BRO-221-05.47 Bridge Replacement

Background

ODOT District 9 selected Woolpert to provide road and bridge design services for the BRO-221-05.47 bridge replacement project over White Oak Creek. The existing structure was built in 1948 and featured single-span steel pier caps, a fracture critical element generally undesirable in bridge design and to be avoided when possible. The superstructure was rehabilitated in 1986, and a subsequent project in 2010 modified the channel and armored the area at the forward abutment. Despite these mitigations, it was found that the stream had scoured approximately 16 feet since 1948, decreasing the bridge’s original 30-foot drilled shaft embedment to just 14 feet. This increased the risk of undermining the piers, which could have resulted in a catastrophic structural failure, and thus necessitated total replacement of the bridge.

Challenge

Due to the stream’s high variability and the extreme scour present, hydraulics presented a challenge that Woolpert was well-equipped to address. The stream is generally low, but swells rapidly after storm events, and StreamStats indicated flow rates of 21,100/26,700 cubic feet per second for the 25/100-year storms. The model showed that with piers present, the contracted flow velocities averaged 23 feet per second with isolated areas at or higher than 25 feet per second, as opposed to approximately 17 feet per second upstream and downstream of the site. At these velocities, and given high channelization shown by FEMA floodplain maps, the team faced limited design options. The recommended solution was a single-span bridge, which a 2D mesh model showed would reduce velocity through the bridge area and at the forward abutment to a maximum of 17 feet per second.

Solution

Woolpert’s team performed survey, roadway, complex 2-dimensional hydraulic analyses, complex bridge design, geotechnical engineering, limited right of way, and subconsultant mentorship (Stone Environmental) to develop their experience in bridge design. Initial services were for a structure type study and hydraulic analyses for bridge replacement, which included four roadway alignment alternatives and five structure type alternatives ranging from basic design to aesthetic (three-span steel beam, three-span concrete beam, single-span plate girder, steel-rigid frame/slant-legged girder, and single-span open spandrel arch). Due to the major scour evident at the site, emphasis was placed on foundation and geotechnical designs as well as slope stability methods to mitigate further scour in the channel. Services also included a retaining wall justification study for analysis of grading impacts to a hillside area adjacent to the structure, followed by selection as a soldier pile and lagging wall.

Outcome

Based on Woolpert’s type study and the results from hydraulic analysis, the District selected a single-span, composite steel plate girder alternative to eliminate the need for midstream substructures. At 225 feet, this would be the longest bridge of its type in the state, and design was correspondingly a challenge. The structure is 33.33 feet wide with a 20-degree skew and supported on semi-integral abutments founded on drilled shafts. A 100-inch-deep Hybrid Plate Girder was designed, with 70ksi steel used for the flanges, and 50ksi steel for the web.

Benefits

The retaining wall and abutment installations were successful, as were placement of the long beams. A deck pour sequence was analyzed to develop composite action at the two ends of the span prior to the center pour. MiDAS finite element modeling was used to analyze the results of this sequencing, with a field-tested concrete strength required to achieve a composite condition in the end spans. During construction, however, it was found that the model underestimated the resulting deflection when the center pour was made, generating a slightly lower profile than anticipated. This did not pose a structural issue, but drainage and roadway geometry were double-checked to verify there were no significant ramifications for those designs.

The finished bridge offers a resilient structure that is well equipped to face extreme weather events made more frequent by the effects of climate change. Woolpert received an ACEC Ohio Honor Award for this project in 2023.