What is Steel Trestle Bridge?

Steel Trestle Bridge is a temporary or semi-permanent bridge structure, typically assembled rapidly from steel components (such as steel pipe piles, structural steel beams, Bailey panels, etc.). It is widely used in engineering construction, temporary access routes, emergency repairs, and disaster relief scenarios.

Structure of steel trestle bridge

1. Modular Design
   Primarily employs standardized components (e.g., Bailey bridge panels, steel pipe piles, H-shaped steel beams, connectors), enabling rapid assembly, disassembly, and reuse.
2. Foundation Types
• Steel Pipe Pile Foundation: Most common. Piles are driven into the soil using vibratory hammers/pile drivers, with tops connected to pile caps or bent caps.
• Temporary Pile Cap: Utilizes concrete caps + group piles in areas with poor soil conditions.
3. Superstructure
• Main Girders: Bailey panels, built-up steel beams (e.g., double I-beams), prefabricated steel box girders.
• Decking: Anti-slip steel plates, precast concrete panels, or timber decking.
4. Connection Methods
   High-strength bolts, pin connections, welding (less common to facilitate disassembly).

Typical Application Scenarios of Steel Trestle Bridge

1. Engineering Construction
• Construction access bridges across rivers/canyons (e.g., hydropower projects, railway/highway construction).
• Material transport channels for deep foundation pits.
2. Temporary Transportation
• Emergency replacement for damaged bridges (e.g., after floods/earthquakes).
• Temporary pedestrian bridges for large-scale events.
3. Special Operations
• Support platforms for pipeline installation or equipment assembly.
• Temporary docks/piers.

Design Key Points (Including Load Standards)

Steel trestle bridge design must comply with AASHTO LRFD (Temporary Structures section) or local codes (e.g., State DOT standards). Core considerations include:

1. Design Loads

2. Load Combinations (AASHTO LRFD for Temporary Structures)

• Strength Limit State:
  1.25×DL+1.75×LL+0.5×(Wind/Current Load)1.25×DL+1.75×LL+0.5×(Wind/Current Load)
  (Note: Live load factor may be reduced to 1.5–1.6 for temporary structures per code).
• Stability Limit State:
  Verify pile foundation overturning/sliding (Combination: DL + Wind + Current Load).

3. Special Design Principles

• Reduced Safety Factors: Allowable stresses may be increased (e.g., steel: 0.9Fy0.9Fy​ vs. 0.6Fy0.6Fy​ for permanent structures).
• Fatigue Control: Check stress amplitude at Bailey panel pin holes/bolt connections (per AASHTO Fatigue Truck model).
• Deformation Limits:
• Girder deflection ≤ L/300 (L = span length).
• Horizontal displacement at pile top ≤ 25mm (ensuring traffic safety).

Construction Essentials

1. Geotechnical Investigation
   Identify bearing strata for piles in advance to avoid settlement (especially in soft soil areas).
2. Rapid Construction Techniques
• Full-span lifting of Bailey bridge units; modular block-style splicing of steel pipe piles.
• GPS-guided pile positioning; vibratory hammer driving (>30 piles/day).
3. Safety Measures
• Install fall protection nets, load limit signs (e.g., MAX 50t, SPEED 10km/h).
• Regularly monitor pile settlement and beam deformation (total station/sensors).
4. Corrosion Protection
   Hot-dip galvanizing or periodic coating (use weathering steel for coastal trestles).

 Classic Case: Bailey Bridge Trestle

• Structure: Steel pipe piles + Bailey girders (single/double/triple truss configurations).
• Span Arrangement: Standard span: 9–15m (single span); large spans up to 30–45m (reinforced trusses required).
• Load Capacity: A 12m single-span Bailey bridge can carry HS20 truck load (~320 kN total).

Design Mantra:
"Secure foundations, robust beams, reliable connections, comprehensive verification"
—Simplified calculations suffice for temporary trestles, but critical joints (pile-to-beam, Bailey pins) demand meticulous design!

Code References

1. U.S. Standards:
• AASHTO LRFD Bridge Design Specifications (Temporary Structures section)
• ASCE 37-14: Design Loads on Structures During Construction
2. Chinese References:
• JTG D64: Specifications for Design of Highway Steel Bridges
• JT/T 728: Fabrication of Assembled Highway Steel Bridges