Slab on grade design
Slab on grade design
(OP)
I am looking to design a slab on grade as a standard (non site specific) foundation. Does anyone have a good rule of thumb to use when little info is known?
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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RE: Slab on grade design
NO good answer to your question without better info esp concerning soils.
Around here we use perimeter footings with SOG. In parts of Texas I know they use post tensioned slabs.
Need more info
RE: Slab on grade design
RE: Slab on grade design
http://www.nceng.com.au/
"A safe structure will be the one whose weakest link is never overloaded by the greatest force to which the structure is subjected" Petroski 1992
RE: Slab on grade design
RE: Slab on grade design
RE: Slab on grade design
Get some help on this one. 747's cost around $200 million PLUS!!!
There are worse things than clay!!
RE: Slab on grade design
RE: Slab on grade design
2% chance = if you don't design for it, it will DEFINITELY go there. Take Mike's advice and get some help, using super-thick slabs.
RE: Slab on grade design
Also - is the plane just going to taxi on it OR land on it. TWO different loading conditions.
As slta said - if there is a 2% chance - I can almost guarantee you it will happen next week.!!!
RE: Slab on grade design
"Just taxiing" is actually a more severe loading condition then landing. Ends of runways and taxiways see more load than the part where there is uplift on the wings.
RE: Slab on grade design
RE: Slab on grade design
RE: Slab on grade design
RE: Slab on grade design
If it is a pavement, design it as such. You will need to know wheel loadings and load frequency. For concrete you generally design so that the tensile stress at the bottom of the slab does not exceed 50% of the modulus of rupture of the concrete...then you don't have to worry too much about the number of load repetitions.
If it is a hangar slab, design everything but the integral footings as a pavement and then design the integral footings for the building loads...then tie the two together, considering lateral thrust resistance as well.
The US Army Corps of Engineers has some pretty good info on concrete pavement design for aircraft.
RE: Slab on grade design
As a matter of fact. Hitler had the Autobahn built with very thick roadways that often were two or more miles dead straight. Why - so they could use them as runways if necessary,
The USAF even explored that possibility after WW2. My Dad was there and flying F-86s.
You could surely land a lot of planes on I-70 in Kansas!!
RE: Slab on grade design
RE: Slab on grade design
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Slab on grade design
I am not familiar with the design of pavement slabs for aircraft wheel loadings, so I am just thinking it through... I agree that air speed over the wing generates uplift making the plane lighter - by this I can see how a plane 'taking off' would be less load than taxiing.
However considering a plane landing we are talking about initial dynamic impact, then under full brake with aileron + elevators creating down force to bring the plane to rest in short distance - Hard to imagine this loading condition is going to be less that a near stationary plane?
Thinking about a mass opposing gravity vs working with gravity, I would have thought that takeoff<taxi<landing?
RE: Slab on grade design
Due to the elastic response of a rigid pavement, the forward speed of the aircraft lessens the load that the bottom of the pavement feels.
The next time you fly out, look at the pavement and you'll probably see more evidence of maintenance on the taxiways than the runways.
RE: Slab on grade design
I don't know about official, but it is how I remember it being taught in my one airport engineering class. The principal was that central areas of the runway, and I don't remember how much, could be designed for 75% of the loading seen by the ends and taxiways. I have never been involved in the design of airfield pavements, so don't know if they are actually built that way today or not.
RE: Slab on grade design
I have felt the resonant quality you mentioned before whilst taxiing around and also noticed it by the deflection (or 'bouncing') of the wings. There would be a substantial saving in designing the central areas to 75% of loading due to the large area of a typical runway.
RE: Slab on grade design
The Portland Cement Assoc. used to have a very good text on Aircraft pavements and I still use their airport program for designing slabs (mostly for rack loading).
Dik
RE: Slab on grade design
hokie66...that is the keel section and you are correct.
RE: Slab on grade design