By Kim Smiley
On the afternoon of January 10, 2016, the deck of the Nipigon River Bridge in Ontario unexpectedly shifted up about 2 feet, closing the bridge to all vehicle traffic for about a day. After an inspection by government officials and the addition of 100 large cement blocks to lower the bridge deck, one lane was reopened to traffic, with the exception of oversized trucks. Heavier trucks are required to detour around the bridge with the main alternative route requiring crossing into the United States. This failure is still being investigated and it isn’t known yet when it will be safe to open all lanes on the bridge.
More information is needed to understand all the details that led to this failure, but an initial Cause Map, a visual root cause analysis, can be built to illustrate what is currently known. The first step in the Cause Mapping process is to fill in the Outline to document the basic background information (the what, when and where) and the impacts to the organization’s goals resulting from the issue. For this example, the bridge was damaged and significant resources will be needed to investigate the failure and repair the bridge. The closure of the bridge, and subsequently having only a single open lane, is also having a sizable impact on transportation of both people and goods in the area. It is estimated that about $100 million worth of goods are moved over the bridge daily and there are limited alternative routes.
Once the Outline is completed, the Cause Map is built by asking “why” questions and visually laying out the cause-and-effect relationships. Why did the deck of the bridge shift up? Investigators still don’t have the whole answer. The Nipigon River Bridge is a cable stayed bridge and bolts holding the bridge cables failed, resulting in the deck of the bridge being pulled up at an expansion joint. Two independent testing facilities, National Research Council of Canada in Ottawa and Surface Science Western at Western University, are conducting tests to determine the cause of the bolt failures, but no information has been released at this time.
The Nipigon River Bridge is a new bridge that has only been open since November 29, 2015. Some hard questions about the adequacy of the bridge design have been asked because the failure occurred so soon after construction. Officials have stated that the bridge design meets all applicable standards, but investigators will review the design and structure during the investigation to ensure it is safe. Ontario winters can be harsh and investigators are going to look into whether cold temperatures and/or wind played a role in the failure. Eyewitnesses have reported a large gust of wind just prior to the bolt failure. Investigators will determine what role the wind played.
The Cause Map can easily be expanded to incorporate new information as it becomes available. Once the Cause Map is completed, the final step in the Cause Mapping process is to develop solutions to prevent a similar problem from recurring. In this example, adding the concrete blocks as counter weights allowed one lane of the bridge to be opened in the short term, but clearly a longer-term solution will be needed to repair the bridge and ensure a similar failure does not occur again.