Bridge Analysis Workflow — Worked Examples

Example 1: Choose the Right Model Fidelity

A straight, simply supported, four-girder highway bridge has regular spacing, negligible skew, and no unusual curvature. The immediate design question is the positive flexural demand in an interior girder.

Example 2: Verify Reactions by Equilibrium

A simply supported 24 m line-girder model carries a uniform dead load of $45\text{ kN/m}$ and a concentrated permanent load of $180\text{ kN}$ at midspan.

Engineering conclusion: A sophisticated model that fails equilibrium is not a valid design model.

Example 3: Keep Construction and Composite Stages Separate

A steel plate girder carries its own weight and the wet concrete deck before composite action develops. After curing, the hardened deck participates in composite flexure and later carries barriers, wearing surface, and live load.

Example 4: Build a Moving-Load Moment Envelope

A two-span continuous bridge is checked at closely spaced response stations.

Example 5: Produce a Design Handoff for an Interior Girder

A verified global model has been completed for a continuous composite bridge.

Engineering conclusion: A design handoff must preserve the physical origin of the forces so the designer can verify that each resistance check uses the correct demand.