ramblings of a construction inspector 1

[boffintech]

We have 1’-6” foundation walls with verticals of # 9 @ 12” OF and # 8 @ 12” IF and horizontals of # 5 @ 12” EF. The contract drawings have a wall section detail (side view) that clearly shows the horizontal bars inside the vertical bars on both IF and OF mats. The foundation walls are different from the shearwalls which have the horizontals bars outside of the vertical bars on both IF and OF mats. However, the plan view detail depicting the typical wall corners, ends, and intersections only shows horizontal bars outside of the vertical bars on both IF and OF mats. All wall corners, ends, and intersections require “U” bands lapped with the horizontal bars.

Of course the rebar bender made the U bands to fit outside of the verticals as the typ detail shows. U bands are only shown in the typ detail (plan view) not in the wall section detail (side view).

At the beginning of rebar placement for a large section of foundation wall I informed the contractor (prime) of this discrepancy: that the U bands were fabricated to fit on the outside of verts rather than the inside of verts where the horizontal bars were. An RFI was sent up and an answer was sent back down. The contactor (rebar sub) told me that the engineer wrote that it was OK for the U bands to be on the outside. Three days later (1 day rebar + 2 days formwork) after the rebar was installed and 90% of the formwork was in place and with concrete scheduled just hours away I just happened to eyeball the RFI on the contractor’s desk and the answer read the exact opposite of what the rebar sub said it read. The engineer clearly wrote that on shearwalls the U bands were to be on the outside of verts and on foundation walls the U bands were to be on the inside of verts. I instantly picked up the phone and called the guy and said hey they have it reversed from your answer on the RFI. He said I was reading right that the U bands were to be on the inside of verts for fdn walls. I brought this to the attention of the contractor and that I would have to report this discrepancy in the inspection report.

With the prospect of having to change 3 days worth of work to get those U bands right, the contractor got the boss of the engineer to change the RFI to now read that all U bands could be placed on the outside of verts regardless of where the other horizontal bars were.

Did the rebar sub pull my chain and tell me a fib or were the instructions which went from prime to formwork sub to rebar sub lost in translation? We may never know for sure but my old SOP of “If it isn’t in writing it doesn’t exist.” has been firmly reinstated. Seeing is believing, right?

Also, what's the big deal on these U bands if they are inside or outside and lapping or not lapping with the horizontal bars? They are just for containment, right?

 

[WillisV]

Boffintech - good question regarding the location of the U-bars. I believe the answer as to "what's the big deal on e U-bands if they are inside our outside..." really has more to do with why the horizontal reinforcing is placed on the inside our outside. The U-bars are then placed to match the horizontal reinforcing location to maintain the required minimum concrete cover (if the verticals were detailed and placed to have the horizontal bars on the inside and then the U-bars on the ends were placed on the outside then the cover would not meet the required minimum).

The situation you pointed out is fairly typical - shearwalls have horizontal rebar on the outside and foundation walls etc. have it on the inside. This is primarily because foundation walls are resisting bending and you get a large effective section depth if your main vertical rebar is closer to the ouside of the walls (thus placing your horizontal rebar on the inside of the vertical rebar).

For shearwalls which are resisting in-plane forces it doesn't matter as much and therefore the extra confinement of the vertical bars provided by the horizontals on the outside as well as the easier constructibility of horizontals on the outside typically lead to that arrangement.

 

[JStephen]

Possibly the situation is that the initial RFI response was rather arbitrary, and after finding that it was done the other way, they checked their calcs and found either way would meet the strength requirement.

 

[henri2]

While all this was taking place was the enforcing jurisdiction informed about what was going on?

 

[dicksewerrat]

You did what any good inspector should do. Now if there is a problem down the road, it is on the engineer, not you.

Richard A. Cornelius, P.E.

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