Should a structural Engineer design MSE walls?
Should a structural Engineer design MSE walls?
(OP)
Should structural Engineers design MSE walls and if so, is it there responsibility to check the Global stability?
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Should a structural Engineer design MSE walls?
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RE: Should a structural Engineer design MSE walls?
Usually the geotechnical will do the global stabilty including the equivalent fluid pressures, drainage requirements, bearing capacity, etc.
RE: Should a structural Engineer design MSE walls?
RE: Should a structural Engineer design MSE walls?
In my opinion, you have two scenarios. Either the structural has designed such walls in the past and has an idea of geotechnical parameters to expect from the soils report or is new to mse walls. If he is experienced, he may take the values from the soils report or use more conservative parameters. Say if equivalent fluid pressure of 45 pcf is given, he may use 55 pcf.
If however, he is new to such wall designs, I think it is prudent to learn from literature or just pass up the project to others who have more experience.
If there was a failure and a suit was filed, experts from both sides will pinpoint as to the likely cause. Say it was lower than design earth pressures, then the structural will be out of harms way, although he has spent some money to get to that point.
RE: Should a structural Engineer design MSE walls?
RE: Should a structural Engineer design MSE walls?
regards
Amanpreet
RE: Should a structural Engineer design MSE walls?
Internal stability is usually the reponsibility of the specialty contractor/designer of the MSE wall (i.e., Tensar, Reinforced Earth Co., etc.)
Jeff
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com
RE: Should a structural Engineer design MSE walls?
RE: Should a structural Engineer design MSE walls?
FHWA publication NHI-00-043 gives formulas for determining if tiered/superimposed walls can be designed independently or not. Also included are guidelines for stability analyses for multiple-wall situations. The PDF can be dowloaded for free from FHWA at http://www.fhwa.dot.gov/bridge/geopub.htm
It is, in my opinion, essential reading for MSE and RSS design and analysis. And an excellent example of US tax dollars at work.
Hope this helps,
Jeff
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com
RE: Should a structural Engineer design MSE walls?
While the FHWA and AASHTO have coined approaches to design of these walls there are many more developments that are equally sound and have been proven through actual field monitoring.
Where a bridge structure is involved, there is need for both the geotech and structural engineer to be involved. For non-bridge structures, the geotechnical engineer should be sole designer.
The design of the MSE wall is not only passing on geotechnical parameters to the structural engineer especially if it a geosynthetic or wire mesh reinforced wall. One of the issues of the design is the facing elements which can be lead to overconservative designs if there is not a good understanding of lateral load transfer to the facing. This depends on the rigidity of the geosynthetic or wire msh inclusions amongst others.
RE: Should a structural Engineer design MSE walls?
It's important to remember that the design rules for MSE walls (FHWA, AASHTO, BS8006, Clouterre) are simplified methods which have adapted the theory based on empirical observations. If you don't understand why, for example, the state of stress within the MSE mass varies (and differs depending on the type of reinforcement) then you shouldn't be designing a MSE wall. An engineer with at least a solid grounding in soil mechanics is best placed to make judgements about the behaviour of the mass when one strain rate is supressed. Also the design rules, because they are based on empircal observations fall apart when applied to novel cases. A geotech is likely to have more sophisticated tools to evaluate the overall stability of MSE structures in unusual applications (three or more tiers is a great example.)
On the other hand geotechnical engineers tend to be clueless about practical aspects of MSE wall design. Ask a geotech about the facing panel design and you are likely to get a blank stare. Structural engineers also tend to have a better feel for evaluating materials, loads and their application to structures such as parapets and anchor slabs and performance criteria when these criteria are driven by the supported structures (pavements or bridges).
I guess where I tend to end up on this issue is that a structural engineer is usually perfectly competent to handle MSE wall design or checking when he understands the basic theory of MSE walls, the MSE application is standard and incorporates standard materials, and the wall is founded in very competent soils.
In all other cases the structural engineer would be best advised to get specialist geotechnical input.
RE: Should a structural Engineer design MSE walls?
RE: Should a structural Engineer design MSE walls?
You must pay very close attention to the bid specifications as in many cases it will tell you who is responsible for the different aspects of design.
When in doubt contact a qualified geotechnical engineer who has experience in MSE walls.