Dowels to Transfer Large Wheel Loads

[SgtYui]

I've got a new concrete ramp that needs to be tied into an existing building slab. The problem is this vehicle produces wheel loads of 100kips on a 3'x3' contact area. Can any reasonable amount of dowels be sufficient to transfer these massive wheel loads into the existing slab? We considered cutting back into the existing slab to create an inclined surface for the connection, have shear friction and some amount of concrete bearing help transfer the loads. We then realized however that the end of the existing slab is heavily reinforced and decided against it.

Any ideas would be greatly appreciated.

 

[KootK]

It's conceivable that you could construct a shear connection at the joint that would be as strong as monolithic concrete. We could provide better recommendations if you supplied a dimensioned cross section at the joint. How thick are the two slabs? Are there edge beams? What are the support conditions for the slabs in the vicinity of the joint?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SgtYui]

See attachment for dimensions.

 

[KootK]

Cast an edge beam at the top of the ramp to distribute the load laterally. Then connect the two opposing edge beams with a bunch of small diameter dowels developed for fy on each side to get shear friction working across the roughened joint.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SgtYui]

The only part I worry about it assuring the concrete remains in contact with each other. If the two slabs were to pull away from each when the concrete cures then the load is going to be supported mainly by the dowels.

 

[KootK]

Cast the last few feet later, like a delay strip?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[EngineeringEric]

Just use a bunch of 1" or 1.25" smooth dowels. load sharing dowels down the length... I think this should be no different than those placed during construction for air ports, heavy roads, and so forth... Or maybe i am missing something?

See a google image search for "dowel bar placement" to see what is often done.

 

[SgtYui]

The difference is that we are trying to tie into an existing slab rather than pouring new construction. Also I don't think smooth dowels would do anything to help hold the slabs together besides what little the epoxy can offer. One thing I failed to mention earlier is that this area can get temperatures ranging from -40F to 100F throughout the year causing the concrete to shrink and expand. I would think some sort of deformed bar would be necessary to avoid pullout failures of the dowels.

 

[dhengr]

SgtYui:
Have you been driving these same wheel loads over the edge of the existing slab, with no ill effects? There is a concrete cutting device (cutting equipment, water cooled) which looks much like a chain saw, with a bar and diamond impregnated chain for cutting the conc. At about the same elevation that you show your dowels, I would plunge this into the existing slab edge about 4 - 5", btwn. the #4 ties @ 8" which run up the face/edge of the existing slab. These slots in the existing slab get a 8 or 10" long steel bar which fits the cut slot. These are your shear mechanisms and distribute/tolerate much more shear than a round dowel will. Pavement designers (DOT’s., etc.) are using these shear plates instead of dowels at pavement joints for this very reason. You will also need some dowels in tension to tie the two slabs together. Then the controlling shear cap’y. becomes what the bottom half height of the existing slab edge, plus the #4 ties @ 8" will allow, as some sort of a corner break-off (break-out) load. In the new ramp slab, you should also extend/turn the rebars, shown in side view, down as ties at the edge of this new slab, on either side of each of the new shear bars. Check this new slab and ties just as for the existing slab, as mentioned above. Tool the top of the joint and fill it with a proper joint filler/sealer system. Then try your high strength grout, but I don’t have much hope of that lasting long. It might get moved and broken up by the wheel loadings.

 

[Ron]

I see several issues with your concepts, not the least of which is that your grout filler will not last.

You loading configuration is strange. What is it? 100kips is a high load, typical of an industrial application; however, the "footprint" you gave is quite large.....if your info is correct, this indicates that your load transfer is likely less critical than you might think.

Another issue here is that you are planning to use bonded dowels across a dynamic joint. Generally not a good idea. One side of the dowel should slip. Cracks will develop at the ends of bonded dowels. If you are concerned about the sloped slab sliding down, you can put a thrust block at the bottom of the slope to prevent that.

I don't have any capability to do a sketch right now, but will attach one when I get back to my office.

Please provide additional info on what is loading the slabs.

 

[thaidavid40]

All the potential answers to this task that I have seen here seem to rely only on concrete solutions. I suggest that the two slabs be poured with a slight gap between them (to allow for thermal movement), and then a thick, load-bearing, steel cover plate be used to span the gap. That would allow for carrying the wheel loads, accommodating the thermal movements, and protecting the leading edges of both slabs.

Thaidavid

 

[SgtYui]

Ron: The load is being provided by a coal truck weighing 837kips, four wheels per axle, so about 100kips per 3'x3' tire contact area. Can you explain the thrust block a little more or point me somewhere to look? The only references I could find for thrust blocks were all in reference to piping systems. Sorry if my sketch was misleading, I meant to say tie bars instead of bonded dowels to keep the slabs in aggregate interlock. Though that might not be possible considering how long the ramp is (>100') and the bars would need to be anchored into the existing slab with some sort of epoxy.

 

[CTW]

SgtYui-
I'm curious about the 3:1 chamfered edge on the existing slab. Do you know why it was constructed this way? Is the existing slab part of a building? The way it's reinforced at the edge looks like the slab may be integral with a grade beam.

 

[SgtYui]

Yes the existing slab is part of an unloading building for the coal truck. I'm not sure why the slab was shaped that way, even at the moment that edge is covered by gravel to the top of concrete.

 

[CarlB]

Tha 3:1 sloped face to the concrete may be to help avoid an exposed concrete corner, which would cause more impact when hit by a tire. Or perhaps a snow plow.
i've seen this concept used at the edge of a concrete hardstand for heavy aircraft. The asphalt leading up to it would form ruts in the wheel path, exposing the concrete edge (if not ramped) which would be an unpleasant bump.