Impact wall design

[ajk1]

Has anyone ever dealt with an impact wall of the sort illustrated in the attached sketch? The area to the right of the wall will be used to temporarily store leaves until they are scooped up by a loader and lifted into a truck to be taken away. Our client tells us that the wall should be designed for the impact from the loader hitting the wall. The area is open to the weather.

Our engineer's question is whether the footing has to be designed for the full effect of the impact of the loader against the wall. I would have thought so, but I am posting this here to be sure.

The idea is that the slab-on-grade to the right of the wall in the attached sketch is where the leaves are piled and the loader operates. This area will have a 300 mm thick concrete slab reinforced top and bottom and the slab will be tied to the wall by dowels to take the force from the wall into the slab. The extent of the slab is something like 30 m x 90 m. There is no slab to the left of the wall. Everything will be on engineered fill.

QUESTIONS:

1. Does the footing have to be designed for the full effect of the impact of the loader against the wall?

2. Any ideas on how to resist the reactive force at the bottom of the wall footing (The wall will be tied into the reinforced slab-on-grade by dowels).

3. Any thought on making a "moment connection" between the slab-on-grade to the right of the wall and the wall? Is this the best way to take out the forces? Then the footing at the bottom of the wall need not resist any force from the impact, since it could all be resisted by the slab-on-grade to the right of the wall.

 

[theonlynamenottaken]

1)
The footing itself should probably be designed for the full effect of impact, but a large portion of the geotechnical reports I've reviewed over the years have suggested a higher allowable soil bearing pressure for short duration loads. If the soil pressure is governing the footing size then see what the geotech says in this regard.

2 & 3)
Relying on the slab-on-grade for horizontal translational support through slab tension seems reasonable, but relying on the SOG as a rotational support does not. The flexural stiffness of the slab being bent upwards seems negligible relative to the rotational stiffness of the footing pressing into compacted soil.

An idea... what about ditching the footing altogether and designing the wall as L-shaped, with the horizontal leg of the "L" being a thickened portion of the slab-on-grade? It seems the self-weight of the loader would then help resist wall overturning??

Also, the assumed slow down distance in your attachment seems generous. Seems like the slowdown distance would be be 1/4 of that value or less...

 

[ajk1]

To theonlynamenottaken (Structural)

Thank you for your thoughts and comments.

The problem with deleting the wall footing is that I believe that in some locations there is a grade difference and the wall is required to retain that grade difference. Also, it will remove the 1.2 m of frost protection from under the wall and the wall could then move up and down with the frost action.

The footing is much stiffer than the slab, as you say, but does that matter -- the soil will compress and the footing will rotate and the slab-on-grade (s.o.g.) will then pick up the moment.

One issue is that the s.o.g. has no frost protection, but we can place insulation under the s.o.g., although I do not know if we have to put insulation under the entire area of s.o.g, or only under say for 5 m from the wall and let the remainder of the s.o.g. move up and down with frost. Perhaps the engineered fill can be made non-frost susceptible...we can discuss with the geotechnical engineer.