Bridge Expansion Joint for Box Girder Bridges: Internal and External Joints

Box girder bridges require expansion joints at both the external deck surface and, in some cases, at the internal diaphragm within the box girder cell. The internal joint is a less common but important detail that must be designed to prevent water infiltration into the box girder interior. External deck joints on box girder bridges are similar to joints on other bridge types, with the same movement range and waterproofing requirements. The main difference is the deck cross-section, which includes the top flange of the box girder. The joint must be designed to fit the top flange geometry, which may include a variable width and a cambered surface. Internal diaphragm joints in box girder bridges are required when the box girder is divided into segments by intermediate diaphragms that are not connected to the deck joint. Water that infiltrates the deck joint can accumulate in the box girder cell if there is no internal joint to collect and discharge it. An internal drainage trough below the deck joint collects this water and discharges it through drain pipes to the outside of the bridge. Access for inspection and maintenance of internal box girder joints requires man-access hatches in the box girder diaphragms. The hatches must be large enough for a person to pass through with inspection equipment. The internal environment of the box girder can be confined and poorly ventilated, requiring confined space procedures for inspection and maintenance. Corrosion protection of internal box girder components is critical because the internal environment can be humid and corrosive. Stainless steel drainage troughs and galvanized steel components are preferred for internal use. The internal surfaces of the box girder should be coated with a corrosion-resistant paint system to prevent corrosion of the structural steel. Ventilation of box girder cells is important for preventing condensation and corrosion. Ventilation openings in the diaphragms allow air circulation within the box girder. The ventilation system must be designed to prevent water ingress while allowing adequate air circulation. Regular inspection of the ventilation openings is required to ensure they are not blocked by debris.