Wrong Column Rebars Splice Location 1

[timlim12]

I need urgent response on this, please help.

The 40-storey bldg that we designed is currently under construction and is now on the 14th flr. The problem is that the bldg constructor had a huge mistake on the placing of column rebars making the location of the rebar splice very near the column joint and some columns have 100% of the rebars spliced. we cannot adjust the rebars cause the lower flr has alrdy been poured w/ concrete.

we all know that this is very unacceptable because this could be a weak pt. when an earthquake strikes.

also the code requires that for a seismic zone 4 region (which where we are), the column splice zone should be located at the center-half of the column height, and the maximun no. of rebars to be spliced at one section is 30% (or 50%) of the total no. of bars.

we have trouble on addressing this issue. chipping the concrete would be time-consuming and by far the most unacceptable solution. we also consider using mechanical couplers but estimate shows that its very costly (and besides we dont know if this is acceptable with the code).

anyone knows some solution with these?

thanks in advance..

 

[hokie66]

You designed the building, the "bldg constructor" has built it incorrectly. If that is the situation, it is his problem. Have him propose a solution. Would be a shame to have to demolish 14 storeys, but maybe that is what it takes.

 

[prsconsultant]

I assume these columns are part of your lateral system and this problem occurs only at the 14th floor. If so, the only feasible option is to chip out 24" of concrete at the columns and use mechanical couplers. Note that the mechanical splices have to be staggered by a minimum of 24".

 

[shin25]

You probably can opt for welded splice. I am thinking that this mistake happened only at 14th floor. ACI-318-02 R12.15.3 writes-

"A mechanical or welded splice should develop at least 125% of the specified yield strength when located in the high tensile stress in the reinforcement. Such splice need not be staggered, although such staggering is encouraged where the area of reinforcement provided is less than twice that required by analysis."

 

[timlim12]

hokie66

yes we could just say that its their prob, but that not how it goes around here. i thnk it should be a team effort to find a solution 4 this. thnks anyway.

 

[timlim12]

prsconsultant,

yes the columns are part of the lateral system, and mechanical couplers is what we had primarily in mind, but cost is expensive and we have to wait for weeks for its availabilty.

 

[Dinosaur]

Welded splices may be much less appealing than you think. Most rebar is ASTM A615, which is a grade that does not have a good reliability in welding. The weldable grade of rebar is ASTM A706. This is available but in much shorter supply than the ASTM A615. If you opt to wled the rebar, I recommend getting a specialty group including CWIs involved. Refer to the AWS D1.4 Code for more information.

 

[Lion06]

I agree with hokie66. Have the contractor propose a fix. If you are willing to go to bat for him and bail him out of any screw up he makes he is less likely to pay as much attention to your drawings as he should.
Additionally, if you choose to "help him out" and come up with a fix for him I am not sure why you are so considerate of the cost to the contractor (i.e. the cost of the mechanicial couplers).
This is his mistake, not yours..... dont take so much headache on as a result of his failure to properly follow teh contract documents.

 

[shin25]

ASTM A615 is weldable as long as all the requirements for welding are followed including the preheat and maximum equivalent carbon content. You may have to get your hands on the mill certificates.

 

[Zambo]

Is it correct that the column splice has to be at the centre half of the column height? Why? And in the case of columns with beams on top surely the splice will be at the top of the column.

I doubt for alignment reasons that retro-fitting couplers will really help, although they may help on paper with respect to complying with code.

Should the critical splice location be shown on the drawings? Were they? If not was the contractor required to check the code for splice locations? My point being that it is not always clear cut that the contractor is 100% wrong, if there is any doubt the Designer has responsibilities to the Owner to assist with rectification to ensure the buiding is delivered in time and on budget.

Is there a possibility by revisiting the calculations and adjusting factors such as as-cast concrete grade that the columns will satisfy requirements?

 

[MarcbSE]

I agree that the two best options are chipping out enough concrete to relocate the splice, or provide mechanical couplers.

Chipping out concrete may be more expensive, but could probably be completed in less time.

Mechanical couplers may be less expensive, but you said it would take weeks to get - thus delaying progress.

I would provide these two options to the contractor and let them select which option works best for them when considering both cost and time. As mentioned in previous posts it IS their mistake and responsibility to provide the fix even when the EOR assists in identifying the acceptable repair options.

 

[dik]

Is the rebar weldable?

Dik

 

[Zambo]

Ah... I missed the point. The top of the bars haven't been cast in yet>

Is it possible to drill and epoxy grout additional bars to compensate.

 

[PMR06]

Why is chipping so unacceptable? Remember something has to give... cost, effort, time.

Why not saw off the columns down to an elevation above the desired splice point, chip the concrete to expose bars for lapping, then build a new cage on up?

BTW, who reviewed the rebar shop drawings?

 

[Bobber1]

If the columns are part of your seismic restraint system, ACI 21.2.5 requires the rebar to be A706, or A615 with special ductility requirements. So you may have weldable A706 bars in your columns.

Bob

 

[Rjeffery]

Who did the reinforcing steel inspection for the 13 other floors???

 

[msucog]

i'm reminded of a saying we use:
"you can have it cheap, fast, and good quality...now, pick any two."

i suggest letting the contractor propose the fix. if you propose the fix and it fails, you'll be the one completely on the hook for his mistake. the contractor is going to say, "well they missed the mistake too, proposed the fix, okayed the fix, reevaluated the fix, and signed off on the fix. therefore the fix-failure is the responsibility of the engineer". i suggest you forget the "team player" attitude and buddy system when dealing with contractors.

 

[civilperson]

An option is to confine the splice region in a steel "jacket" far enough beyound the splice to develop the rebar strength. I will design this fix if you would be interested.

 

[haynewp]

I was also going to suggest to at least consider what is being used for seismic upgrading of concrete frames in your area. FRP wraps (not a lot of testing I do not think for seismic joints) or other jacketing. Be prepared to bill for your time researching the method and making sure it would pass the building department as a substitute for the detailing that was missed. However, it may end up not being any more desirable than the chipping and welding stuff.

 

[engphila]

Its obvious who's at fault (the contractor) and how the QA was missed (the inspector) but the client won't be impressed with the detective work. Rather there needs to be options for successful completion of this project. Looks like cutting the column and chipping out to expose the rebars is the way to go.

Soliciting remedies from the contractor keeps him involved with the solution - try this first. Then, offer several additional options, together with schedule and cost impact. When a consensus is achieved, present a united front to the suits and get the job done TOGETHER. In the end, everyone should be involved, as this is after all a profession, right?

These things happen continually in this field - how we manage them is how we will be remembered. This time you may be bailing the contractor out - next time he may be doing the same for you.


engphila