Steel reinforcement damaged by mechanical hacking 1

[erisew]

Our Contractor at site has damaged existing steel reinforcement while hacking our RC slab in preparation to cast an extension. Was wondering if there are any guidelines out there (or rule-of-thumb) on how much the steel bar can be damaged mechanically by hackers and still be considered 'acceptable'/'safe'. i.e. in terms of loss of cross sectional area or some other measurable criteria.

The steel bars are actually starter bars that were cast in the slab in the previous phase for us to lap with when we extend the structure for the next phase (which is about 5 years in between phases). The steel reinforcement is Grade 500. (i.e. chracteristic yield stress of 500N/mm2)

I'm actually writing from Malaysia, so we usually refer to British Standards / BS-EN on stuff like this, but I couldn't find any guidance on this matter in BS8110. Any input on this matter is greatly appreciated.

Lester Seow.

 

[csd72]

I doubt that you will find anything in the code as this has infinite variables.

I will usually loook at it from the point of view that if the full bars are required for strength then any deterioration is not accepatable, but if the bars are only partially stressed then it may be okay if it looks like it has sufficient portion of strength left.

You need to use your engineering judgement.

 

[scottiesei]

I would forget about lapping the bars. Try epoxy embed into the existing slab.

 

[scottiesei]

I was assuming that you were talking about a slab on grade, btw.

 

[CJPW]

I agree with csd72. Engineering judgement would be the best option. Whilst BS8110 has safety factors involved to take into account material characteristics etc. it all depends on how servere the loss of cross section is. If the slab is designed to the absolute minimum reinforcement required to carry the applied loads then adding additional reinforcement would be your only real option. Do you know what grade concrete the slab is? & how old is the building?
since the concrete will gain strength with age you might just get away with cube tests on the existing concrete to give you a service stress and thus justify a slightly reduced steel area.

 

[Lion06]

scottisei-
I would guess that if bars were placed in the last pour to lap with that the load must be transferred into these existing bars. If you epoxy into the slab, that will only develop the bars being epoxied in, it will not develop the existing bars. I think this might be a problem.
I would agree with csd72.

 

[civilperson]

Instead of lapping with concrete to transfer strength, try welding to the damaged bars with preheat and longitudinal filet welds.