Wheel Load on Slab-on-Grade
Wheel Load on Slab-on-Grade
(OP)
A crane truck operats on a slab-on-grade (6" thick, with mesh raber at mid-height), other than the punching shear, my supervisor asked me to check "bending" of the slab.
Have you ever done this? Is there any significant bending developed under the wheel in the slab supported by compacted sturcutral subgrade (100%)?
Thanks for advice.
Have you ever done this? Is there any significant bending developed under the wheel in the slab supported by compacted sturcutral subgrade (100%)?
Thanks for advice.






RE: Wheel Load on Slab-on-Grade
This site will be of tremendous help for you since they have all kinds of notes, tables and details and other details plus software. http://www.concreteparkinglots.com/
Save your money, do not put mesh because it hardly ever gets in the proper position. It is like pulling teeth with contractors top get them to do the right thing.
Good luck
RE: Wheel Load on Slab-on-Grade
ACI 360R "Design of Slabs on Grade" has chapter 4.2 "Vehicle Loads" and Appendix A has information and example with charts for different soil conditions, wheel loads and spacing. This publication is VERY helpful.
Another publication is CRSI Engineering data report number 33 "The structurally reinforced slab-on-grade" has information on slabs with rebars. It will give you amount of reinforcement if slab is not thick enough.
Try to find those and good luck. (I used them for floors with forklift and truck loads.)
RE: Wheel Load on Slab-on-Grade
I agree absolutely! Use rebar, not mesh.
A crane truck operats on a slab-on-grade (6" thick, with mesh raber at mid-height), other than the punching shear, my supervisor asked me to check "bending" of the slab.
Is the crane a temporary condition, or will it be used for the life of the pavement? If the crane loads represent the planned use of the pavement, then you need to pay careful attention to the subgrade as well as the pavement thickness and reinforcement.
You will also need to carefully plan the location of the expansion joints so that you can add reinforcement in those areas, assuming the pavment will be wider than 20 feet and joint intersections may be subject to repeated crane wheel loadings. These pavement corners tend to break off under repeated heavy wheel loads - so additional bars are needed within about three or four feet of the joint if you care about the pavement life and appearance. They should run 45° to the main bar pattern (both ways.) Size and spacing of the extra bars? I'd use No. 5's at 12 inch spacings - in addition to your normal reinforcement. That's 4 layers of bars; you will have to thicken the pavements in those areas, too.
These details are not needed for most RC pavements because of the difference in loads and the usual absence of joint intersections where heavy wheel loadings are likely to occur -
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.
RE: Wheel Load on Slab-on-Grade
RE: Wheel Load on Slab-on-Grade
When I specify reinforcement I state that the placement of chairs, or what I prefer is concrete blocks having the same f'c as the concrete to be placed, used as chairs, be located such that the maximum deflection in the bars (or WWF) is no greater than 1.5" when supporting the weight of the workers. This ensures that a) the workers can walk on the reinforcement without pushing it all the way down, and b) provides for adequate stiffness so that as they the workers pass over, the reinforcement will spring back to the original location.
In the documents referred to by others you will find that there is both positive and negative bending in the slab. Therefore reinforcement placed at the mid-depth accomodates both. The positive moment is directly below the wheel load and the negative moment occurs between wheels on the same axle. Similar analyses are used for high storage rack post spacing as well as fork lift traffic and their related loads.
One last observation. I reviewed a construction failure where the contractor had pushed the WWF down to the bottom of the slab. It was a reinforced slope pavement under a bridge. Besides walking on the WWF and pushing it down, the contractor did not notify my firm that they were going to make the pour so we were not present on site to instruct them to pull the WWF back into position ( as we had on a previous pour). Well they also did not follow our plans that instructed them to turn the side walls down and embed a minimum of two feet into insitu soil. This bridge was over a creek that had been flooding regulary - so much so the original rip rap slope protection had been washed away a few months earlier due to a 100 year storm event. This contractor refused to watch the weather reports and did not adequately protect his work. In a few days after placing the reinforced concrete slope pavement it rained, the creek waters rose and eroded the side of the slope pavement, water then piped underneath the pavement and washed all the soil from under the pavement. Gaps as large as two feet deep by 12 to 20 feet wide were observed. We made them tear out the slope pavement. Now the reason for this story: I was there to observe the demolition and thought that it would go quickly since the reinforcement was not located in concrete as specified and it was a nominal amount. They used a medium size bull dozer to attempt to break up the slab. The reinforcement had been completely pushed down to the bottom of the slab. This could be seen after the waters receded; remember the free span of this slab is now as much as 20 feet wide with a 2 foot gap beneath. Th dozer could not break up the concrete from the side so the operator climbed the "cat" up on top of the slab. Now I don't know what the weight of this unit was but it had to be at least a few tons. The slab did not break; It took them most of the day to ripp that "inadequately" reinforced slab apart. The reinforcement was only for temperature steel as it was not designed for beam action or even traffic of any kind common to typical pavements. I do not use this example to state that it is acceptable to allow the pushing of the reinforcement down to the bottom. In time the reinforcement, in contact with the subgrade would have corroded and further reduced the tensile capacity of the section. However, the slab was extremely strong at that point in its life.
I'm sure that contractor will never believe that all the care engineers emphasize with respect to reinforcement placement is NOT justified based on the level of difficulty they had removing that particular slope pavement. They might not care but our clients will when after a few years cracks start to develop in their pavements (due to improperly placed reinforcement). When that occurs who are they going to call - most likely not the contractor but the engineer that provided the plans.
RE: Wheel Load on Slab-on-Grade
This is a new slab-on-grade, the operation of crane is kind of temporary, for equipment installation and maintenance (once a couple of years). Thanks pmkPE for the advice and story, I'll use reber and check the stiffness of it w.r.t. chair location.
p.s. is there a simple way to calculate the bending?
Regards,
RE: Wheel Load on Slab-on-Grade
My specifications instruct the contractor to make the check in the field. That way I don't dictate to them where to place the supports. Its a performance requirement to limit deflection to 1 1/2". How they choose to do it is up to them.
RE: Wheel Load on Slab-on-Grade
RE: Wheel Load on Slab-on-Grade
RE: Wheel Load on Slab-on-Grade
Driving fast is no answer, where most of these mesh systems come from, aircraft landing strips on the Bering straights Aleutians and Italy and France, but then things were lighter in those days and they often sank when at rest.
The note as indicated by another reply is your bedding materials must have a good granular effective stress, but perhaps of importance is the lack of shear stress imposed by the wheel forms on the formed surface and water retention causing pond hollows to form, as mesh is designed to flex the only way to prevent this is to either design a sliding slab that pulls back, or fix a rigid system (re-bar as indicated by others) and "float" it.
agreed. But the Forestry Commission has experience of this with access load bearing sites on bog as do the Institute of Hydrology from Plynlimon, Wales Wallingford England
MikeHydroPhys
mdshydroplane
RE: Wheel Load on Slab-on-Grade
Concrete Floor Slabs on Grade Subject to Heavy loads, Department of Army and the Air Force
Army TM 5-809-12
AF AFM 88-3, Chapter 15
Also don't forget to check ACI, as they have a special cicular on this too.
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: Wheel Load on Slab-on-Grade
Is there a way for civilians to get their hands on the Army Tech Manual?
Thanks,
DPA
RE: Wheel Load on Slab-on-Grade
try:
http://www.usace.army.mil/publications/armytm/tm5-...
you can find all kinds of technical manuals (TM) and engineering manuals (EM) starting at
http://www.usace.army.mil/publications/
RE: Wheel Load on Slab-on-Grade
Wow, What a lifesaver. I was looking at a three week wait from the U Book Store for the Ringo and ANderson book and here is all I need right on line. Hope I can do you a favor that big someday.
I have been trying to give you a star from this site but there seems to be a malfunction today. I'll try it again later.
Thanks again
DPA
RE: Wheel Load on Slab-on-Grade