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Office building featured in case study of ACI 562 webinar by NCSEA

Office building featured in case study of ACI 562 webinar by NCSEA

Office building featured in case study of ACI 562 webinar by NCSEA

(OP)
Yesterday I attended a pre-recordered webinar by our local SEA on ACI 562: CONCRETE REPAIR CODE presented by Dr. Keith Kesner and one of the three (albeit brief) case studies presented was an office building as follows:



After a few minutes of 'googling' I identified the building and its location, but I won't share it here.

5 floor levels, repetitive, simple, rectangular plan layout. What was the EoR thinking?
  • Span-to-depth (L/D) of 60!
  • 12" square columns for a 5 level building
  • No drop panels, caps.
The building was constructed in early 2000's, was in service for approx 10 years, and after multiple investigations/reports, it was deemed unsafe and closed by the building official.

It was repaired/strengthened at a cost of more than $20M (there were building envelope, plaza deck and other issues too). Obviously there were lawyers and insurance companies involved and the EoR settled.

This post may be somewhat more appropriate in the Engineering Failures and Disasters forum, except that it does not fall into the classic definition of failure/disaster, but oh-boy what a screw up.

RE: Office building featured in case study of ACI 562 webinar by NCSEA

(OP)
It appears that the information provided in the case study at the webinar is in conflict with this:

Quote (Investigation Report)

The building's floors are formed by 10-inch post-tensioned flat plate elevated floor slabs that are supported by reinforced concrete columns and walls. In the office building, the 10-inch floor slabs span 38 feet. Shortly after the property opened, cracking was reported in wall, ceiling, and floor finishes.

L/D still up there at > 45, but better than 60!

RE: Office building featured in case study of ACI 562 webinar by NCSEA

Ingenuity,

Come on, you have to tell us more than that.

I would think that $20M repair due to strength and serviceability issues is a failure. It does not have to fall down to be a failure, that is a collapse! Severe Strength and serviceability problems means it has failed 2 Limit States.

RE: Office building featured in case study of ACI 562 webinar by NCSEA

Disgraceful.

RE: Office building featured in case study of ACI 562 webinar by NCSEA

(OP)

Quote (hokie66)

Disgraceful.

It is indeed.

Quote (rapt)

I would think that $20M repair due to strength and serviceability issues is a failure. It does not have to fall down to be a failure, that is a collapse! Severe Strength and serviceability problems means it has failed 2 Limit States.

Yes, you are right. When the building in 2010 was classified by as 'imminently dangerous' and closed, it has failed.

Quote (rapt)

Come on, you have to tell us more than that.

I found several reports of the building via some google-digging. Some very detailed reports in documentcloud.org, which I won't share to protect the guilty, but here is a brief summary pertaining to the PT slabs. There were also issues with the building envelope and facade too, related to the slabs design shortcomings:

1. P/A of 450 psi in many areas;
2. PT was balancing 200% of self weight in many shorter spans;
3. Measured midspan deflections of 4" in dominant long spans;
4. Punching shear demand/capacity ratios of 3+; See photo below! One reports mentioned that closed-tie 'shear heads' were used but I can not confirm this.
5. Axial shortening of +1-1/2";
6. In-situ concrete compressive strengths of less than 4,000 psi after 10 years;
7. Numerous construction-related defects too.
8. Lateral force resisting system was also undersigned.



Original construction cost was about $30M in 2000.



RE: Office building featured in case study of ACI 562 webinar by NCSEA

About 30 years ago, a similarly designed and constructed building in Brevard County, Florida was under construction. It was also a 5-story building. Failed from punching shear, along with errors in the height of the rebar chairs that were used and a variety of other design and construction issues. Building collapsed, pancaked the slabs, killing 11 people. The collapse led to the enactment of the Florida Threshold Building law and designation. After that, all buildings of a certain size and/or occupancy were required to be inspected by an authorized "Special Inspector" (not to be confused with the term "Special Inspector" under the International Building Code......different requirements). The project was the infamous (at least in Florida) Harbor Cay Condominium collapse.

My point is that such things happen all too often. My firm was involved in the investigation of the failure of a parking garage under construction in Jacksonville, Florida in December 2007. Underdesigned and marginal construction. One person died.

RE: Office building featured in case study of ACI 562 webinar by NCSEA

(OP)
Ron,

I recall reading the NIST report some time back on the Harbour Cay collapse. I also remember reading in another reference to this collapse (Feld & Carper, 1997) that the structural engineer was a retired NASA engineer who hired another retired NASA engineer to perform the calculations and Prof Norbert Delatte made a point that:

Quote (Prof Norbert Delatte)

…structural engineering isn’t rocket science. Evidently, it is considerably more difficult

Reference: "Beyond Failure: Forensic Case Studies for Civil Engineers". ASCE Press, 2009,Delatte 2009, p. 153.

And this by Gene Corley:



Reference: CASE STUDY - Collapse of Harbour Cay Condominium" ASCE/SEI

RE: Office building featured in case study of ACI 562 webinar by NCSEA

Ingenuity....yes, the engineers were practicing outside their areas of expertise (obviously). Not that it helps much, but they lost their licenses, forever.

I'm not sure I completely agree with Corley. The SE does not guarantee that mistakes won't be made, though I do agree that the more rigorous the exam process, the lower the chance of missing one of the "fundamentals" of a design. I'm pretty sure that when that failure occurred, there was no SE licensure. I was hired by an attorney for the rebar producer to review the rebar shop drawings and compare to the design. Had just gotten started when the whole thing was settled.

RE: Office building featured in case study of ACI 562 webinar by NCSEA

(OP)

Quote (Ron)

...was involved in the investigation of the failure of a parking garage under construction in Jacksonville, Florida in December 2007. Underdesigned and marginal construction. One person died.

I found this OSHA report on that project. Link to OSHA Report. Some horrific collapse photos.

Quote (Ron)

The SE does not guarantee that mistakes won't be made...

True. Reduced but not eliminated. Experience matters.

RE: Office building featured in case study of ACI 562 webinar by NCSEA

Quote (Ingenuity)

Experience matters

This was the first thought that entered my head when I viewed this thread. For the life of me, I can't understand why some kind of minimal, qualified, anonymous, third party review isn't required for each and every building constructed everywhere. Heck, you could probably still buy an afternoon of Bill Baker's time for $1500 which wouldn't even amount to 0.1% the cost of a modest building. And I'm sure it wouldn't have taken Bill fifteen minutes to pick up on the deficiencies here.

I've worked for a lot of firms in a number of jurisdictions including one of the laxest out there, Canada. In my opinion, none of the following is adequate QC:

1) internal firm QC. Everybody likes money.
2) government official QC. They're generally not serious structural engineers.
3) rockstar university professors (talkin' to you California). Also generally not serious engineers.
4) Quantitative checks at the expense of experienced judgement. Quantitative checking usually amounts to junior people checking easy/non-critical things. It also doesn't add enough value per dollar to make sense.
5) Relying on the SE licensure gauntlet. It helps but even the California SE process is superficial compared to being a practicing structural engineer in my opinion.

I used the Bill Baker example only semi-facetiously. I bet even a mandatory 60 minute review by an experienced third party would eliminate almost all problems like this.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Office building featured in case study of ACI 562 webinar by NCSEA

(OP)

Quote (KootK)

And I'm sure it wouldn't have taken Bill fifteen minutes to pick up on the deficiencies here

I think maybe even a first year grad at SOM's office would have picked up on the punching shear, and related issues, within a cursory review...

RE: Office building featured in case study of ACI 562 webinar by NCSEA

KootK,

Not disagreeing at all, but making rules does not necessarily help

I know of a very small country in Asia where a full independent design review of every structural design is required by qualified design reviewers before the design is approved for construction. These reviewers tend to be older experienced engineers. And they do a very thorough design check. They go through every line of the designers calculations and pick up the smallest mistake.

Unfortunately they do not check that what is in the calculations is actually on the drawings!

Ingenuity,

You got a couple of comments in there before I could. I assume it suffered from all of the problems you and I have been warning about for about 20 years?
- Designed by average moments
- with banded distributed tendon pattern
- allowed for live load reduction
- with a tension stress at supports close to the tensile strength of the concrete based on average moments.
- assumed uncracked under this average moment condition for deflections
- and no normal reinforcement added in the bottom because stress less than the limit
- Designed using a computer program that the designer did not understand in an area of design that he did not understand with supervisors who did not understand
- and deflection calculations were based on a long term multiplier
- with no consideration of restraint effects

Making Punching Shear work must have been fun on 12" square columns with a 8-10" slab on 38-40' grid!

RE: Office building featured in case study of ACI 562 webinar by NCSEA

In my eyes, a review shouldn't involve detailed looks at the design engineer's calculations. The design is reviewed, not the math. A reviewer should be looking primarily at the contract documents. If calc reviews are involved, it should be to clarify any oddities that the reviewer found independently.

95% of structures can be reasonably reviewed in a few hours on a couple of pieces of paper. You check the math on the major gravity and lateral systems using rough loading, then you qualitatively review the detailing to make sure important things have been captured in the design and that there's a load path. During that review, you identify anything that looks non-standard or is critical to the load path and do rough numbers on those.

Then you sit down with the design engineer and ask questions about weird things you found, or just about the choices made. That gives you an idea of whether the design was thought through and whether the engineer actually understands what they did.

That's enough to catch dangerous levels of negligence and doesn't get you captured in someone else's math.

I don't care if a review catches a member being a size too small, or deflection being out. I care if there's a life safety issue or the designer doesn't know what they're doing.

The number of times I've caught massive misunderstandings in seismic load application, blind use of software that spit out a number that was off by an order of magnitude, or lack of attention to load paths in delegated engineering is terrifying and dangerous. However, it's also obvious on a reasonably high level review.

RE: Office building featured in case study of ACI 562 webinar by NCSEA

(OP)

Quote (rapt)

- Designed by average moments CORRECT
- with banded distributed tendon pattern CORRECT
- allowed for live load reduction NOT SURE. THE REPORTS I READ DID ANALYSIS BASED UPON FULL LL
- with a tension stress at supports close to the tensile strength of the concrete based on average moments CORRECT
- assumed uncracked under this average moment condition for deflections CORRECT
- and no normal reinforcement added in the bottom because stress less than the limit THERE WAS SOME ADDED BOTTOM REBAR
- Designed using a computer program that the designer did not understand in an area of design that he did not understand with supervisors who did not understand CORRECT. THE EoR LEFT THE COMPANY AND THAT MEANT THE SOLE REMAINING ENGINEER, ALBEIT IN-EXPERIENCED, TO FEND FOR HIM/HER SELF.
- and deflection calculations were based on a long term multiplier CORRECT. FIELD MEASURED DEFLECTIONS WERE 2 x THAT FROM THE CALCULATIONS
- with no consideration of restraint effects APPEARS SO. VERY SIGNIFICANT AXIAL SHORTENING EFFECTS EXPERIENCED BY THE BUILDING ENVELOPE, INCLUDING MAJOR GAPS IN THE WINDOW FRAMING, AND DISPLACED MASONRY

Making Punching Shear work must have been fun on 12" square columns with a 8-10" slab on 38-40' grid!I DON'T THINK THEY DID GET IT TO WORK, BUT ONE OF THE MANY INVESTIGATION REPORTS MENTIONS THAT CLOSED-TIE 'SHEAR-HEADS' WERE USED IN ORTHOGONAL DIRECTIONS. I ASSUME THE SITE CREWS HAD DIFFICULTY IN PLACING SUCH REBAR

RE: Office building featured in case study of ACI 562 webinar by NCSEA

(OP)

Quote (TLHS)

In my eyes, a review shouldn't involve detailed looks at the design engineer's calculations. The design is reviewed, not the math. A reviewer should be looking primarily at the contract documents. If calc reviews are involved, it should be to clarify any oddities that the reviewer found independently.

I agree. For internal review, do a somewhat thorough design drawings review, do some brief independent hand-based calcs, mark-up a set of drawings with questions for the engineer/designer, and maybe ask the engineer/designer submit the design calcs purely to see if it is orderly and rational, not to review the actual detailed numbers.

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