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Footing Cure Time?

fehujber said:
but I don't need 'tude.
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Agreed. I was suprised myself how few resources most smaller Building Departments have. We often pass on (and receive) our "gently" used copies of codes and standards to other jurisdictions through our local Code Officials Association.
 
The relevant provision of ACI 318 is Section 6.2 dealing with removal of forms, shores, and re shoring. In this section dealing with removal of forms and shoring they are talking about suspended slabs and not slabs on grade. Earlier ACI 318 mentions that the code does not apply to typical slabs on grade.

The key point is that for suspended concrete construction you do not remove the shoring until the concrete is strong enough to reach its strength. If removal is before the implied 28 days then there should be concrete cylinder results.

I believe that there is also a requirement that the concrete strength reach a certain value before application of post tensioning reinforcement but you will not have post tensioning unless there is an engineer involved

The basic rule is that if the design is fully compliant with the IRC there should not be a problem. If there is an engineer on the project the engineer on the project should make the call when this is important. Beyond Section 6.2 an inspector without engineering training will not be able to interpret ACI 318 to make a determination.

If there is an engineer on the project and the inspector cannot find any reference to when forms and shores can be removed it would be appropriate to ask that the engineer clarify the documents.

What this points out is that there is a strong oral tradition whereby information is passed down from individual to another and as a result it is often wrong. When this happens we do things without knowing. Supervisors are not always right. This does not mean that you do not do what you are told.

On a related subject if a building is designed by an engineer the plan checker for the structural work should be an engineer. A building official who takes the attitude that an engineering plan check is not needed because there is a professional engineering stamp is not fulfilling his duty.
 
fehujber said:
Please make no mistake. If I am wrong I learn and apologize. If there is no section supporting my position it stops then and there. I have had many instances when I was unable to recall or find a specific code section. I have even suspended enforcement of specifics when I was unable to put my fingers on what I knew was there, but once I find it don't mess with me again. In this case I have been following a standard that was taught to me years ago if it is wrong it is wrong and I will cease enforcement in this direction. No problem. What really agrivates me is a pompous person beating me up for the error of trusting a person who was considered extremely knowledgeable in code. I should add that when this particular point was "taught" to me I disagreed having come out of 40+ years of construction and thousands of feet of footings, retaining walls, endwalls, headwalls, curb and sidewalk, (all of it still standing) but you did NOT question that boss/mentor. In most of my prior positions I have had the ACI library at my disposal however the Township I am currently in does NOT have it. I figured this would be a good source for some clarity. I did receive many good answers and am grateful for all input, but I don't need 'tude.
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You had that much field experience and didn't know that inspectors are quite often FOS? (just like everyone else)

Argumentum ad verecundiam is typically considered fallacious reasoning, and it is good that you are questioning it.

But the best solution still requires a purchase of the relevant document.

As for attitude, "CONtractor" does not indiate a professional one.
 
Papio Bldg Dept said:
Agreed. I was suprised myself how few resources most smaller Building Departments have. We often pass on (and receive) our "gently" used copies of codes and standards to other jurisdictions through our local Code Officials Association.
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A professional can always purchase a copy on their own before they require stuff to be torn out and redone.

Sorry, I don't buy the excuse.
 
brudgers said:
A professional can always purchase a copy on their own before they require stuff to be torn out and redone.Sorry, I don't buy the excuse.
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An excuse is always an excues. Yes they can, and should...and I don't believe that excuse is still for sale in this thread. It is, however, the current reality, and circumstances leading to that reality are irrelevant in terms of what actions are to be taken going forward. When I came over from the private sector, I was not allowed to bring the firm's library with me, and on the meager salary I received, was unable to afford duplicating that library with one simple amazonian purchase. Each year I make it a priority to ensure that we assign and spend as much of our budget towards that end, however in the meantime we look to our neighboring jurisdictions to assist us with specific references, much as this forum does, and in some cases turn to specialized professionals for guidance.
 
Perhaps in my brevity I misled. I did not force the removal, My superior insisted I reject the footing. The contractor questioned and objected, my superior quoted the ACI and had the wall removed. THIS WAS IN 2006!!!! I simply asked (last week) that the contractor wait for adequete strength prior to drilling 8" into fresh concrete and was met with resistance. The story about removal was just for background.
 
fehujber welcome, and please don't take offense to the yapping. We all have our crosses to bear and occassionaly "Solum gratia", like simon the people on this forum will help.
 
USACE Specifications for Cast in Place Concrete based on ACI MCP-4 and ASTM C39 (referenced in IBC);

3.3.11 Removal of Forms and Supports

After placing concrete, forms must remain in place for the time periods specified in ACI/MCP-4. Do not remove forms and shores (except those used for slabs on grade and slip forms) until the client determines that the concrete has gained sufficient strength to support its weight and superimposed loads. Base such determination on compliance with one of the

following:

a. The plans and specifications stipulate conditions for removal of forms and shores, and such conditions have been followed, or

b. The concrete has been properly tested with an appropriate ASTM standard test method designed to indicate the concrete compressive strength, and the test results indicate that the concrete has gained sufficient strength to support its weight and superimposed loads.

Prevent concrete damage during form removal. Clean all forms immediately after removal.

3.3.11.1 Special Requirements for Reduced Time Period

Forms may be removed earlier than specified if ASTM C39/C39M test results of field-cured samples from a representative portion of the structure indicate that the concrete has reached a minimum of 85 percent of the design strength.
 
I assume that ACI MCP-4 refers to the 2004 edition of the ACI Manual of Concrete Practice. The ACI MCP includes many documents that are not always consistent with each other, some of which are guidelines and others are standards. Thus from a contractual perspective this reference is almost meaningless.

Putting the validity of the reference asside the concerns they are dealing with are already addressed in ACI 318 as noted above. The issue is confused by the fact that USACE has decided, as an owner, to get involved in signing work off before the contractor proceeds. This approach is not reflected in the IBC.
 
This is the non-BS answer from ACI (similar to USACE specifications) http://www.concrete.org/FAQ/afmviewfaq.asp?faqid=28:

Technical Questions - ACI Concrete Knowledge Center

Stripping time for forms

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Q. Does ACI provide information on how long to wait before stripping forms?

A. There are some important general requirements related to stripping time in ACI 318-05, Building Code Requirements for Structural Concrete. Section 6.2.1 states:

“Forms shall be removed in such a manner as not to impair safety and serviceability of the structure. Concrete exposed by form removal shall have sufficient strength not to be damaged by removal operation.”

There are additional default requirements contained in 301-05, "Specifications for Structural Concrete," the primary one being in Section 2.3.2.5:

“Unless otherwise specified, leave formwork and shoring in place to support the weight of concrete in beams, slabs, and in-place structural members until concrete has reached fc′…”

ACI 347-04, “Guide to Formwork for Concrete,” Section 3.7.1, gives direction regarding who is responsible for determining when the form stripping operation can begin:

“Although the contractor is generally responsible for design, construction, and safety of formwork, criteria for removal of forms or shores should be specified by the engineer/architect.”

As stated in ACI SP-4, Formwork for Concrete:

“Since early form removal is usually desirable so that forms can be reused, a reliable basis for determining the earliest proper stripping time is necessary. When forms are stripped, there must be no excessive deflection or distortion and no evidence of cracking or other damage to the concrete, due either to removal of support or to the stripping operation. Supporting forms and shores must not be removed from beams, floors, and walls until these structural units are strong enough to carry their own weight and any approved superimposed load, unless provision has been made to allow for anticipated temporary construction loads, as for example in multistory work. In no case should forms and shores be removed from horizontal members before concrete has reached the strength specified by the engineer/architect for form removal.”

ACI 347.2R-05, “Guide for Shoring/Reshoring of Concrete Multistory Buildings,” provides detailed information regarding the practice of stripping formwork and placing reshores in multistory building construction.
 
ACI 301, ACI 347, ACI 347.2R, and ACI SP-4 are not referenced in the building code and cannot be relied on by the building official unless the Owner's engineer voluntarily referenced them is the construction documents. There is a difference between ACI providing guidance on a topic and the building official being able to enforce compliance with that guidance.

ACI 347, ACI 347.2R, and ACI SP-4 are guides and are not written in mandatory language. It is ACI's position that Guides and similar documents should not be referenced in project specifications for these reasons. This position is clearly printed on the first page of each of these documents.

Thus ACI 318 Section 6.2 is the only thing that a building official can fall back on. The reality is that for residential projects permitted by the IRC, with no engineer involved, it is very very unlikely that a problem will result from building on young concrete. Two possible areas of concern are concrete trucks driving on green concrete and agressive backfilling retaining walls before the concrete got strong enough.
 
I was talking to one of our contractors who specilized in concrete work for over 20 years in CA. When I asked him about a requirement to wait 72 hours before stripping forms he said it was a standard practice because the form boards aided in keeping moisture in the concrete and thus helped in reaching the proper strength. Now he was talking multiple story concrete buildings not SFR's
 
Just set the concrete on fire and see if it passes strength tests!
 
Mule said:
Just set the concrete on fire and see if it passes strength tests!
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If you can set the concrete on fire, curing time is the least of your problems.
 
brudgers said:
Concrete does not need to be fully cured before CMU walls can be erected. 1000 lbs of loading per square foot is less than 8 psi - i.e. not even 00.5% of final strength for 3000psi concreted

And of course, type III cement develops most of its strength within 24 hours - if early loading with full structural loads is critical.

In other words, you have picked up the bad habit of making up code out of whole cloth.

The best course would, of course, be to just enforce the code as written.
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I agree, I've poured many footings and then come back after lunch and started setting wall forms. If you can walk on the footing you're good to go. These are not grade beams.

Bill
 
codeworks said:
"and regarding my gruffness", i'm glad i don't deal with you on a daily basis, sir
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I think that the only one getting called out for this was 'McGruff (he is a crime) Dog'
 
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