Global warming and forensic engineering investigation

Subtitle: Climate change for intelligent people

(Following is a guest-blog by Gary Bartlett, P.Eng. on global warming.  I’ve added a few introductory remarks relating Gary’s concerns about what is being reported in the popular media to forensic engineering investigation)

Introductory remarks: Global warming and forensic engineering 

A forensic engineering investigation of whether or not global warming is taking place might resolve the matter once and for all.

The scientific method underlies both the forensic engineering investigative process and the scientific investigative process.  A difference is that the results of a forensic investigation are closely examined in a court of law and rejected if found wanting.  On the other hand, the results of a scientific investigation, as sometimes reported, might not have received the same kind of exacting scrutiny.

This is particularly the case if the ‘scientific’ investigation is more in the nature of junk science serving the interests of the reporter rather than science.  Or the results of the science are modified to reflect the personal interests of the scientist or his/her employer.  Or simplied by the media with their sometimes questionable motives.

Articles in the Globe and Mail, Saturday, February 23, 2013, are relevant.  The one by Elizabeth Renzetti on the muzzling of government scientists, page A2.  A second by Margaret Wente on the questionable effect of global warming on the polar bear population, page F2.

Forensic engineering investigation must collect evidence – and follow the evidence where it leads, in resolving an issue objectively and with certainty.  The opInion of a forensic engineer is judged in a court of law for its objectivity.  The certainty with which the opinion is held is also solicited of the forensic engineer in assigning weight to the engineer’s results and opinion.

In a forensic engineering investigation, we form a hypothesis based on what we know, develop and carry out tests of the hypothesis, and, based on the results, confirm, modify, or refute the hypothesis (Ref. 1, 2, 3, and 4).  We carry out more tests of a modified or a new hypothesis.  An exhaustive implementation of that process solves the problem in most cases, if it can be solved, and enables an objective opinion to be rendered with considerable certainty.

G. Dedrick Robinson and Gene D. Robinson III don’t seem to believe that process has been followed to completion yet in an evaluation of the fact or otherwise of global warming.  For example, they believe that evidence such as the history of the earth has not been considered properly in an investigation of global warming.  They state their views in their book, “Global warming: Alarmists, Skeptics, and Deniers; A geoscientist looks at the science of climate change“.

If this is true – that the scientific method has not been rigorously followed in evaluating the fact or otherwise of global warming, it’s a serious omission.  The evaluation would not stand up to the most gentle of cross examinations in a court of law never mind the aggressive examination to which the results of a forensic engineering investigation are sometimes subjected.

What have Robinson and Robinson found in their look at the science of climate change that would not be tolerated in a forensice engineering investigtion?  Some of their findings are reviewed below in a guest-blog.

References

  1. American Society of Civil Engineers (ASCE), Guidelines for Failure Investigation 1989
  2. ASCE Guidelines for Forensic Engineering Practice 2003
  3. Steps in the forensic engineering investigative process.  Posted October 26, 2012
  4. What is forensic engineering?, published, November 20, 2012

(The following guest-blog of a recently published book on global warming has been contributed to The Forensic Engineering Blog by Gary Bartlett, P.Eng**)

Guest-blog: Climate change for intelligent people

A)     INTRODUCTION

I think that most of us understand that we need to be somewhat careful about believing everything that we hear and read.  Nonetheless, the media seem destined to accept verbatim the pronouncements of those with vested interests in perpetuating myths about the climate with little or no attempt being made to validate what they are told.  The result is a never-ending stream of terrifying pronouncements worthy of Chicken Little based on no science or on junk-science or on deliberately manipulated statistics.  That kind of stuff can wear a person down and truly cause one to wonder if maybe *they* are correct.  Well I was getting nervous, in any case.

Herein is an attempt to dispel some of the myths regarding climate change.  It is based on a 2012 book entitled “Global Warming: Alarmists, Skeptics & Deniers; A Geoscientist looks at the Science of Climate Change” by G Dedrick Robinson and Gene D. Robinson III, available from http://www.amazon.com/Global-Warming-Alarmists-Geoscientist-ebook/dp/B0070YUCXE.

The major attributes of this book are:

a)      The authors do not enter any debate with those with other agendas, whether they be political or economic or media-driven.  This book is a discussion of science as it impacts the climate of Earth, no more and no less;  and

b)      Conclusions reached in this book are based on scientific fact, historical data;, measurable trends, and peer-reviewed information.

B) PURPOSE

My purpose in summarizing the major facts contained in the reference is simply to encourage others to maintain a certain amount of cynicism when reading information found in the media on the whole topic of global warming.  If what one reads is not, or it cannot be, supported by science, then it’s best to move on.

C) BOOK’S MAJOR POINTS

Here is my attempt to provide a précis of the major conclusions – all fully supported in the book to which I have referenced – which should cause most people to take and maintain an open mind whenever they hear prognostications on the topic of global warming.  Readers owe it to themselves to obtain the book and read the detail to substantiate my summary.

1)      OMG, we are in a period of climate change!  Guess what: there has never been a steady state in climate since as far back as science has been able to infer temperatures.  By no means can current changes in temperature be described as even slightly unique or unusual.  Ignore the term entirely when heard used with the adjective *alarming*.

The more that one drills down into the details of planet temperature variations, the more that temperature variation profile begins to resemble a fractal.  Trying to forecast the future based on the nano-dimensioned period of, say, 50 years of temperature records is roughly equivalent to trying to estimate the shape of Halifax Bedford Basin from close examination of a foot-wide section of beach at the foot of the Dingle Monument a few miles away.   At high tide.

2)      The Greenhouse effect will kill us?  Yes, there is a greenhouse effect.  It has been known about for centuries.   Unfortunately one hears the term in a negative sense, but it is exactly the opposite.  Without the greenhouse effect (it prevents solar heat from escaping back into space), this planet Earth would be entirely frozen and life would have never developed.  The major controlling criterion (95%) that governs the extent of the greenhouse effect is water vapour, not carbon dioxide.  Doubling the current amount of carbon dioxide is equivalent to less than a 2% change in the amount of water vapour.

3)      Carbon dioxide is a pollutant?  That’s a strange way to view the product that all human life produces with every exhalation.  It is even tougher to accept that negative connotation when carbon dioxide is of absolute fundamental criticality to photosynthesis.  Plants demonstrate proportionally better results in an enriched carbon dioxide environment.  While carbon dioxide may be increasing in the atmosphere (although blaming that rise on humans is grossly unfair), current carbon dioxide levels are roughly 1/10 of what they have been for most of the history of the planet.

4)      Huge amounts of carbon dioxide are released from the burning of fossil fuels Well, huge is a relative term, but fossil fuels as a carbon sink amount to a total 4,000 GigaTons whereas limestone as a carbon sink is estimated at 100,000,000 GigaTons.  Carbon that enters the atmosphere from natural sources such as animal respiration and from the weathering of limestone greatly exceeds anything that humans are doing.  One needs to study the system which processes and then circulates carbon dioxide around the planet (it is a closed system with a turn-around time measured in years!) to provide a better feel for how much guilt is really appropriate for you to feel after committing the sin of using the remote control to start the car and letting it warm up at idle on a winter morning.

5)      Earth’s temperatures are being driven up by increases in carbon dioxide That would indeed be unique since well-established history over millions of years shows that temperature increases (periods of global warming) were followed by increased levels of carbon dioxide, not the other way around.  In the current scary environment, cause and effect are mistakenly being employed backwards.

6)      Global temperatures are rising?  Not for the past 17 years.  See  http://www.thegwpf.org/ipcc-head-pachauri-acknowledges-global-warming-standstill/.

7)      Computer models are the answer?  No, computer models are not (yet, if ever) the answer.  The planet is a huge system which defies modelling to the degree at which confident predictions are credible.  Most forecasts of impending climate horror are coming, not from a scientific analysis of historical facts, but are generated by  inadequate models which suffer from many unknowns when they try to manipulate the data and peer into the future.  Some of the unknowns in their algorithms are very critical in determining the final outcome of a climate predictive computer run.  That is, a tiny change in the estimate of any one constant in the algorithm can cause huge variations in the resulting conclusions.  The track record of general circulation model predictions of the past give no cause for confidence in their ability to predict the future, yet they are being heavily relied upon in the popular press (while more meaningful geophysical history is ignored),

8)      Data and graphs tell the story, right?  No, that’s not right.  It is appallingly easy to manipulate data to support a forgone preferred conclusion by taking it out of context, or by playing with X- and Y-axis scaling, etc, just to identify too common distortions.  Numerous well-known public presentations show conclusions that are not peer-reviewed and are not true except in the sense that they have been carefully selected and/or carefully presented or are specifically defined in words intended to deceive — all so as to support the position the presenter has espoused.  Run, if anyone uses the word “correlation”.  Here we need the rigour of science from respected sources.

9)      Ice; Two problems:

  1. All the ice in the world is melting?  Everyone talks about the melting of all the Arctic ice to the north of Canada as if that were the end of the story; no-one talks about an off-setting gain in ice near the south pole; and
  2. We shall die from rising sea levels? The sea level is rising already and has been for 18,000 years.  The rise has been three-hundred and fifty feet so far over that period, and the world and the planet are coping.  If all the ice in the Arctic were to melt and add to the oceans, the rise would be not be very exciting because most of the northern ice fields are already floating on water.  If the Arctic ice were to melt, the oceans do not rise any more than does the water in a glass of sarsaparilla after the ice-cube melts. [The opposite is true of Antarctica but the ice pack is building there]

D) GRATITUTOUS ADDITIONAL COMMENTS

The writers of the book from which I have been so freely cribbing, did not say any of the following things.  They are mine.  They are based on the qualifications that I claim below (which when added up amount to nearly zero):

  1. Sun spots: Historical geophysical data would suggest that the climate (temperature) of the planet is greatly affected by sun spots.  Current data suggest that the planet could be entering into a period of back-to-back low 11-year sunspot cycle periods similar to what is known as the Maunder Minimum which had been observed centuries before.  Since good High Frequency communications propagation is directly proportional to the number of sunspots, this tentatively predicted period represents a prolonged bad-news situation for the amateur radio operator.    It may also be bad news for the planet since global temperature can be shown as being related to the quantity, location, and characteristics of sun spots.
  2. The Maunder Minimum:  The many scientists among amateur radio operators who specialize in propagation prediction have access to all known recorded history of sun spot numbers which they analyze for recognizable repetitive patterns.  Others plot the data against the planet’s temperature, and if history repeats itself as perceived from these patterns in these consolidated plots, there is a case to be made that the next equivalent to the Maunder Minimum will result in less heat reaching earth from the sun.  Because of fewer sunspots (which are hotter than the normal sun’s surface temperature), that will see the planet grow colder to the point that the earth could enter a mini ice-age.   Freezing to death with no one to talk to is an unpleasant thought.
  3. History   A big contributor to the problem associated with current reactions to “global warming” is that people do not read history.  Big storms are nothing new.  A hurricane in Newfoundland in 1775 killed four-thousand (4,000) people.  It made Hurricane Sandy look like child’s play. The term “monster” does not truly apply to Sandy when considered against previous storms.
  4. Complicity People do not want to admit their own contribution to the catastrophic destruction that follows relatively common weather events.  The severe damage from Hurricane Sandy was caused by bad human decisions when the consequences were easily predictable.  Channels to incoming seawater waterways had been narrowed, thereby exacerbating tidal surges;  private residents happily built things on known flood plains;  condos and apartment buildings and businesses installed emergency generators and their control panels  in their basements.  And so it goes.

**Author’s Apology

**Gary Bartlett, P.Eng. is not a geoscientist, astrophysicist, meteorologist, nor does he know anything about those hard topics.  The closest he can come to claiming smarts in those areas is that he knows a guy - a long-time friend, who specialized for years in consulting geotechnical and environmental engineering, and now practices forensic engineering (Eric E. Jorden, M.Sc., P.Eng.).  Oh, but Gary has faithfully watched professional weathermen Monty, Rube, Peter and Kailin on CBC-TV.

Gary Bartlett, on the other hand, does recognize well-written material with a thorough bibliography from respected sources, he does understand the significance of terms such as “peer-reviewed”, and he does value the demonstration of the proper scientific method as taught by UNB BScEE 1962-67.  [His essential cynicism can be traced to a career spent exclusively in the aerospace industry, but that’s a different topic]

He really, really hopes that readers of this blog will buy the referenced book (see more about the author in the attached, below) to find out all the other encouraging fact-based peer-reviewed science that is collected there.  And it’s an easy read, too.  To top it off, Gene Robinson is personable and cooperative, too.  To my surprise, he responded quickly to my request that he review the above précis of his book for accuracy, and his reply caused me to repair a couple of incorrect statements, and allowed me to  strengthen others.  I release it with confidence.

Attachment:

From FORBES

http://www.forbes.com/sites/sap/2013/02/08/the-world-in-2033-big-thinkers-and-futurists-share-their-thoughts/.

The World In 2033: Big Thinkers And Futurists Share Their Thoughts

On Global Warming: Gene Robinson

“Twenty years ago, alarmists were already predicting calamitous effects in the near future from a warming planet due mainly to petroleum and coal combustion. The 1990 best-seller Dead Heat painted a nightmarish picture of our world in 2020-2030 when the temperature would average six or seven degrees greater. The first IPCC reports of 1990 and 1995 supported such scary scenarios, giving them an aura of scientific respectability. What actually happened is that the mean global temperature since 1993 increased about 0.2 degree C through 2012 with most of that occurring in the record year of 1998, at the peak of a thirty-year warming trend. Since then, the global temperature has plateaued with no clear trend up or down. Because the flattening is at the high point of a warming trend, each year has to be among the warmest recorded years, as the media tirelessly trumpets. What a convenient way to mask the fact that although CO2 has continued to increase, temperature has not, in spite of the computer models.

What, then, can we project for global warming in 2033? Instead of the abrupt warming that alarmists always say is about to start, my rather cloudy crystal ball says global temperature is more likely to continue showing no clear trend or to be at the beginning of a cooling trend. Alarmists will continue to blame every severe weather event on climate change and to oppose all energy projects except solar and wind. All studies supporting the alarmist view will continue to be publicized in the liberal media while all studies reaching conclusions in opposition will be ignored. Liberal politicians will still support schemes to tax carbon by trying to scare people of what will happen without them, even as the skepticism of ordinary people continues to increase. Grants will still be doled out to scientists whose previous results supported the politically correct view while proposals from skeptics go unfunded. In short, just as little has changed with regard to the politicizing of the global warming theory in the last twenty years, little is likely to change in the next twenty.”

Dr. Gene D. Robinson is Professor Emeritus at James Madison University in Virginia and author of Global Warming: Alarmists, Skeptics & Deniers – A Geoscientist Looks at the Science of Climate Change, available at Amazon and most book stores. He is also the publisher at Moonshine Cove Publishing, LLC.

 

Update: The role of a professional engineer in Counsel’s decision to take a case

Subtitled: Counsel, what part of “No” can’t you pronounce? 

(This is an update of an item posted in 2012 – see Ref. 2, as part of a series on the role of a professional engineer assisting counsel in civil litigation – see Bibliography below

We all must decline a case sometime, in engineering and in law, in the best interests of the injured party and ourselves.  We don’t always do that – say “No” when it’s in order.

For certain, we would decline because we believe the party doesn’t have a case, or we don’t have time to handle.

But, we must also decline because the problem is outside our area of expertise.  Or we don’t have sufficient expertise yet in an area we would like to practise.  Including the expertise to project manager the case that would be argued by more experienced counsel or professional engineers. 

I am investigating three failures and accidents now that were referred to me by two well experienced professional engineering colleagues who felt, on being contacted by counsel, that the problem was outside their area of expertise.  They were correct in this regard and it was professional of them to recommend another.

I do not take cases where the failure or problem appears to involve mechanical or electrical engineering.  Nor cases where a traffic accident has occurred involving a collision between two or more vehicles.  I just don’t have qualifications or experience investigating and analysing the cause of these types of problems.  

However, I would take a case where the traffic accident involves a structure on or near the highway.  For example, the Rankin fatal motor vehicle accident that appeared to involve a pile of salt on the highway - a structure to an a engineer.  Or a fatal step ladder accident that appeared to involve a defect in the step ladder – also a structure to an engineer.  

I take cases that involve the failure of a structure or damage to a structure, particularly those cases involving the foundations, also cases involving environmental contamination, flooding, and drainage.  

It’s important when recommending another professional engineer or lawyer that you have specific knowledge or experience of the person being recommended in the area of expertise required.  Recommending someone carries considerable responsibility.  There are some individuals and organizations that don’t recommend people in the event the recommended person doesn’t work out.

I’ve worked on three cases where I wondered about the experience of counsel in civil litigation.  In two cases it seemed like open and shut cases for the plaintiffs but they lost.  In one of these, relevant engineering investigative data, that had been reported to the plaintiff, did not seem to get presented in a timely manner to the defense, as noted by the judge.  In a third case, the plaintiff was near the discovery stage when it was realized that relatively expensive engineering investigation was needed that couldn’t be justified by the possible award. 

We must say, “No”, when we are evaluating whether or not to take a case if it’s outside our area of expertise in law or engineering, and only recommend another lawyer or engineer if we have reliable knowledge of our colleague’s expertise. 

Original post

(I’ve made small changes to hopefully make it easier to read)

Civil litigation tentatively begins when counsel meets with a potential client.  The purpose is to gather information to help him or her assess the merits of the case and decide if he should take it.

A professional engineer could have a role in this meeting, or in consultation shortly afterwards.  This is particularly the case if the legal and technical issues are likely to be complex requiring extensive engineering investigation to support a reliable opinion.

Some cases shouldn’t go forward

I’ve seen cases that should never have gone forward.  Not because of a lack of technical merit but because of the client’s limited financial resources to bear the cost of the forensic engineering investigation necessary to determine the cause of the problem.  These would be costs learned about after a claim was filed and discoveries held – and only after a professional engineer was retained to investigate the technical issues.

Information counsel wants

During the meeting, counsel obtains information from the client’s description of the problem and the damages he believes he has incurred, documents provided by the client, knowledge of witnesses, answers to questions raised by the lawyer, the lawyer’s past experience of similar matters, and comments by an expert on the technical issues.

Expert can make or break a case

One of several important considerations covered by the meeting and the lawyer’s review of the facts is the need for an expert on the case.  An expert can make or break a case and if thought to be necessary should be chosen carefully and retained early (Ref.1).  Even if only retained briefly to support counsel’s assessment of merit, in the event counsel decides not to take the case.

If a professional engineer is not included in the meeting, then counsel might confer with one later during his review of the facts prior to making a decision about taking the case.  The engineer would, of course, review the information from the meeting, particularly the documents, and identify the technical issues prior to counseling the lawyer.

The engineer can also provide very preliminary comment on the engineering investigation needed to address the technical issues and to formulate an opinion on the cause giving rise to them.  The engineer would educate counsel by outlining some of the tasks that would need to be carried out during an investigation and the time to do these – factors that can have a significant impact on the cost of litigation.

Client’s ability to bear costs

If the technical issues are complex – and the engineer can certainly help determine that, the monetary claim for damages likely to be substantial, and the lawsuit quite lengthy then this will affect the client’s litigation costs.  The client’s ability to bear these costs is important information in counsel’s decision on taking the case.  An engineer can have a role in assisting counsel make that decision.

Tasks a professional engineer can carry out in assisting counsel

Following are tasks that a professional engineer – or any expert for that matter, could carry out during or shortly after counsel’s first meeting with a potential client to assist counsel’s decision about taking the case.  The list is highlighted in blue and bold to break up a long list of tasks and hopefully make the list easier to read – there’s no special significant to what is blue or bold.  There are a lot of helpful suggestions for counsel in the following:

  1. Attend and audit the meeting for technical issues, or meet with counsel shortly afterwards
  2. Review client’s descriptions of the problem and the reasons for claiming damages
  3. Read available documents
  4. Review witness’ statements as soon as taken by counsel
  5. Begin identification of potential technical issues
  6. Begin identification of technical documents counsel to seek
  7. Familiarize counsel on the typical stages and tasks in a forensic engineering investigation, the fact of unexpected follow-up investigations, the fact that investigations can lead in unexpected directions, the time required, and the difficulty estimating costs 
  8. Identify physical evidence, tangible exhibits and possible demonstrative evidence
  9. Brief counsel on parties that might be involved in the potential litigation and their relationship to the technical issues
  10. Provide information that would facilitate early settlement
  11. Note unfavourable evidence for the potential client’s claim
  12. Remind counsel that only one side of the story is known.  The opponent’s story and documents could give rise to a small shift in the technical facts and alter the complexion of the claim
  13. Tentatively assess the technical merits of the case with respect to the potential parties
  14. Outline preliminary engineering investigation and the major tasks involved
  15. Speculate on follow-up investigations
  16. Identify specialists that may be required
  17. Speculate on the order of magnitude of investigative costs
  18. If counsel decides to take the case, and position letters are appropriate, ensure that demand letters, and responses, are based only on well-established technical facts and data as known at the time

References

  1. Stockwood, Q.C., David, Civil Litigation, A Practical Handbook, 5th ed, 2004, Thompson Carswell
  2. The role of a professional engineer in Counsel’s decision to take a case.  Published June 26, 2012

Biliography

  1. What is forensic engineering?, published, November 20, 2012
  2. Writing forensic engineering reports, published, November 6, 2012
  3. Steps in the civil litigation process, published, August 28, 2012
  4. Steps in the forensic engineering investigative process, published October 26, 2012
  5. The role of a professional engineer in counsel’s decision to take a case, published June 26, 2012
  6. The role of a professional engineer assisting counsel prepare a Notice of Claim, published July 26, 2012
  7. The role of a professional engineer assisting counsel prepare a Statement of Claim, published September 11, 2012
  8. The role of a professional engineer assisting counsel prepare a Statement of Defence, published September 26, 2012
  9. The role of a professional engineer assisting counsel prepare an Affidavit of Documents, published October 4, 2012
  10. The role of a professional engineer assisting counsel during Discovery, published October 16, 2012
  11. The role of a professional engineer assisting counsel during Alternate Dispute Resolutionn (ADR), published November 16, 2012
  12. The role of a professional engineer assisting counsel prepare for a Settlement Conference, published November 29, 2012
  13. The role of a professional engineer assisting counsel prepare for a Trial Date Assignment Conference, published December 12, 2012
  14. The role of a professional engineer assisting counsel prepare for Trial, published, December 19, 2012
  15. Built Expressions, Vol. 1, Issue 12, December 2012, Argus Media PVT Ltd., Bangalore, E: info@builtexpressions.com, info@argusmediaindia.com

 

Gabion retaining wall collapse results in litigation

(The following is one in a series of cases I have investigated that illustrate the different forensic engineering methods I use to investigate the cause of failures and accidents that result in civil litigation.  The methods are described in some detail)

The investigation of the wall collapse is reported under the following main headings with several sub-headings:

  • The case (a description of the collapsed gabion wall, the legal/technical issues, and my client)
  • Forensic engineering investigation of the failure and the methods used
  • Cause (of the collapse)
  • Post mortem (an engineering “rule of thumb” might have prevented the collapse)

The case

Description of collapse

The gabion wall was on the shore of a harbour in eastern Canada.  The wall was 10 feet high and more than 100 feet long.  There were short wing walls to the main wall aligned shoreward.  A “gabion” is a wire basket about 3 feet by 3 feet in section and 10 feet long filled with course stone several inches in size.

The wall was being constructed to reclaim land on the seaward side of a quite large townhouse property.  The wall fell over just before construction was complete.  It was rebuilt before I was retained.

Legal/Technical issue

At issue was the cause of the wall’s failure.  This was in connection with a claim of damages against the designer and his insurance company.

Client

I was asked by the plaintiff, a property manager who was acting on behalf of a contractor, to determine the cause of the collapse.

Forensic engineering investigation

My forensic engineering investigation relied on the following methods.  The methods are described in more detail below:

  1. Examining the site of the rebuilt wall
  2. Studying photographs taken of the collapsed wall
  3. Studying a design sketch of the wall
  4. Interviewing two workers who were on the wall at the time it failed, including one who slid down with the wall on a piece of construction equipment as it fell over
  5. Interviewing the design engineer
  6. Reviewing design principles for coastal and marine structures
  7. Reviewing weather and sea conditions at the time of the failure

Description of methods of forensic engineering investigation

1. Examining the site of the rebuilt wall

This initial site visit and visual assessment is standard in an engineering investigation and an important initial task by a forensic engineer (Ref. 1).  Drawings and photographs are fine but picking up a concrete impression is important.  It’s well recognized that, “A picture is worth a 1,000 words”.  However, a visual assessment is invaluable.  This is so even if the collapsed structure has been rebuilt as was the case with the gabion wall.

I was able to see how the toe of the gabion wall was constructed where it was exposed to the scour and erosive forces of wave action in the harbour.

I also saw the location of the townhouse with respect to the wall.  The contractor had expressed concern that construction of the wall as designed would undermine the townhouse.  A simple rule of thumb ruled this out.

2. Studying photographs taken of the collapsed wall

Photographs are important, and sometimes all we have.  They are particularly important when detailed photographs are taken during construction.  They are also important when taken of the failed structure that is subsequently removed before the forensic engineer gets there.  The latter was the case in this instance.

The photographs showed the actual wall construction and that it failed in a quite classic manner – it just tipped, tilted, leaned over along most of its length.  The exception was where the wall was tied in and anchored to the wing wall at one end.  It remained upright there.

3. Studying a design sketch of the wall

It goes without saying that a professional engineer investigating a failure would want to know how the failed structure was designed and intended to be built.  This is a standard task in a forensic investigaion.

The sketch showed how the design engineer originally wanted the base of the wall constructed and the toe of the wall protected against scour and erosion.  Simple rules of thumb suggested the base design was adequate.  The toe protection was less so.

4. Interviewing workers

Interviewing workers is a standard task in a forensic investigation.  The interviews sometimes provide quite valuable information on conditions at the moment of failure.

I interviewed two workers who were on the wall at the time it failed, including one, an equipment operator, who slid down with the wall on a piece of construction equipment as the wall collapsed.

In engineering analysis we speak at times about a “trigger” in a failure.  All conditions are present – or nearly so, for a structure, a wall, an earth slope, etc., to collapse.  The trigger pushes the structure over the edge in a sense.  Sometimes there is heavy rain – the trigger, just before a landslide.

The construction equipment just back of the gabion wall at the time was the trigger in this case, an extra surcharge/weight on the wall.

5. Interviewing the design engineer

We always want to talk with the design engineer when investigating a failure but often don’t have the opportunity during the investigative stage.  This lack of opportunity is particularly the case when the design engineer is the defendant in a civil action.

In this case, however, the design engineer was quite professional in agreeing to talk with me.  His design was okay in the short term.  It turned out that a change he approved during construction caused the problem.

The change involved reducing the width of the base from about six feet – 2/3 the height of the wall, to three feet – 1/3 the height of the wall.  The change was made because the contractor said he couldn’t build a six foot base.  He also expressed concern that the townhouse would be undermined.  Consideration of a simple rule of thumb would have raised an alarm that the wall would not be stable with a three foot base.  Another rule would have demonstrated that the townhouse was not endangered.

6. Reviewing design principles for coastal and marine structures

Reviewing the design prinicples applicable to a situation is standard fare in a forensic engineeing investigaion and I did this.  I was particularly interested in the requirements for protecting the toe of the wall against scour and erosion due to sea conditions.

7. Reviewing weather and sea conditions at the time of the failure

This is also standard fare during a forensic investigation and in this case it tied in with reviewing the design principles mentioned above.  Sea and weather conditions were calm at the time of the wall collapse.

Cause

I concluded, based on the evidence, that the wall failed because of a change in the design of the wall during construction.  The principle defect was that the base of the 10 foot wall was not wide enough at three feet.  I also found that the toe of the wall was not well protected against wave action in the harbour.

Post mortem

There is a rule of thumb in the design of conventional gabion retaining walls that the width of the base of the wall must be about 2/3 the height of the wall – about 6.5 feet in this case, not 3.0 feet as agreed during construction.  A design engineer starts off with this conventional wall geometry and then checks that the rule of thumb holds in the particular case.

There are lots of rules of thumbs in engineering,  They expedite matters but must always be checked.  And they should always be referenced when the pressure is on to change things during construction.

The matter was settled out of court.

References

1. “Technical” visual site assessments: Valuable, low cost, forensic engineering method.  My blog posted on this site, September 4, 2012

How Mother Nature may have her way with us

I read the item about the three-storey residential structure being built in Halifax collapsing in high winds – failing, in engineering terms.  The building’s frame fell down shortly after 1:30 p.m. last Thursday damaging a car parked below.  Workers had left the site shortly before.  See The Chronicle Herald, January 31, 2013.

High winds also caused construction scaffolding to blow down at another site.  The winds restricted access to the harbour bridges.  Gusts were clocked in excess of 85 kilometres per hour in the area, and up to 105 kilometres per hour on one occasion.

What happened?

Acts of God?  Mother Nature having her way with us?  Excessive structural loading?

Some people involved in civil litigation, and others in the insurance industry, might see such collapses as “acts of God”.  Many others might see the incidents as examples of Mother Nature’s wrath.

I see collapse of the residential building as quite possibly an example of wind loading that the structure was incapable of withstanding – the wind was just too strong.  The building structure was not designed to carry such wind loading – at least, at that unfinished stage of construction.  Or possibly the structure as designed was capable but wasn’t constructed according to the design.

When structures are “weak”

It’s not likely so well known to people, in general, that some structures are at their “weakest” when they are under construction - more susceptible to failure.  The design engineer sometimes needs to pay more attention to the construction phase than to the completed phase.  Nor is it likely well known that professional engineers are not always involved in the design and construction of residential buildings and other small or seemingly unimportant structures.

Mother Nature’s loads

The loads on a structure come from Nature.  I think an entire book could be written on the concept of “load” in engineering.  But, possibly, simply put, a load on a structure is anything that the structure must stand up to, or provide for, and still function as intended.

For example, obviously, the weight of the people using a building and the weight of the equipment in the building.  Less obviously, the weight of a structure – the structure must be able to hold itself up.  We now know about wind “load”, the pressure of the wind on a building, and, by extension, also on towers, and on traffic signs along highways.  But, what about earthquake loading – the shaking that all manner of structures in an earthquake prone area must provide for?  And frost action on retaining walls and garden pathways.  All loads from Mother Nature.

Here is more information on where loads on structures come from – sent by Mother Nature and to be dealt with by professional engineers.  They can be categorized as vertical or horizontal loads.  They might also be separated into loads above the ground, at the ground surface, and below the ground:

Vertical Loads

1. Dead loads

All materials in nature have weight, called dead weight when used to form a structure – it doesn’t move around once in place.  Materials like timber, steel, concrete, plastic, and earth.  Design engineers must ensure the structure can support itself; it’s own dead weight.  And that the foundation soil material below can support all the other materials above.  Dead weight is often the greatest weight on a structure.

2. Live loads

Live loads do not usually provide such heavy loads on a structure, but they are important because they often derive from the occupancy of a structure – people.  They can also be caused by vehicles, as in a parking garage.  Storage of materials in tanks and bins generates live loads.  These objects all have weight that can be moved around; they’re “live” loads.

3. Snow loads

In northern climes, snow is another heavy load on a structure.  This material doesn’t move around once it falls and drifts into place, usually on a roof.  The nice, light stuff is light; the wet stuff is very heavy, as we all know when we must shovel it.

4. Rain water

Rain water can impose quite a load on a roof if its removal isn’t provided for properly.  When it falls on accumulated snow on a roof the combination of snow plus rain is a considerable load on a building’s roof.

5. Frost action

When wet soil freezes, particularly saturated soil, it expands – about 9%, and imposes a very great load on any part of a structure with which it has contact.  It moves everything in its path, verticallly, horizontally, and everywhere in between.  It’s not practical to resist it, the forces are so great.  In some types of soils ice lens can form and the expansion is much greater than 9%.  Foundations below the ground, and structures at ground level, like retaining walls and highways are affected.  Design engineers provide for the load from frost action by ensuring it doesn’t develop in the first place.

6. Wind

We mentioned wind above.  We all know how wind can push things over.  Less is known about how the wind can “pull” things over – called suction pressure in engineering.  It acts in all directions.  It’s the kind of wind pressure that pulls sail boats across the water and causes air craft wings to lift.  It’s a load that is being applied every time the wind blows on a structure.  It’s certain to have been a factor in the collapse of the three-storey residential building.  Design engineers know about it and provide for it.

7. Earthquake loads

Earthquake loads are considered to act in both a vertical and a horizontal direction.  They can result in large forces on a structure.  Providing for these forces when Mother Nature sends them our way is not as well understood.  Design engineers do their best with the analytical tools that are available.

8. Temperature

Construction materials expand and contract as the temperature changes.  Provision must be made for this in design.  All bridge decks have a gap between sections of the deck to accommodate the expansion of the deck in warmer weather.  Otherwise, the bridge deck would buckle – an engineering failure.  Concrete floors in buildings have expansion joints for the same reason.

Horizontal Loads

1. Earth pressure

Earth – Mother Earth, can impose a pressure on a structure and must be allowed for in design.  An obvious example of a horizontal pressure due to the earth is the pressure on a retaining wall or a basement wall.

A less obvious example of a vertical pressure due to earth is the pressure on a sliding surface that, if too great, will result in a landslide.  It’s called overburden pressure in this situation.  Design engineers can provide for these earth pressures.

2. Water pressure

Water, one of Mother Nature’s great materials, can cause problems if not considered.  Dams forming reservoirs are an obvious instance where water pressure must be provided for when designing the dam.  Less obvious is the allowance that must be made for the pressure that results from the water that flows through an earth dam.  This happens and it’s normal.  Also less obvious, water pressure must be provided for in bridge design less it cause scour and erosion around the bridge piers.

3. Dynamic loading

I wonder how many readers know that bridge decks are designed to resist the dynamic load that results when a number of vehicles all put their brakes on at the same time?  This load is related to several factors including the weight of the vehicles – weight that is characteristic of all materials in Mother Nature’s realm.