Speaker 9: Dennis Engel of Washington State Department of Transportation
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TACOMA NARROWS BRIDGE Law Seminar Presentation
August 27, 2007
Dennis Engel, P.E. WSDOT Project Engineer Tacoma Narrows Bridge Project Office
Law Seminars International | Transportation Planning | 8/27/07 in Seattle, WA
Speaker 9: Dennis Engel of Washington State Department of Transportation
Page 2
History Prior to 1940 the only way across the Tacoma Narrows, a fast moving section of Puget Sound separating Tacoma and Gig Harbor, Washington, was by ferry. The other option would require someone to drive approximately 95 miles through Olympia and back north to Gig Harbor. On July 1, 1940 the first Tacoma Narrows Bridge was opened to traffic. This bridge was nicknamed Galloping Gertie because of the gyrations the bridge did during periods of wind. Unfortunately this bridge collapsed on November 7, 1940 in a forty mile an hour storm. The second Tacoma Narrows Bridge was opened to traffic October 14, 1950. The existing bridge had a configuration of four lanes, two in each direction. There was no barrier in the middle to protect vehicles from opposing traffic and had a small pipe curb to protect pedestrians from vehicles. Legislation Substitute House Bill No. 1006 was signed into law on May 15, 1993. This bill allowed effective July 1, 1993 the development of public-private initiatives (PPI) for transportation projects. In January 1994 the Washington State Department of Transportation (WSDOT) issued a request for proposal for improvements meeting SHB 1006. In May proposals were delivered to WSDOT for several different projects to finance, design, build and operate transportation improvements. Two of the proposals were for the construction of a new Tacoma Narrows Bridge. Private Partnership WSDOT selected United Infrastructure Washington (UIW) in August 1994 to move forward as a private partner on the development of the new Tacoma Narrows Bridge Project. An extensive public involvement process was started that included an advisory vote on the new bridge. A Major Investment Study and Environmental Impact Statement was also started. The Final Environmental Impact Statement was issued January 2000. The Peninsula Neighborhood Association challenged the legislation in court. The Washington Supreme Court ruled in November 2000 that the project was in violation of a previous RCW regarding tolling and maintenance of the existing bridge.
Law Seminars International | Transportation Planning | 8/27/07 in Seattle, WA
Speaker 9: Dennis Engel of Washington State Department of Transportation
Page 3
The Washington State Legislature revised the RCW in June 2002. This revision also changed the project from a Public-Private Partnership to a Design-Build project with WSDOT taking the lead on financing and oversight of the project. UIW’s agreement was completed at this time. Design-Build Contract Prior to the revision of the RCW, UIW had selected a Design-Build team known as Tacoma Narrows Constructors (TNC). TNC is a joint venture of Bechtel Infrastructure Corporation and Kiewit Pacific Company. TNC then hired a joint venture design team of HNTB and Parsons Transportation Group. WSDOT was given the authority to move forward with the project and use the Design-Builder already selected. Construction Design of the project had started July 16, 2002 when the Design Build Agreement was signed. Most of the design was completed in the first year. Since this is a Design-Build project, some aspects of the construction could be started almost immediately. The New Tacoma Narrows Bridge construction was started with a ground breaking ceremony on October 5, 2002. The first item of work on the project was starting the two and one half miles of roadway that was part of the overall project. Included in this are two new interchanges and a new bridge crossing SR16 at 24th Street NW. The roadway was widened to accommodate an additional HOV lane in each direction along with wider shoulders. Caissons Bridge work started with the building of two cutting edges for the caissons, the in water foundations for the bridge towers. The cutting edge is an 18 foot tall steel structure 80’ wide x 130’ long. This was constructed at Todd Shipyards in Seattle. Built on the ways and launched like a ship, the cutting edge has 15 hollow cells that have air domes welded in the bottom. The air domes allow for the structure to float. After the cutting edge was launched it was towed to the Port of Tacoma. At the Port the first 48 feet of walls were constructed using concrete. Exterior walls were four feet thick with interior walls three feet thick. After constructing the first 48’ the caisson was towed out into the Tacoma Narrows. It was then attached to 32 anchors drilled into the seabed. This held the caissons in place during construction. Each time ten feet of walls were built the caisson would sink approximately nine feet.
Law Seminars International | Transportation Planning | 8/27/07 in Seattle, WA
Speaker 9: Dennis Engel of Washington State Department of Transportation
Page 4
Once the caissons reached the seabed, at a depth of 150 feet, the cells were flooded and divers removed the air domes. Soil below the air domes was removed by a derrick barge with a clam shell bucket. Enough soil was removed to lower the caisson approximately 67 feet. A 25 foot thick concrete seal was poured in the bottom of the caisson. A distribution cap was constructed on top of the caisson as the base of the towers. Towers The next phase of construction was the towers. The top of the towers are at an elevation of 510 feet. This was built by a self climbing forming system called a bird cage. The bird cage was an enclosed work platform that had several levels. The lower level was used for concrete finishing. The middle level was where the 17.5 foot concrete forms were placed. These forms were able to roll back away from the reinforcing steel to allow tying and placement of rebar, then roll back for pouring. The top level of the bird cage allowed for the placement of reinforcing steel and the concrete. The contractor followed a cycle of a new lift of concrete every 4 days. The concrete delivery system was unique for the project. A portable batch plant was set up for the project. TNC built a temporary walkway along the bottom chord of the existing bridge that allowed for worker access and two slick lines for pumping concrete from the shore out to the existing towers and then across to the new caissons and towers. Concrete trucks would deliver the concrete from the batch plant to the pumps located on either end of the bridge. For the caisson pours a barge with two placing booms was used for the concrete delivery. Tower concrete placement was accomplished using a concrete bucket and tower crane. Catwalk The catwalk was an 11.5 foot wide work platform that followed the alignment of the suspension cable. This is what the ironworker crews used for access and worked from for the spinning of the main cable, compacting the cable, installation of the cable bands and suspenders, and the final painting. The catwalk was made of wire mesh allowing you to see through it to the water some 500 feet below. Cable The main cable wire starts at the anchorages and goes back and forth across the bridge, wrapping around the strand shoes at the anchorages. The cables are made up of 19 strands or bundles of wire. Each strand has a cross section of 464 wires in it for a total of 8,816 individual wires in each of the two main cables. The strand shoes are locked into the concrete at the anchorages. Once the cable was placed, hydraulic compactors were used to compress the 8,816 wires into a twenty and one half inch diameter cable. Temporary cable bands were then installed to keep the size and shape.
Law Seminars International | Transportation Planning | 8/27/07 in Seattle, WA
Speaker 9: Dennis Engel of Washington State Department of Transportation
Page 5
Bands/suspenders Large permanent cable bands were then bolted to the cable. These bands have the suspenders draped over them. The suspenders are the wire rope that actually attach the bridge sections to the main cables. Deck sections The deck sections were prefabricated in Koje, South Korea at the Samsung Heavy Industries ship yard. A total of 46 deck sections weighing approximately 450 tons each were constructed. The deck sections were loaded onto a transport ship in three separate loads. Once the ship arrived in the Tacoma Narrows it was anchored under the Gig Harbor side span. Four anchors held the ship in place, this allowed the ship to be moved in any direction while remaining anchored. The deck sections in the Gig Harbor side span were lifted directly off of the ship into place, where the permanent suspenders were attached. The main span and Tacoma side span were handled differently. Each deck section was lifted off the ship. The ship was moved out of the way using the ship’s anchoring system then the section was lowered onto a barge. The self propelled barge moved the section into place under the cables. A pair of large lifting gantries on the cables would then lift the sections into place. Some of the decks were placed over shore requiring another method of moving the deck sections. The deck was lifted by the gantries sitting on the main cables. Once the deck was lifted into the air the deck was attached to temporary suspenders. The temporary suspenders were installed slightly ahead of the deck section. The lifting gantries would then lower the deck section and because of the angle of the suspenders the deck section would go through a controlled swing towards shore. The gantries would then move forward on the cables and repeat this trapeze operation until the section reached it’s final position. Once the deck sections were installed, the joint between two deck sections would need the steel deck plate surface welded together and the rest of the truss section bolted together. Each joint used approximately 2,600 high strength bolts to connect them together. Deck Finishing The cables, suspenders and bolted sections all required a three coat paint system to protect the steel from the harsh salt water environment in the Tacoma Narrows. The deck plate received a water proof membrane and then two inches of Trinidad Lake Asphalt for a driving surface. Existing bridge
Law Seminars International | Transportation Planning | 8/27/07 in Seattle, WA
Speaker 9: Dennis Engel of Washington State Department of Transportation
Page 6
As part of the project, the 1950 bridge received some needed upgrades. The most important was bringing sections of the bridge up to current seismic codes. Some of the approach bridge columns were encased in steel and grout to keep them from buckling in a major event. Some steel sections of the west approach structure were removed and replaced with new stronger supports. The deck surface was ground and overlayed with asphalt and a new better safety rail for vehicles was installed. Tolling To pay for the bonds that were sold to finance the construction of the project, tolling has been implemented. The tolling company TransCore was hired to develop, supply and install the electronic tolling for the project. Tolls are collected in one direction only, traffic going to Tacoma from the Gig Harbor area are required to pay. Currently the tolls are $3.00 for manual lanes with $1.75 a trip for electronic tolling. The reduced toll for electronic tolling is only planned to be in effect for one year. Tolls are set by the Washington State Transportation Commission. A citizen advisory committee was set up to advise the commission on toll rates. There are six manual toll lanes where vehicles exit the freeway stop at a toll booth, pay and then re-enter the highway. The other option is to have a transponder that links to a pre-paid account. Vehicles can travel at the speed limit and not even slow down to have the tolls paid electronically. More than 60% of the vehicles have been using the electronic tolling since opening day. Opening On July 15, 2007 WSDOT had a public celebration of the opening of the new bridge. The morning started with a fun run of over 10,000 people. It was estimated that over 50,000 people participated in the opening celebration. People were allowed to cut ribbons that stated “I cut the ribbon on the new Narrows Bridge” and keep them as a souvenir as well as being allowed to walk across the bridge. By 11:00 pm that evening traffic was flowing across the new bridge.
Law Seminars International | Transportation Planning | 8/27/07 in Seattle, WA
