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Learning / bridge engineering

girder

Longitudinal bending demand

Lesson review: expert verification remains open

This lesson has received a full-context editorial review and a check of its technical explanations. Selected arithmetic has been checked separately. This is not independent engineering sign-off.

Checks needed for project use

  • Bridge component studies and adjustable examples still need an independent bridge-engineering review, including applicability, load models and detailing guidance.
  • Specialist review remains for: Use a beam for bending and shear, grillage for load sharing, shell elements for web panels and local details. Composite stages need separate section properties and locked-in stresses; a concrete girder also needs prestress losses and time effects. The girder calculation is a local idealisation; it does not verify the displayed bridge or applicable design requirements.

These are educational models and exercises. Check their assumptions before using the results. The full technical content and every diagram have not yet been independently verified.

Concrete and steel calculations retain their stated first-generation Eurocode teaching basis. Use the standards and amendments specified for your project; do not mix generations without an appropriate design basis.

Read the lesson register and outstanding review notes

Loads and actions

Main girders collect deck reactions plus self-weight. Eccentric traffic introduces torsion; staged slab casting can govern unbraced steelwork. Repeated traffic loads produce fatigue stress ranges.

Choose a model

Use a beam for bending and shear, grillage for load sharing, shell elements for web panels and local details. Composite stages need separate section properties and locked-in stresses; a concrete girder also needs prestress losses and time effects.

Design considerations

Compare deeper webs, wider/thicker flanges, closed boxes and closer cross-members. Check section resistance, shear buckling, lateral-torsional buckling, stiffeners, fatigue and deflection. The section workbench below isolates elastic steel properties.

Durability and maintenance

Avoid details that trap water on bottom flanges. Provide access around stiffeners and splices. Fatigue repairs must address the stress range and load path rather than only covering a crack.

Longitudinal bending demand

One member, constant stiffness, static UDL. A continuous bridge or transverse load distribution needs a different global model.

For one 28 m simple beam: Mmax = wL²/8; Vmax = wL/2.

M = 3920.0 kN·m; V = 560.0 kN