11.2 Incremental launching and segmental construction
5 min read•july 30, 2024
and are game-changing techniques in bridge building. These methods allow engineers to construct bridges in challenging locations with minimal environmental impact and disruption to traffic.
Both approaches involve building bridges in sections, either by pushing from one end or assembling in place. They require and careful planning but offer speed, precision, and flexibility in bridge design and construction.
Incremental Launching Principles
Assembly and Pushing Process
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Push up | Hydraulic jacks pushing the fire truck up and stab… | Flickr View original
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River Esk Bridge Launch (3) © Andrew Tryon cc-by-sa/2.0 :: Geograph Britain and Ireland View original
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Together we stand & lift!... | Launching of Flyover bridge s… | Flickr View original
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Push up | Hydraulic jacks pushing the fire truck up and stab… | Flickr View original
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- Incremental launching assembles bridge superstructure on one side of obstacle and pushes it longitudinally into final position
- Superstructure constructed in segments on behind abutment, with each new segment cast against previous one
- Launching nose (lightweight steel structure) attached to front of bridge reduces bending moments and deflections during launching
- push bridge forward in small increments (15-25 meters at a time)
- or piers along launching path reduce span lengths and control deflections
- Bridge deck prestressed longitudinally withstands varying stress conditions during launching and final position
Monitoring and Control
- Careful monitoring of alignment, deflections, and stresses crucial throughout launching process
- Ensures structural integrity and proper positioning of bridge
- Utilizes advanced surveying equipment (total stations, laser scanners)
- Real-time data analysis allows for immediate adjustments during launching
- Strain gauges and accelerometers monitor structural behavior
- Regular inspections of bearings and temporary supports conducted
Design Considerations
- Bridge geometry must accommodate launching process (relatively straight alignment preferred)
- Cross-section design optimized for both construction and final service conditions
- Prestressing system designed to handle varying stress states during launching
- Launching nose design critical for reducing cantilever moments at leading edge
- Temporary and permanent bearings must accommodate horizontal movements during launching
- Consideration given to thermal effects and time-dependent deformations (creep, shrinkage)
Segmental Bridge Construction
Segment Fabrication and Assembly
- Segmental construction builds bridge in small sections (segments) assembled to form complete structure
- Segments precast off-site or cast-in-place (precast offers quality control and reduced on-site time)
- adds segments symmetrically on both sides of pier for equilibrium
- connects segments and provides structural strength and continuity
- Specialized equipment (, launching gantries) transports and places segments accurately
- ensures precise fit between adjacent segments
- applied at segment joints for additional bonding and waterproofing
Advantages and Applications
- Allows rapid bridge , minimizing traffic disruption and environmental impact
- Particularly advantageous for long-span bridges or viaducts in challenging terrain
- Enables construction of complex geometries (curved alignments, variable depth)
- Reduces requirements compared to traditional cast-in-place methods
- Facilitates standardization and repetition in segment production
- Well-suited for water crossings and environmentally sensitive areas
- Allows for simultaneous work at multiple locations along bridge alignment
Construction Techniques
- Span-by-span method assembles entire spans sequentially using underslung gantries
- Progressive placement technique adds segments one by one from piers towards midspan
- Precast segmental balanced cantilever construction ideal for long-span bridges
- Cast-in-place segmental construction using for site-cast segments
- Hybrid systems combining precast and cast-in-place elements for optimized construction
- Use of temporary stays or props to support cantilevers during construction
- connect cantilevers at midspan, ensuring continuity
Incremental Launching vs Segmental Construction
Construction Approach
- Incremental launching builds entire cross-section in segments and pushes forward
- Segmental construction assembles individual segments in their final position
- Launching requires casting yard and equipment at one end of bridge
- Segmental construction may utilize multiple construction fronts simultaneously
- Launching subjects bridge to varying stress conditions during construction
- Segmental methods offer more flexibility in span arrangement and bridge geometry
- Both reduce need for falsework and formwork in sensitive or difficult-to-access areas
Structural Considerations
- Incremental launching results in more uniform bridge appearance due to continuous casting
- Segmental construction may have visible joints between segments
- Launching requires careful design of temporary and permanent prestressing systems
- Segmental bridges typically have higher post-tensioning requirements
- Launching method limited to straighter alignments and more uniform span lengths
- Segmental construction allows for variable depth and curved alignments more easily
- Both methods suitable for concrete and composite steel-concrete bridges
Equipment and Resource Requirements
- Incremental launching needs specialized launching equipment (hydraulic jacks, rollers)
- Segmental construction requires segment transport and placement equipment (gantries, cranes)
- Launching method demands larger casting yard area at one end of bridge
- Segmental approach may require multiple precast yards or on-site casting facilities
- Both methods benefit from skilled workforce familiar with specialized construction techniques
- Launching often requires less formwork but more temporary supports
- Segmental construction may have higher initial equipment investment but offers more versatility
Factors Affecting Bridge Construction Selection
Site Conditions and Constraints
- Bridge length and span configuration influence choice (uniform spans favor launching)
- Site accessibility and available construction space impact decision
- Soil conditions affect foundation design and temporary support placement
- Presence of obstacles (waterways, existing structures) may limit construction options
- Climate and weather patterns influence construction schedule and method suitability
- Seismic considerations may favor one method over another
Project Requirements and Objectives
- Desired construction speed and project timeline influence method selection
- Environmental considerations (minimizing impact on ecosystems) affect choice
- Bridge's horizontal and vertical alignment complexity may limit incremental launching
- Aesthetic requirements and desired bridge appearance factor into decision
- Future maintenance and inspection needs considered in construction method selection
- Project budget and financing structure impact feasibility of different methods
Technical and Economic Factors
- Structural system and materials (concrete, steel, composite) influence method compatibility
- Economic factors (equipment availability, labor costs, material transportation) impact selection
- Local expertise and contractor experience with specific techniques guide decision-making
- Availability of specialized equipment and materials in project location
- Long-term durability and performance expectations affect choice
- Potential for standardization and prefabrication opportunities considered
- Risk assessment and mitigation strategies for different construction methods evaluated
Key Terms to Review (28)
AASHTO LRFD: AASHTO LRFD stands for the American Association of State Highway and Transportation Officials Load and Resistance Factor Design. It is a design methodology that incorporates reliability-based principles into the structural design of bridges, ensuring safety and performance by applying factors to loads and resistances based on their statistical characteristics. This method connects directly to various aspects of bridge engineering, including design, analysis, and evaluation processes.
Arch bridge: An arch bridge is a type of bridge that uses an arch-shaped structure to support the load, relying on the natural strength of the arch to distribute weight. This design not only provides great aesthetic appeal but also offers structural efficiency and stability, making it a common choice in bridge classification. Arch bridges can vary in materials, spans, and construction techniques, influencing their application in different settings.
Assembly: In the context of bridge engineering, assembly refers to the process of putting together various structural components to form a complete bridge. This includes the connection and integration of prefabricated parts, ensuring that they fit together accurately and safely. The assembly stage is crucial in both incremental launching and segmental construction methods, as it dictates the overall integrity and performance of the bridge structure.
Balanced cantilever method: The balanced cantilever method is a construction technique used for building bridges, where segments of the bridge are constructed outwards from a central support or pier in a balanced manner. This approach ensures that the forces and moments acting on the structure are evenly distributed, allowing for efficient load management and structural integrity during construction. It is particularly advantageous for long-span bridges, as it reduces the need for temporary supports and minimizes disruption to the area below.
Cantilever Bridge: A cantilever bridge is a type of bridge that is supported on one end and extends horizontally, using a structure that projects into space, often with the other end anchored to a support or counterweight. This design allows for longer spans without the need for intermediate supports, making it ideal for crossing wide obstacles. The unique load distribution in cantilever bridges influences various aspects of their design and construction process.
Casting yard: A casting yard is a designated area where concrete components for bridges and other structures are fabricated using specialized molds and casting techniques. This space is critical for ensuring that segments are produced under controlled conditions, which leads to improved quality and consistency. The casting yard facilitates the efficient assembly of components used in construction methods like incremental launching and segmental construction.
Closure Pours: Closure pours refer to the final concrete placement that fills the gap between segments of a bridge structure, ensuring a seamless connection between them. This process is crucial in both incremental launching and segmental construction techniques, as it helps to create a continuous structural element that enhances the overall integrity and load distribution of the bridge. Proper execution of closure pours is vital to prevent issues like cracking or weak points in the structure.
Deflection Analysis: Deflection analysis refers to the study of the deformations and displacements that a structure experiences under load. This is particularly important in bridge engineering, where ensuring that deflections remain within allowable limits is crucial for both structural integrity and user safety. In the context of construction methods like incremental launching and segmental construction, understanding deflection is essential for maintaining proper alignment and performance throughout the building process.
Epoxy: Epoxy is a type of thermosetting polymer that is created through the reaction of an epoxide resin with a hardener. This unique combination provides excellent adhesive properties, chemical resistance, and durability, making it a popular choice in construction and engineering applications. Epoxy is commonly used in the bonding of structural elements and for creating protective coatings, which is especially important in techniques like incremental launching and segmental construction where strong connections are crucial.
Erection: In the context of construction, erection refers to the process of assembling and positioning structural elements to form a completed structure, such as a bridge. This term is crucial as it involves not only the physical act of putting together various components but also ensures that they are accurately aligned and secured for stability and safety. Proper erection techniques are essential for maintaining structural integrity during construction and achieving desired design specifications.
Eurocode: Eurocode refers to a set of European standards for the structural design of buildings and civil engineering works, providing a common approach to the design and assessment of structures across Europe. It establishes guidelines that ensure safety, serviceability, and durability while facilitating harmonized design processes and practices.
Form travelers: Form travelers are specialized construction devices used in bridge engineering to support and shape the concrete during the construction of bridge decks or segments. These travelers are movable forms that can be adjusted to different spans and configurations, allowing for efficient incremental launching and segmental construction techniques. By providing the necessary support for the concrete until it gains sufficient strength, form travelers facilitate the creation of complex bridge geometries while optimizing the construction process.
Formwork: Formwork refers to the temporary or permanent molds used to shape and support concrete during its curing process. It plays a critical role in the construction of structures, ensuring that the concrete maintains its intended shape and strength until it hardens. The use of formwork is essential in various construction methods, including those that involve placing concrete on-site or in a factory setting.
Hydraulic jacks: Hydraulic jacks are mechanical devices that utilize hydraulic force to lift heavy loads or apply force. They operate on the principle of Pascal's Law, which states that when pressure is applied to a confined fluid, it is transmitted undiminished throughout the fluid. This capability makes hydraulic jacks particularly useful in construction techniques like incremental launching and segmental construction, where they provide precise lifting and positioning of bridge segments.
Incremental launching: Incremental launching is a construction technique used to erect bridges by gradually pushing segments into place from a support point, typically on one end of the structure. This method allows for efficient and cost-effective construction, particularly for long-span structures, as it minimizes the need for scaffolding and heavy equipment on-site. By utilizing this technique, engineers can also enhance safety and reduce disruptions to the surrounding area during construction.
Launching gantry: A launching gantry is a specialized construction equipment used to erect bridge segments by lifting and moving them into place during the incremental launching and segmental construction processes. This device provides the necessary support and control to transport heavy concrete segments from a staging area to their final positions on the bridge structure. By utilizing a launching gantry, construction efficiency is improved, and the risk of structural damage is minimized during the assembly of large spans.
Load Distribution: Load distribution refers to the way in which loads are spread across a structure, impacting how forces are transferred throughout its components. Understanding load distribution is essential for assessing structural integrity and ensuring that all parts of a bridge can handle applied loads effectively, which is critical across various bridge designs and types.
Load Testing: Load testing is the process of evaluating the performance of a structure under specific loads to ensure it can withstand expected stresses without failure. This assessment is critical for ensuring safety and durability, especially in engineering fields. By simulating real-world conditions, engineers can identify potential weaknesses and improve design efficiency, which is vital for structures like arch bridges and during construction methods like incremental launching and segmental construction.
Match-casting: Match-casting is a construction technique that involves creating identical precast concrete segments that fit together seamlessly during assembly. This method is commonly used in the construction of bridges, allowing for precision in alignment and connection of components, which enhances overall structural integrity and reduces construction time.
Post-tensioning: Post-tensioning is a method used in construction where high-strength steel tendons are tensioned after concrete has been cast, providing additional strength and allowing for longer spans and thinner structures. This technique is essential in enhancing the performance of concrete beams and slabs, allowing them to withstand greater loads and reducing the risk of cracking and deformation.
Precast concrete: Precast concrete refers to a construction product produced by casting concrete in a reusable mold or form, which is then cured in a controlled environment and transported to the construction site. This method allows for high-quality control and precision in the fabrication of concrete elements, making it a popular choice in various construction techniques, particularly in segmental construction and incremental launching methods.
Segment lifters: Segment lifters are specialized construction equipment used to handle and position precast concrete segments during the assembly of segmental bridges. These devices play a crucial role in both incremental launching and segmental construction processes, ensuring that the segments are accurately placed and securely fastened. By providing the necessary lifting capability, segment lifters facilitate efficient construction while maintaining safety and structural integrity.
Segmental construction: Segmental construction is a method used in bridge engineering where a structure is built in distinct segments or sections that are joined together to form the complete bridge. This technique is particularly advantageous because it allows for the construction of longer spans and can reduce the overall weight of the bridge while maintaining structural integrity. Additionally, segmental construction often allows for more efficient use of materials and can facilitate easier transportation and assembly at the site.
Site Safety: Site safety refers to the measures and practices implemented to ensure the well-being of workers and the public during construction activities. It encompasses protocols, training, and equipment used to prevent accidents and injuries, especially in complex operations like incremental launching and segmental construction, where heavy materials and equipment are involved. Maintaining site safety is crucial to minimize risks associated with construction hazards and ensure compliance with regulations.
Specialized equipment: Specialized equipment refers to tools and machinery that are specifically designed for particular tasks or functions within a construction project. In the context of construction techniques like incremental launching and segmental construction, this equipment is critical for enhancing efficiency, safety, and precision in the building process. Utilizing the right specialized equipment allows engineers to manage complex operations while minimizing risks and ensuring high-quality outcomes.
Stress Analysis: Stress analysis is the process of determining the internal forces and moments within materials and structures when subjected to external loads. It helps engineers understand how structures respond to various stresses, enabling them to ensure safety, functionality, and durability in design. This technique is crucial in evaluating the performance of different construction methods, including the incremental launching and segmental construction of bridges, where understanding how components react under load is essential for successful implementation.
Structural Stability: Structural stability refers to the ability of a structure to maintain its equilibrium and resist deformation or collapse under applied loads and environmental conditions. This concept is crucial during the construction phase, where temporary supports and load conditions can affect the overall integrity of a structure being built, especially when using methods like incremental launching and segmental construction.
Temporary supports: Temporary supports are structural elements used during construction to hold up a structure until it can support itself. These supports are essential in processes like incremental launching and segmental construction, as they provide stability and safety while different components of the structure are being assembled or launched into place.