Steel Plate Girder Bridge Design — Worked Examples

Example 1: Separate Erection and Composite Flexural Stress

A steel girder carries a non-composite construction-stage moment of $M_1=4.2\text{ MN}\cdot\text{m}$ using steel-only section modulus $S_s=0.42\text{ m}^3$. After the deck hardens, later loads cause an additional composite-stage moment $M_2=6.0\text{ MN}\cdot\text{m}$ using composite section modulus $S_c=0.78\text{ m}^3$ at the same steel fiber.

Example 2: Preliminary Plate-Girder Proportioning

A 42 m simply supported bridge requires a trial steel plate girder. Clearance permits a structural depth near 2.0 m.

Engineering conclusion: preliminary proportioning creates a rational starting section; it is not a substitute for code checks.

Example 3: Decide Whether Intermediate Stiffeners Are Needed

A high-shear region near a support uses a relatively slender web.

Example 4: Bearing Stiffener Design Workflow

A girder end reaction is delivered through a concentrated bearing region.

Example 5: Fatigue Detail Controls a Flange Transition

A flange plate transition is structurally adequate for factored strength, but the weld geometry lies in a high repeated live-load stress-range region.

Engineering conclusion: fatigue can govern a detail that is comfortably adequate in gross-section strength.