50 DI Sixth Street Viaduct.Indd
Total Page:16
File Type:pdf, Size:1020Kb
INDUSTRY INNOVATION Busy on set Los Angeles replaces famous Hollywood backdrop By Vic Martinez and Michael Jones Often seen looming above riverbed car In 2004, a seismic vulnerability study Contributing Authors chases along the Los Angeles River, the bridge, was conducted that concluded the weak- like many celebrities, is more complicated ened state of the 3,500-ft viaduct put it at ne of America’s most famous underneath the surface than the public persona high risk for failure in a major earthquake. it has projected since it was built in 1932. Due to the viaduct’s geometric design and and recognizable bridges, the When the bridge was just 20 years old, safety deficiencies, the city of Los Angeles’ O Sixth Street Viaduct, has been its concrete supports began to disintegrate, Bureau of Engineering now had a convinc- caused by a chemical reaction known as alkali ing argument for replacing the bridge. used to represent Los Angeles’ more gritty silica reaction. Over the years, costly restor- What they didn’t have was a replacement side in countless movies, music videos ative measures attempted to save the structure, design concept that would be worthy of but none worked. the iconic viaduct. and TV commercials. 50 August 2015 • ROADS&BRIDGES ROADSBRIDGES.com 51 “The Ribbon of Light” features 10 pairs of arches, canted at 9°, forming a single stress ribbon running the whole length of the viaduct. The initiative to build a new bridge to list: AECOM, HNTB Corp. and Parsons Vic Martinez, HNTB’s project manager, replace the structure drew worldwide atten- Brinckerhoff. remembers numerous follow-up calls and tion in 2012 when the city of Los Angeles held The selection process for the Sixth Street meetings, where his team walked Bureau an international competition for a design Viaduct replacement was as extensive as members through HNTB’s philosophy, concept that would capture the imagination the Bureau had ever experienced. The three methodologies and cost estimates. of a city that had long ago fallen in love with finalists submitted proposals complete with After significant deliberation, members the Sixth Street Viaduct. architectural design reports. Each team then of the Bureau of Engineering and Caltrans gave a 90-minute presentation followed selected the concrete network tied arch, a Different song and dance by a 90-minute Q&A session. For the next collaboration between HNTB and architect Nine teams responded to the Bureau two weeks, each finalist participated in four Michael Maltzan. Their decision was of Engineering’s call for qualifications. 20-minute public presentations with Q&A unanimously supported by the Design Three entrants made the final short sessions at four separate venues. Aesthetic Advisory Committee, nine Write in 781 engineering, architecture and urban- Part of the family Designed to match the family of Los planning professionals, as well as residents Dubbed “The Ribbon of Light,” the dis- Angeles River bridges and to pay respect to the of surrounding neighborhoods, local tinctive structure features 10 pairs of starchy former bridge, the concept includes an 80-ft businesses and river advocates. white arches. A striking visual, the concrete arch over a western set of railroad tracks, a “It felt like we had just won the World arches are canted at 9˚, an industry first, and 50-ft arch over the river, an 80-ft arch over an Series,” Martinez said. seem to skip across the urban L.A. landscape, eastern set of railroad tracks, a series of 30-ft “We asked the Bureau of Engineering forming an iconic stress ribbon that runs the arches and a 50-ft arch over U.S. Highway 101. to bring the best of the best to the city length of the viaduct. Each arch will be illuminated by LEDs, of Los Angeles to design the new Sixth “We know first-hand the architectural creating a dramatic, energy-efficient nighttime Street Bridge, and they certainly deliv- brilliance this new Sixth Street Viaduct design effect. Rather than using streetlight poles on ered,” said Los Angeles City Councilman represents and look forward to seeing it come the bridge, HNTB designed an LED-lighted José Huizar. alive,” City Engineer Gary Lee Moore said. barrier between the bike lane, sidewalk and LIGHT TOWERS WE DO MORE THAN DESIGN EQUIPMENT. WE POWER YOUR SUCCESS. GENERATORS At Doosan Portable Power, we’re known for engineering solutions that make customers more productive. Visit www.DoosanPortablePower.com to fi nd the dealer nearest you and fi nd out how we can help you achieve: • Maximum fuel economy • Unparalleled productivity • Region-specifi c emissions solutions COMPRESSORS DoosanPortablePower.com | 800.633.5206 Write in 782 ©2014 Doosan Infracore Portable Power roadway. The accent lighting will accentuate engineer. “We leaned on those experiences “We were bumping up against the upper the arches while lowering light pollution. and they paid off.” design limit,” Jones said. “To make the arch “From a distance, it appears as if someone The $419 million Sixth Street Viaduct project rib work at a height greater than 60 ft, we took a long white ribbon and laced together the went into construction this spring on budget were going to have to make it quite a bit communities of Boyle Heights, the Arts District and on schedule with only slight modifications larger, which would cost quite a bit more, so and downtown Los Angeles,” Martinez said. or enhancements to the original concept: we decided to keep the standard 7-ft by 3-ft Connectivity is one of the Bureau’s main structural size.” project goals, and HNTB built in added Modified columns meet design criteria. features to promote it. As HNTB began analysis of its concept against Sliding seismic isolation bearings “The new bridge will invite more traffic design criteria, it became evident the viaduct’s increase resiliency, safety. The bridge will and improve connectivity with stairway access distinct X-shaped column configuration be the world’s first concrete network tied and bike ramps placed intermittently along its would need to be modified. arch built integrally with Y-bents in a high alignment,” Martinez said. “After detailed discussions with the seismic zone. As Councilman Huizar said, “The new contractor and the architect, we moved to a Y HNTB designed the Sixth Street Viaduct bridge will not only bring people from Point A configuration instead,” Jones said. replacement to exceed the latest seismic codes to Point B, but to Point C—the bridge itself.” The single Y column rises up from the by placing sliding seismic isolation bearings ground with the arms branching out in at mid-height in the columns, a first for the Building off experience opposite directions leading into graceful U.S. bridge industry. Because of the bridge’s unique configura- arches. The concrete arms use grade 80-ksi The bearings isolate the viaduct from the tion, HNTB developed project-specific rebar reinforcement as opposed to 60 ksi, a damaging effects of seismic ground motions. design criteria, including requirements for first for California bridges. Seismic isolation is achieved when the seismic design. force exceeds a certain friction value. At that “We had significant experience developing Arch heights reduced to meet design moment, the bearing breaks free and slides design criteria for complex Caltrans’ projects, parameters. At the same time HNTB modi- up a concave surface. Once the displacement including the Tom Lantos Tunnels at Devil’s fied the columns, it reduced the height of the demand of a 1,000-year event is exceeded by Slide and the Gerald Desmond Replacement arches from 80 ft to 60 ft over the railroad a factor of about two, the bearings gradually Bridge,” said Mike Jones, HNTB’s lead bridge tracks and from 50 ft to 30 ft over the river. stiffen and transfer forces to the structure in AQUATECH AMSTERDAM 2015 AND STORM WATER SOLUTIONS PRESENT THE EVENT’S FIRST-EVER STORM WATER PAVILION Aquatech Amsterdam, the leading trade show for process, drinking and SPONSORS: wastewater, presents the inaugural Storm Water Pavilion in 2015, sponsored by Storm Water Solutions magazine. Interested in sponsoring an exhibitor station or delivering a presentation at the Storm Held Nov. 3-6, in Amsterdam, the Netherlands, Aquatech Amsterdam’s Storm Water Pavilion? Contact Steve DiGiorgi at Water Pavilion will feature exhibitor stations/promo-points along with a Storm 805.708.5344; [email protected] Water Stage for exhibitor presentations. Take advantage of this opportunity to see what’s new in storm water and erosion control products and services at this international event, attended by 20,000 professionals. Grab a seat for the on-stage presentations and Q&A sessions, and discuss industry developments with your peers in the Pavilion’s networking zone. The official Storm Water Pavilion sponsor WE’LL SEE YOU AT THE PAVILION! www.estormwater.com a conventional way, providing a secondary & Environmental Design certification for of January 2015, up to eight CM/GC team back-up system. buildings, Envision encourages sustainability members co-located in HNTB’s office to work “Essentially, the bearing moves uphill. and resource efficiency. The Bureau of Engi- through the project details. The farther it goes uphill, the more resistance neering’s goal is to achieve a platinum-level “It’s indicative of the collaboration the it picks up,” Jones said. “The second the Envision rating. project has enjoyed,” Jones said. earthquake stops, the bearing slides back to a neutral position, acting as a self-centering Dealing with diffi culty Gathering place device. When the ground begins shaking, The Sixth Street Viaduct design features 20 On Feb. 20, 2015, the city of Los Angeles those motions cannot move through the complex knuckle joints. According to Jones, held a groundbreaking ceremony for the Sixth isolator.