A UC San Diego-government research project has resulted in the development of composite technology that has been applied to a new highway bridge on State Route 86 near the Salton Sea.
The Kings Stormwater Channel Bridge, which officially opened on May 18, is unique in that it is primarily composed of glass and carbon composites. ‘This project could open the door for a complete rethinking of what engineers consider as structural materials for buildings and bridges,’ says Professor Frieder Seible, the project’s designer, and chair of the Irwin and Joan Jacobs School of Engineering’s renowned Department of Structural Engineering at UC San Diego.
Several of the bridge’s main components contain no steel rebar. Instead, the girders and deck supports are structural shells – tubes made of lightweight carbon fibre-reinforced polymers (CFRPs) which are filled with concrete at the construction site. The advantage of using composites over traditional materials is that detailed, timely, and costly rebar work can often be eliminated. In addition, composites do not corrode like steel rebar, are up to five times lighter than steel, and can be installed without the use of heavy construction equipment.
Caltrans, who partnered with UC San Diego and DARPA (Defense Advanced Research Projects Agency) on the transfer of materials and technology from the defence industry to the civil sector, is anxious to monitor the performance of these new materials. ‘The Kings Stormwater bridge provides Caltrans with the performance and durability data required for acceptance of advance composite materials in bridge design and construction. These fibre reinforced polymer materials, especially the carbon fibre composites, are ideally suited for harsh and adverse environments and are expected to reduce maintenance and extend the service life of bridges,’ explains Jim Roberts, Chief Deputy Director of Caltrans.
In addition to the application of new materials and design/construction concepts, Caltrans and the university have jointly deployed an advanced instrumentation and monitoring system, in an effort to monitor – as well as evaluate the state of the bridge under service load (namely heavy haul traffic between Mexico and Los Angeles through the Imperial Valley) and seismic input. In this context, Seible and colleagues have joined forces with the new California Institute for Telecommunications and Information Technology [Cal-(IT)2], a partnership between UCSD and UC Irvine. Cal-(IT)2 is one of four institutes funded through Governor Gray Davis’ California Institutes for Science and Innovation program.
One of the institute’s key projects is to prototype a new environmental monitoring infrastructure that can collect data from a wide variety of sensing devices, communicate it to a central archive facility, and visualise and analyse it in a NASA-style ‘control room.’ This infrastructure will be used to demonstrate the power of science-based policy guidance and decision making related to concerns of importance to Californians (i.e. health of the civil infrastructure, seismicity, water pollution, and snowpack level as related to the supply of drinking water). ‘Caltrans is very interested in developing health monitoring systems for the bridges which can detect structural problems and deficiencies prior to catastrophic failures or prolonged road closures,’ said Dr. Charles Sikorsky, Senior Bridge Engineer with the Caltrans Office of Earthquake Engineering.
‘This project will further propel the use of advanced composite materials into the enormous infrastructure market,’ explained Bob Randolph, project manager for the DARPA Program. The co-operative program has been ongoing at the Jacobs School over the past several years to develop additional uses for composite materials that have typically been used in military and aerospace applications.
The carbon shell system (CSS) technology was developed and tested at the Jacobs School. The shells, which are long, hollow tubes, are ‘stay in place’ forms designed to replace rebar and the conventional temporary forms for constructing girders, columns and beams. In this particular project, the shells are used for the girders. ‘Using carbon shells in the Kings Stormwater Channel Bridge is revolutionary as it enables carbon stay in place forms to compete in the multi-billion dollar construction market,’ explained Professor Gil Hegemier, UCSD project leader of the DARPA research program on the use of Advanced Composites for Bridge Infrastructure Renewal.
The carbon shells were created off-site using a process called filament winding. Alliant TechSystems, the manufacturer of the girders, used factory equipment typically employed for aerospace applications to make the transportable ‘stay in place’ forms. ‘ Finally, Martin Marietta, the company responsible for building the bridge’s deck, used glass (GFRP), another composite material tested and validated in the UC San Diego/DARPA Program. ‘We see this as a successful stepping stone into new construction technologies that will save both time and money,’ stated Dr. Dan Richards, Manager-Composites Program.