abusementpark...I do failure investigations for a living. That accounts for about 70 percent of my business. The remainder is structural design of specialty structures.
JAE makes some excellent points, and he's exactly right as usual, with one unfortunate exception...well, haven't had girls throwing panties from the jury box yet, but one can always hope...after I finish this post I'll tell a story about that one.
I came from a structural design/testing background. Getting asked to determine cause of failure is a natural adjunct to that, so I just somewhat drifted into it.
It is almost always interesting, technically challenging, and profitable. Where else can you get paid for research in the commercial realm?
Actual testimony occupies very little of my time. This years I will have testified more than the past 3 or 4 years altogether (so far 4 depositions and 2 trials...3 more depos scheduled, 2 mediations, and 1 trial later in the year). That's unusual for me. Usually I spend most of my time doing investigative and research work for the litigation process.
It's not difficult to get billable time, but cash flow is not always great, particularly if you're being paid by an insurance company. I get a retainer on almost all projects, so that helps a bit.
A few tips for this type of work...
1. Don't "stretch" the technical conclusions. Make them as irrefutable as possible. If you think you're right about a premise, validate it from several angles/sources. Remember, there will be an expert for the other side who will likely disagree with you. Make sure you're right!
2. Ask yourself if your answer would be the same if you were working for "the other side". If you can honestly say "yes", then you have the right attitude for this work.
3. Don't be an advocate for your client's position. Tell them your opinion, whether it is good for their case or not. They can only defend something if the know the truth...not just what they want to hear.
4. Not all clients have the right position and often they don't have a technical foundation for their claim. If they don't, do them a favor and tell them as soon as possible...they will save money and can prepare a better mitigation of their deficiencies.
5. Work for both plaintiffs and defendants
OK...here's the story as told to me by one of the opposing attorneys in a case in which I testified....
It was a roofing case on a hotel in NE Florida. The roofer screwed up the flashings and didn't properly seal penetrations from the other subs (AC/Electrical) that were done before the roofing was completed. He violated the building code with respect to the roof drainage (scuppers were too high to drain properly, causing ponding near the scuppers).
Jury was mostly men. I went through and explained the deficiencies, told them what I recommended for remediation. I was working for the hotel owner in this case.
The contractor's attorney hired a roofing contractor, a female who looked like she had just stepped off a magazine cover. Never in over 30 years of consulting including over 15 million square feet of roof inspection and consulting, had I seen the likes of this "roofer".
According to one of the opposing counsel, who told me later after my testimony, I did a nice job of explaining the technical issues and my recommendations for remediation were well accepted by all parties until....she testified!
She was only asked a couple of questions...her background (she was a licensed roofing contractor and ran her husband's roofing business), did she understand the drainage issues (yes), did she agree with the repair recommendations (no...they didn't need to do anything to the existing roof...the ponding was no big deal..she wasnt' asked whether that would void the roofing warranty..it did!)...she got up and left...and according to the attorney...every eye followed her ass out of the courtroom!.. In short, she cleaned my clock...30 years of engineering experience down the drain for nice legs!! Oh well.
Also, this attorney loves to repeat the story whenever I'm involved in a case with him or against him. Maybe in another 10 years it will go away!! Fortunately my client thought is was all rather funny...even though it reduced his award by some $30k.
I came from a structural design/testing background. Getting asked to determine cause of failure is a natural adjunct to that, so I just somewhat drifted into it.
After two years out of college, doing structural design for an industrial manufacturer, I went to work for one of the largest geotechnical/materials engineering consulting companies in the country. I was hired as a "materials engineer", due to my structural background. We did construction materials testing (soils, concrete, structural steel, wood, roofing, and variety of other materials). I became a certified welding inspector, achieved certification as an industrial radiographer, and a couple of other nondestructive testing certifications. I would do the engineering consulting during the day, and work on a radiography crew at night (what can I say..I was young and stupid...but I learned a ton of stuff). I then was put in charge of the geotechnical laboratory where we did all kinds of geotechnical lab testing (consolidation, triaxial, direct shear, permeability, classification, etc.). Again, a different area of practice with lots of hands-on experience. I've personally done almost all of the common tests done by geotechnical and materials engineers for construction support, many times over.
Then got involved in testing amusement rides for the large permanent parks in Central Florida, because I had already been involved in a lot of their building inspection and testing during construction, and they developed a confidence level with me and my collective band of misfits (engineers who were bored with the mundane and liked the challenge of different things). Did a lot of dynamic strain measurements and corresponding dynamic structural analysis. Successfully predicted fatigue failures in two of the major rides at one of the parks and helped them to develop solutions to these.
I've developed a reputation over the years for working on the oddball projects that others didn't want to play with. I'm a firm believer that engineering principles apply to almost everything and if you use your capabilities you can usually solve most problems. In the meantime, I've also designed over 600 aluminum framed structures, including long span trusses.
All throughout this tenure, I worked on determining cause of failure in a variety of construction materials (soils, concrete, structural steel, aluminum, roofing, waterproofing, sealants, pavements, etc.). I got to determine the cause of failure of several prominent pavement failures (two international airports and a military airfield), each time working in conjunction with international pavement experts from whom I learned a lot and applied that to my everyday practice.
I've thus far had a career that others do not get exposed to. I've never really specialized in any one area, always trying to soak up what I can learn in many different areas and cross-apply them.
I really enjoy what I do. I'm very, very fortunate.
That certainly sounds like a very interesting path with an eclectic array of experiences.
I've developed a reputation over the years for working on the oddball projects that others didn't want to play with. I'm a firm believer that engineering principles apply to almost everything and if you use your capabilities you can usually solve most problems.
I think I am definitely in philosophical agreement with you in these statements.
I only have couple years of experience and have been working in a traditional structural design office. It is enjoyable, valuable experience. However, some of the more interesting work I have done has been the oddball projects. Recently, I wrote a damage assessment report for a fire event in a structure and really enjoyed the whole process.
abusementpark...keep it up! I've done a variety of fire damage investigations, including wood, concrete, and structural steel. Again, it was my testing background that helped through these. For instance, I know through testing that:
...plastics usually melt at various temperatures, but generally when they get over 400 degrees F, they burn up...if the plastics in a fire did not burn up, then I know (approximately) what temperatures I'm dealing with.
...concrete spalls at much lower temperatures than it degrades. When the moisture in concrete turns to steam, it expands and can spall the concrete. That occurs at 210 degrees F to 300 degrees F. If the concrete actually loses strenght and starts to "powder", we know that the temperature exceeded 800C for a long period of time (usually at least 4 hours).
...wood can char at various temperatures, depending on the species..we can then determine the duration of the fire exposure and the effect on the properties of wood.
I recently sat in on a webinar offered by ASCE on structural investigations of fire damage. Alexander Newman (the presenter) gave a lot of good info and rules of thumb similar to the guidelines you listed above.
However, his direction on the decision-making process for fire damage to wood structures was left a little open for interpretation. He indicated that there are different schools of thought on which level of charring indicates a wood member needs to be removed and replaced. Apparently, the criteria for removal varies from any level of charring, to 1/16" of section loss due to charring, to 1/4" of section loss due to charring. This was more of a visual inspection criteria. I don't recall if he gave any direction on how to correlate a observed temperature to a level of damage to physical properties (like you referenced in your post). Can you elaborate of these factors for wood members?
abusementpark...the correlations are not great, as you might imagine. If the plastic parts are immediately adjacent to the wood parts, you can draw some conclusions...usually it isn't that clear.
I typically will take core samples of the wood at the neutral axis to determine affect. The cores are usually 1/4 to 1/2 inch in diameter and I cross section them and look at them under a stereomicroscope. I can then see the true depth of effect, not just the charring depth.
In fire damaged wood, the charring is one affect, but the cell structure change in the wood is another. When the cellular structure of the wood collapses, it is structurally affected, whether there is visible charring or not.
So through the stereomicroscope you can visibly determine if there has been damage to the cellular structure of the wood? We have been operating under the impression that if there is no charring at all then the wood member can stay, Sounds to me that you are saying that damage can still be done to intrinsic properties of the wood just due to the heat?
Is there a certain level of charring depth where you would summarily decide that the member needs to be replaced?
In general, when there is no charring, the section can stay, as long as you account for the potential reduced structural properties of the wood, as well as the obvious section loss from charring.
I use the microscopy to help me define the notional charred layer, not just the obvious char layer (the fissured, high shrinkage depth). That way if it is salvageable, we know the general depth that we would need to compute the reduced section properties. Further, when we see cell shrinkage, we know that there has been some (though undefined)loss of strength in the wood. Depending on the exposure time, this additional depth can range from essentially zero to as much as maybe 1/4 inch. This would mostly apply to heavy timber members. Typical dressed 2x sections are usually "damage apparent".
We decide on an individual basis which members can stay, based on the section loss and the estimated property reduction in the remaining section.
Is is OK just to use the approach you've been using? In general, yes. If you have to justify your decision at a later time, it is better to have gone through a methodical process to arrive at the same decision!! At least that way, you have the backup of research, not just an opinion. Attorneys have a knack for making good, rational engineering judgment decisions seem less so in testimony!
In my opinion, the authority on fire damage to structural wood is Robert White at the National Forest Products Laboratory. He has written extensively on the subject and most of his publications are available for download.
amusementpark
There can be a lot of damage to wood cellular structure without charring depending on the length of exposure.
Using a stereomicroscope can help determine the depth of damage with or without charring. You might want to look up subjects on 'destructive distallation'. As Ron notes, the depth of damage can be better determined by microscopic evaluation than visually; it is often deeper than observed by the naked eye.
If it's truss damage, I generally have a colleague run the truss to determine maximum loaded members (he has access to truss manufacturers' software). I then select the areas that I want to core samples.
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