60 percent design review

Marlow Street footbridge

A 42 m steel box-girder crossing over the canal: loads, deflection and the construction plan.

Structures GroupFictional project, sample deckOctober 2026

The bridge in three numbers

42mMain span
3.0mClear deck width
186tSteel weight

Design basis

What the structure must carry

Loads

  • Pedestrian crowd: 5.0 kN/m2
  • Maintenance vehicle: 7.5 t
  • Wind on deck and parapet

Limits

  • Deflection under 1/800 of span
  • Vertical frequency above 3.4 Hz
  • Design life 100 years

Deflection check

Midspan deflection passes with margin

δ = 5wL4 ÷ 384EI = 38 mm
L
Span, 42 m
52 mm
Limit, L/800
73%
Utilisation

Utilisation by member

Every member is under 90 percent; the bottom flange governs.

MemberUtilisation
Bottom flange86
Web at support79
Top flange71
Bearings58
Ultimate limit state, governing combination

Materials

Weathering steelBox girder, S355
ConcreteAbutments, C40/50
HardwoodDeck planking

Programme

From approval to opening

  1. Detailed design

    Drawings issued for tender.

  2. Abutments

    Piling and concrete.

  3. Lift

    Girder craned in one night.

  4. Opening

    Handover and inspection.

Review comments

Mark up the drawings

Lead Structures Groupstructures@example.com