Otay River Bridge Meets Engineering Challenges

Engineers faced many challenges with the Otay River Bridge, a 2008 Concrete Bridge Award winner, in San Diego, Calif. The bridge is a critical link that carries four lanes of traffic across the wide Otay River Valley, a seasonal river and environmentally sensitive area that is home to a number of protected plants and animals. Construction needed to take place with minimal site disturbance while adhering to strict constructability and seismic performance standards.

These challenges were met with the selection of a segmental bridge. Spanning a total of 1,012 meters, the bridge is broken into ten spans of 90.5 meters and two end spans of 53.5 meters. It has a twin trapezoidal box girder configuration, connected by a longitudinal cast-in-place concrete closure. The contractor used the balanced cantilever method of construction where the segments were delivered over the completed portion of the deck to minimize site disturbance. The Otay River Bridge is a model for bridge construction and achieves the goals of constructability, seismic performance, and environmental sensitivity.

Read more on the Otay River Bridge:

“Precast Segmental Bridge Forges Link For Toll Road”, by Wayne Endicott, Aspire, Spring, 2007

“The Otay River Bridge”, by Ben Soule and Daniel Tassin, Structure Magazine, July 2007

Alkali-silica reactivity (ASR) is a chemical reaction that sometimes occurs when the silica in certain aggregates reacts with alkali hydroxides in cement paste after the concrete has already hardened (cured). This can create cracks in the concrete and can be tremendously damaging to the performance of concrete.

If supplementary cementitious materials (SCMs) such as fly ash, silica fume, slag, or metakaolin are present in the concrete mixture, they fight to help control this potentially damaging mechanism. These materials can be added at batching as separate concrete ingredients or as components of blended cements. Tests should be performed to determine the correct dosage of SCM to control ASR. Tests can also be run on the coarse and fine aggregates prior to their use in the concrete to determine their potential for ASR. Low-alkali portland cement can also be specified for a bridge project in areas where low-alkali cement is known to adequately control the reaction. More on ASR in concrete.

For more information on mitigating ASR in concrete bridges, attend the ASR Workshop (see below) at the 2010 Concrete Bridge Conference, February 24-26 in Phoenix, Ariz. Register for the conference at the NCBC Web site.

Register Now for the 2010 Concrete Bridge Conference

The 2010 Concrete Bridge Conference, to be held February 24-26 at the Hyatt Regency in Phoenix, Ariz., is sponsored by the National Concrete Bridge Council, and co-sponsored by the Federal Highway Administration, U.S. Department of Transportation.

The theme of this year’s Conference is “Achieving Safe, Smart, and Sustainable Bridges” and will include many technical sessions, a tour of local bridges, a reception featuring the presentation of the 2010 Concrete Bridge Awards, and an exhibit area. The conference will have five focus areas:

• Smart Bridges
• Non-Destructive Evaluations of Bridges
• Durable Bridge Decks
• Sustainable Bridges
• Innovative Design and Construction.

We welcome attendees and exhibitors for the conference. Both can register for the conference at the NCBC Web site.

ASR Workshop To Be Held at 2010 Concrete Bridge Conference

The Federal Highway Administration will sponsor a workshop on Alkali-Silica Reactivity (ASR) in Bridges and Structures at the upcoming 2010 Concrete Bridge Conference to be held February 24-26. The workshop will help bridge engineers and inspectors understand ASR and recognize symptoms, discuss the tests for ASR, and present options available to mitigate ASR in bridges. The speakers will also cover case studies in structures. A panel discussion will be included where the audience can ask questions of the experts. Register for the conference.

Mississippi Plans 21 Concrete Bridges with Stimulus Funds

Mississippi Department of Transportation (MDOT) will be undertaking 23 stimulus bridge projects with $114.5 million in stimulus funds, which will replace, repair, or newly construct 35 bridges. Of those 35 bridges, the superstructure materials for 22 of those have been identified, and 21 of them will be built of concrete.

In addition, MDOT is undertaking 37 state bridge projects in 2009 through their traditional federal-aid construction process, and these will replace, repair, or newly construct 45 bridges for over $259 million. Of these 45 bridges, 23 have been identified so far as prestressed or reinforced concrete bridges.

MDOT estimates that more than 49,000 cubic yards (cy) of structural concrete, 158,000 linear feet (30 miles) of prestressed concrete piling, and more than 125,000 LF (23 miles) of prestressed concrete bridge beams will be used on all of the stimulus and state bridge projects identified to date. For more information on Mississippi’s stimulus program, visit the MDOT Web site.

2009 Professors’ Seminar Offers Concrete Help

The 2009 Bridge Professors Seminar was held August 6-7 in Skokie, Illinois and 21 professors attended. The professors were sponsored by PCA Regional Promotional Groups, Cement Association of Canada regions, and other local cement and concrete industry groups. The seminar was conducted by PCA and co-sponsored by the Precast/Prestressed Concrete Institute and the Post-Tensioning Institute. Each professor received seminar notes as well as electronic copies of presentations and design examples.

The professors’ seminar is offered once a year in an effort to provide training and resources in state-of-the-art procedures for concrete bridge design implementing the AASHTO LRFD Bridge Design Specifications. The training and resources enable professors to introduce a new bridge design course into their school’s curriculum or to include bridge content into existing reinforced and prestressed design courses. The professors are also better able to help their local Departments of Transportation when bridge design questions arise.

Contact Sue Lane for information on how you can attend next year’s seminar.

Get Free Admission to World of Concrete 2010
Exhibits: February 2-5, 2010
Seminars: February 1-5, 2010
Once again, PCA offers free registration and a discount on seminars to the World of Concrete in Las Vegas, Nev. You can save as much as $65 on exhibit hall entry fees and $30 on each course you sign up for. Register now.