Engineer's role - shoring/reshoring 1

[JAE]

Just a general question. On a concrete structure, is the engineer of record (EOR) commonly responsible for either approving or outlining the required shoring reshoring of multi-story concrete projects?

I know that the load carrying capacity of any floor is primarily known by the engineer and no other. Therefore, it makes sense that the EOR should reply to a request by an owner to write a letter acknowledging that if the concrete strengths are OK and shoring can be removed.

 

[Taro]

For typical concrete buildings in my area, formwork and shoring is almost exclusively designed by the contractor (or an engineer hired by the contractor). It is considered part of the contractor's means and methods. The Engineer of Record is not responsible unless the contractor hires the EOR to provide this service.

 

[JedClampett]

To stay away from this kind of question, we put language like this in our specs; "Shoring shall not be removed until the concrete has reached full strength." Most of our work is not multi-story, however.
I'd be careful. If the contractor ends up supporting a couple of floors of new construction off a floor that you told him to pull the shoring from and it fails.....

 

[Ron]

JAE...in my area, shoring and reshoring are "delegated engineering functions" requiring review by the EOR, or at the least by a "Special Inspector" when the building meets a certain classification (based on size, occupancy, or complexity) known as a "Threshold Building". The "Special Inspector" must be an Architect (don't ask!) or P.E., separately certified by the State. Shoring and reshoring are part of that inspection.

Under this premise, all shoring and reshoring must be designed by a licensed professional engineer, delegated by the EOR.

I know that other states do not follow a similar protocol. Many require that shoring/reshoring be designed by a P.E., but do not place greater emphasis than that.
Ron

 

[JAE]

Thanks, all, for the replies.

My situation was not critical in that the concrete strengths were way above the 28 day required for both floor and roof. I just balked at signing a letter to the owner stating that shoring could be removed and reshoring was not required.

I wasn't directing the design of the shoring/reshoring. Nor was I determining the step-by-step staging of it all. I was simply asked to respond whether it was OK to pull the shoring. I would think that our specs covered it all, as we clearly stated the conditions for this.

In fact, we have been getting lots of other letter requests lately from various clients - some of which are quite absurd in my opinion. They tend to be requests for letters stating that such and such piece of structure is OK if built according to the plans. I normally don't mind saying that if they build something per my plans its OK...but its just weird that they ask for letter saying such an obvious thing...like they don't believe I will stand behind my plans and seal.

 

[Ron]

JAE...your situation is not unique, but the whole thing is and should be troubling to the profession. These requests are further evidence that each day our services are more and more being viewed as a commodity, not as a professional service that is backed by education, integrity, ethics, and licensing. In this respect, our engineering societies have failed us as a profession, by doing what we as engineers do best...get down in the trees and fail to see the forest! But alas, our engineering societies are composed of....engineers, thus we have only ourselves to blame!

Ron

 

[Taro]

I sometimes get requests from contractors to review their construction procedures (shoring, temporary construction platforms, etc.). I would warn you not to get involved with this unless you are contractually obligated to do so. You can end up taking on a lot of liability for thing that you don't have control over.

 

[DTGT2002]

Issues of shoring and reshoring are always diffucult topics, as few viable current resources exist as a guide, and little direction is given in any standard building code. Certainly a response is required whenever a problem, or request is made of an engineer by his or her client, what the response shoudl be is another matter entirely.

I am a formwork engineer by trade and a civil engineer by training. I am responsible for the design and execution of formwork/falsework for multi-story reinforced concrete structures.

Shoring and reshoring should most certainly be addressed in the general conditions of any structure. This is a basic building code requirement. How this is addressed has no clear guide. Perhaps the best way is to specify shoring design by a Professional Engineer familiar with practices of Shoring and Reshoring, with required review/approval of the engineered shoring system by the EOR.

It is certainly in the best interest of the EOR to review, even if the review is not lengthy, the practices and procedures used to construct a design project.

Is the EOR responsible for shoring/reshoring? Probably not in a typical contract. Should the EOR review shoring and reshoring procedure? Definitely. Must the EOR specify at what strength the concrete is safe to strip? Without a doubt.

As to thoughts of the state of the industry where the design is questioned by requests to strip at an earlier date, a general contractor would like a self supporting building ready to dry in as soon as possible. This requires the removal of shoring as soon as possible. To make this a happen, a good relationship is required between the EOR and the contractor and perhaps the specialty contractor providing the shoring system. If the client wants the shoring removed to all for HVAC work, the structure must support itself, and EOR is the only party who may truly say if the structure can handle itself at this time. It serves the EOR to address this issue, and if the structure is not adequate to self support without it's entire structural system, that is a decision for the EOR, not the contractor.

Many questions routed to the EOR may seem absurd or moronic, but are usually recieved out of context.

I apologize for the long winded answer. I may need to write a book on the conflicts, trials and tribulations of the Formwork Engineer, bastard child of structural engineering.

Daniel Toon

 

[DTGT2002]

"I would think that our specs covered it all, as we clearly stated the conditions for this."

To me, The wording of specifications can sometimes border on legalese, and a letter, or RFI for clarification is a far smaller annoyance than designing a solution for a problem, or a lawsuit over a design that failed in construction, even if the EOR is not at fault.

A lot of the "boilerplate" section of specifications include lines like "the structural system is designed to function only as a complete system and is not capable of supporting itself until the structure is complete." So how does a person without specific structural training take this? The building is structurally unsound until topped out? Thus, the barrage of letters and requests to verify conditions.

Additionally, many assumptions affecting design are made to reach a final structural design. Many of these assumptions are not communicated in the final design. Ensuring that none of these assumptions are violated is an important responsiblity of the EOR.

 

[mrock93]

One question that occurs to me: if formwork is to be stripped early based purely on concrete cylinder tests, can the concrete be assumed to be adequate to support final design load? For example, if 28 day strength is reached after 7 days, can the concrete in place be assumed to be adequate in all aspects for full design load?

 

[RiBeneke]

mrock93
In respect of strength, yes the concrete will be adequate.
However, in the case of slabs and similar structures, deflection may sometimes also be an issue. The development of creep "resistance" and the development of cylinder strength in concrete are not always comparable at a point in time. Thus a slab may have the required cylinder strength, but may still be subject to relatively high creep, and by loading it early, the long-term deflections may exceed what is desirable. Detailed info on your concrete would be required to determine if this is, in fact, a problem.

 

[BigH]

Just wondering if any of the falsework guys have ever seen the bamboo falsework in Hong Kong??? It is amazing to see this type of falsework on tall buildings under construction - up 30 stories or more!!

Any comments?

 

[RiBeneke]

DTGT2002
Much of my work involves supportwork design, which is normally done for the contractors or for the supportwork supplier, and I can sympathise with you. Frequently the information provided to the contractor is limited to design floor loads on the floors.
It is clearly uneconomic to go through all the reinforcing schedules and reverse engineer and re-analyse the entire building.
One must do the calculation on the floor loads provided, taking due note of any unusual stability details and concentrated load details.
Then present one's calculations to the contractor with the proviso that they are based on the loads provided, and that the original designer must confirm that this is in order.

 

[DTGT2002]

I've never seen bamboo, but I have seen live trees used in Honduras, green wood cut and used as shores, and left long enough to root and grow again. I went back to the same spot a year later, and the low rise hotel was finished and looked good. I guess it is a lot like the live fence posts I have also seen. Amazing how quickly wood can grow again.

Often, the Structural Specifications and the general conditions of the project will REQUIRE two levels of reshoring, with language that does not allow for any less OR any more levels of reshoring. Any deviations from two levels in my building reshoring design will typically invite an angry call from the General Contractor with additional calls or a conference call from the EOR asking why on Earth would you ever have anyhting other than two levels of reshoring?

There are plenty of reasons why, not limited to choice of shoring system (loose stick shoring provides a much more uniform load than a flying truss system, as such, the large point loads in a truss system require more levels of reshoring in a typical case), a building requires more or less than two levels of reshoring. The EOR shoudl certianly be interested in the construction of HIS/HER building. The approval and review of the EOR does not relieve any liability from the shoring/reshoring contractor, but the building and all that affects it structurally is still the main concern and liability of the EOR. It seems to me that the construction industry as a whole has moved away from quality production and rather spends so much times covering them selves that the details of the building are secondary.

But enough ranting.

Daniel

P.S. if anyone here is in Atlanta, I am probably not talking about you

 

[cap4000]

The ACI-347-YR is being drafted this year in an effort to finally address this complex reshoring issue.Its only taken around 55 years,floor collapses and deaths for the incentive. The main authors in 1963 produced the first real document. Grundy and Kabaila were the pioneers.