Steel Sheet Pile Structures Seminar 9

[Qshake]

To all,

I just attended a seminar entitled "Design of Steel Sheet Pile Structures" in the midwest and wanted to make mention of it to the group.

The seminar was extremely informative, professional, and carried 0.6 CEUs. It was developed and presented by Dr. Richard Hartman of Hartman Engineering out of Buffalo, New York. The seminar topics included cellular cofferdams, braced applications, anchored installations, and finally a brief overview of the development of new sheet pile sections.

As usual, the material for each topic consist of case studies in failures. In my opinion, this affords the attendee the benefit of knowing what kind of failure exist without experiencing it. Knowing this type of information helps the engineer to properly design structures. Examples for each application are provided with the course material.

If you get a chance and you do a lot of work with sheet pile structures, this would be worthwhile.

 

[Ron]

Q,
You bring out a good point...learning from other's mistakes. One part of that is that we learn something; and the other part is that many failures are caused by good engineers doing good work, but they just happen to be on the edge of a performance envelope that comes back to bite them. Granted, many failures are caused by incompetence, negligence and other issues, but all too often we forget that most of us like to practice in the warm, fuzzy middle while many times our only progress in the profession is made by those willing to occasionally think outside the box.

 

[Ginger]

Q / Ron

Thanks for the info. In the UK we have a similar course/ seminar which is run by Professors Burland & Potts at Imperial College, London. To anyone within reach of the college, this 3 day course is the "State of the Art" course to take and covers all forms of temporary and permanent retaining walls and covers standard analyses through to finite element approaches. I highly recommend it.

On the subject of failures, from my experience in designing a wealth of large cofferdams and retaining walls, is that failures are primarily related to a lack of understanding of the ground and groundwater conditions and how they react to construction activities. The strength of the support materials and the basic analysis methods of structures are well known. However, there is always seemingly insufficient information on the ground and I feel that engineers should devote the majority of their effort on the design of such structures into investigating and better interpreting the soil data they have at their disposal.

Regards



Andy Machon
Andy@machona.freeserve.co.uk

 

[Qshake]

Andy, I couldn't agree with you more about the ground water and geotech/hydraulics concerns.

Just another point to make: in our country it is often common practice to lay the burden of the sheet pile structure on the shoulders of the contractors. Not every contractor see the need to involve a consultant who specializes in these structures, as a result the client ultimately pays for this poor judgement. However, if we, the consultant, were to design the sheet pile structure then we are encroaching on "means and methods" and the contractors balk at the idea.

Food for thought!

 

[Hariharan]

With regard to sheet pile design, has there been any major
advancement in the method of calculation of the earth pressures
beyond what has been used since several dacades, and found in
text books?- Some of the researchers have tried to perform finite
element analyses, but have not yet come up with a simple model.
The old analysis methods, I think, are too simplistic for today's
analytical environment, and computer oriented engineers! May be
very conservative as well?

 

[Qshake]

In many areas I agree that FEM has opened our eyes in terms of the behavior of a variety of responses to loads, excitations, or temperature flucuations, however, I stop there when it comes to analysis of retaining wall structures and the like. In those instances I prefer to use the old addage "if it ain't broke...then don't fix it". Inherent in simplicity is conservatisism, this is a good thing and that ideology is used not only in retaining structure design but in the housing industry too. When is the last time we heard of a FEM of a residential dwelling?

Lastly, I don't beleive that engineers should needlessly sit on the computer developing complex FE models for simplistic structures. And no I am not an old prude, rather an experienced consulting engineer and educator.

Whooops! I should get off my soapbox now...sorry! :-]

 

[Ginger]

Q

The view from the soapbox looks great !! Can I join you up there?

You do point out a dilemma as to whether a contractor should approach a consulting house for their temporary works design or not. I write from the perspective of a contractor's in-house design engineer. Usually, we design our own temporary works from the small through to the very large. The benefits to my employer are:-

1. The design encompasses our company's preferred construction methods.
2. We can specify the plant and materials we have at our disposal.
3. We have a vested interest in designing economically as the cost for the construction of the works is usually already set in stone in our tender price.
4. We can rapidly respond to site requests for design changes.

I have only had cause to go to a consulting engineer recently due to lack of in-house resources. I'm afraid that the solution we got (and paid handsomely for) was less than ideal. In my experience it was overdesigned, made construction of the permanent works very difficult, cost extra money for the consultant to revisit areas we weren't happy with and ultimately delayed the job. And this was a cofferdam analysed by finite element methods !!

I think one reason for this is that the consulting engineer will tend to take a more conservative view in general. They do not have the vested interest in redesigning to suit the contractor's site staff requirements as they are providing a service for which they only get paid once. They tend not to want to have to change things without being paid extra for the re-design work. Another problem is that the consultants will not usually have the specialised knowledge for certain types of temporary works that the contractor has and does not therefore bring this knowledge into the design.

I realise that these are generalisations and I don't wish to decry the work done by consulting engineers, however, for temporary works especially, let the contractor do the design if he has the capability.

As for finite element versus traditional methods: I,m with you on this one. The main benefit of FE over traditional rethods is that the ground settlements can be better predicted by FE. This is important in structurally sensitive areas. Otherwise, the methods we have had at our disposal for many years work well and settlements are usually limited to reasonable levels
Regards

Andy Machon
Andy@machona.freeserve.co.uk

 

[Qshake]

Andy, as usual I've engaged my mouth before my brain. Thank you for noting that there are as many consulting firms who should be designing special structures as there are contractors.

 

[Ron]

Never one to shy away from a soapbox, here's my 2 cents (is that a tuppence?).....

A timely discourse since one of my colleagues and I were just this morning discussing the current trend to analyze everything by computer and forget the hand calcs. We see a trend in the younger engineers to want to use a computer for everything. A case in point was that my colleague had just received a project for his review that had about 10 pages of printout for a simple frame to hold some equipment. It probably took the engineer 15 to 30 minutes to create the model and produce a pretty package, but the thing he lost was his ability to SEE the analysis/design process. When we switched from slide rules to calculators, many forgot the concept of "order of magnitude" and thus began a tendency to believe the numbers without noodling the answer. Some of the younger guys are amazed when some of us gray hairs will give a "near" answer while discussing the problem and before doing any calculations. We stress that this comes not from great intelligence, just an experienced eye that is supported by a brain that can still do order of magnitude calculations at will, though occasionally dulled by a well-deserved beer!!

While FEA is a great tool, it is only as good as one's ability to conceptualize a proper model and its constraints. While I do FEA for some things, I still use the back of a napkin for others. I hope I don't stop that under the time/delivery pressures of projects these days.

Andy makes a terrific point for the need for practicality and tempering in a consulting practice. As consultants we must continually strive to be practical and pragmatic in our approach. It takes some effort, but it is extremely worthwhile for us to remain in close contact with contractors and suppliers to make sure we still know how things are being constructed and which materials are more popular, cost effective and user friendly to accomplish a task.

OK...so I said 3 cents worth for a penny's value!! Typical consultant!!!!

 

[Qshake]

Ooops! A correction...my last response I meant to say "there are as many consultants as there are contractors who should NOT be designing special structures". Sorry.

Ron, you are the greatest. Really, my hat is off to you and your napkin...if I have the opportunity I will buy you a beer myself!

 

[Ginger]

Ron

Please be assured that I will never be properly dressed without a thruppenny bit napkin in my top pocket from now on (and of course a ball point pen as my fountain pen tends to run!!) A neatly folded napkin is so much more stylish than carrying a laptop around.

Best Regards


Andy Machon
Andy@machona.freeserve.co.uk

 

[Ron]

Q / Andy....thanks. I like a good laugh early in the morning. We have to remember that if we take ourselves too seriously, others might begin NOT TO DO SO! A big risk, since obviously we engineers have all the right answers and others sometimes fail to recogize that fact.(ask any Architect!)

Also, Andy you don't need a fancy leather case for the napkin and it won't set off the metal detectors in the airports. One major caution....don't use the napkin to wipe the beer from your chin. That's what the back of your hand is for. It's such a pain to prepare presentable calculations on a soppy napkin. Who knows, maybe the napkin will replace the pocket protector!

 

[Hariharan]

The discussion has taken a slightly different, but extremely interesting
path. I am a grey hair myself, and believe in hand/ calculator approach
in the beginning before going to a computer (if required) for a refined
analysis. You get the feel for the numbers, and a confidence in the results.
This has worked well with my engineers as well.

However, the point I wanted to make was the theoretical basis should
be sound. Otherwise, you are not too sure if you are conservative or
unconservative. I did not get the feeling that we are necessarily
conservative with fixed earth / free earth methods for sheet pile walls.
I would have liked a researcher to do a number of FEM analyses,
some model tests, correlate the two and come up with simple
models for routine design. FEM is not practical nor necessary for
routine designs.

Regarding consultant vs contractor: My group designs marine structures,
and the construction methodology is the first item we decide upon. The
structural system and the design follows, and the design has generally
turned out to be attractive to contractors and economical. Yes, erection
aids, and other temporary components should preferably be designed
by the contractor, and the consultant can verify these. We do such
verifications. It gives the opportunity for the designer to know the
intricate requirements of construction aids etc.

Hariharan

 

[Ginger]

Ron

Thanks for the tip about soppy napkins. I'm tempted to vote this for "Tip Of The Week". PS-How does the new jacket fit?? Starting to look like Dennis Hopper yet?

Hariharan

I realise that my comment about consulting engineers was a generalisation and I probably selected the wrong consultant for this scheme.

I agree with your suggested approach and the need to approach construction methodology as the first point of order in the design. You are obviously an experienced engineer; most graduates/ young engineers do tend to leap straight into the analysis.

As for the fixe/free earth approach, again I agree that these methods are still relevant and not necessarily conservative. In the UK there is some debate as to the suitability of these methods under certain propping conditions (there is a perceived view that singly propped walls under certain conditions have their prop load underestimated). However, again I come back to the interpretation of soil data and the correct selection of soil parameters. These methods are reliable if the soil parameters are correctly assessed. We also produce sensitivity calcs (changing parameters to note effects) for our standard calcs as well as FE calcs.

CIRIA (

http://www.ciria.org.uk)

have produced some excellent research lately on the subject of retaining walls and propped excavations based on a multitude of monitoring on cofferdams etc and have compared them with back analyses of commonly used design approaches.

Regards


Andy Machon
Andy@machona.freeserve.co.uk

 

[Ron]

Hi Guys...still looking on the jacket. Trying to find one that isn't too warm for the climate (though today it's a bit chilly for northern Florida).

Andy...got the Dennis Hopper spirit, just haven't mastered "the look".

 

[Qshake]

Ron, where I'm from the Harley Jacket never goes out of style whatever the season...In fact, I've always gotten it confused with a really big tattoo! I'm really envious. But maybe we'll soon have a number of engineers outfitted and we'll all meet at that big harley social whereever that is, I'm sure it is in need of a couple of guys with harley jackets, pocket protectors and oh yea, extra napkins for some theory!

Way to go Ron!

 

[Riz]

Hello Qshake,
Please can you let us have the website or email address of R. Hartman - the course presenter.
Regards
Riz

 

[Qshake]

Sorry, I don't have a website address for Dr. Hartman or Hartman Engineering. BUT, I do have Hartman's snail-mail address:

Hartman Engineering
4910 Ransom Road
Clarence, New York 14031-2114

Clarence is near Buffalo, NY.