Richard E. Hart, Oregon Department of Transportation
Spring Creek in Klamath County, OR, is spring fed and is approximately 2-1/4 miles (3.6 km) in length from its source to its confluence with the Williamson River, at about 1/8 mile (0.2 km) downstream of the U.S. 97 overcrossing. The creek is about 60 ft (18 m) wide and is a favorite of fishermen and rafters regardless of its short length. The U.S. 97 highway bisects Collier Memorial State Park and Logging Museum grounds with a 160 ft (49 m) Oregon Department of Transportation right-of-way on each side of Spring Creek. Primarily due to the proximity of its source, the flow of Spring Creek fluctuates only a few inches between the low and high flow conditions.
The name of the original bridge was the Romeo and Juliette Bridge. However, local people referred to it as Collier’s Promenade Bridge—originating from newspaper articles written during its construction. The replacement bridge is now known as Collier’s Promenade Bridge.
The Romeo and Juliette Bridge was a reinforced concrete deck girder bridge with a 60-ft (16.29-m) long main span incorporating a radial girder haunch. This produced an arched appearance with 19-ft (5.79-m) long cantilevered approaches. It was constructed in 1946 and was unique among Oregon bridges. This bridge had walkways beneath the bridge that were cantilevered from the architecturally treated abutments. The walkways allowed park visitors access to each side of the Collier Memorial Park without crossing U.S. 97 at grade. The unique bridge design was due to the involvement of Conde B. McCullough of Oregon historic coastal bridge fame. This design is now believed, through documentation, to be one of the final bridge designs that Mr. McCullough may have influenced in the state.
Thus one can follow, or at least understand, why in mid 2003 the original idea of a simple precast, prestressed concrete slab bridge developed into something that would resemble the original structure, while incorporating modern concepts and methodologies.
The Replacement Bridge
The new structure’s general architectural appearance was developed by the preliminary design team in collaboration with the State Parks and Recreation Department and the State Historic Preservation Office to preserve the look and feel of the original bridge. Construction of the replacement structure was complicated by the proximity of the park and endangered aquatic species known to spawn within 1/4 mile (400 m) downstream. This led to the request from biologists, that the use of cast-in-place concrete over the stream be limited.
Collier’s Promenade Bridge is 140 ft (42.7 m) long with a single main span of 82.5 ft (25.0 m). It has a width of 85.5 ft (26.1 m), which includes the northbound and southbound lanes of U.S. 97, a turning lane for the Park access, shoulders, and two 9-ft (2.75-m) wide walkways outside the modified F rail.
The bridge was constructed using staged construction while the original bridge continued to carry all the traffic. Once traffic was moved to the completed stage, the original bridge was demolished and the remaining section of the new structure completed. The total bridge cost was $3.2 million.
High Performance Concrete
High performance concrete (HPC) containing silica fume was specified for all concrete above the foundations. The inclusion of silica fume in the HPC is intended to extend the life of the structure by limiting the migration of chloride ions from deicing solutions. An added benefit of the HPC concrete in reference to the deck is the increased resistance to abrasion from the use of studded tires. The concrete used above the foundations can be further separated into the cast-in-place (CIP) concrete and the precast, prestressed concrete used only in the girders.
The following table provides the specified and average measured compressive strengths of concrete used for the different components of the bridge.
2. Measured at 28 days except for release strength
3. Release strength specified as 6500 psi (44.8 MPa)
Other than the unique architectural treatment of the CIP concrete, the most striking item of interest on the bridge is the one-of-a-kind precast, prestressed concrete girder system. The 12 girders are radially haunched with a 42 in. (1.07 m) depth at midspan and 102 in. (2.59 m) depth at each bearing. The prestressing strand is symmetrically placed in the bottom quarter of the girder at midspan and continues horizontally to the ends of the girder. The radial haunch produces an effective strand eccentricity in the girder. The exterior three girders on each side of the structure have a 6-in. (150-mm) diameter standard steel structural pipe placed 1 ft (305 mm) from the top of the girder to accommodate utilities.
Originally, the girders were to be pretensioned for shipping and then post tensioned for live load. However, the precaster had installed a new high capacity casting bed so it was possible to apply all the prestressing force before casting.
Further Information
For further information about this bridge, please contact the author at [email protected].
Acknowledgement
The author acknowledges the assistance of Dr. Keith Kaufman, of Knife River Corp., Harrisburg, OR, and Denny Holm, owner of Holm II, the Bridge Contractor, Stayton, OR, for thinking this would be a fun project to cap his career.
