Rebar weight related
Rebar weight related
(OP)
I am a chemical engr but presently looking after petrochem project construction cordination.I came across a typical problem. All the rebars used in silo structure are less than normal weight i.e. in the range of 94% to 97%. Individually they are acceptable but are the collectively OK






RE: Rebar weight related
RE: Rebar weight related
RE: Rebar weight related
Thanks. What is the standard practice for design ? Do we consider the negative tolerance as the base case ? If so, then even if all the rebars are within negative tolerance limit, the structure will be safe enough. Could you please advice based on standard practice if its acceptable ? What would be implication?
RE: Rebar weight related
What is more interesting is the tensile strength, again I don't have the code in front of me but I assume the tensile strength is based on the theoretical area of the bar, not calculated from the unit weight. If all your rebar complies with the tensile strength requirements then I recommend that you should also rest at ease regarding the unit weight.
RE: Rebar weight related
Mike McCann
MMC Engineering
RE: Rebar weight related
RE: Rebar weight related
You should also be able to get a mill report for the steel for the purposes of composition. Where are you and what is the appropriate standard referred to in the project specifications?
Dick
RE: Rebar weight related
The weights are not measured but taken from mill report only. However the mill uses ASTM standard to report(I suppose)
RE: Rebar weight related
RE: Rebar weight related
To answer your question directly about what area is used in the design, it is the nominal bar area, not with the tolerance deducted.
RE: Rebar weight related
A mill reprot in most industries is just a report of sampling from a run of materials produced and not the materialls supplied to a specific project or even where the materials were used in the elements of a project.
There is no substitute for sampling of materials on site if the is a real question of compliance.
As an example, in the cement industry, a mill report is routinely supplied to users/dealers. This is for an average of the product produced and posibly shipped immediately, unless the shipment was made from a general inventory.
Once it(the product)gets to the first distributor/dealer/manufacturer it may be put into a mingled inventory.
Once the product is at the construction site, there may or may not be a link to the specific material referenced in the mill report. The hope of identifying the specific material in an element is nearly impossible unless it has a tag on it. This is when it can be definitely identified and tested.
If you are dealing with a material that has no provision for oveage quatities/qualities the importance of minimal underages is not really important, unless there is a breach of the basic specificarions backed up by actual tests.
Dick
RE: Rebar weight related
If there is no link of the produce delivered to site and the mill certificate, the product is removed from site or segregated until it can be proven to be in compliance. That's the best way to handle it. The contractor is charged (he stipulated in his contract) that he would use compliant materials. If he can't "prove" it, then he is in non-compliance. (I realize that for many jobs this line of reasoning may seem overkill - or not followed - I have typically worked on large jobs (several hundred million so contrator's requirements are quite clear).
RE: Rebar weight related
RE: Rebar weight related
Take into account that the actual yield strength of the bars is going to be well above the 60ksi minimum assumed for design. Probably well in excess of 6%.
F(assumed)=As(assumed)*Fy(assumed)
F(actual)=0.94(As(assumed))*1.06(Fy(assumed))=0.9964F(assumed)
You really have nothing to worry about.
RE: Rebar weight related
RE: Rebar weight related
RE: Rebar weight related
Mill reports are usually not a substitute for prudent enforcement for a project under construction. Just because ASTM standards may have been used for the testing procedures, that does not have mean the rebars meet the project specification for the material in question. Testing procedures are different product/material specifications.
ASTM standards and/or procedures have to power until adopted by a legal entity or applicable code. Until that happens, they usually considered a "state of the art" document.
Based om your reading of the mill reports you are concerned, so it is your call. Like most ASTM product standards, there is a provision on payment. If additional testing beyond the contract is done, usually the person requesting the pays if the materials meet specifications. If the material fails there usually is procedure for retesting or possible rejection with costs born by the contractor or supplier, depending on contract documents.
Once you have complete information it can be turned over to the structural engineer (in this case) to determine if he feels the products are adequate for the design.
Dick
RE: Rebar weight related
RE: Rebar weight related
I am totally unfamiliar with silo design (and tension rings, for that matter). How is it that Fy is not important in the strength of these structures?
RE: Rebar weight related
RE: Rebar weight related
When considering ring tension in silos, tanks, etc., it is normal practice to use maximum reinforcing stresses due to service loads, a different approach from ultimate strength design. This is to limit crack widths. Elongation of the reinforcement is PL/AE, so the area is the important thing, not the ultimate or yield strength of the bar.