grouted masonry vs prison break

[boffintech]

http://www.wnbc.com/news/14865097/detail.html#

Check out this picture of the masonry wall through which those prisoners in that NJ prison escaped.

It doesn't appear that any grout was ever in that cell on the left with that vertical rebar.

 

[PatBethea]

I saw this picture earlier today. Can one of you structural guys explain to me why there is rebar in an unfilled cell? Is that something that a contractor got a way with or do you typically call out that type of thing? Also, why wouldn't you fill every cell in a prison design?

 

[msquared48]

Pat:

It was probably a contractor error, never discovered during the inspections, assuming there were some.

You're absolutely correct in your thinking here.

Mike McCann
McCann Engineering

 

[whyun]

In the west coast, we fully grout all cells with reinforcing at 8" o.c. each way (though it may far exceed what's required for structural design) for prisons.

On the other hand, I've seen many residential fence walls that fell down after the Northridge Earthquake that had bars with no grout.

 

[boffintech]

Why is rebar is an unfilled cell?

Geezzz, how about a total breakdown of the inspection and observation process.

 

[msucog]

i've seen house foundations where mortar bags were stuff down about 12-16 inches into the cells and then grout poured on top. funny funny contractors...this reiterates what i've said before based on my contracting experience: never ever trust a contractor because i can guarantee you don't know the whole picture.
from what i've heard about discussion from prison jobs, the rebar is closely spaced and all cells fully grouted. the only jobs with more reinforcement and grout is big bank jobs...and they add lasers and all sorts of other cool stuff.

 

[boffintech]

msquared48 Contractor error? You are far too generous.

First week of masonry on one of my jobs. And I am not making this up, but I just received an RFI in which the masonry contractor requests a deviation from the code required consolidation and re-consolidation of grout. He believes that the "vibration" delivered to the grout by wet sticking the rebar into the grout is sufficient to satisfy the requirements ACI-530 3.5 E and thus a mechanical vibrator in not needed and at any rate the inspector (that's me) is just mean and a nit-picker.

 

[boffintech]

msucog that's a good one: empty sacks stuffed in the cells to stop them up so less grout is used, very cleaver. However, since reinforced masonry design is based on the reinforcing steel carrying all of the internal tensile forces I'm not real sure if those empty sacks are going bond the rebar to the block. Could be a problem...

I have similar one for you. Ever seen paper towels stuffed in the stressing pockets of post-tensioned tendons so one doesn't have to mix up so much grout to patch the pocket-former holes!

 

[msucog]

boffintech, that's every job for me. i have been told on the last 3 of 4 jobs that i'm picking on them. i can only look at them with disbelief. that's before i bring up reconsolidation. they simply blow my mind at what is acceptable to them...(that's the reason i left contracting for my lower paying job as an engineer--for some reason that seems backwards).

 

[PMR06]

I think both the inspector and contractor need to be locked up in that cell, and spend a lot of time looking at what their lack of hard work accomplished.

 

[hokie66]

I have sometimes joked on prison jobs that I have been involved in that I should leave a knockout panel in case I was ever sent inside. Maybe the guys who filled the cores had the future in mind, and their forward thinking worked.

 

[concretemasonry]

I worked with a construction manager, architect and a general/masonry contractor prior to design and construction of a maximum security facility. It was fascinating!!

A number of wall sections (20to 30) were built and were subjected to consulatants (ex-inmates) and others (a srange group) with the challenge to get through them. The same process was used on the windows(lighters/matches, vasiline and sugar were best) and on fixtures. The project ended up with a structure of some poured in place walls with postensioned slabs and many, many 8" reinforced ( 8" or 16" o.c.) CMU walls grouted solid since solid grouting was cheaper. The biggest challenge was building and anchoring the many interior CMU walls to the slab and ceilings without coring into cables.

The problem obviously rests with the inspection and implementation since the constructability is not a problem if the details are thought out in advance.

I have also seen residential basement concrete contractors that always had 4- 4' lengths of #5 bars and few standard lengths that were always on hand. When an inspector came around, the short lenghts were inserted into the fresh concrete and the full lengths made obviously ready and available if needed. The contractor only bought a few legths each year to replace any that might have been used. - The ironic thing is that the footings did not need any longitudinal reinforcement by code, but the contractor always got a high rating from the inspectors.

 

[hokie66]

Did he pull the bars out and wash them for reuse after the inspector left?

 

[patswfc]

PMR06

Whats the point of locking them up in that cell. They could break out without much difficulty, if they want to!!

 

[PMR06]

patswfc, OK, you're right! Maybe they should be locked in a different cell with a copy of the original plans and a photo of that hole.

 

[msquared48]

These guys were put in an empty cell - so of course they broke through an empty cell to get out. Stands to reason to me...

The ridiculous part of the inspection is that you can tell if a cell is grouted with a hammer. It's so easy. The sound difference is unmistakeable.

Mike McCann
McCann Engineering