Understanding the Closure of the Spiketon Ditch Bridge

Our community has recently seen the closure of the Spiketon Ditch Bridge, a decision that has raised many questions. To provide clarity and insight, we’re sharing detailed findings from the assessments conducted and the ongoing efforts to ensure public safety, as communicated by Tiffany Odell, Senior Planner at Pierce County Parks.

The Reason Behind the Closure

The decision to close the Spiketon Ditch Bridge came after a detailed assessment conducted by Western Woods Inc. Tiffany Odell shared the information she received from the bridge engineering team, highlighting the critical condition of the bridge. According to their analysis based on 'allowable stress design', the top chord of the bridge was found to be 205% overstressed with just the dead load present, far exceeding the maximum allowable stress limit of 100%.

Expert Assessment and Concerns

In response to Tiffany Odell’s inquiry, Western Woods Inc. provided the following explanation: 

“We usually start seeing failures at stress levels of 210%. This represents that 5% lower exclusion level where if 100 beams were overstressed at 210%, we would expect to see 5 of them broken. We are not there yet, but approaching it. The problem is that 205% number increases to 245% with only 1 more inch of lateral deflection (6-inches total) and no increase in axial load. I was on the bridge when a smaller-framed person ran across, and the top chord experienced a lateral deflection of another 3-4 inches at each step. Assuming the lower end (3-inches) and that live load is negligible (using dead load axial only), the top chord is now stressed at 327%, which is well beyond the average 2.5 safety factor.

Adding to that, we can’t control how many people use the bridge at a given moment. If the bridge is open, it is open to have as many people that happen to be crossing it at that moment (1-20? realistically based on what I saw). So for me, the inability to control the traffic (1 person at a time, no running, walk softly, no one who has a larger frame or carrying anything….) and the fact that any more lateral deflection at the rotten section could cause failure of the top chord (a primary load-carrying member) are the two leading factors that lead to my recommendation to close the bridge.

I consulted with the other engineer who was on the inspection with me (18 years of experience), the president of the company (25 years of experience) and the Chief Engineer (41 years of experience) and we all agreed with this recommendation. My superintendents who were there for another site visit (45 years of experience doing this type of work between the 2 of them) also agreed with the recommendation. They are usually the ones to push the envelope because they work with structures on the edge of collapse or in a collapsed state on a daily basis."

This high stress level underlines the inherent risks associated with continued use of the bridge, leading to the unanimous agreement among seasoned engineers and superintendents for its closure.

Moving Forward: Steps for Resolution

Pierce County Parks, under the guidance of Tiffany Odell, is actively addressing the safety issues of the Spiketon Ditch Bridge through swift and decisive action. In a detailed email to Bob Myrick, a member of the Foothills Coalition, Tiffany outlined the immediate steps being taken:

"I think you recall from our recent communications that we are moving forward to hire a consultant to assist with the Spiketon Ditch Bridge. We are looking into opportunities for emergency contracting and permitting to try to expedite this to the extent possible. We’ll continue to share information as it becomes available. I’ve been designated as the point-of-contact for the project, so please send any further questions my way, and I’ll do what I can to get you a timely response. Things are moving, and we continue to learn more as we progress. I’m also developing frequently asked questions and a project website to provide more abundant public information on the closure. I’ll send out an announcement via our Foothills Trail alerts listserv when that is available (sign up at: www.piercecountywa.gov/foothillsalerts)."

Tiffany also emphasized the importance of community leadership in managing the situation: "In the meantime, as I mentioned previously, I would so appreciate any leadership you can provide within the trail community to discourage trespassing on the bridge or private properties."

A consultant has been hired to assist with these necessary measures, and efforts are being made to develop a dedicated project website along with a frequently asked questions section. This will ensure that the public remains fully informed about the ongoing efforts and any developments. Furthermore, to stay updated with the latest news and information regarding the bridge closure, community members are encouraged to sign up for alerts at Foothills Trail Alerts.

Conclusion

The safety of our community remains our highest priority as we deal with the closure of the Spiketon Ditch Bridge. We understand the inconvenience this may cause and appreciate the community's cooperation and understanding as we work towards a swift and safe resolution.

For continuous updates and more detailed information, please sign up for alerts at Foothills Trail Alerts.

Sign-off

Thank you for your understanding and support. Your safety and well-being are our highest priority as we navigate this situation together.