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Examoogle • User • info@examoogle.com • EE-2024-8821
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The bed block is generally cast with concrete grade
M 15
M 20
M 25
M 30
M 15
A bed block (or bearing block) is a structural component used in bridge engineering to distribute concentrated loads from bridge girders onto the substructure (piers or abutments). Standard practice in bridge maintenance and construction specifies the use of M 15 grade concrete for these blocks to provide adequate bearing strength while maintaining workability.
A bed block (or bearing block) is a structural component used in bridge engineering to distribute concentrated loads from bridge girders onto the substructure (piers or abutments). Standard practice in bridge maintenance and construction specifies the use of M 15 grade concrete for these blocks to provide adequate bearing strength while maintaining workability.
σbearing=AeffectiveP — Bearing stress calculation where P is the load and A is the contact area of the bed block.
The bed block acts as a load-transfer medium, preventing local crushing of the pier cap by increasing the effective contact area. By adopting M 15 grade, the design ensures the compressive stress transferred to the substructure does not exceed the permissible limits defined by bridge codes like IRC (Indian Roads Congress).
Bed blocks serve as transition elements between bridge superstructure and substructure.
M 15 is the minimum recommended concrete grade for non-structural or bedding applications in many bridge codes.
Proper curing and alignment of bed blocks are critical for uniform load distribution.
Higher grades like M 20 or M 25 may be specified if the design load intensity is unusually high.
Protects pier cap from concentrated load cracking
Allows for leveling of girder bearings
Provides a uniform surface for installation
Requires additional labor for formwork installation
Adds dead weight to the substructure
RCC T-beam bridges
Plate girder bridges
Stone masonry abutment repairs
M 15 grade concrete signifies a characteristic compressive strength of 15 N/mm² at 28 days.
Using higher grades unnecessarily increases costs without significantly improving functional utility for bed blocks.
B, C, and D are higher grades of concrete usually reserved for structural members like beams, columns, and decks.
A is correct — The bed block is typically cast with M 15 grade concrete to ensure efficient load distribution without over-engineering.
Always remember that in bridge engineering, concrete grades for bearings and leveling courses are lower than those for structural components to ensure compatibility and economic efficiency.