Steel Bridges



1. What is Steel Bridge?

As the name implies, a steel bridge is a bridge in which the main material is steel. Steel bridge members are easy to fabricate and are widely used in bridge construction due to the high tensile strength of steel materials. Steel has tensile and compressive strength, and the ability to bend without cracking or breaking. Moreover, steel bridges do not undergo dry shrinkage or creep as loads are applied over time.


  • Fig. Steel bridge

Some important properties of steel bridges include:


1. Compared to concrete bridges, the self-weight is relatively light and long-span bridges can be constructed.
2. It is possible to manufacture durable and homogeneous quality materials in large quantities, and quality assurance is possible because the elements are manufactured in controlled environments.
3. Design and construction of stunning bridges to match surrounding landscape is possible.
4. Easy to inspect for deterioration or damage; easy to repair/reinforce or dismantle; materials are recyclable.




2. Main Components of Steel Bridge

  • Fig. Main components of steel bridge


3. Types of Steel Bridge

A. Steel Box Girder Bridge

A Steel Box Girder Bridge refers to a bridge that is completed by assembling a box-shaped girder made of steel plates on site → mounting it on the pier with a crane  installing formwork  pouring concrete to the upper slab. It is the most widely used bridge type among steel bridges, and it is mainly applied to curved bridges and straight bridges with spans of more than 30m.


Generally, steel box girder bridges can be subdivided into rectangular boxes and trapezoidal boxes depending on the shape of the section, and further divided into single cell boxes, multi cell boxes, etc. depending on the configuration of the section.


  • Fig. Steel box girder bridge

B. Steel Truss Bridge

A steel truss bridge is a bridge composed of only trusses. If the span of the bridge is too large, there is a disadvantage that it takes a lot of time to manufacture the members, but it is a representative railroad bridge that has the advantage of having light members and it is easy to construct.


Typically, the bridge is constructed by connecting elements using triangular shapes. The loads acting on the structure are distributed from the center and are optimized. It is assumed that each member of an ideal truss is connected by pins; therefore, no moment is present and only tensile and compressive forces act on the nodes. Since the members are connected by pins, only tensile and compressive forces are present, and they are transmitted only in the direction of the connections depending on the direction of each force and the equilibrium conditions.


  • Fig. Steel truss bridge

C. Steel Arch Bridge

A steel arch bridge is a bridge in which the structure is curved and harmonized with the surrounding landscape. The arch members themselves are mainly subjected to compressive forces and are alternately supported on solid foundations so that both ends of the arch do not move. Steel arch bridges are designed so that the horizontal reaction forces generated by the vertical loads act effectively, and reduce the cross-sectional forces of arch members.


Arch bridges are used for long-span bridges after suspension and cable-stayed bridges.


  • Fig. Steel arch bridge

An example of a structural analysis model for steel bridge design is shown in the figure below.


  • Fig. Steel bridge model