Tolt Hill Bridge 1834A emergency repairs
Bridge repairs underway
Latest update: April 17, 2018
Repair work on the Tolt Hill Bridge 1834A is scheduled to begin Monday, April 23. Set-up, including the staging of equipment and materials, begins Thursday, April 19. The repair work includes retrofitting truss joints, replacing bolts with higher strength bolts, and adding new bolts and splice plates. During construction, beginning April 23, one lane will be open for motorists to cross the bridge. A signal will be set up to alternate the direction of traffic across the bridge. The signal will be in place 24/7 while work is being performed. A one-week full closure of the bridge will occur during the summer. The exact dates of the full closure have yet to be determined. The public will be provided with notification two weeks prior to the full closure. The repair work is expected to finish this fall. The current six-ton load restriction will remain in place during construction. Once the repair work is complete, the weight restriction on the bridge will be lifted.
April 9, 2018 - Update
Repair work on the Tolt Hill Bridge 1834A is anticipated to begin at the end of April 2018. This webpage will be updated and a Road Alert email/text will be sent out when the start date is determined. To sign-up for Road Alerts, click the red Stay Connected button on the right side of this page.
March 12, 2018 - Update
A construction contract for repair work has been executed. Garco Construction will perform the work which is anticipated to begin this spring and last approximately six months. During construction one lane will be open for motorists to cross the bridge. A signal will be set up to alternate the direction of traffic across the bridge. This will be in place 24/7 while the work is being performed. In addition, a one week full closure of the bridge will occur during the summer. Garco Construction will provide a schedule which we will post on this webpage. Please check back for updates.
Nov. 14, , 2017 - Update
On Monday, Nov. 20, between 9 a.m. - 1:30 p.m., King County is coordinating with the Washington State Department of Transportation to utilize an Under Bridge Inspection Truck to perform a four-hour inspection of the joint connection details of the steel trusses on the Tolt Bridge. The information from this inspection will be utilized in the final design effort for the bridge’s repair. This work requires lane restrictions. Traffic will be flagged through the work zone.
Oct. 3, 2017 - Update
Engineers are working towards having a bridge repair design completed by the end of this year. Construction is anticipated to begin in early 2018, although a schedule has not yet been set. We will continue to update this page as we receive more details. Please consider signing up for Road Alert emails and texts to receive the latest information. To sign-up, click HERE.
July 17, 2017 - Update
The Tolt Hill Bridge is scheduled to reopen at 1 p.m. on Monday, July 17 with restrictions. Engineers have determined it is safe to allow traffic on the bridge where each vehicle is six tons or less fully loaded. Bikes and pedestrians are also allowed.
July 14, 2017 - Update
Engineers have completed an in-depth analysis of the loads the Tolt Hill Bridge can safely carry. They have determined it is safe to allow traffic on the bridge where each vehicle is six tons or less. For example, a fully loaded pickup truck would be less than six tons. Load restriction signs will be posted on the bridge. Future closures for repairs are likely, but not yet determined.
On Monday, July 17, when new signage is available and can be deployed, the Tolt Hill Bridge will reopen to noncommercial pickup trucks, passenger vehicles, bikes and pedestrians.
Bridge repairs still need to take place, and will likely result in some future closures. More information on repair efforts and related closures will be available when design experts determine the best approach to repairs. We will continue to keep you updated on this webpage and through the email and text alert system. To sign up for the alert system, click the red “Stay connected” button on the right side of this webpage. Updates will include progress of the repair design, the repair schedule once determined, and potential traffic impacts to motorists during construction.
July 11, 2017 - Closure update
From Saturday, July 15 at 6 a.m. to Monday, July 17 at 5 a.m., a second phase of road resurfacing work will take place on NE Novelty Hill Road from 243rd Avenue NE to West Snoqualmie Valley Road NE. This work is a continuation of last weekend’s road resurfacing project (July 7-10) and requires a full weekend closure. This route is listed as a detour option for motorists impacted by the Tolt Hill Bridge closure. Emergency service vehicles will be able to use this section of NE Novelty Hill Road during the July 15-17 closure. Click HERE to see the map.
July 7, 2017 - Closure update
The county is consulting with the Washington State Department of Transportation bridge experts, the Federal Highway Administration and a design engineering firm to discuss next steps for the bridge, including whether or not the bridge can be safely reopened to limited traffic. The county’s consultant design engineering firm is developing a repair design, reviewing the new federal methodology for determining the load a bridge can carry, and will work with a design expert who specializes in this type of bridge (steel truss design). A contractor will also be hired to provide a review of the project design. As soon as we know more about the repair plan and load rating results, we will post an update on this page and send out a Road Alert email and text. To sign-up for Road Alerts, click the red “Stay Connected” button on the right side of this webpage.
>> Also see other previous updates
On this page
- Latest update
- Reason for closure
- Closure schedule
- Detour routes
- Bridge history
- Frequently-asked questions
Brent Champaco, Community Relations Planner
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Reason for closure
Following the 2007 collapse of the eight-lane bridge on Interstate 35W in Minnesota, and the federal decision to allow heavier trucks on roadways, the Federal Highway Administration (FHWA) developed new requirements for rating the load that a bridge can carry.
The new requirements for load ratings require all bridges to be load rated using the new criteria by 2022. For the first time, agencies are now required to review gusset plates, which are thick sheets of steel that connect structural elements of truss bridges. There are about 36,000 bolts fastening the plates on the two 300-foot long steel trusses of the Tolt Hill Bridge.
King County had structural engineers review the work of the private contractor who designed the Tolt Hill Bridge. They discovered discrepancies between the design calculations and the actual construction.
The bridge will be closed beginning at 8 p.m. on Friday, June 16 for an indefinite time to design and implement repairs. The bridge currently shows no visible issues, and has been inspected on a biweekly basis since March 8, 2017. The last bridge inspection took place on June 13, 2017.
No dates have been set yet for repair work or reopening the bridge.
What is the closure schedule?
Details on the repair work and schedule will be posted on this webpage as soon as they are determined, along with updates and photos. Sign up for emails or text alerts by clicking the red “Stay Connected” button to the right. Detours will be in place for motorists. Please see the detour map on this webpage.
Tolt Hill Bridge 1834A history
Tolt Hill Bridge 1834A opened for public use on May 30, 2008 and is owned and maintained by King County. It is located over the Snoqualmie River on Northeast Tolt Hill Road west of the City of Carnation. It replaced the original Tolt Hill Bridge 1834A, which was built in 1922 and was located approximately 125 feet upstream. The new bridge is approximately 1,000 feet long and consists of two 300-foot long steel trussed spans, a short approach span on the west side, and three 120-foot long concrete girder spans on the east side of the river. The average daily traffic/ADT of this bridge is approximately 3,000 vehicle trips.The bridge has two travel lanes and two shoulders. It is regularly monitored and inspected.
The bridge was built nine years ago, why is the county just now discovering a problem?
Following the 2007 collapse of the eight-lane bridge on Interstate 35W in Minnesota, and the federal decision to allow heavier trucks on roadways, the Federal Highway Administration (FHWA) developed new requirements for rating the load that a bridge can carry. The FHWA developed new formulas for analyzing the structural integrity of existing bridges for the purpose of understanding the load that bridges can carry in their current condition.
FHWA and the Washington State Department of Transportation (WSDOT) issued the new calculation methodology and required that all state and local bridges to be evaluated by 2022 using the new criteria. As part of the evaluation, agencies are required to review gusset plate connections, which are thick sheets of steel bolting together the structural elements of truss bridges. There are about 36,000 bolts fastening the plates on the two 300-foot long steel trusses of the Tolt Hill Bridge.
King County conducts visual inspections of all bridges every two years, and has completed inspections of Tolt Hill Bridge 1834A on that schedule. Rating the load of a bridge is complex work that is performed when a bridge shows signs of stress or deterioration; otherwise load rating is performed on an infrequent basis. There have been no signs of stress or deterioration on the bridge. In any case, this is a new FHWA rating criteria that did not previously exist for evaluating the structural integrity of bridges and key components.
The evaluation process is very complicated using the new testing protocol. Initial results did not seem consistent with a relatively new bridge that the county had directed be built to the 2005 bridge construction codes. The county immediately engaged a third party consultant to review our preliminary determinations, and provide even more detailed analysis. The consultant structural engineers agreed with our findings and identified additional concerns. Since this is a new calculation and review process, as soon as we had this information, we reviewed our process with WSDOT bridge engineers, and immediately following, moved to emergency closure.
How come this has not come up in routine inspections?
This is a new and complex structural engineering calculation designed to identify the weight that the bridge and its connections can carry. King County conducts visual inspections of all bridges every two years, and has completed inspections of Tolt Hill Bridge 1834A on that schedule. Agencies infrequently load rate bridges; this complex work is only needed and performed periodically or if the bridge shows signs of stress or deterioration. There have been no signs of stress or deterioration on the bridge. In any case, this is a new FHWA rating criteria that did not previously exist for evaluating the structural integrity of bridges.
Was there any validation of the work performed by the contractor when the bridge was built?
The county competitively hired a private design firm to design the bridge and oversee the construction. The county evaluated the qualifications and experience of the firm and key project team staff to ensure that the firm had appropriate licensed and experienced structural and other engineers.
It is the professional practice of those licensed engineers to have peer review of their calculations and quality control review of their final design and construction drawings. The design firm is solely responsible for all calculations and design review. Owners do not recalculate the work of hired design firms. During construction, the county does have construction inspectors that compare the constructed bridge to the construction plans developed by the design firm. The bridge was constructed according to the construction plans developed by the private design firm. The issue found was from the design phase and not the construction phase. Calculated values of the various bridge items (gusset plates and bolts) were incorrectly shown on the construction plans.
Why is this considered an emergency? Why couldn't work be done incrementally to bring the bridge up to compliance?
Based upon the new calculations and using the current standards, there are a couple of key connections between steel beams on the underside of the deck (“cords”) that may not be able to safely support the bridge itself or any additional weight. We are continuing to review the calculations and perform additional analysis, but at this time, the analysis indicates it is not safe to have traffic on the bridge.
Was any consideration given to lowering the weight limit of the bridge (to just cars, no trucks) rather than closing it completely?
Yes, initially we hoped the results would allow us to load limit the bridge and allow some vehicles and traffic. Based upon recent calculations using the mandated standards, there are a couple of key connections between steel members on the underside of the deck (“cords”) that may not be able to safely support the bridge itself or any additional weight. We are continuing to review the calculations and perform additional analysis, but at this time, the analysis indicates it is not safe to have traffic on the bridge.
The structural engineers have enough information at this point to know that there are concerns, mathematically, with structural integrity. We carefully considered whether load limiting was an option at this point. It is not, based upon the standards in the new calculation formulas and what we know at this time. If we learn more that will let us reach a different conclusion, we will make adjustments.
How long have you been reviewing this issue?
A series of increasingly detailed calculations have been performed over the last couple of weeks. An outside consultant was engaged to review our initial calculations and results, and to look in more detail at the strength of individual gusset plate connections, given that these are new processes and the threshold results were so anomalous. The consultant engineers identified a couple of key gusset plate connections between steel members on the underside of the deck (“cords”) that may not be able to safely support the bridge itself or any additional weight based on the most current standards.
Can't you let bicycles and pedestrians use the bridge?
Yes. As of July 17, 2017, bikes and pedestrians are allowed on the bridge.