WSDOT Working to Correct Structural Problem on New I-405 HOV Ramps in Kirkland
Engineers with the Washington State Department of Transportation have discovered a structural problem in the construction of new HOV direct access ramps at NE 128th Street in the Totem Lake area of Kirkland. The problem does not pose any safety risk to the traveling public and will be repaired before the new ramps open to traffic. These repairs will delay the opening of the new transit flyer stops until summer 2007, adding an estimated $2 million to $3 million to the cost of the project.
WSDOT’s initial investigation indicates that the structural problem is a result of design errors. WSDOT engineers designed the bridge and ramps.
In this innovative design, transit flyer stops are cantilevered out from either side of an HOV freeway ramp. Insufficient reinforcing steel was embedded in the roadway between the cantilevered transit flyer stops. As a result, the roadway between the flyer stops is cracking.
“We have reviewed our quality control and quality assurance process for our bridge designs and we have taken steps to ensure that independent checks are completed before plans are released for consideration,” said John Conrad, Assistant Secretary for Engineering and Regional Operations.
WSDOT engineers confirmed that contractor Max J. Kuney Construction of Spokane, Washington built the structures correctly and in accordance with the design. The HOV direct access ramps are funded by Sound Transit and are part of the I-405 corridor bus rapid transit system.
In December 2006, WSDOT and contractor Kuney Construction noticed cracks in the concrete on the new HOV ramps located in the median of I-405. These cracks were parallel to cantilevered bus stops which jut out on both sides of the ramps just to the north of the new NE 128th Street bridge. Crews noticed the cracks after they removed the temporary construction supports from the structure.
In the weeks that followed, engineers surveyed the structure, found that the cantilevered sections had settled, and that the amount of the most significant settlement approached one inch. WSDOT then brought in its bridge specialists, who determined that the cracks resulted from a lack of sufficient steel reinforcement in the concrete between the cantilevered sections.
After developing several designs to correct the problem, it became apparent that the only option to ensure long-term performance and durability of the structure was to completely remove and rebuild all of the ramp surface between and including the cantilevered sections.
WSDOT and Sount Transit still expect to open the new NE 128th Street bridge and ramps from the south side of the bridge this spring. But WSDOT now estimates a delay of four to six months to open the north ramps and transit flyer stops.
WSDOT has a well-established review and approval process for design plans. High-level engineers with years of experience specializing in design and construction of highway structures reviewed the plans, but failed to catch the design weakness that led to this problem. WSDOT will also review plans for all similar structures.
The I-405 Totem Lake Freeway Station Project is primarily funded by Sound Transit. The new HOV ramps in the I-405 median will allow buses, vanpools and carpools to enter and exit the freeway without merging through three lanes of traffic. The NE 128th Street bridge will provide a new east-west route across I-405 for all drivers.
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