Bridge Expansion Joint for Bridges in Seismic and Volcanic Regions

Regions with both seismic activity and volcanic hazards present unique challenges for bridge expansion joint design. The joint must accommodate seismic displacements while also resisting the effects of volcanic ash fall and, in extreme cases, lava flow. Volcanic ash fall is a significant hazard for bridges near active volcanoes. Ash can accumulate on bridge surfaces, including in the expansion joint gap, blocking drainage and adding weight to the bridge deck. The joint must be designed to allow ash to be flushed out by rainfall or manual cleaning. Drainage systems must be designed with larger capacity to handle the increased sediment load from ash fall. Ash chemistry can be aggressive to rubber and concrete materials. Volcanic ash typically has a pH of 3-5 when wet, creating an acidic environment that can attack concrete and some rubber compounds. The joint materials must be specified with adequate resistance to the expected ash chemistry. Concrete edge beams should be protected with a chemical-resistant coating in volcanic regions. Seismic design for volcanic regions must consider the potential for large earthquakes associated with volcanic activity. The seismic hazard in volcanic regions can be higher than in non-volcanic regions due to the tectonic activity associated with the volcanic system. The seismic gap must be designed for the maximum expected seismic displacement. Lava flow is an extreme hazard that can destroy bridges in its path. While expansion joints cannot be designed to resist lava flow, bridges in lava-prone areas should be designed for easy replacement after a lava flow event. Modular joints that can be quickly replaced are preferred for bridges in high-risk lava flow areas. Monitoring of bridges in volcanic regions should include seismic monitoring to detect precursory seismic activity that may indicate an impending eruption. Bridge closure procedures should be established for different levels of volcanic alert. Post-eruption inspection of bridges should check for ash accumulation, acid damage, and seismic damage.