Build Up Girder - BUG

Girder bridges are the simplest bridge type in structure and consist of steel beams shaped to an I-section or box section, called a plate or a box girder bridge, respectively. This kind of bridges are comprised of deck slabs, on which vehicles and people pass, and of main girders supporting the deck slabs. Deck slabs include RC deck slabs, steel deck slabs, composite deck slabs, and PC deck slabs. This system is stabilized by cross girders and cross bracings at certain intervals.

Bridges where the deck slabs and the main girders work together to resist loads are called Composite Girder Bridges.

The two most common types of modern steel girder bridges are plate and box. The term “girder” is often used interchangeably with “beam” in reference to bridge design.

A plate girder is a built up I-beam section, used to carry heavy loads. It is made by riveting or welding the steel plates in I-beam shape. Spans of 9.15 m and above are made with web plates and flange plates to form built up beam or I-section.

In general, effective spans of BUG are of about 25 to 150 meters.

It is mainly constructed in the areas where there is very high traffic and the bridge is to be constructed for a longer span.

The deck refers to the roadway or the walkway of the BUG. Mostly, the deck may be made up of steel grids or reinforced concrete slabs.

Supporting Structures:
The superstructure of the BUG contains supporting structures of steel or concrete that supports the deck. These structures mainly include the girders, diaphragms or cross-braces, and sometimes even the truss or arch system.

Girders and bracing are the most commonly adopted supporting structures.In such a system of girders and bracing, the girders act as the primary load support whereas the bracing provides the external stability.

A. Plate Girder:
This Type of bridge is fabricated by welding plates together to create the desired shape. Usually, the large steel plates of desired thickness are cut into the flanges and webs from the plates in the desired length and shape.

The plate girder offers great flexibility in terms of height and shape. The span of the plate girder bridge can range from 10 meters and more than 100 meters (33 feet to more than 330 feet).

B. Box Girder:
As the name itself implies, a this type of Bridge is box-like in shape. This type of Girder Bridge offers high resistance to torsion and is mostly used when the bridge is likely to be subjected to torsion or toppling effects.