Bixby Bridge, also known as Bixby Creek Bridge, on the Big Sur coast of California, is one of the most photographed bridges in California due to its aesthetic design, "graceful architecture and magnificent setting". It is a reinforced concrete open-spandrel arch bridge. The bridge is south of San Francisco and south of Carmel in Monterey County on State Route 1.
Before the opening of the bridge in 1932, residents of the Big Sur area were virtually cut off during winter due to blockages on the often impassable Old Coast Road, which led inland. The bridge was built under budget for $199,861 (equivalent to $ in dollars) and, at , was the longest concrete arch span in the California State Highway System. When it was completed, it was the highest single-span arch bridge in the world, and it remains one of the tallest.
The land north and south of the bridge was privately owned until 1988 and 2001. A logging company obtained approval to harvest redwood on the former Bixby Ranch to the north in 1986, and in 2000 a developer obtained approval to subdivide the former Brazil Ranch to the south. Local residents and conservationists fought their plans, and both pieces of land were eventually acquired by local and federal government agencies. A $20 million seismic retrofit was completed in 1996, although its width does not meet modern standards requiring bridges to be wide.
Location
The bridge is "one of the most photographed features on the West Coast" and in the world. It has been featured on "postcards, TV ads, everywhere," according to Debra Geiler, project manager for the Trust for Public Land. The bridge's location on the scenic Central Coast of California, the parabolic shape of the arch, the tall spandrel columns, and the architectural piers contribute to an "intense aesthetic experience." "It's the gateway to Big Sur and the interior has never been logged. The land is pristine." Zad Leavy, former executive director of the Big Sur Land Trust, described the land as "the most spectacular meeting of ocean and land in the entire United States."
Characteristics
The bridge is in total length and wide, with of clearance below, and has a main span of , which places 50% of the total roadbed above the arch. The arch ribs are five feet thick at the deck and nine feet thick at the springing line, where they join the towers at their base. The arches are four and one-half feet wide. The bridge was designed to support more than six times its intended load.
The two large, vertical buttresses or supporting pillars on either side of the arch, while aesthetically pleasing, are functionally unnecessary. Engineers of later arch bridges such as the Frederick W. Panhorst Bridge omitted them from the design. The Rocky Creek Bridge and the Malpaso Creek Bridge to the north are also open-spandrel arch bridges built of reinforced concrete.
Construction
The state first began building Route 56, or the Carmel–San Simeon Highway, in 1919. A number of bridges needed to be constructed, the largest among them across Bixby Creek.
Bridge design
State engineers considered two alternatives to crossing the creek, an inland route and a smaller bridge, or a coastal location and a larger bridge. The inland route would have needed an tunnel cut through the Santa Lucia Mountains to a bridge upstream. The engineers selected the coastal route because it was safer, more scenic, and least affected the environment.
California state highway engineer C. H. Purcell and bridge engineer and designer F. W. Panhorst considered whether to build a steel or concrete span. A steel bridge would cost more to build and maintain, as the sea air would require expensive ongoing maintenance and painting. A steel bridge was also less in keeping with the natural environment. Using concrete reduced material costs and allowed more of the total cost to be paid to workers, which was a positive aspect of the design during the Depression. They chose concrete in part because it would not only reduce both construction and maintenance costs but would also echo the color and composition of the natural rock cliff formations in the area.
The state awarded a contract for $203,334 to the lower bidder, Ward Engineering Company of San Francisco, on August 13, 1931. Construction began on August 24, 1931.
Design and materials
Over of Douglas fir timber, used to build a high falsework to support the arch during construction, was transported from the railroad terminal in Monterey over the narrow, one-way road to the bridge site. The falsework, built by crews led by E. C. Panton, the general superintendent, and I. O. Jahlstrom, resident engineer of Ward Engineering Co., was difficult to raise, because it was constantly exposed to high winds. Some of the falsework timbers were . It took two months to construct the falsework alone. When high waves threatened the falsework foundation, construction was halted for a short time until winter storms abated.
The crews excavated of earth and rock. Eight hundred and twenty-five trucks brought in 600,000 pounds of reinforcing steel. Sand and gravel were supplied from a plant in Big Sur.
Construction required 45,000 sacks or of cement which was transported from Davenport, near Santa Cruz, and from San Andreas. Crews began placing concrete on November 27. The concrete was transported across the canyon on platforms using slings suspended from a cable above the creek.
The bridge was completed on October 15, 1932, although the highway was not finished for another five years. At its completion, the bridge cost $199,861 and, at , was the longest concrete arch span on the California State Highway System. The bridge was necessary to complete the two-lane road which opened in 1937 after 18 years of construction. The completion of construction was celebrated with a ribbon-cutting ceremony led by Dr. John L.D. Roberts, who had conceived of the need for the road.
Rainbow Bridge
After the bridge was completed, it was at times known as the Rainbow Bridge, due to the presence of the Rainbow Lodge resort on the creek upstream from the bridge. It was operated by former Army Captain Howard Sharpe and his wife, Frida. After timber harvesting was no longer profitable, Sharpe bought the Bixby Creek Canyon ranch in 1919. He built a dirt road from the lodge up the canyon to Bixby Landing on the point northwest of the canyon mouth, and another road down to the beach at the mouth of Bixby Creek. He sold part of his land to the state as part of the bridge right-of-way in 1930. When the bridge was completed and tourists no longer needed to descend to his lodge on the creek, he built a new lodge on the highway north of the bridge.
Seismic retrofitting
The bridge was retrofitted beginning in 1996 with an analysis by bridge engineering company Buckland & Taylor as part of the Caltrans Phase II seismic retrofit program. In their detailed evaluation of the bridge's seismic vulnerabilities, they were challenged to find a solution that met several difficult issues, including severe load factors, extremely limited physical access, maintaining the appearance of the existing historical structure, and a requirement by the State of California that at least one lane of the bridge remain open at all times. The crux of the design was the longitudinal post-tensioning of the entire bridge deck from end to end.
The $20 million seismic retrofit began in May 1998. The cost of the retrofit was considerably increased by the requirement to preserve the historical look of the bridge. Prime contractor Vahani Construction of San Francisco was assisted by Faye Bernstein & Associates and Waldron Engineering. To reinforce the abutments supporting the bridge deck at either end, engineers put in place a floating slab, continuous with the deck, keyed into a massive pile cap with six diameter cast-in-drilled-hole (CIDH) piles behind each abutment. To support the towers, engineers designed a full height structural wall that was integrated within each of the two existing towers. During the retrofit, they removed the top portion of the towers, including the roadway, and replaced them with a prestressed diaphragm that anchors the full height of the vertical tower. The diaphragm simultaneously distributes the vertical prestressing forces uniformly to the new concrete structural wall and the existing tower's concrete.
The deck, which curves from one end to the other, was reinforced by adding heavily confined edge beams encasing high strength steel along the inside face of the exterior longitudinal girders underneath. These rods extended from one end of the roadway to the other. The reinforced edge beams ensure continuity across the many expansion joints and help distribute the bending strains due to lateral flexure. In addition to the reinforced edge beam, four large prestressing tendons were installed the length of the bridge along the underside of the deck slab. These tendons are stressed to pre-compress the concrete deck to approximately 800 psi and also serve as flexural reinforcement along with the high strength rods. Finally, engineers found a way to reinforce the bent columns attached to the arch, which possess complex and varying geometric challenges. They encased the bent columns with thin, lightweight, composite carbon fiber jackets that provide the necessary degree of confinement to ensure ductile response and also mimic the original design.
In addition to the analyses performed by Buckland and Taylor, Caltrans commissioned Lawrence Livermore National Laboratory to perform an independent study of the structure both with and without the proposed retrofit measures in place. The final report, which was published in June 1999, concludes that the retrofit appears to be appropriate even for earthquake ground motions including near-field displacement pulses, which were not considered in the original analyses.
As a result of the retrofit, the continuous, stiffened deck has four lateral reaction points: two new massive abutments anchored by large-diameter, cast-in-drilled-hole piles. The two towers are strengthened and anchored to rock with tie-down anchors within the towers. The arch ribs are laterally supported at their crowns by new shear keys that link them to the reinforced deck. The expensive retrofit, completed in November 2000, still left the bridge officially classified as "functionally obsolete" because at in width, the bridge is less than the standard required of newly built bridges.
History
The land near the bridge was historically occupied by the native Esselen people who visited the coast seasonally to harvest shellfish and to fish offshore. When the Spanish established the California mission system, only a very few were not baptized and conscripted, and they soon left the mountains to work on the nearby ranches. Governor Juan Alvarado granted the land from present day Carmel south to Palo Colorado Canyon, two miles north of Bixby Creek, to Marcelino Escobar in 1839 as part of the Rancho San Jose y Sur Chiquito. The land was later acquired by Alvarado's brother-in-law José Castro. Castro noted the existence of a Native American trail from Monterey to Palo Colorado Canyon in 1853, when he filed a map of his grant.
Originally Mill Creek
Bixby Creek is named after pioneering Yankee businessman Charles Henry Bixby. Originally from Livingston County, New York, he arrived in California in 1852 and remained for five years. He returned east before coming back to California. After some success raising cattle in Sonoma County, he obtained a patent on April 10, 1889 for south of Bixby Creek, and later bought additional tracts of land on the north side of the creek, between it and Palo Colorado Canyon.