Using Rowe's moment reduction factor

[Awre]

I came across this document about using the reduction factor

http://www.vulcanhammer.net/geotechnical/itl-tr-01-4.pdf

Is it recommended to use Rowe's moment reduction on anchored or cantilevered sheet piles analysis?

When should we consider using the moment reduction factor and under what criteria? Or is it a matter of judgment?

Do we have to use Rowe's moment reduction method on sheet piles analyzed using ProSheet or is it already taken care of?

 

[FixedEarth]

When you analyze an anchored flexible wall, like a sheetpile, you can use two popular methods-the free earth support method or the fixed earth support method. Rowe, refined the free earth support method with his moment reduction curves in the 50's.

Answers to all of your 3 questions can be found in most foundation engineering texts-for example, Geotechnical Engineering -Foundation Design by John Cernica, 1995.

Once you are familiar with both methods, you may choose one of the methods and then set up your own spreadsheet and decide that you don't need a commercial software. The problem with using a software, when you are not familiar with hand methods is that you don't have the capability to gauge the output.

 

[Awre]

Thanks,

Although there're conditions and curves that help in selection of the proper rowe's reduction coefficient, I came also across a paper the recommends usin the rowe's reduction coefficient if the limit state design was utilized in the analisis vs. working stress design (WSD)

see page 6/7 and 7/7 of the attached:

http://pubs.nrc-cnrc.gc.ca/rp/rppdf/t96-107.pdf

What's your take on this?

 

[FixedEarth]

There are many methods-There is the swedish method, Das method, Broms method and the list goes on and on. If you want to make a living designing earth retaining structures, it is worthwhile investing in several fundamental books. Then after reading several hundred pages, you will develop a clear understanding of flexible wall design.

For example, Blum, is credited with the fixed earth method. Some designers, follow, Tscetobarioff method which takes the point of contraflexure at the dredge line. Others, like Teng, say it is at 10% of the retained height. The umteenth book that I purchased had one paragraph that said, researchers found using less than 10% of H as point of contraflexure produces less than conservative tierod force. So instead of finding it out the hard way on a real life project, I learned it from a summary of research reports in a pricey text. In summary, it is worth getting decent library so you can read about the topic and pick your favorite way of solving this wall type.

 

[dcarr82775]

I have not had a chance to look through the papers, but I often reduce bending moments in anchored soldier beams and sheetpile because the stiffness of the wall is concentrated near the reactions (anchor and base) and so a greater portion of the load gets applied in these areas and reduced bending moments. Basically soil arching.

 

[TertiaryStresses]

I find that the application of bending moment reduction is usually dependent on non-technical aspects of the job. Do you trust the General Contractor and Shoring contractor enough to give them a more aggressive design? Anchored walls are usually installed to protect adjacent structures, so would it be better to use a higher bending moment to justify a stiffer wall and control the deformation?

 

[csd72]

The UK guidance on timber framed excavations (yes we still use them over here) allows a reduction of between 25 and 50% for arching.

Not necessarily directly correlated but a worthwhile comparison nonetheless.

 

[VoyageofDiscovery]

I have checked existing sheetpiles against limit state design and found that the sheetpiles are way underdesigned. LSD is not realistically applicable to flexible walls at this time. Beyond this experience will determine when you want to apply Rowe's reduction, it is always good to have something in the pocket though.