Box girder bridge
Concrete box girder bridge (double with common deck)
Ancestor:	Tubular bridge
Related:	jetway, skyway
Descendant:	Cable stayed bridge, segmental bridge, viaduct
Carries:	Pedestrians, automobiles, trucks, light rail, heavy rail
Span range:	Medium
Material:	Steel, reinforced concrete, prestressed concrete
Movable:	Possible
Design effort:	High
Falsework required:	Yes, if cast-in-place reinforced or prestressed concrete is used, which is typical for freeway overpasses

A box girder bridge is a bridge where the main beams comprise girders in the shape of a hollow box. A tubular bridge is a Bridge built as a rigid Box girder section within which the traffic is carried The word “jetway” is sometimes used for a high-altitude airway. Early examples of skywalks Copenhagen, Denmark: skywalk connecting courts building to adjacent uses 18th century Faaborg A As its name implies a segmental bridge is a Bridge built in short sections (called segments i A viaduct is a Bridge composed of several small spans The term viaduct is derived from the Latin via for road and ducere to Falsework consists of temporary structures used in Construction to support spanning or arched structures in order to hold the component in place until its construction is sufficiently A bridge is a Structure built to span a Gorge, Valley, Road, railroad track, River, Body of water A girder is a support beam used in Construction. Girders often have an I beam cross section for strength but may also have a box shape Z shape The box girder normally comprises either prestressed concrete, structural steel, or a composite of steel and reinforced concrete. Prestressed concrete is a method for overcoming the Concrete 's natural weakness in tension. Structural steel is Steel construction Material, a profile, formed with a specific Shape or cross section and certain standards of Composite materials (or composites for short are engineered Materials made from two or more constituent materials with significantly different physical or chemical Reinforced concrete is Concrete in which reinforcement bars (" Rebars quot or fibers have been incorporated to strengthen a material that would otherwise be The box is typically rectangular or trapezoidal in cross-section. In Geometry, a rectangle is defined as a Quadrilateral where all four of its angles are Right angles A rectangle with vertices ABCD would be denoted as A trapezoid (in North America or a trapezium (in Britain and elsewhere is a Quadrilateral (a closed plane shape with four linear sides that has at least one In Geometry, a cross section is the intersection of a body in 2-dimensional space with a line or of a body in 3-dimensional space with a plane etc Box girder bridges are commonly used for highway flyovers and for modern elevated structures of light rail transport. For specific light rail systems many of which use the words "light rail" as part of their name see List of light-rail transit systems. Although normally the box girder bridge is a form of beam bridge, box girders may also be used on cable-stayed bridges and other forms. A Beam Bridge is a direct descendant of the Log bridge, now more normally made from shallow steel 'I' beams, box girders, A

Advantages and disadvantages

Compared to I-beam girders, box girders have a number of key advantages and disadvantages:

• Better resistance to torsion, which is particularly of benefit if the bridge deck is curved in plan
• Larger girders can be constructed, because the presence of two webs allows wider and hence stronger flanges to be used. I-beams (also known as W-beams or double-T esp in Polish and German) are beams with an I- or H-shaped In Solid mechanics, torsion is the twisting of an object due to an applied Torque. A flange is an external or internal Rib, or Rim (lip for strength, as the flange of an Iron beam or I-beam This in turn allows longer spans
• More expensive to fabricate
• More difficult to maintain, because of the need for access to a confined space inside the box

Construction

If made of concrete, box girder bridges may be cast in place using falsework supports, removed after completion, or in sections if a segmental bridge. Span is a section between two intermediate supports eg of a beam or a Bridge. Confined space is a term from labor - Safety Regulations that refers to an area whose enclosed conditions and limited access make it dangerous Falsework consists of temporary structures used in Construction to support spanning or arched structures in order to hold the component in place until its construction is sufficiently As its name implies a segmental bridge is a Bridge built in short sections (called segments i Box girders may also be prefabricated in a fabrication yard, then transported and emplaced using cranes. A crane is a lifting machine equipped with a Winder, Wire ropes or Chains and sheaves that can be used both to lift and lower materials and to

For steel box girders, the girders are normally fabricated off site and lifted into place by crane, with sections connected by bolting or welding. If a composite concrete bridge deck is used, it is often cast in-place using temporary falsework supported off the steel girder.

Either form of bridge may also be installed using the technique of incremental launching.

Development of steel box girders

The key events in the development of the steel box girder bridge were three serious disasters, when new bridges collapsed in 1970 (West Gate Bridge and Cleddau Bridge) and 1971 (Koblenz Bridge). The West Gate Bridge is a large cable-stayed box girder Bridge in Melbourne, Victoria, Australia. The Cleddau Bridge on the A477 road spans the River Cleddau between Neyland and Pembroke Dock, Wales. 51 people were killed in these failures, leading to the formation of the Merrison Committee and considerable investment in new research into steel box girder behaviour.

Single box girder bridge (concrete), Australia. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag For a topic outline on this subject see List of basic Australia topics. A similar bridge on this river was fabricated ashore and pushed across its pylons

Single box girder bridge (steel), flyover above eastern approach of the San Francisco-Oakland Bay Bridge. Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 The traffic could only be rerouted for a few hours during the night, so this entire segment was prefabricated nearby, brought in on specialized trucks, and placed on its pylons using large cranes. Note numerous bolts used to fasten the segments together, required as this is designed to survive a nearby 8. 5 magnitude earthquake without damage and it is also founded upon poor quality soils that tend to induce intense ground motion

Erskine Bridge, near Glasgow. The Erskine Bridge is a cable-stayed Box girder bridge spanning the River Clyde in west central Scotland, connecting West Dunbartonshire Glasgow (ˈglæzgoʊ is the largest city in Scotland and third most populous in the United Kingdom