rebar clear distance

[boffintech]

Am inspecting on a job that has some 24"x28" columns with 20 #11 verts and #4 ties @ 12". As usual, the dog-legged dowels from the level below are not arranged perfectly so as to allow the column cage to be set with the dowel/vert splice lap front/back in the thickness of the column. Almost always the dowels/vert splice lap is side-by-side along the face of the column. So basically there is 2 to 3' zone at the bottom of the column where there is 1/2" or less between the vert bars.

This condition certainly doesn't appear to satisfy the requirements of ACI-318-05 7.6. However, how big a deal is this condition considering that the limits of the condition are isolated to the bottom 2 to 3' of the column?

ACI 318-05
7.6 — Spacing limits for reinforcement
7.6.1 — The minimum clear spacing between parallel
bars in a layer shall be db, but not less than 1 in. See
also 3.3.2.
7.6.4 — Clear distance limitation between bars shall
apply also to the clear distance between a contact lap
splice and adjacent splices or bars.

 

[JAE]

So you have on the 24" face only 1/2" between ALL bars? 6 pairs of bars per face would equal:

(24" - 3" cover - 1" ties - (6 x 1.41" dia)2) / 5 spaces =
0.62" between pairs of bars....is this right?

I think that the 7.6.1 limit of db or 1" is primarily concerned with horizontal bars and the difficulty in getting the coarse aggregate to flow with the concrete between the bars.

In a vertical bar case such as yours, that isn't as big an issue but the placement of the concrete would have to be carefully done to get concrete between the form and the vertical bars and not rely on the concrete flowing from inside the column, through the bars to the outside layer.

Section 7.6.4 deals with the space between the paired-splice combo and the next adjacent paired-splice combo of bars so this just reinforces that you have a problem.

It can be a big deal if these splices are part of a moment frame. With a moment frame you have very large column end moments right at the splice (assuming the splice is just above the floor line).

 

[boffintech]

column is 24"x28" and the detail shows 7 verts on the 28" side: corners have 2 bars bundled.

So I should have 4 spaces of 2.55" between pairs:
(24" - 3" cover - 1" ties - (7 x 1.41" dia) / 4 spaces = 2.55"

They essentially ignored the bundling of 2 bars/each corner and placed 7 verts equal spaced on the long side. The verts/dowels are virtually side-by-sde.

A sledge hammer will not persuade the interior #4 tie to its correct position.

I'll shoot you a pic later today.

 

[boffintech]

Here's the pic.

 

[msquared48]

"They essentially ignored the bundling of 2 bars/each corner and placed 7 verts equal spaced on the long side."

I assume that making them comply with the drawings is out of the question?

In lieu of that, I would spec a change, at the contractor's expense if necessary, to a pea gravel concrete of the same strength and slump.

Option three - use staggered Cad welds - the contractor should love that.

Mike McCann
MMC Engineering

 

[hokie66]

boffintech,

As I assume you are inspecting someone else's design, why are you asking us rather than asking the design engineer?

 

[msquared48]

Good Question... ?

Mike McCann
MMC Engineering

 

[boffintech]

Well, that is a good question...

First off I want to understand the reasons WHY it is or is not important, and when it is or is not important.

Secondly, on this particular job I'm not the QA (code required special inspector) but rather the contractor's QC. The contractor interjects himself as a buffer or filter between me and the EOR. So sometimes I get an answer like "He's OK with that." or "We always do it like that." or "That's industry standard." I have no way of knowing if he really asked the guy or not. I'm required to turn my reports in MS-Word format unsigned; I'm pretty sure they just change them to say whatever they want.

Since the recession started, well, you know, I don't want to get myself "laid off" for being some kind of nit-picking trouble maker who isn't a team player, some kind of stickler for actually putting it in like those crazy cRaZy CRAZY drawings. Back during the boom years I'd just put myself on a different job so I wouldn't have to deal with this kind of BS, but this is last big job we have, maybe for a while.

Soooooooooooo, you may be asking yourselves why doesn't the Special Inspector (the independent third party, the owner's representative), write it up and/or ask about it. I'd say: fear. "It's 10 pounds of sh*@ in a 5 pound sack! How the heck else CAN WE DO IT!?"

Besides, it's on the "approved" shop drawings, what could go wrong?

 

[Ron]

boffintech...Do you work for a company that is working for the contractor, or do you work directly for the contractor as an employee. Providing reports in a changeable format is not a good idea, obviously, and might be illegal depending on where you're located. Further, if you do not work for the contractor as an employee, your company is usually obligated to provide engineering review of your reports prior to providing them to clients.

Depending on how one interprets ACI 318, the aggregate size of the concrete should be no greater than 1/5 of the spacing or 1/2 of the spacing. In either case for your application, you'd have to be using very small coarse aggregate.

 

[boffintech]

I work for a company that is working for the contractor. I don't want to provide reports in a changeable format but we're the point of rocking-the-boat vs. being unemployed.

My company is not obligated to provide engineering review of my reports prior to providing them to the client because I neither perform data generating tests nor make any engineering judgments; I simply perform observations/inspections of the work.

 

[msquared48]

"I'm required to turn my reports in MS-Word format unsigned; I'm pretty sure they just change them to say whatever they want."

I trust that you are saving dated and signed copies of all the reports to CYA? And I do mean yours...

Mike McCann
MMC Engineering

 

[Zambo]

Surprising they don't manage to get it right after a couple of attempts.

I assume they cast with either a tremie tube or pump tube dropped down the centre of the column. What does the concrete look like at this lower lapped section. I would be expecting honeycombing and repairs that would be more of a hassle to do than getting the cage right in the first place.

If the cast concrete looks good I think you ought to check again maybe there aren't as many of these side-by-side bars as it first appears.