“Without fully-developed design guidelines and construction plans and specifications, the benefits of jointless bridges may not be fully realized,” says Allen.

Monitoring Jointless

To better understand how jointless bridges perform, VTrans initiated a research project, Performance Monitoring of Jointless Bridges, to gain a thorough understanding of how jointless bridges respond to thermal movements, and to dead and live loads in a northern climate.

“The primary research objectives were to provide VTrans engineers with the knowledge and quantitative data to design and construct cost-effective, efficient, safe, reliable and low-maintenance structures,” Allen says.

This ongoing project has three phases. Phases I and II, completed by Wiss, Janney, Elstner Associates in 2002, included a formal literature search and the development of an instrumentation plan. VTrans applied the information and knowledge gained from the research to develop design guidelines, contract plans and specifications, and has used the documents to build several integral abutment bridges since 2002.

Now, the 2010 VTrans Structures Manual will include guidelines and procedures for integral abutment design developed from the Phase I research. “With the application of the Phase I research findings, integral abutment bridges have become the preferred structures at VTrans,” Allen says.

For Phase III, the University of Massachusetts-Amherst is conducting research, which includes modifications to the Phase II instrumentation plans, installation and monitoring of instrumentation, data analysis and reduction, and preparation of a final report. Phase III should be completed in February 2013.

Crack meters in reference pile enclosures (bottom) measure the longitudinal and lateral displacements on East Montpelier Bridge in Vermont.

The Phase III research involves three bridges: a straight bridge with a 141-foot span in Middlesex; a 121-foot-long bridge with a 15-degree skew in East Montpelier; and a curved-girder, two-span continuous structure with 11.25 degree of curvature and a total length of 226 feet in Stockbridge.

Instrumentation on these bridges includes pile and girder strain gauges, earth pressure cells, displacement transducers, inclinometers, tiltmeters and thermistors – devices used to measure temperature differences.

At a University of California-Berkeley demo, (top) triple pendulum isolators (twin stainless steel facing concave devices with ‘pendulum’) above the bridge column bents allow the bridge superstructure to move with a seismic event.

“Tangible economic benefits [of this research] include reductions in maintenance and construction costs,” says Allen. “The construction cost savings result from eliminating cofferdams and from using less concrete and reinforcing steel in the substructure and superstructure.”

The integral abutments, he says, have a typical height that is less than that of a conventional abutment, reducing the quantity of excavation and backfill materials. In addition, integral abutments require fewer piles for support than do conventional abutments. Indirect benefits include savings from a more rapid construction schedule, which decreases user costs; fewer environmental impacts, such as less sediment pollution of streams; and better access under the bridge for wildlife passage, because the structures are longer.

Berkeley’s New Seismic Bearings

In May 2010, the University of California-Berkeley demonstrated three new permutations of seismic bearings that could radically change how bridge superstructures are protected in case of an earthquake.

Over 100 engineers, researchers, media representatives and members of the public were on hand to witness a demonstration of a new isolated bridge system at the PEER Earthquake Simulator Laboratory at the university’s Richmond Field Station.