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..

 

[Tomfh]

i suggest you forget the "team player" attitude and buddy system when dealing with contractors.

Sad but true. 95% of the time it's a one way street.

 

[DTGT2002]

As stated earlier, who inspected the lower levels and are you certain they are correct and acceptable?

If the rebar was detailed in such a way that the splices are not in acceptable loactions, and the splice that has now been noticed is only near a plane where the splice would be in a non seismic frame, has the detailing or installation been off from the get go?

Concrete removal is not fun, but it is possible to do quickly and well. Please maintain a friendly relationship with all involved. That said, the pain and cost or forcing an alternate solution will likely cause more pain than fixing things now.

In a recent situation, we were told carbon fiber could only be used to wrap a round column for our application. We had square columns. To form, reinforce, and wrap the squares to round would have been far more work than to delay briefly and chip and correct.

It is also key to find out who is the player truly responsible for the issue and work with them (even if it requires bringing in their higher ups) to review the situation and consequences.

Often times, a general contractors take on the repair work may differ from a concrete specialty contractor which may again differ from a rebar sub or designer.

Bring everyone to the table, outline what you need and expect and look for mutually benificial solutions.

Best of luck.

Daniel Toon

 

[civilperson]

Square columns can be confined with steel "wraps".

 

[rt06]

Without knowing details of your structure system, I guess your 40-story building is unlikely to be purely special moment frames. Is it a dual system ? Maybe you can look into changing the type of your concrete moment frame and see if it works (I am not familar with high seismic zone building design, just a thought). Then your detail requirement can be relaxed.

 

[msucog]

was there a site specific seismic assessment performed using shear wave velocity analysis? i would presume a building that large has already had that done due to the potential cost savings of getting a better seismic site class and SDC as well as evaluating the seismic effects on the structure. however, we often see designers unaware of the difference between determining the seismic site class with soil test borings versus the shear wave velocity. it may be worth the money to revisit this aspect if the final numbers were close to providing a better site class. also, IBC allows up to a 20% reduction in the seismic design parameters. perhaps if a better site class/SDC could be achieved "after the fact", then it might help out with the actual required reinforcement. (i'm not a structural engineer so i don't specifically know the extent that everything is effected by a change in the seismic site class and ultimately the seismic design category)--it's a long shot but thought i'd throw it out there