Here are some notable examples:

• Sunshine Skyway Bridge, Florida: A 4-mile-long cable-stayed bridge built using the balanced cantilever method.
• Jiaozhou Bay Bridge, China: The world's longest bridge over water, constructed using the cantilever erection method.
• Viaduc de Millau, France: The world's tallest bridge, featuring a cable-stayed main span erected using the balanced cantilever method.

Span by span erection of precast segmental bridges is a highly efficient and effective construction method that continues to gain popularity worldwide. By leveraging the advantages of prefabrication and sequential erection, engineers and contractors can achieve faster construction times, enhanced safety, improved quality, and reduced costs. This comprehensive guide provides a thorough understanding of the techniques, design considerations, and equipment used in span by span erection, empowering professionals to optimize their bridge projects.

Span-by-Span Erection of Precast Segmental Bridges: Introduction

5 out of 5

Language	:	English
File size	:	7403 KB
Text-to-Speech	:	Enabled
Enhanced typesetting	:	Enabled
Print length	:	24 pages
Screen Reader	:	Supported

FREE