Bixby Creek Bridge
|Bixby Creek Bridge|
Bixby Creek Bridge from its northern end
|Design||reinforced concrete open-spandrel arch bridge|
|Total length||714 feet (218 m)|
|Width||24 feet (7 m)|
|Height||280 feet (85 m)|
|Longest span||320 feet (98 m)|
|Clearance below||260 feet (79 m)|
|Construction begin||August 24, 1931|
|Construction end||October 15, 1932|
|Opened||November 27, 1932|
Bixby Creek Bridge, also known as Bixby Bridge, is a reinforced concrete open-spandrel arch bridge in Big Sur, California. The bridge is located 120 miles (190 km) south of San Francisco and 13 miles (21 km) south of Carmel in Monterey County along State Route 1. Prior to the opening of the bridge in 1932, residents of the Big Sur area were virtually cut off during winter due to the often impassable Old Coast Road that led 11 miles (18 km) inland. At its completion, the bridge was built under budget for $199,861 (equivalent to $3.5 million in 2015) and was the longest concrete arch span at 320 feet (98 m) on the California State Highway System. It is one of the tallest single-span concrete bridges in the world and one of the most photographed bridges along the Pacific Coast due to its aesthetic design and location.
Beginning in about 1855, travelers followed a very rough and dangerous track from Carmel south towards Big Sur. At Bixby Creek, the road turned 11 miles (18 km) inland and then led to the Post Ranch on the Rancho El Sur.:4–2 The 30-mile (48 km) trip could take three days by wagon or stagecoach.:24 The single-lane road was closed in winter when it became impassable. Coast residents would occasionally receive supplies via a hazardous landing by boat from Monterey or San Francisco.:4–4
Bixby Creek takes its name from Charles Henry Bixby, from Livingston County, New York, who arrived on the Monterey Peninsula in 1868. He purchased large tracts of land in the Big Sur area and harvested the lumber, producing shakes, shingles, railroad ties, trench posts and tan bark. He processed these through a sawmill built along the creek and shipped them from a landing he built on the coast.
After it was built, the bridge was at times referred to as the Rainbow Bridge. This stems from a nearby resort, Rainbow Lodge, which was operated for a period of time by an Army Captain, Howard Sharpe and his wife, Frida. After lumbering came to an end, the Sharpes bought the ranch in the Bixby Creek Canyon in 1919. Sharpe built a dirt road from the lodge up the canyon to Bixby Landing and another road down to the beach at the mouth of Bixby Creek. He sold part of his land to the state to form part of the bridge right of way in 1930.
The state first began building Route 56, or the Carmel-San Simeon Highway, to connect Big Sur to the rest of California in 1919. A number of bridges needed to be built, the largest among them across Bixby Creek.
The engineers considered two alternatives to crossing the creek, either an inland route and a smaller bridge, or a coastal location and a larger bridge. The inland route necessitated an 890-foot (270 m) tunnel cutting though the Santa Lucia Mountains to a 250-foot (76 m) bridge upstream. The engineers selected the coast 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.
Over 300,000 board feet (700 m3) of Douglas fir timber, used to build a 250-foot (76 m) 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 10 by 10 inches (250 mm × 250 mm). 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 4,700 cubic yards (3,600 m3) of earth and rock and used 45,000 sacks of cement during construction. Eight hundred twenty-five trucks brought in 6,600 cubic yards (5,000 m3) of concrete and 600,000 pounds of reinforcing steel. Sand and gravel were supplied from a plant in Big Sur.
Crews began placing concrete on November 27. The cement was transported from Davenport, near Santa Cruz, and from San Andreas. Material was transported across the canyon from platforms using slings suspended from a cable 300 feet (91 m) above the creek. The bridge was completed on October 15, 1932. At its completion, the bridge cost $199,861 and, at 320 feet (98 m), 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 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 challenges, 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 72-inch (1,800 mm) 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 the bridge is less than 9.8 metres (32 ft) wide as required of newly built bridges.
The bridge is 714 feet (218 m) long, with 45% of the roadbed above the arch; 24 feet (7.3 m) wide; over 280 feet (85 m) high; and has a total span of 320 feet (98 m). 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.
In popular culture
The bridge is “one of the most photographed features on the West Coast” due to its pleasing aesthetic design and because of its location along the scenic Central Coast of California, and has frequently been used in automobile commercials. The bridge has become a regional landmark and was used in the opening sequences of the television series Then Came Bronson, the films Play Misty for Me and The Sandpiper. The bridge was also in the seventeenth episode of the first season of the NBC's show Heroes ("Company Man"), even though the scene was set in Texas. The bridge figures prominently in posters and other publicity material of the Big Sur International Marathon. An outline image of the bridge forms the logo for Central Coast ABC, the area's ABC Television Network affiliate on KSBW-TV (Channel 8.2).
The bridge was commemorated in an Express mail stamp issued on February 3, 2010. The United States Postal Service introduced a $18.30 definitive stamp designed by Carl T. Herrman of North Las Vegas, Nevada. The stamp features a color digital illustration of Bixby Creek Bridge in California, by Dan Cosgrove of Clarendon Hills, Illinois.
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- California Views: BCB from the Pat Hathaway collection
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- Pollock, P.E., Brad. "Safeguarding Bixby Bridge". Retrieved December 10, 2012.
- Wilson, J. G. "Innovative Techniques for the Seismic Retrofit of Bixby Creek Concrete Arch Bridge" (PDF). P. E. L. Panian. Retrieved December 9, 2012.
- McCallen, David; Noble, Charles; Hoehler, Matthew (1999). The seismic response of concrete arch bridges – With focus on the Bixby Creek Bridge. Carmel, California (PDF) (Technical report). Lawrence Livermore National Laboratory. UCRL-ID-134419.
- "Bixby Creek Bridge". Buckland & Taylor. Retrieved December 10, 2012.
- Bixby Creek Bridge (1933) at Structurae
- Concrete Arch Bridges California Canyon April 1933, Popular Mechanics
- Elliot, Arthur L. (1983), "Esthetic Development of California's Bridges", Journal of Structural Engineering 109 (9): 2159–2174, doi:10.1061/(ASCE)0733-9445(1983)109:9(2159).
- California Views: BCB Historical Collection
- "Bixby Creek Bridge $18.30". US Postal Service. Retrieved December 10, 2012.
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