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Design of a Simply Supported Bridge Beam

This structural form is commonly used for bridges, particularly shorter spans up to 30m. The simply supported beams can be joined up "continuously" to form several spans indefinitely, using intermediate piers. Design is simple and construction, fabrication is also simple. A more complex structural form would involve continuous beams,  cantilevered beams or segmental sections over one or several intermediate supports.

The procedures outlined below summary guidelines by which you can follow, to carry out design for a simply supported bridge beams. The beams can be steel I-girders, universal steel beams or precast pre-stressed or post-tensioned concrete. Use of steel I-beams and girders are increasingly popular due to ease of construction, fabrication, and with better methods of corrosion protection now available. However some countries have particular preference to concrete precast beams either pre-stressed in factories or post-tensioned on site, or segmented post-tensioned from factory produced standard sections. The choices for bridge engineers are really open but in many cases controlled by local authorities requirements.

The general Bridge Beam Design Procedures are as follows :-

  1. Prepare Design Criteria - codes & standards, properties of materials, unit weights, concrete and steel grade, rebars, foundations, soils, etc.
  2. Prepare Bridge Information/Data - structural forms, spans, deck, carriageway, usage, highway classification.
  3. Bridge Sketches/Drawings - elevation, cross-section, beam, slab, foundations, piers, abutments, earth slopes embankment.
  4. Properties of Beam Sections - steel beams , precast beams, composite beams
  5. Calculate Bridge Loads - determine notornal widths, calculate dead loads, life loads: UDL, KEL, HB loadings.
  6. Determine Load Factors - at Service Limit State and & Ultimate Limit State.
  7. Calculate Designed Loads - factored loads for service and Ultimate limit state.
  8. Calculate Designed Forces - prepare structure force diagram, bending moments and shearing forces at service an ultimate limit states, tabulate data.
  9. Design of Beams - steel or concrete precast.
  • For Steel Beams - design of beam for moment and shears due to construction dead loads, and dead & life loads for composite section at service limit state, and checked at ultimate for composite section.
  • For Precast Concrete Beams, designed and checked for stresses at Transfers, Service and Ultimate Limit state, design for tendons type, positioning and prestressing forces

Worked Examples

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Authur- Philip Goh (B.Sc, MIEM, P.Eng. MICE, C.Eng)
MEC Engineers, Civil & Structural Engineer
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Authur- Philip Goh (B.Sc, MIEM, P.Eng. MICE, C.Eng) MEC Engineers, Civil & Structural Engineer HP: 016-8672189, Email: Widget: email cloaker