Montgomery Avenue Bridge Replacement

The historic Montgomery Avenue Bridge, originally built in 1913, has served as a vital connection in northwest Philadelphia for over a century. The 126-foot-long concrete-encased steel girder bridge had severely deteriorated and was surrounded by 100-year-old masonry walls, residential neighborhoods, and businesses while spanning five active railroad tracks. Through an open-end agreement with the City of Philadelphia Department of Streets, Modjeski and Masters (M&M) took on the challenge of designing its replacement. Despite its compact size, the project presented unique engineering and construction challenges, including a 50° bridge skew, a 100-year-old brick sewer beneath the proposed abutment, strict clearance requirements from the railroads, and the complexities of working within a dense urban environment.

To address these complexities, M&M utilized advanced 3D finite element modeling, which accounted for out-of-plane effects, girder deflections, and transverse rotations. A critical challenge was the 4’-6” diameter brick sewer, located 35 feet below grade and directly beneath a proposed abutment. Since relocation was not feasible, our engineers innovatively introduced a discontinuity in the pile cap, designing two independent cap portions that spanned the sewer. During construction, the sewer’s actual location necessitated two additional redesigns of the abutment foundation, ensuring precise alignment with the existing infrastructure.

The project also required careful attention to protecting the nearby historic masonry walls. Prefabricated modular wingwalls (TWalls) were implemented as an alternative to traditional wingwalls, offering enhanced protection while accommodating tight space constraints and avoiding conflicts with vertical sewer pipes. To further mitigate lateral loads on the vertical piles and existing masonry walls, M&M specified ultra-lightweight foamed glass backfill, reducing stress on these critical elements.

To address the strict clearance requirements for the railroad, our engineers designed concrete end diaphragms to accommodate future bearing replacements, with integrated jacking support. Shear studs were added to steel girders, and additional reinforcement was introduced in the end diaphragms to ensure composite action between the materials. These innovative solutions exemplify M&M’s expertise in overcoming complex challenges, while designing a safe, functional, and enduring bridge for the City of Philadelphia.