roof diaphram 1

[franklewis3]

With a CMU exterior and bar joist 7' centers, steel decking (1.5b22)and NO perimeter angle to tie roof diaphram to walls - CAN THE CONTRACTOR EVEN GET AWAY WITH THIS?

 

[Mattman]

There isn't much detail in your post, but if it is not in the plans the contractor shouldn't build it. He is not an engineer; he should not be determining what is required for the diaphragm. He does not have the knowledge.

If you are the engineer and know what is needed for this particular situation, draw it up and issue an RCOP pronto so that he can do the work to get the diaphragm distrubute the shear to the walls properly.

As designers, we have enough problems when contractors don't build to the plans, try to do it "the way we've always done it", etc. I don't think we should be complaining when they build it to the plans but the plans are wrong. We should own up to our omissions, fix the plans, and be done with it.

 

[whyun]

Whoa there Mattman. It dangerous for the contractor to knowingly omit something that he feels should be present.

I do not expect the contractor to second guess then engineer, but he should issue RFI (same as RCOP?) before continuing.

Who pays for the correction is a different topic all together.

 

[Mattman]

Whoa there, whyun.

From franklewis3's posts here and in thread507-33808, it does not appear that the contractor feels there is a problem. He is not "knowingly omit(ting) something that he feels should be present."

He is a contractor, not an engineer, and it sounds as if he does not have the knowledge to recognise this as an incomplete-and dangerous- installation. If he did recognise it as such, he would submit an RFI- he does not want a building that he is putting up to collapse any more than anyone else does.

If franklewis3 recognises the danger, he must be proactive. Depending on his role in the project, he must correct the design (if EOR or AOR), direct the EOR to correct the design (if Owner), or inform the owner of the situation and have the owner direct the engineer to correct the design (if franklewis3 is a third party).

Just telling the contractor he his wrong and getting mad about it without correcting the drawings/design will accomplish nothing. The contractor obviously needs direction and needs documentation of the change, to protect himself legally and financially.

 

[whyun]

Mattman,
sorry for the confusion. My whoa was for your comment "if it is not in the plans the contractor shouldn't build it". Yes, contractor is not obligated to provide something that is not in the drawings. But if it is something obvious that is missing, he shold alert the engineer.

i think we are along the same wavelength.

regards.

 

[DaveAtkins]

An angle is not always necessary to transfer wind load out of a steel deck and into CMU. A K joist has a "rollover" capacity of about 1650# (see "Designing with Steel Joists, Joist Girders, and Steel Deck, by Fisher, West, and Van de Pas). An angle is probably necessary PARALLEL to the joists, however.

 

[JedClampett]

We do a lot of municipal work. Our more sophisticated clients use "Front End" documents from EJCDC. In these it clearly states that the Contractor "shall promptly report in writing to ENGINEER any conflict, error, ambiguity or discrepancy ..." I think this is common language in all contracts.
It continues that the Contractor is not responsible to pay to correct this error if he notifies the Engineer. I guess I don't understand why the contractor wouldn't ask the question. He could get paid at Change Order rates to fix it if it is an error by the engineer. If it's not, he covered himself by asking.

 

[whyun]

shouldnt the perimeter angle ledger be provided to transfer the diaphragm shear to the CMU wall at least?

Seismic zones, it is definite requirement. But for wind only zones, similar detailing provisions should apply for windward and leeward force applied to the horizontal projection of the building.

 

[oijammu]

Is the contractor is ultimately responsible for any failures caused due to faulty designs? The man on the street does not know the Architect/Engineer,it's the contractors reputation on the line!

 

[samdamon]

Inreresting post. My two cents is that if a Contractor feels something is missing or wrong, he should definitely submit an RFI or otherwise ask the question. Its true that Contractors sometimes do not understand what drives parts of the structural design (especially concerning lateral loads, I believe), but I think there is no harm in listening to questions or comments about the design from the field. However I wish they would come while everything is still on paper, and not in the middle of construction. My impression is that builders rarely go through the drawings thoroughly before construction (This is not a criticism, there may be many reasons for this) and when questions do come about how something was done or if something was missing, they always seem to come during the building phase.

Getting back to the original post, there are several ways to get the shear in the edge of a roof deck diaphragm down into the resisting element besides using a continuous angle. The deck can be wrapped down over the joist ends using bent light gauge and attached to the block (You probably want a continuous bond beam in the wall just below this), or if the loads are light enough perhaps the rollover resistance of the owj connection cited in one of the posts will be enough.

From a practical perspective, attaching joists to block without a bearing plate or other embed can be difficult to have done properly, imho. So if the angle is not requested on the con docs, a different load path needs to be considered. Is it too late for that? Is everything up?

Regards.

 

[JedClampett]

I agree with SamDamon. I, for one, would rather answer 10 RFI's mistakenly questioning the design than miss one where I made a screw-up. I've also had cases where I've requested the contractor to submit an RFI as a mechanism for fixing a design problem. I'd rather come clean, explain I made a mistake and get it right than try to bury it.