The new State Route 191 bridge replacement project in Stroudsburg, Pa., faced many obstacles in design and construction. The project involved replacing a steel through-girder bridge that passed through one barrel of an existing concrete railroad tunnel. This tunnel, which supports railroad tracks that could not be disturbed, needed rehabilitation, and the bridge structure carrying the roadway over the overflow channel in one cell of the tunnel needed to be fully replaced.
The original tunnel rehabilitation and reconstruction plan included creating a 345-ft-long reinforced concrete culvert structure inside the tunnel and two new post-tensioned reinforced concrete approach spans. However, the winning contractor teamed with an engineer to develop a better plan using a precast concrete design that brought innovation to the approach structures and helped coordinate the timing and scheduling of the multiple site activities required for the complex project.
To facilitate delivery and erection using readily available cranes and delivery trucks, the new plan used segmental bridge design features and details normally reserved for long-span structures. Segmental bridge design and structural post-tensioning are not normally used by this owner; however, they recognized that an innovative solution was required to provide a “side opening,” and saw that using a precast concrete edge girder with post-tensioning would address that need. The new design also used similar load paths to the cast-in-place model with modifications to use precast concrete to reduce field work and accommodate the time schedule.
Monolithic Edge Girder
The design of the approach span structures had to account for the unique arrangement of the overflow channel of the creek, which takes two 90-degree bends under the spans. To accommodate this layout, the design involves a precast concrete deck transverse to the roadway and supported by new integral abutments under the outside shoulder. Because the box culverts were designed with the top slab spanning perpendicular to the direction of traffic, standard design software could not be used; instead, a more rigorous analysis using finite element software was used to develop the live-load forces.
The project team wanted to take advantage of the efficiency of fabricating multiple precast concrete segments with the same forms, so each segment was made a common length. Once the 78 precast concrete sections were on site, the team used two Taylor “Big Red” industrial lift trucks working side by side to move the individual box-culvert segments through the tunnel and into their final position on a new abutment foundation. The resulting structure will be more durable than the original plan to use existing abutments.
The precast concrete edge girder was cast monolithically with the precast concrete deck slab to keep precast concrete unit weights within acceptable limits for handling and erection. The 11-to-12 girder segments were post-tensioned in the field after erection on temporary supports. The joints in the precast concrete segments and edge girder were designed to use 8000-psi grout, which was readily available in the state and thereby avoided the need for less readily available solutions.
Eliminating the cast-in place concrete formwork and temporary falsework reduced the duration of the on-site work, which extended into cold weather months, and helped with the overall project schedule.