Steel–Concrete Composite Box Girder Bridges Introduction Typical Sections General Design Principles Flexural Resistance Shear Resistance Stiffeners, Bracings, and Diaphragms Stiffeners • Top Lateral Bracings • Internal Diaphragms and Cross Frames Yusuf Saleh California Department of Transportation Lian Duan California Department of Transportation Other Considerations Fatigue and Fracture • Torsion • Constructability • Serviceability Design Example Introduction Box girders are used extensively in the construction of urban highway, horizontally curved, and long-span bridges. Box girders have higher flexural capacity and torsional rigidity, and the closed shape reduces the exposed surface, making them less susceptible to corrosion | Saleh Y. Duan L. Conceptual Bridge Design. Bridge Engineering Handbook. Ed. Wai-Fah Chen and Lian Duan Boca Raton CRC Press 2000 13 Steel-Concrete Composite Box Girder Bridges Introduction Yusuf Saleh California Department of Transportation Lian Duan California Department of Transportation Typical Sections General Design Principles Flexural Resistance Shear Resistance Stiffeners Bracings and Diaphragms Stiffeners Top Lateral Bracings Internal Diaphragms and Cross Frames Other Considerations Fatigue and Fracture Torsion Constructability Serviceability Design Example Introduction Box girders are used extensively in the construction of urban highway horizontally curved and long-span bridges. Box girders have higher flexural capacity and torsional rigidity and the closed shape reduces the exposed surface making them less susceptible to corrosion. Box girders also provide smooth aesthetically pleasing structures. There are two types of steel box girders steel-concrete composite box girders . steel box composite with concrete deck and steel box girders with orthotropic decks. Composite box girders are generally used in moderate- to medium-span 30 to 60 m bridges and steel box girders with orthotropic decks are often used for longer-span bridges. This chapter will focus on straight steel-concrete composite box-girder bridges. Steel box girders with orthotropic deck and horizontally curved bridges are presented in Chapters 14 and 15. Typical Sections Composite box-girder bridges usually have single or multiple boxes as shown in Figure . A single cell box girder Figure is easy to analyze and relies on torsional stiffness to carry eccentric loads. The required flexural stiffness is independent of the torsional stiffness. A single box girder with multiple cells Figure is economical for very long spans. Multiple webs reduce the flange 2000 by CRC Press LLC FIGURE Typical cross sections of composite box .
