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Bridge Inspection

December 8, 2017

By Adam Polley, PE – Project Engineer and
Steve Myer, PE – Senior Associate and Watertown Office Manager

Federal, state, and local governments build and maintain safe and effective transportation infrastructure for the movement of goods and people. Keeping bridges in good working order is a big part of that commitment, and federal guidelines require bridges to be inspected every two years.

Clark Engineering has been inspecting bridges in South Dakota for the last 15 years. With nearly 3,500 inspections completed since 2007, Clark is one of the most prolific bridge inspection service providers in South Dakota. We now inspect nearly 950 structures every two years, and our practice continues to grow.

Our teams are busy during inspection season, which typically runs from May to early November. Field work needs to be completed by the end of summer to allow time for paperwork to be completed in September and October.

Why Bridge Inspection?

We recognized a need and built a practice that meets clients’ needs and satisfies their reporting requirements. Because we have up-close familiarity with our clients’ structures, we are able to help prioritize and plan for future improvements. At the heart of our bridge inspection service offering is a commitment to helping our clients maintain safe infrastructure for the people who use it every day.

Tools of the Trade

Most of the tools our inspectors use on the job are relatively low-tech. A lot can be accomplished with a hammer, level, tape measure, walking stick, and the inspector’s eyes. A boat anchor comes in handy as a weight at the end of 100-foot tape when the inspector needs to measure the depth of the channel when the bridge being inspected is over water.

There are some tools that are a bit more technologically advanced.

The snooper truck: These are necessary when the inspector is unable to safely view the underside of the bridge from a hoist below. The truck is parked on the bridge deck, with an arm extending over the side of the bridge to allow the inspector to see the underside of the bridge without the need for a hoist or complicated climbing gear. Snooper trucks are really effective in situations where the bridge is very high, crosses fast-moving or otherwise dangerous waterways, or crosses an active rail line.

The drone: This is the latest technological tool available to us for bridge inspections. It allows us to see parts of bridges we would otherwise be unable to access. Earlier this year, we used a drone to inspect a bridge where ordinary equipment was not feasible. This particular bridge was quite deteriorated and did not have adequate room on its deck for a snooper truck. The bridge was over a railroad, so our inspectors were unable to use a boom lift to view the underside. By using a drone, we were able to evaluate the structure and provide a meaningful inspection report to the client.

Specialized Expertise and Follow-Through

Load rating is a procedure to evaluate the adequacy of various structural components to carry predetermined live loads. Bridge structures are rated upon completion of original construction and whenever a change in condition suggests that the current rating may have changed.

Existing bridges are rated to prioritize an owner’s needs, assure the traveling public’s safety, and facilitate the safe passage of goods. Bridges that cannot safely carry statutory loads, based on a load-rating evaluation, should be load posted, rehabilitated, or replaced.

Clark’s team is skilled in routine inspections, as well as fracture critical and emergency inspections. We are familiar with county and city bridges of varying configurations and materials. We use spreadsheet and computer modeling programs to facilitate the load-rating evaluation. We can also provide failure analysis and risk analysis as needed. In fact, one of Clark’s bridge engineers is a PhD who has done research on refined safety evaluation for in-service structures for eight years and helped write the code in China for load rating in-service structures.

After the inspection and load rating are completed, our bridge engineers meet with clients to develop and refine repair and replacement plans. Results of the inspection are used to prioritize needs so our clients can be pragmatic in planning, budgeting, and issuing overload permits.

Keeping Clients Involved and Informed

Our typical process involves meeting with the client before we start the inspections. The purpose of this meeting is to gather information about changes they have noticed or bridges they think might be problematic. When the inspections are completed, we meet with the county superintendent to share our findings. On occasion, we will present these findings to the county commissioners, depending on the desires of the client.

The Inspection Report

A typical inspection report includes the following elements:

  • Cover Page
  • Information Page (location, size, type of bridge, etc.)
  • Recommendation Page (repairs recommended by the inspector)
  • Approach Page (roadway condition)
  • Bridge Deck Page
  • Superstructure Page
  • Substructure Page
  • Channel Page
  • Channel Profile
  • Load Ratings (if necessary)
  • Cost Estimate (if the structure is functionally obsolete or structurally deficient)
  • Pictures (two are required)

In addition to the typical report requirements, we include a bridge sketch and a good amount of photos. By taking photos of the known elements of concern and any new areas we identify, we are able to monitor trouble spots over time to keep track of deterioration. Only two photographs are required for inclusion in the report; by taking extras, we are ahead of the game in terms of documenting the structure’s condition.

Oddities Encountered on the Job

Once in a while, we encounter something out of the ordinary during a bridge inspection. On one occasion, we found that a farmer had deposited several dead pigs under the bridge. On another inspection, we discovered half of the bridge abutment was missing.

We also encountered a bridge support that was seriously deteriorated. Fortunately, the preliminary design plans had already been submitted to the SD DOT for replacement of the structure because the client planned for its replacement due to deterioration identified during our previous inspections.

In 2014, our team was inspecting bridges in Lincoln County. We had completed half of the assigned bridges before a large flood event. After the floodwaters dissipated, we went back to a bridge we’d already inspected and found that some approach roadways were washed out. The county closed the bridges and Clark helped coordinate with FEMA to secure funding for repairs.

Some Closing Thoughts

Bridge inspections are our first step in helping clients create a five-year plan for their transportation infrastructure. We document everything and help them prioritize repairs and replacements.

Bridge inspection can help save lives. Think about emergency responders who need to get to where they’re needed quickly and safely. Monitoring and maintaining bridges keeps this critical infrastructure functional to allow these life-saving trips to happen without detours and delays.

Our engineers find this work incredibly rewarding. This is where they put their education and training into practice to have a direct and positive impact on the safety of the traveling public.