--- title: "Classification of bridges by structure, material, loading" subject: "Transportation Engineering II" chapter: 5 key: "semester_7/transportation_engineering_ii:bridge-classification-structure-material-loading" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/bridge-classification-structure-material-loading site: BCT Engineering --- # Classification of bridges by structure, material, loading Transportation Engineering II · Chapter 5: Introduction to Bridge and Tunnel Engineering - Asked in: 2066 Bhadra, 4+4 marks - Video: [Types of Bridges [Based on Type of Super Structure, Materials of Construction, Purpose of Use]](https://www.youtube.com/watch?v=nTYzZp2K7j8) — Engineering Concepts - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/bridge-classification-structure-material-loading - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-5 ## Question Classify the bridges according to their structure, material and loading. Draw a sketch of the bridge with all its components. ## Short answer Bridges are classified by structure (simply supported, cantilever, arch, truss, girder, suspension, cable-stayed), by material (timber, masonry, RCC, PSC, steel, composite), and by loading (highway with IRC classes A, 70R, AA, B; railway; footbridge). A typical sketch shows superstructure (deck, girders, parapets), bearings, and substructure (abutments, piers, foundations). ## Answer #### Classification of bridges #### By structure (static system) - **Simply supported, continuous and cantilever** bridges. - **Arch, rigid frame, truss, girder, suspension and cable-stayed** bridges. - **Beam/slab and box girder** bridges. #### By material - **Timber bridges:** temporary or light bridges. - **Masonry (stone/brick):** arches and piers of short spans. - **Reinforced concrete (RCC):** slab and T-beam bridges. - **Prestressed concrete (PSC):** long girders and box sections. - **Steel:** truss, plate girder and Bailey bridges; **composite** bridges (steel girders with a concrete deck). - **Others:** FRP, and bamboo/rope (e.g. suspension trail bridges in rural Nepal). #### By loading (IRC:6 / Nepal Bridge Standards) - **Highway bridge** (carries road vehicles: IRC Class AA, 70R, A, B). - **Railway bridge** (railway loading). - **Footbridge** (pedestrians and light loads, e.g. a 5 kN/m² footway load). - **Pipeline, aqueduct, viaduct and combined road-rail** bridges. - Class A is the standard live load; Class 70R/AA are for heavy tracked and wheeled vehicles on national highways; Class B is for temporary bridges. #### Sketch of bridge with components A bridge has a **superstructure** (above the bearings) and a **substructure** (bearings, piers, abutments and foundations), plus approaches and protective works. ```text Approach Parapet/Railing Deck slab Approach slab ________________________ slab ____ ____|_____|_____|_____|_____|____ ____ \ | [girder][girder][girder] | / Wing \ |Bearing Bearing | / Wing wall |Abutment [ PIER ] Abutment| wall | | | | | HFL ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Scour level - - - - - - - - - - - - - - - - [Footing] [Pile/Well] [Footing] ``` **Superstructure** - **Deck slab and wearing coat:** carry the traffic loads (IRC Class A/70R/AA loading as per IRC:6) to the girders. - **Girders/trusses/arches:** the main load-carrying members that span between supports. - **Cross girders/diaphragms:** give lateral stability and distribute the load. - **Parapets, railings, kerbs and footpaths:** provide safety for vehicles and pedestrians. - **Expansion joints and drainage spouts:** allow thermal movement and remove surface water. **Bearings:** transmit reactions from the superstructure to the substructure and permit rotation and movement (elastomeric, roller and rocker types). **Substructure** - **Abutments:** end supports that also retain the approach fill, with **wing walls** and **return walls** that hold back the earth. - **Piers:** intermediate supports carrying the vertical load, with a pier cap and bed block. - **Foundations:** open (spread) footings, piles, wells or caissons that carry the loads to sound strata below the scour depth. **Others:** approach embankment and approach slab, **protective works** (guide bunds, spurs, apron, pitching) and river training works. The design HFL, LWL and scour level are marked on the section. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which material group is used for long girders and box sections? A. Timber B. Masonry C. Prestressed concrete (PSC) D. Bamboo and rope Answer: C. PSC is used for long girders and box sections; RCC is used for slab and T-beam bridges. (Key point: Classification by material) 2. Which loading class is used for heavy tracked or wheeled vehicles on national highways? A. Class A B. Class B C. Class 70R D. Footbridge load Answer: C. Class 70R is for heavy tracked or wheeled vehicles; Class A is the standard live load and Class B is for temporary bridges. (Key point: Classification by loading) 3. Which of the following belongs to the substructure? A. Girders B. Bearings, piers, abutments and foundations C. Deck slab and wearing coat D. Parapets and railings Answer: B. The substructure consists of the bearings, piers, abutments and foundations; the deck, girders and parapets are superstructure. (Key point: Superstructure vs substructure) 4. What is the role of an abutment together with its wing walls? A. To act as an intermediate support carrying vertical load only B. To permit thermal movement of the deck C. To distribute load between girders D. To form the end support and retain the approach fill Answer: D. Abutments are end supports that also retain the approach fill, with wing and return walls holding back earth. 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