concrete failure along steel surface

[elibintner]

Hi everyone; looking for some great tips on this one.

There has been a failure of a concrete bulkhead(headwall) at the mine where i work. The likely cause of this failure is from a loader dumping above this headwall and the vibrations travelling down thru the steel and into the concrete surrounding the steel.

I am advising for the existing concrete to all be chippped away, the rebar to be replaced and fresh concrete to be installed ( a basic reno job).
My questions are:
Is there a material that can be placed between the steel and concrete to dampen the vibrations. perhaps high density rubber or some form of structural insulation?
Also; how long should the concrete be left to cure before introducing it to vibration and stress?

thnks a bunch............

 

[Ron]

You do not want to place anything between the rebar and the concrete. The purpose of the rebar is to reinforce the concrete, typically in tension, but also in compression and shear in some instances. It is imperative that the concrete and steel bond well together for this to work.

Your presumptive cause of failure does not seem plausible. The actions you have described result in low frequency vibrations. I suspect the magnitude of the load is more prominent as a cause than the vibrations that occur as a result of the load.

If you could describe the way the concrete failed it would be a bit more helpful.

Concrete transmits vibration, not just the steel. Yes, they transmit sound wave at different velocities, but both are fairly high, particularly with low frequencies. High frequency sound or vibration in concrete gets dispersed because of the voids and other discontinuities and path interruptions that occur in concrete, as high frequencies generally tend to have low amplitudes that can't "jump" the discontinuities.

 

[miningman]

I agree the cause of this incident is unlikely related to vibration. In order to get an idea of the structure, is this a surface or underground location?? What type of machinery is dumping the load?? A 2 yard scooptram or a 200 tonne rocktruck??

How long has the structure been in place days / weeks / years??

Any nearby blasting with high peak particle velocities???

 

[elibintner]

thanks for the replies .

the machine that is dumping into the the hopper above the concrete headwall is a 988 loader; this is above ground inside of a building.
the concrete has just disintegrated; falling out onto the floor in large chunks. the concrete that is still in place is attached to the rebar that was used to reniforce the concrete.
if vibration isn't the problem perhaps the caocrete needs to be thickened to supply it with more mass to provide strength?

eli.

 

[cvg]

concrete needs to cure until it has reached it's design strength - which you need to establish. It sounds like you may need a structural concrete suitable for heavy, dynamic loading 4,000 or 5,000 psi. You need to also check to make sure you have sufficient steel. You can make this renovation, but until you check the design, you may find that you will continue to have problems.

 

[miningman]

Sounds as if you are suffering failure due to impact and/or abrasion. Headwall is a term I am not familiar with so Im having some trouble envisioning the exact geometry. Nevertheless it also sounds as if repair work will cause a significant interruption to production. You should probably investigate the use of steel wear plates or used rail to protect the concrete from direct impact from the load in the 966.... if its sulphide rock, there are some really heavy stones in that bucket.

 

[clandry]

I am currently designing a retaining wall to resist the impact from a CAT 988G loader. The wall I am replacing was damaged severely from a combination of the loader impact and steel corrosion (caused by the rebar being exposed to large cracks from the impact force of the loader). Due to limited area, the client opted for bollards filled with concrete to protect the wall rather than pour a ~25' wide 2'-6" thick footing for a 3' thick wall. The bollards are placed so the tires hit them when the loader's bucket is over the load-in pit.

You need to realize that the loader weighs 110k without any attatchment or load. It will be very expensive to build the monument required to keep the loader from demolishing the wall. However, bollards may not be feasable in your case. If there is repeated abrasion on the wall, you may want to look into some type of high strength coating on the concrete surface. I used Permacoat 4000 as manufactured by chemproof (

http://www.chemproof.com).

I hope this helps...

 

[csd72]

elibintner,

sounds to me like you need to talk to a structural engineer with heavy industrial experience on this one, it is not something that can be commented on accurately without actually seeing the site.

There may be other peripheral clues on the site that a more experienced eye would pick up.

The most important thing that you should be aware of as an engineer is the limitations of your knowledge.