Impact load on top of the concrete wall

[bkal]

Hello forum,

I need to look into a case of a steel beam (box cross section) falling on top of a reinforced concrete wall. I am considering two cases: (i) the beam falling freely and (ii) the beam swinging about one of its ends (please see attached for an explanation). The wall in question has return walls away from a potential impact location; it has no slab on top of it.

I am aware of various approaches to assess effects such as penetration, perforation and scabbing of reinforced concrete walls / slabs when impact direction is perpendicular to their plane. However, I am not aware of any work regarding objects impacting on the edge of the concrete element in direction of the plane of the element. Any pointers or ideas on how to approach this would be appreciated.

We are also looking into dismissing this case based on a probability (low) of the beam actually falling.

Thanks in advance.

 

[WARose]

However, I am not aware of any work regarding objects impacting on the edge of the concrete element in direction of the plane of the element. Any pointers or ideas on how to approach this would be appreciated.

Are you talking about the scenario you have where it [appears it] will impact the corner of that wall? I'm not aware of any approach either. Most of the means to estimate penetration distance in concrete (from impact) are built around a good amount of edge distance. This may be a case of: you assume the corners are spalled off from impact.....and fixed later.

EDIT: Another approach might be to have impact areas covered with epoxy grout (bonded to the rebar). BASF makes some good, high impact grouts. Chockfast is another good one.

But that might get expensive.....so the "fix later" option may be best.

 

[STrctPono]

I would be looking at armoring those edges with some angle iron with welded studs embedded into the wall.

EDIT: After re-reading this, it's possible that this is an existing RC wall so embedded angle iron at the edges wouldn't actually work in that case. Just throwing out ideas, but for an existing wall if you are worried about damaging it, it sounds like you need a high impact energy absorbing material like a rubber, quarry belt, or foam.... Can you get yourself a come-along and strap some old rubber tires down on the top of the wall?

 

[bones206]

I've seen the following approach to concrete plate elements with in-plane impact loads:

1) Axial impact - Consider the wall as an elastic bar and set the kinetic energy of the missile (beam) equal to the compressive stress from impact using the following formula:

Then compare that stress to an allowable of your choosing.

2) Lateral impact (shear wall action) - set the kinetic energy of the beam falling equal to the shear + bending strain energy in the shear wall.

Since the beam would likely deform and absorb some of the kinetic energy, you could also account for that when estimating the kinetic energy transmitted to the wall. Both of the above approaches are more for a global check, and not helpful for estimating the local spalling/perforation of the wall at the impact point.

 

[WARose]

@STrctPono: That's a excellent idea. When I did scrap metal bins for steel manufacturers, we did a lot of armor plating (over reinforced concrete).....and part of that (at the corners) is what you are showing. However that may present a problem if it is a existing wall (like you said) or the cost effectiveness thing I was talking about (above).

@ OP: I checked a couple of impact/contact stress texts I have.....and the corner issue (likely to emerge with chamfered edges) is a tough one. The stress there is a singularity (i.e. likely to result in damage). Perhaps some other edge shape would be better.....but it's still hard with concrete to get a reliable stress as most Hertzian contact stress problems are built around elastic/plastic surfaces (not brittle stuff like concrete).

 

[dhengr]

Bkal:
On any wall, if your sketch proportions are off a little, the swinging beam could impart a fairly significant lateral load to the top of the wall, along with a vert. component. You better check this. On an existing wall, you want to try to impart the beam impact load near the center of the wall thickness, and to minimize the potential lateral component. You also want to distribute that loading over some length distance on the wall. Finally, you want something that crumples under the impact load to absorb some of the impact energy. Fix a light WF or I beam, fairly thin webs to the center of the top of the wall, so it crushes or rolls over, in the web, upon impact. 4’ sections of this beam can be replaced after an impact and crushing, and it prevents the beam from hitting the corner of the conc. wall.

 

[HTURKAK]

Er. bkal ,

Your Internet country domain (EN, GB) . If so, you may follow with the applicable code BS-EN 1991-1-7.

Annex C (Dynamic design for impact ) provides the necessary info.

In this case, you may assume Soft Impact (the structure is assumed elastic and the colliding object rigid ).

Excerpt from the same,

 

[bkal]

Thanks to everyone for helpful information.

Bones - whish book is your quote taken from?

 

[bones206]

It is from Roark's Formula for Stress and Strain, 7th Edition.