Analysis of Thapathali Bridges and Its Neighboring Structures (structural steel Point of view)

There are two bridges at Thapathali, old one and new one. The old one was constructed in 1967 AD and the new was constructed in 1995 AD. The length of both the bridges is 184 m and have width of 6 m. These bridges fall on the category of Beam Bridge. A beam and slab or composite bridge is the one where a reinforced concrete deck sits on the top of steel I-beam, and act compositely with them in bending. The reinforced concrete acts as the compression member and the steel structure acts as a tension member. The beam and slab construction is multi girder type. Generally the span is short in Beam Bridge because, unlike truss bridges they do not have built in support. The only support is provided by pier.  

The main girder is I-section. The web resists the shear forces whereas Plate Sections and Angle sections are combined to form I-section. Angle beam is present as cross girder. The primary function of these cross-girders is to support the deck slab. The girders may, however, need to perform the secondary function of preventing the slab from buckling in compression.

the flanges resist most of the bending moment experienced by the beam. I-section is efficient in carrying bending and shear loads. However, it inefficient in carrying torsion. In case old bridge, several

Steel is protected against corrosion by paint coating. Modern specification usually consists of a sequential coating application of paints or alternatively paints applied over thermally sprayed metal coating to form duplex coating system. The protective paint coating comprises of primer, intermediate coat and finish coat.

The neighboring poster stand comprised of C-section and Hollow Structural section in addition to I-section and Angle section in the beam. Channel beam are used where the flat, back side of the web can be mounted to another flat surface for maximum contact area. They are sometime welded back to back together to form a non-standard I-beam. Hollow Structural Section (HSS) are commonly used in welded steel frames where members experience loading form multiple direction. They may be circular, rectangular or square and have excellent strength to torsion.