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
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 :-
- Prepare Design Criteria - codes & standards, properties of materials, unit weights, concrete and steel
grade, rebars, foundations, soils, etc.
- Prepare Bridge Information/Data - structural forms, spans, deck, carriageway, usage, highway
- Bridge Sketches/Drawings - elevation, cross-section, beam, slab, foundations, piers, abutments, earth
- Properties of Beam Sections - steel beams , precast beams, composite beams
- Calculate Bridge Loads - determine notornal widths, calculate dead loads, life loads: UDL, KEL, HB
- Determine Load Factors - at Service Limit State and & Ultimate Limit State.
- Calculate Designed Loads - factored loads for service and Ultimate limit state.
- Calculate Designed Forces - prepare structure force diagram, bending moments and shearing forces at service
an ultimate limit states, tabulate data.
- 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
- For Precast Concrete Beams, designed and checked for stresses at Transfers, Service and Ultimate Limit
state, design for tendons type, positioning and prestressing forces
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Authur- Philip Goh (B.Sc, MIEM, P.Eng. MICE,
MEC Engineers, Civil & Structural Engineer