Fireproof tunnel for vertical bridge structure

Vertical bridge structures with tunnel-like passages can be effectively protected from fire using a combination of passive fireproofing systems, including spray-applied coatings, fire boards, and reinforced concrete fire-resistive designs.

Passive Fire Protection Systems

Spray-applied fireproofing is widely used for tunnel and vertical structures. Systems like CAFCO FENDOLITE M-II / ISOLATEK Type M-II are internationally tested and can be optimized for thickness to prevent concrete spalling and structural collapse under fire exposure. These coatings are designed to keep concrete surfaces below 380°C (716°F) for up to two hours, simulating severe fire scenarios such as a gasoline tanker fire over a large surface area . Components include keycoats, retention meshes, anchors, and optional reflective topcoats for durability and visibility. Fire boards and cladding provide protection for steel elements within tunnel-like structures. These panels, often referred to as steel encasement or fire cladding, shield structural steel from high thermal loads and are integrated with emergency escape routes or maintenance walkways . Fire-rated cable trough covers can also be installed to protect electrical systems while sustaining dynamic loads.

Concrete Fire-Resistive Design

Reinforced concrete in vertical tunnels is vulnerable to explosive spalling, which occurs when trapped water vapor rapidly expands at temperatures between 300°C and 450°C, weakening the concrete and steel reinforcement . Fireproofing strategies include:

• Using lightweight fireproofing mortars or coatings applied to concrete surfaces.
• Ensuring adequate layer thickness based on fire exposure duration and intensity.
• Testing according to RWS fire curves or ASTM E3134 standards, which evaluate fire resistance for both horizontal and vertical orientations, including spalling and fire-resistive material performance .

Testing and Standards

Fireproofing systems for tunnel-like structures should comply with recognized standards:

• ASTM E3134 specifies fire testing for concrete linings and fire-resistive materials, including surface burning, spalling, and joint performance .
• Rijkswaterstaat (RWS) fire curve is a benchmark for tunnel fire testing, simulating severe fuel-based fires and ensuring materials prevent concrete surface temperatures from exceeding critical thresholds .
• NFPA standards provide guidance on fire safety for tunnels and limited-access highways, emphasizing both active and passive protection measures .

Implementation Considerations

• Material selection should consider the concrete mix, structural orientation, and expected fire load.
• Layer thickness optimization ensures cost-effective protection without compromising structural integrity.
• Integration with ventilation and emergency systems enhances safety for both users and maintenance personnel.
• Full-scale testing or field trials are recommended to validate laboratory findings under real-world conditions . By combining spray-applied coatings, fire boards, and reinforced concrete design, vertical bridge structures with tunnel-like passages can achieve robust fire resistance, minimizing the risk of spalling, structural failure, and human hazards during fire events.