|On December 21, 2001, the Tennessee Department of Transportation (TDOT) notified the City that the Netherland Inn Bridge must be closed effective January 4, 2002 to truck traffic and January 11 to all traffic due to the increased possibility of localized failures in the floor beams that support the bridge decking. The closure is a result of a TDOT inspection performed on December 4, 2001|
|that revealed an acceleration in the rate of deterioration of the integrity of the floor beams with one crack increasing in length from approximately 1' 2" to 7' 8" since June 2001.|
|The majority of the deterioration is typical metal fatigue, e.g., cracking, corrosion, bending, and has been most prevalent in the "superstructure" of the bridge which includes the floor beams, trusses, and connection plates. Over the last 5 years, the TDOT bridge inspections have noted only slight increases in the physical deterioration of the bridge and the overall bridge rating ("poor") has not changed. However, in December 2001 the inspection revealed evidence of a more rapid rate of decline in the floor beams so TDOT downgraded the condition of the superstructure from "poor" to "serious" - with the overall bridge rating remaining at "poor".|
|The general poor condition of the bridge structure was first noted in the biannual TDOT inspections in the mid-1990s. In response to these findings, the City had an independent engineering firm develop repair recommendations and established funding to effect the necessary repairs. However the repair work was subsequently deferred when the City was notified that the bridge was accepted|
|into the federal bridge replacement program and a city/state|
|project contract was signed in 1999. The decision to defer the repair work was supported by the fact that the rate of decline in the bridge structure had been slow and no critical failures were identified within the projected time frame for bridge replacement.|
|As reported at the October 21, 2001 BMA meeting the replacement bridge is presently in the design phase at TDOT. TDOT has developed|
|preliminary engineering plans that propose to replace the bridge at the same alignment as the current bridge with the addition of approximately 20' - 25' of bridge width. By choosing to maintain the existing alignment, significant private property (including one occupied home) will have to be acquired for right-of-way purposes, traffic (12,000 vehicles/day) in and out of downtown Kingsport will have|
|to be rerouted for an estimated 2-4 years (TDOT estimate),|
|and the City will have to design and construct a temporary sewer at an estimated cost of $500,000.|
|Based on the prospective adverse impacts of using the same bridge alignment, the City requested TDOT consideration of alternative bridge alignments. As a starting point for discussion purposes, City engineering staff suggested one alternative alignment concept (pictured above) to demonstrate the opportunity to improve traffic safety, eliminate the need to acquire row that would displace a family, reduce the need for traffic detouring, and avoid temporary sewer construction costs.|
|The alternative alignment would involve constructing all, or portions of the new bridge, to the immediate south of the existing bridge, prior to removing the existing bridge. This option would allow traffic to continue unimpeded and the sewer could remain in place and be transitioned over to the new bridge once it was constructed. This alignment would slightly alter the approaches at each end of the bridge (which would improve the traffic safety issues related to the side street entrances located at either end of the bridge) but it would also impact the parking area at Riverfront Park and portions of the Rotherwood Mansion property.|
|In December 2001 TDOT agreed to reevaluate alternative bridge alignments and advised the City that the possible impacts of alternative alignments on Riverfront Park and the historic property at Rotherwood Mansion would require federal review. TDOT staff noted that the federal review process is likely to add 2-3 years to the overall project length and TDOT staff cautioned that after their review the federal agencies could choose to deny any alignment that unnecessarily impacts existing parkland or historic lands. In the interest of protecting the property owner, maintaining traffic flow, improving traffic safety and avoiding costly temporary sewer infrastructure, the City staff were moving forward with preparations for the federal review process.|
|Until the December 4th inspection, the information on the bridge condition supplied by TDOT indicated that the service life of the bridge was adequate to fit within the timeframe for the new bridge design and construction. The overall bridge rating had not changed in over 5 years and communications with TDOT engineers as recent as October 2001 had indicated that the bridge structure should accommodate the additional time required for a 2-3 year federal review and new bridge construction estimated at 2-4 years by TDOT.|
|The December inspection findings were the first indication that the bridge structure may be entering a more critical and unpredictable state of decline earlier than anticipated in which segments of the distressed metal floor beams may be nearing their tolerance threshold and have begun to show signs of deterioration that could lead to localized failures beneath the bridge decking. TDOT inspection engineers noted that the inspection findings do not indicate that bridge failure is imminent, however the unpredictable nature of metal fatigue and heavy traffic loading on the bridge warrant bridge closure until repair measures can be implemented or a new bridge is constructed.|
|The TDOT inspection engineers explained that a localized failure in a floor beam could create a depression in the bridge decking immediately above a failing beam that if left unattended could ultimately lead to a hole in the surface of the bridge. The engineer added that typical interim/temporary repair measures for problems of this nature include attaching reinforcing plates to distressed areas. Determination of the extent of plating and reinforcement measures would necessitate an engineering study to calculate the bridge strength requirements and to design a repair plan that ensures public safety and conforms to state bridge standards until a new bridge is built.|
The Department of Public Works has been in contact with TDOT inspection personnel in both the regional office in Knoxville and headquarters in Nashville to gauge the severity of the condition of the bridge and to explore mitigation measures, e.g., weight/load restrictions, temporary repairs, additional bridge condition monitoring, etc. that might allow the limited reopening of the bridge in the near future. The preliminary discussions with TDOT suggest that given the recent increase in the rate of deterioration and unpredictability of localized failures in the weakened metal beams any mitigation would have to include repair of critical structural supports. City engineering staff estimates that the best case scenario for the repairs to be designed and constructed would be 6 months at a cost between $200,000 to $500,000.
Given the extent of design, engineering and right-of-way work still required for any of the bridge alignment options (including the TDOT recommendation to keep the existing alignment), the bid for new bridge construction is not likely to occur any sooner than Spring 2003 and finish in the 2005-06 timeframe. With an approximate 1-2 year window before new construction would occur (with the closed bridge idle), staff is actively exploring critical repair options that would restore the bridge to traffic for an approximate 5 year timeframe.
A "Bridge Activity Schedule" is summarized on the next page, and it is evident from the its contents that the City must make some decisions on how to proceed over the next 6-12 months in order to select a critical path to address the immediate, short and long term issues related to the bridge. A decision flow diagram is also displayed on the page following the activity schedule.
Public Works is leading a team of staff from Police, Fire, and Traffic to develop a bridge closure response plan that ensures the maximum protection of public safety in rerouting traffic around the closed bridge. This staff team has developed a series of recommendations that include detour signs, emergency response routing, traffic restrictions on inadequate roadways in impacted neighborhoods, signal re-timing, and intersection improvements to ensure the safe and convenient travel for cars and trucks. To facilitate the development of a bridge closure plan the City hired the services of a traffic engineering firm with expertise in the area of traffic detouring. The detour routing is provided on the attached map.
The principle elements of the detour plan include:
1. Closure of the Netherland Inn Bridge.
View the Powerpoint Presentation as presented to the BMA. The presentation is offered in parts to help ease the download and is optimized for Internet Explorer. Please be patient as the slides contain animation.
|View the activity chronoloy for the Netherland Inn Bridge replacement.|
|Click here for information on the Fort Robinson/Center Street Detour restrictions.|
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