On occasion, when blogging about the nature and methods of forensic investigation, I’ve wondered, just how many different structures are there in the built environment? And are some more difficult to design and build than others? If so, are some more prone to accidents and failures than others?
I have answers of sorts in the following. But, like me, you are unlikely to believe anything more than an estimate even if I were to try that.
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A structure is something (such as a building) that is built by people. It’s also a place where accidents and failures can happen.
Tunnels, bridges, canals, retaining walls and towers are all structures. Also cars, trucks, helicopters and trains. And patios, decks and raised flower beds.
It might also be something in the natural environment that is used by people. Like the foundation soils supporting a building or a tower. Also the slopes off to the left or right along our highways.
It’s usually a cut slope if it rises from the highway – the natural soil has been cut into or excavated to form the slope. It’s a fill slope if it drops away from the highway – excavated soil has been dumped there and forms a slope. These slopes assume the angle of repose of the soil, which varies for different soils.
All this excavating and dumping to construct a highway – another structure – so it can get to where it’s going.
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One source listed 124 different engineering projects and classified these according to their complexity from Least Complex (#1) to Most Complex (#4). (Ref. 1) The classification took into account the number of parts or stages making up a project, their interrelationship, and the effort involved in analysing, designing and constructing the project. Generally, the more parts, the more complex.
Examples of Level #1 are simple commercial buildings and storm and sanitary sewers, and of Level #3, ferry terminals, grain silos and small dams.
Almost all engineering projects involve a structure as distinct from a system or process, like a computer network.
Some of the interrelated parts of a bridge include the foundations soils, the foundations, the abutments, the piers and the bridge deck.
If it’s a suspension bridge like across Halifax Harbour there are also the main cables, the towers above the piers supporting the main cables, the anchors on the bank or shore at the ends of the cables and the vertical, suspender cables that tie the bridge deck to the main cables. (Ref. 2)
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The next time I was driving after drafting the above I noted still more structures not included in the count of 124. Albeit smaller ones like traffic lights at an intersection, gates at railway crossings, tall propane storage tanks at service stations and armored stone on an eroding shore line. But still structures that can fail in some way or result in an accident.
And failures or accidents can happen at any of the 10 stages in the life of a structure, not just during the construction stage or service stage. (Ref. 3)
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If a building, a single structure, can fail in 209 ways, excluding what happens in the basement (Ref. 4, 5), how many ways can each of the 124 different structures in the built environment fail, during each of the 10 stages in the life of each structure? What would the total look like?
Just think of those 124 structures each with several interrelated parts and each part with several components. A component that doesn’t work properly or breaks completely is a failure.
The stairs in a building are a component of the building structure. The chute at the bottom of a grain silo is a component of the silo. The railing along the edge of a bridge deck that prevents you driving or falling into the river or harbour is a component of the bridge structure.
The National Research Council of Canada (NRC) found in a study that the lowly, humble basement of a building can fail in hundreds of ways. (Ref. 6) What does that tell you about the number of ways failure can happen in the built environment?
(It occurred to me on reading the 185 page report by NRC that the study procedures and processes are a guide for analysing the cause of failures and accidents in structures, in general, other than just basements)
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I was tempted but refrained from trying to multiply some of these numbers together to get an estimate of the likely 1,000s of ways failure can occur in the built environment. It boggles the mind.
Thank heaven we also have good engineering in the built environment and most of the 124+ structures and the many ways each can fail – at least 209 for a building – get through the 10 stages of their life without failure or accident. We don’t want failures but they do occur and engineers learn from them. (Ref. 7)
References
- Guideline For Engagement of Consulting Engineering Services, CENS, Consulting Engineers of Nova Scotia, Halifax, NS
- Personal communication, Jamie Yates, Yates Consulting Engineering, Fall River, Nova Scotia, June, 2020
- Stages in the “life” of a structure helps communication between counsel, insurance claims manager and an engineering expert. Posted July 2, 2015
- How many ways can a building fail, and possibly result in civil litigation or an insurance claim? Posted July 10, 2014
- Nicastro, David H., ed., Failure Mechanisms in Building Construction, ASCE Press, American Society of Civil Engineers, Reston, Virginia 1997 (Readily available by interlibrary loan from Memorial University, Newfoundland) (Note: This study did not include failure at the foundation or basement level)
- Swinton, Michael C., NRC-IRC and Kesik, Dr. Ted, University of Toronto, Performance Guidelines for Basement Envelope Systems and Materials, 185 pg, Research Report 199, National Research Council, Canada October 2005
- Petroski, Henry, To Engineer is Human, The Role of Failure in Successful Design, 251 pg. Vintage Books, Random House, Inc., New York 1992
(Originally posted July 8, 2020 and updated September 29, 2020 by Eric E. Jorden, M.Sc., P.Eng., consulting professional engineer, forensic engineer, Halifax, NS, Canada ejorden@eastlink.ca)