September 2008 - Folsom Bridge - Post-Tensioning & Project Tour
posted by Larry J Smith
By: Larry J. Smith, P.E., F.ASCE
SSCI, Chair
Post-tensioning is a method of prestressing concrete to induce forces during the construction phase to counteract the anticipated external loads encountered during the concretes lifecycle.
The ASCE Sacramento Section Construction Institute sponsored a technical presentation and project tour featuring Post-Tensioning of the Folsom Bridge. The Folsom's Bridge is a component of the American River Watershed Project. It is a Federal project that is being constructed by Kiewit and administered by the US Army Corps of Engineers. The concrete segmental bridge will have four lanes for traffic with Class 1 & 2 bicycle facilities. The Folsom Bridge was designed by the Joint Venture Team of CH2M Hill and URS.
The event was co-sponsored with the Society of American Military Engineers Sacramento Post and the Construction Management Association of America Northern California Chapter. Recognizing the need for collaboration between professional societies and associations the event featured a technical presentation and project tour.
Larry Smith, Sacramento Section Construction Institute Chair, and SAME Sacramento Post 2nd VP welcomed the audience of over 200 professionals. Larry welcomed the U.S. Army Corps of Engineers Engineering and Construction Chiefs from the South Pacific Region who made this event part of their quarterly E&C Chiefs Conference being held in Folsom, CA. Special guests were also welcomed including Mr. Joe Kaplin from the San Francisco Chapter of ASCE Construction Institute, Board Members from SAME and CMAA. Special thanks were extended to Diamond-D General Engineering, ARCADIS and Kiewit for sponsoring the event. Mr. Ron Price, Past President of the CMAA Northern California Chapter Management welcomed the audience commented on the importance of so many Engineering and Construction (E&C) Professionals networking and attending this event. Ron reflected upon the strategic alliance fostered between CMAA and SAME as the model for all organizations to follow and to build professional collaboration within the construction industry.
The Sacramento Section Construction Institute is governed by a Board of Directors including advisors from industry. Larry Smith introduced advisor teams from Envirocon, Granite Construction and Kiewit Pacific Company concluding his remarks by recognizing Shannan Balzer and Alex Kennedy (Students invited as CI guests) and a reminder of the Construction Institutes student days September 26 -28 in Burlingame, CA.
Folsom Bridge - Project Highlights and Facts
The American River and Lake Natoma bisect the City of Folsom. For more than 40 years, access across the river had been via the historic Rainbow Bridge and Folsom Dam Road that runs atop Folsom Dam. In 2000, a new four-lane bridge, the Lake Natoma Crossing, was constructed to span the American River at Folsom’s northwest edge to help reduce traffic on the Rainbow Bridge. The Rainbow Bridge still carries motorists, cyclists, and pedestrians to and from Old Town Folsom. The two-lane Folsom Dam Road was closed indefinitely for security reasons on February 28, 2003. At the time of the closure, the road carried approximately 18,000 commuters daily. These commuters are now forced to seek a new route across the American River either across the Rainbow Bridge or across the Lake Natoma Crossing. The new traffic patterns that have evolved are causing severe congestion on City streets and severely impacting the City’s Historic District and adjacent neighborhoods.
The increased traffic congestion, security issues, and public concerns regarding the uncertain future of Folsom Dam Road prompted Congressmen John Doolittle and Robert Matsui to add language to the USACE’s Fiscal Year 2004 appropriation authorizing the Sacramento District and local interests to immediately begin studies for, and the design of, a new bridge crossing downstream of the Folsom Dam. The appropriation also authorized $30 million in Federal funds towards the construction of the permanent bridge. Construction of the bridge will proceed once a cost-sharing agreement with local interests has been executed.
In June of 2004, the CH2M HILL/URS team was contracted by the Army Corps to perform the preliminary alignment studies. In the fall of 2004, the CH2M HILL/URS team was given notice to proceed with the final design.
Construction of the bridge will be heavily influenced by site accessibility constraints, including the rugged topography of the American River canyon directly downstream of Folsom Dam. The roadway profile is approximately 200 feet above the water level. Accessibility is limited by steep canyon terrain and location of existing access roads on Bureau of Reclamation and Folsom Prison property. Steep slopes adjacent to the river, the 150-foot river width, and variable water level resulting from dam discharges makes construction of temporary bridges across river very difficult. The terrain and slope stability conditions will influence construction of haul roads to access pier locations, and construct foundations and piers. Canyon slopes and depth as well as restrictions on river access will influence the cost and feasibility of falsework to construct the bridge. Crane placement will be limited by these same site constraints.
Highlights of the Folsom Bridge project include:
• Construct 2.1 miles of roadway and 1000’ Cast-in-place Segmental Cantilever Bridge.
• Approximately 1.2 million CY Roadway Material.
• Approximately 13,000 CY concrete.
• Approximately 3.2 million LBS rebar.
• Approximately 150 miles of Post Tensioning Strand.
• $75 Initial Construction Contract Amount.
• 22 Month Contract Duration.
Segmental Concrete Bridge Construction
Mr. Dan Hart, Project Manager of Kiewit Pacific Company and CI Advisor welcomed the audience with a brief overview of Kiewit and the Folsom Bridge and Joint Federal Project currently under construction by his firm. Dan introduced the keynote speaker and key members of his staff.
Mr. Carter Masterson, Kiewit Pacific Company, spoke on segmental concrete bridge construction and post-tensioning of segmental concrete.
Segmental concrete bridge construction has become a very important method in spanning deep valleys, wide water crossings, and across highways and existing facilities without the use of costly and often environmentally sensitive falsework.
The concept of segmental bridge construction began in Europe in 1950s. The first cast-in-place segmental concrete bridge was built across the Lahn River in Balduinstein, Germany in 1950. The first precast segmental concrete bridge was built to cross the Seine River, France in 1962. Since then the concept of segmental bridge construction has spread from Europe to all parts of the world.
In 1973, the first U.S. precast segmental concrete bridge was built and opened to traffic in Corpus Christi, Texas. In 1974, the first U.S. cast-in-place segmental bridge was built and opened to traffic near San Diego, California. Since then, hundreds of precast and cast-in-place segmental concrete bridges have been constructed throughout the U.S.A. Improvements and refinements in design and construction have been made over the years.
Carter Masterson highlighted several recent bridges including: Crooked River – Bend, OR; Bunker Hill Bridge – Boston, MA; the “Big I” – Albuquerque, NM; Bay Bridge Skyway – SF, CA; North Halawa Viaduct, Hawaii; and, Benicia Martinez Bridge – Martinez, CA, all having Post Tensioning Elements.
The CH2M Hill/URS Joint Venture Team evaluated three bridge type/ configurations: Cast-In-Place Segmental Post – Tensioned Concrete Box Girder; Steel Plate Girders; and, a Cast-In-Place Segmental Post – Tensioned Concrete Extradosed Box Girder. The Folsom Bridge is a “high demand – high profile” project for the U.S. Army Corps of Engineers and the City of Folsom. Construction costs and schedule were deemed paramount in a bridge type selection report authored by the Joint Venture Team. The report concludes the cast-in-place segmental post-tensioned concrete bridge is the recommended structure based upon lowest cost.
The Folsom Bridge is balanced cantilever construction with segments placed in a symmetrical fashion about a pier. The cantilever tendons are the principal reinforcement of the structural system; they are located in the deck slab and are anchored at the ends of the segment. The midspan tendons, located in the bottom slab near the webs are designed to resist the positive moments in the middle third of the span and the continuity tendons are used as reserve prestressing, designed on the basis of actual deformations measure after closure.
Mr. Masterson provided models and sample hardware used in post-tension operations for the audience to better understand post-tension construction techniques.
Considerations for Designing and Constructing Segmental Bridges.
•Design Fees: Segmental Bridges are non-standard and require specialized designers and software. Plan preparation is longer than for other bridge types because so little is routine.
•QA/QC: Segmental bridges require custom specifications. The AASHTO "Guide Specifications for Design and Construction of Segmental Concrete Bridges" contains basic construction specifications but these need to be tailored for the specific job and integrated with the owners existing bridge specifications. The owner will either need to train his own forces or hire specialists to perform inspections. Early segmental bridge projects frequently had large claims filed for incomplete plans and specifications.
•Continuing Engineering Services: The owner needs engineering expertise during the construction phase to approve shop drawings (contract plans seldom detail every individual segment with every bar length, drain inlet, electrical conduit etc.), evaluate design alterations that improve constructability and troubleshoot inevitable design and construction errors. This is frequently provided by the designer. Claims can mount for the unprepared owner who delays in responding to contractor inquiries.
•Longer Construction Time: Segmental bridge construction requires specialized formwork, falsework and construction equipment. These all delay the beginning of superstructure construction.
State-of-practice for Contractor and Construction Engineering and Inspection Personnel
Contractor Personnel:
The approach used on the Folsom Bridge for assuring the contractor has the capability to successfully complete project was addressed in the Solicitation to include:
• Pre-qualification of contractors before bidding
• Specifying minimum experience requirements for critical contractor personnel
• Specifications for controlling and executing the work.
Pre-qualification of contractors required specific capability to construct segmental bridges.
The solicitation specified the minimum requirements for project critical personnel. Examples of critical positions were:
• Contractor's (Construction) Engineer
• Geometry Control Technician (Foreman)
• Grouting Supervisor (Foreman)
• Grout Manufacture’s Technical Representative
• Stressing Foreman
A minimum of experience (time and structure type) for each of the critical personnel is specified in the contract documents and verification of experience is required to be submitted with the bid documents or after bid and before award. Others have requirements to verify experience before the related phase of work begins. Also, most states require review and approval of replacement personnel. Contractors and key personnel were required to demonstrate past performance on segmental bridge construction.
Construction Engineering and Inspection Personnel:.
The requirements for Construction Engineering and Inspection (CE&I) personnel are fulfilled by a team effort between the U.S. Army Corps of Engineers and CH2MHill / URS joint venture team. Critical elements of this project have been integrated shop drawing review, technical requests for information and oversight of construction by the consultant and government teams.
The Kiewit Pacific Project Team employees approximately 70 craft personnel and 30 salaried personnel. The Corps of Engineers Team is made up of approximately 12 engineers and construction managers with support of 6 engineers from the CH2M Hill/URS Joint Venture Team.
Scholarship Raffle
The luncheon concluded with Mitch Langois, Shannan Balzer and Alex Kennedy, conducted the drawing for prizes donated by Diamond-D General Engineering Company. Proceeds from the raffle support the ASCE Construction Institute Student Days Scholarship program.
Project Tour
Following the luncheon guests assembled at North end of the project site near the intersection of the new Folsom Bridge Road and Auburn-Folsom Boulevard. Mr. Dan Hart and Ric Nickel welcomed attendees and conducted the project tour from Abutment one looking southeast at Pier 2 and across the American River Canyon. Visitors could clearly see the progress on both bridge piers and roadway construction with asphalt paving of the Folsom Bridge Road well underway.
The view from abutment one revealed the details of the form travelers as well as the bottom deck, wing, stem and crown forms. Mr. Hart explained the purpose of the six pier struts each measuring five foot in diameter and weighing 80,000 pounds. The struts are temporary features to counter the forces created on the piers with alternating cantilever segmental construction. From travelers were clearly visible with the north closure segment approximately 75’ away. Iron workers were installing reinforcing steel for the next segment scheduled for the day following the project tour bring the gap some 60’ from closure.
Mr. Hart explained that 50% of the segments have been placed for the new Folsom Bridge with completion slated for spring 2009. The project team from Kiewit, the Joint Venture and the Corps of Engineers remained on site answering questions from the audience all eager to learn and wishing to stay late into the afternoon.