12 recommendations for box girder design:

1. Inside width 4’ minimum
   
2. Inside height 5’ minimum
   
3. Corner seams:

• Closed box (4 sides)
  - Inside width < 4’, use full pen weld. Weld from outside.
  - If the inside width is > 4’, use double fillet welds.
• Open box (3 sides)
  - Use double fillet welds.

4. Avoid full penetration welds

• Bearing stiffeners
• Connection seats

5. Always remember confined spaces rules (good ventilation). Refer to OSHA publication #29CFR 1910-146.

6. Access doors:

• Minimum (2) per box
• One at each end

7. Access holes / Manholes in baffles:

• 2’8" by 3’0" minimum opening size
• Concentric
• 3’0" minimum spacing

8. In service inspection access:

• Hatch opens inward
• Ladder stops
• Ventilation
• Access from end

9. Do not design four-sided boxes using wide flange sections, since access to the inside is not feasible. However, a box girder may be built using bolted/welded cover plates at the top & bottom flange, with diaphragms as needed. Give due consideration for fatigue category. Please see example.

10. FCM – only as necessary –identify.

11. Crossframes:

• CNC equipment to fabricate
• Shop assembled on jigs and fixtures
• Repeatability
• No back to back angles
• No knock down types

12. Communications during design

• Fabricators
• Producers
• Detailers
• AISC / NSBA

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