Tag Archives: structural

Root Cause Analysis - Incident Investigation

Failure of the Nipigon River Bridge

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.

Root Cause Analysis - Incident Investigation

Fatal Bridge Collapse Near Cincinnati

By Kim Smiley

On the evening of January 19, 2015, an overpass on Interstate 75 near Cincinnati collapsed, killing one and injuring another.  The overpass was undergoing construction when it unexpectedly collapsed onto the road below it, which was still open to traffic.

This incident can be analyzed by building a Cause Map, a visual root cause analysis, to intuitively lay out the many causes that contributed to an accident by showing the cause-and-effect relationships.  Understanding all the causes that played a role, as opposed to focusing on a single root cause, expands the potential solutions that can be considered and can lead to better problem prevention.  A Cause Map is built by asking “why” questions and documenting the answers.

In this example, a construction worker was operating an excavator on the overpass when it collapsed.  When the bridge collapsed the worker was crushed by the steel beams he was moving.   The additional weight of evacuator and steel beams on the overpass likely contributed to the collapse.   The overpass was being demolished as part of a project to remake this section of the Interstate and a portion of the overpass had already been removed.  The work that had been done appears to have made the structure of the bridge unstable, but the construction company was not aware of the potential danger so the worker was operating on top of the overpass and the road beneath it was still open to traffic.

A truck driver traveling under the overpass at the time of collapse suffered only minor injuries, but came within inches of being crushed by the bridge. It really was simple luck that no other vehicles were involved.  Had the collapse happened earlier in the day when there was more traffic, the number of fatalities may very well have been higher.  As investigators review this accident, one of the things they will need to review is the fact that the road below the bridge was open to traffic at the time of the collapse.  An additional relevant piece of information is that the construction company had financial incentives to keep the road open as much as possible because they would be fined for any amount of time that traffic was disrupted.

In addition to the safety impacts of this accident, the overpass collapse dramatically impacted traffic on a busy road with an estimated 200,000 vehicles traveling on it daily.  It took nearly a day to get all lanes of the interstate cleaned up and reopened to traffic.  No one wants to close roads unnecessarily and the goal of minimizing traffic is an excellent one, but it has to be balanced with safety.  The collapse of the overpass wasn’t an unforeseeable random accident and the demolition needs to be done in a safe manner.

Root Cause Analysis - Incident Investigation

Ceiling Collapse in London’s 112-year-old Apollo Theatre Injures Dozens

By Kim Smiley

On December 19, 2013, 76 people were injured when a large section of plaster fell from the ceiling of London’s historic Apollo Theatre.  Luckily there were no fatalities as a result, but six people were seriously injured in the accident.

The investigation is still underway, but an initial Cause Map can be built to begin analyzing the incident.  The first step in the Cause Mapping process is to fill in an Outline with the basic background information as well as formally list how the incident impacts the goals so that no part of a multifaceted problem is neglected.  It’s important to understand how an issue impacts all goals, such has safety issues, financial considerations, schedule delays, etc. There are times when different solutions can help mitigate risks to separate goals so it is useful to list all impacted goals for clarity.   Listing the impacted goals will also help focus the investigation on the most important elements.

Another very important part of the Outline is a space where any relevant differences are listed.  Anything that was different at the time an incident occurred is usually a good place to start digging during an investigation.  For this example, there was heavy rain during the hour preceding the ceiling collapse.  It’s also worth noting that the Apollo Theatre is 112 years old.

Investigators have not announced what led to the ceiling collapse, but early speculation is that rain water leaked through the roof and settled onto the plaster.  The theory is that the additional weight from the water was more than the ceiling could handle and it fell, taking a lighting rig and part of a balcony with it.   If this was the case, there will need to be hard questions asked about the adequacy of current building codes and inspection requirements.  Currently, the roof on the Apollo Theatre was only required to be inspected every 3 years.  It appears that the Theatre was up to date on and had passed all required inspections so the required periodicity may need to be re-evaluated in light of the recent failure.

Any suspected causes that haven’t been proven yet can be included on the Cause Map, but are marked with a “?” to indicated that they need additional evidence.  This helps document what has been considered during an investigation and questions that still need to be answered.

To view an Outline and the initial Cause Map of the Apollo Theatre ceiling collapse, click on “Download PDF” above.

 

Root Cause Analysis - Incident Investigation

Hundreds of Garment Workers Killed in Building Collapse

By ThinkReliability Staff

Hundreds are confirmed dead – with hundreds more still missing – as a result of a building collapse in Bangladesh.  The number of people who were in the building when it collapsed is unclear, due to spotty records.  Some sources have suggested the death toll may surpass 1,000.

We can examine the causes that led to the deaths in a Cause Map, which visually diagrams the cause-and-effect relationships that led to the tragedy.  First, we capture the impacts to the goals, which includes the extremely significant impact to the safety goal due to the high number of deaths as well as many other goals, including compliance, production and the impact to the labor goal resulting from the rescue and recovery operations.

The deaths were caused by the collapse of a building which was partially occupied at the time. The building housed five garment factories, as well as a bank and other shops.  Even though cracks appeared in the building   and inspectors requested evacuation and closure of the building, garment workers were ordered back to work.    The bank was evacuated, and the shops were already closed.  Despite deplorable conditions (brought to the attention first by a building fire last November and now by this tragic collapse),  workers (mainly young women)   can still be found to work in the garment industry because the average wages in the country are so low.  Eight people, including the building owner and engineers, have been charged as a result of the collapse.

The building, which was illegally built 3 stories too high, was not up to code and not approved by the government.  The building was built on wetland and used substandard materials for construction. As a result of this collapse, the government has said it will form a committee to ensure the safety of buildings and workers.  Shops in the US and Europe that sell garments produced in Bangladesh have distanced themselves from the companies housed in the buildings while many consumers call for more oversight from these companies, who utilize cheap labor in Bangladesh to create their goods.  The garment industry accounts for 77% of Bangladesh’s exports.

It is hoped that this recent tragedy will increase the attention paid to worker safety by the government within Bangladesh as well as consumers who buy the end product abroad.

To view the Outline and Cause Map, please click “Download PDF ” above.

Root Cause Analysis - Incident Investigation

Deadly Kansas City Walkway Collapse

By Kim Smiley

On July 17, 1981, the second and fourth floor suspended walkways collapsed at the newly opened Hyatt Regency of Kansas City, Missouri.  A dance contest had attracted a crowd and the atrium under the walkway was filled with people.  This accident killed 113 people and injured 186.

The hotel was newly constructed and the walkways were well maintained.  So how did this happen?

A root cause analysis of this accident shows that there were a number of causes that contributed to the walkways collapsing.  Investigation into the accident shows that the structural design of the walkway was inadequate.  A weld failed which allowed a support rod to pull through the box beam and the walkways fell.

Additionally, the weld had greater stress than normal on it at the time of the failure because a large crowd had gathered to watch a danced content.  About 20 people were on second floor walkway and about 40 were on the fourth floor walkway at the time of the accident.  The higher loading combined to the walkway collapse.

Identifying the failure mechanism is important during an investigation, but a thorough root cause analysis needs to take the analysis farther to really understand the causes.  The reason that an inadequate design was built needs to be determined.

In this case, it appears that the design was changed without approval of the structural engineer.  This resulted from a communication error between the fabricator and the structural engineer.  The structural engineer sent a sketch of a proposed walkway design to the fabricator, assuming that the fabricator would work the details of the design himself. The fabricator assumed the sketch was a finalized drawing.   The fabricator then picked standard parts to fit the sketch.  This resulted in a significant change from the original design and dramatically decreased the load bearing capacity of the walkways.

The original design called for continuous hanger rods (a non-standard part that would have needed to be manufactured) that passed through the fourth floor walkway beam box to the second floor walkway, resulting in the ceiling connecting supporting the weight of both walkways.  The fabricator changed the design to use two shorter rods (standard parts) which resulted in the fourth floor walkway supporting the weight of the second floor walkway, which it wasn’t designed to handle.

It’s important to investigate beyond the point of inadequate design to learn what failed in the design process to prevent future accidents from occurring.