Skip Top Navigation

Experts confirm rebar provides pontoon structural capacity

Get Our Mobile App

  • Our Android and iPhone apps include statewide traffic cameras, travel alerts, mountain pass reports, ferry schedules and alerts, northbound Canadian border wait times and more.

Date:  Friday, December 21, 2012

Contact: Suanne Pelley, SR 520 Communications, 206-770-3578, 206-437-5717 (cell)

Expert Review Panel adds new members with additional expertise

SEATTLE – An analysis using computer modeling, onsite inspections and engineering calculations has determined that rebar in corner joints in three completed pontoons for the State Route 520 bridge provides the required structural capacity.

The Washington State Department of Transportation also announced today the addition of two new members to its Expert Review Panel who will assist in the panel’s review of the design, materials, construction methods, and overall integrity of the pontoons.

In November, WSDOT reported that rebar with 90-degree hooked ends was omitted during the first cycle of construction of three longitudinal pontoons – 360-foot-long structures that will be joined together across Lake Washington to provide the backbone of the new, six-lane floating bridge. The end walls were designed to have rebar bent in a 90-degree shape as a design measure to minimize potential cracking in areas where large bolts are used to join pontoons together.

WSDOT launched its own analysis and also engaged engineering firm Parsons Brinckerhoff Inc. to conduct a third-party analysis of the structural capacity of the pontoons.

“WSDOT is committed to ensuring the safety of the traveling public and to building a new floating bridge that will meet the needs of the region for 75 years or more,” said Julie Meredith, SR 520 program director. “So we have been very thorough in our investigation and study of this question about the omitted hook bars in three of the first six pontoons built in the Aberdeen casting basin. We now have confirmation that the structural integrity of the pontoons is sound. ”

WSDOT engineers confirmed that as-built construction records and construction photos verify that the missing hook bars were replaced in pontoons labeled T and U, and in the bottom slab of pontoon V, by adding extra shorter bars with 90-degree hooks at their ends, a method confirmed as structurally adequate. The shorter hook bars, combined with other rebar near the bolt beam area, provide the strength needed at this location.

In addition, analysis conducted by Parsons Brinckerhoff and verified by WSDOT shows that while the top slab of pontoon V does not include the shorter hook bars, it still meets structural requirements because of the extensive steel rebar and added strength from the bolt beam in this location and because the rebar is sufficiently embedded in the concrete. Both of these factors are included in the analysis completed by Parsons Brinckerhoff and verified by WSDOT.

Based on this analysis, “there is no reduction in structural capacity,” WSDOT Bridge and Structures Engineer Jugesh Kapur said.

In related news, two new experts have joined an Expert Review Panel that is providing independent review of pontoon design, construction and structural sufficiency. Steve Tatro is a materials engineer with extensive experience in concrete, design and construction with the Army Corps of Engineers. Mark Leonard of the Federal Highway Administration is a structural engineer with prior experience supervising bridges and structures for the Colorado Department of Transportation. These new members join Chairman John Reilly, Neil Hawkins, Tom Sherman and John H. Clark on the panel.

Following an initial personal review of the floating bridge design, Clark said this week that the design is “conservative” in terms of potential requirements related to traffic loadings and wind and wave forces on the floating bridge.

“This tells me that the structural capacity is in excess of any loads or stresses that will be put on the pontoons when the new bridge is completed, though we have additional work to address end wall cracking that occurred in cycle 1 and make modifications for future cycles,” Clark said.

Project background

Construction on the $367 million SR 520 Pontoon Construction Project broke ground in February 2011 in Aberdeen. Construction on the $586.6 million SR 520 Floating Bridge and Landings Project began in spring 2012. The floating bridge contract requires the new, six-lane SR 520 floating bridge to open to traffic by July 2015, but includes incentives for an earlier opening in December 2014. WSDOT is in negotiations with its contractors for pontoon issues encountered in spring 2012 and has not made an official determination on any potential schedule or cost changes. WSDOT and Kiewit will continue to evaluate schedule opportunities throughout the construction duration.

The latest jobs report counted 832 jobs directly connected to the pontoon and floating bridge project sites in Aberdeen, Tacoma, Kenmore and Bellevue and on Lake Washington.

More information is at www.wsdot.wa.gov/Projects/SR520Bridge/PontoonProgress.htm.

###


< Go Back