Concrete Box Girder Bridge Design Example Pdf Download WORK

Concrete Box Girder Bridge Design Example Pdf Download WORK

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Concrete Box Girder Bridge Design: A Practical Guide with PDF Example

Concrete box girder bridges are one of the most common types of bridges in the world. They offer many advantages, such as high strength, durability, aesthetics, and flexibility in span lengths and widths. They are also suitable for both highway and railway applications.

But how do you design a concrete box girder bridge? What are the main factors to consider? And where can you find a reliable example to follow?

In this article, we will answer these questions and more. We will explain the basic principles of concrete box girder bridge design, the different types of segments and construction methods, and the key aspects of analysis and design. We will also provide you with a free PDF example of a concrete box girder bridge design that you can download and use for your own projects.

So, if you are interested in learning more about concrete box girder bridge design, keep reading!

What are the types of concrete box girder segments?

Concrete box girder segments can be classified into two main types: precast and cast-in-place. Precast segments are fabricated off-site and transported to the bridge location, where they are assembled and connected by post-tensioning tendons. Cast-in-place segments are formed and poured on-site using temporary formwork and scaffolding.

Precast segments have the advantages of better quality control, faster construction, and reduced traffic disruption. However, they also require more complex logistics, higher initial costs, and more precise alignment. Cast-in-place segments have the advantages of lower initial costs, simpler logistics, and more flexibility in geometry. However, they also require more on-site labor, longer construction time, and more traffic disruption.

The choice of segment type depends on various factors, such as site conditions, span length, bridge geometry, availability of materials and equipment, and environmental impacts.

What are the methods of concrete box girder construction?

Concrete box girder construction methods can be classified into three main categories: balanced cantilever method, incremental launching method, and span-by-span method. Each method has its own advantages and disadvantages, depending on the bridge characteristics and site constraints.

The balanced cantilever method involves constructing the segments symmetrically from both sides of a pier until they meet at the mid-span. This method is suitable for long spans, curved alignments, and variable cross-sections. However, it also requires high stability of the piers, complex formwork and scaffolding, and careful control of deflections and stresses.

The incremental launching method involves constructing the segments at one end of the bridge and pushing them along the longitudinal axis until they reach the other end. This method is suitable for straight or slightly curved alignments, constant cross-sections, and short to medium spans. However, it also requires high strength of the segments, special launching equipment and bearings, and large launching forces.

The span-by-span method involves constructing the segments over temporary supports between two adjacent piers and then post-tensioning them together. This method is suitable for medium to long spans, variable cross-sections, and complex geometries. However, it also requires large number of temporary supports, frequent erection and dismantling of formwork and scaffolding, and high traffic disruption.

What are the aspects of concrete box girder analysis and design?

Concrete box girder analysis and design involves several aspects, such as loading, geometry, materials, prestressing, shear, torsion, flexure, serviceability, and durability. Each aspect has its own challenges and considerations that need to be addressed in order to ensure a safe and efficient bridge design.

Loading refers to the forces and effects that act on the bridge due to its own weight, traffic, wind, temperature, earthquakes, and other factors. Loading determines the internal stresses and strains in the bridge components and affects their strength and stability. Loading also influences the choice of span length, cross-section shape, and construction method.

Geometry refers to the shape and dimensions of the bridge components, such as the span length, width, depth, curvature, skewness, and continuity. Geometry affects the aesthetics, functionality, and constructability of the bridge. Geometry also influences the distribution of stresses and deflections in the bridge components and affects their stiffness and stability.

Materials refer to the properties and characteristics of the concrete, steel, and other materials used for the bridge components. Materials affect the strength, durability, and cost of the bridge. Materials also influence the behavior of the bridge under various loading conditions and environmental factors.

Prestressing refers to the application of a permanent force to the concrete before or after it has hardened in order to improve its strength and serviceability. Prestressing can be done by using pre-tensioned or post-tensioned tendons that are embedded in or attached to the concrete. Prestressing reduces the tensile stresses and cracks in the concrete under service loads and increases its resistance to shear and torsion.

Shear refers to the force that acts perpendicular to the longitudinal axis of the bridge component. Shear can cause diagonal cracks and failures in the concrete if not properly resisted. Shear resistance can be provided by using adequate concrete web thickness, transverse reinforcement, prestressing tendons, or shear keys.

Torsion refers to the force that acts along the longitudinal axis of the bridge component and causes it to twist. Torsion can occur due to unsymmetrical loading or geometry of the bridge. Torsion can cause cracking and distortion in the concrete if not properly resisted. Torsion resistance can be provided by using adequate concrete web thickness, longitudinal reinforcement, prestressing tendons, or torsional bracing.

Flexure refers to the force that acts parallel to the longitudinal axis of the bridge component and causes it to bend. Flexure can occur due to gravity loads or temperature changes. Flexure can cause cracking and deflection in the concrete if not properly resisted. Flexure resistance can be provided by using adequate concrete flange thickness, longitudinal reinforcement, prestressing tendons, or continuity joints.

Serviceability refers to the ability of the bridge to perform its intended function without excessive cracking, deflection, vibration, or noise. Serviceability affects the comfort, safety, and appearance of the bridge. Serviceability can be ensured by using appropriate design criteria, analysis methods, materials properties, construction techniques, and maintenance practices.

Durability refers to the ability of the bridge to withstand deterioration due to environmental factors such as corrosion, abrasion, freeze-thaw cycles, alkali-silica reaction, or sulfate attack. Durability affects the lifespan and reliability of the bridge. Durability can be enhanced by using high-quality materials, adequate cover depth, proper drainage systems, protective coatings or sealants, cathodic protection systems, or repair methods.

What is an example of concrete box girder bridge design?

To illustrate the concrete box girder bridge design process, let us consider an example of a three-span continuous precast segmental box girder bridge with balanced cantilever construction method. The bridge has a total length of 300 m and a width of 12 m. The span arrangement is 75 m - 150 m - 75 m. The cross-section of the box girder is shown in Figure B.3.

Figure B.3 – Cross-section of the box girder

The design steps are as follows:

Determine the loading and load combinations. The bridge is subjected to dead load, live load, wind load, temperature load, and prestress load. The load combinations are based on the AASHTO LRFD Bridge Design Specifications.

Determine the geometry and layout of the bridge. The bridge has a constant depth of 3 m and a constant width of 12 m. The segments are 3 m long and have a constant cross-section. The tendons are arranged in two planes within the web and have a parabolic profile.

Determine the materials and properties of the bridge. The concrete has a compressive strength of 40 MPa and a modulus of elasticity of 30 GPa. The steel has a yield strength of 420 MPa and a modulus of elasticity of 200 GPa. The prestressing strands have a diameter of 15 mm and an ultimate strength of 1860 MPa.

Perform the structural analysis and design of the bridge. The analysis can be done using a software program such as midas Civil or SAP2000. The design can be done using the Courbon's method or the AASHTO LRFD method. The analysis and design should consider the different stages of construction, such as casting, prestressing, joining, and service.

Check the serviceability and durability requirements of the bridge. The serviceability requirements include the limits on cracking, deflection, vibration, and noise. The durability requirements include the protection against corrosion, abrasion, freeze-thaw cycles, alkali-silica reaction, and sulfate attack.

Prepare the drawings and specifications of the bridge. The drawings should show the dimensions, details, and reinforcement of the bridge components. The specifications should describe the materials, methods, and quality control of the bridge construction.

A PDF file containing the full example with calculations and results can be downloaded from here.

Conclusion

Concrete box girder bridges are one of the most common and versatile types of bridges in the world. They offer many benefits, such as high strength, durability, aesthetics, and flexibility in span lengths and widths. They can be designed and constructed using different types of segments and methods, depending on the site conditions and bridge requirements. However, they also pose many challenges and considerations in terms of loading, geometry, materials, prestressing, shear, torsion, flexure, serviceability, and durability. Therefore, a careful and comprehensive analysis and design process is essential to ensure a safe and efficient bridge design. In this article, we have explained the basic principles of concrete box girder bridge design and provided an example of a three-span continuous precast segmental box girder bridge with balanced cantilever construction method. We hope that this article has been informative and helpful for you. 4aad9cdaf3