Removing load bearing wall - shoring issues 3

[MikeE55]

I am designing an addition which requires removing about 100 feet of load bearing wall (also serves as shear wall for a single story bldg). I'm replacing it with posts and beams and making frames rigid to handle the lateral loads. This wall supports bar joists spanning about 25 feet. My past procedure is to state on the plans "provide shoring as required". Should the plans include shoring design? I think this is part of the contractor's means and methods, and I don't want to design it. But should I ask for the shoring design to be submitted for approval, and sealed by a PE, etc. What's your standard practice?

 

[haynewp]

JAE that is a good point and another reason that I wonder if by reviewing a shoring submittal we may be sticking our feet into something we shouldn't be altogether. What do you think?

I did find a case here:

http://www.onlineethics.org/CMS/profpractice/ppessays/standard_of_care.aspx

Where it seems to imply that since the EOR asked for a shoring submittal he was in the right.

See under "Unreinforced masonry wall collapse"

 

[RHTPE]

Let's review quickly. MikeE55 stated: "...removing about 100 feet of load bearing wall (also serves as shear wall for a single story bldg). I'm replacing it with posts and beams and making frames rigid to handle the lateral loads. This wall supports bar joists spanning about 25 feet. My past procedure is to state on the plans 'provide shoring as required'. Should the plans include shoring design?"

As I stated earlier, I believe that the Standard of Care owed to a project like this is to insure that the structure is adequate from the time that the first modification is made to the existing structure, completely through to the completion of the new + madified structure. Particularly since you know that you are specifying the removal of a shear wall.

Should your plans include a shoring design? I'd say not necessarily, but they should (at a minimum) include the loads that the contractor-designed shoring is expected to sustain.

Now, is the entire 100' of shear wall going to be removed in its entirety before anything new is constructed? In my NTBH opinion this should be evaluated with the contractor's input. It may be wiser to construct as much of the new portion as possible (before removing the old wall) to prepare for a rapid connection between the two. This way your final design can be realized quicker and safer.

From JAE: "We don't have the statistical data nor the knowledge that the contractor has." Just because a contractor has experience with these kinds of situations doesn't mean he has a clue about the loads or the hazards. He could simply be lucky. Further, his crew on one project may only have one individual (or possibly no one) who has done this kind of work before. Much of the labor force can be local hires for the job, lacking in the accumulated wisdom that you think the contractor should have.

I do not mean to insult contractors. They have a tremendous wealth of experience with regard to how to put something together. They know how to get large pieces of building components from the truck to the proper place in the structure. But they do not always know the effect of their processes on the structural integrity of an individual component or a partially completed assembly. Haven't you ever heard the line "But we've always done it that way, and it works"? That "way" may have eaten up every safety factor that we engineers rely on, and all it takes is one stupid act or mis-step to precipitate a disaster.

The contractor who built L'Abiance Plaza had experience with lift-slab construction ...


Ralph
Structures Consulting

 

[nuche1973]

RHTPE,
I have a dumb question: what is NTBH mean? And to the rest of the forum, thanks for the input. I realized that I should have posted my question in another thread, but luckily the issue discussed was somewhat part of the original thread.

 

[RHTPE]

CCB1 -

NTBH opinion = Never to be humble opinion.



Ralph
Structures Consulting

 

[JAE]

The AISC Code of Standard Practice, section 1.8, clearly suggests that the EOR is not responsible for the "means, methods, and safety of erection of the Structural Steel Frame."

Also, in section 7.10, it states that the EOR should designate on the plans how the lateral-load resisting system works, what portions of the structure contribute to that stability, and recommend areas of shoring that may be necessary. The EOR does not design that shoring, nor does it suggest that the EOR must review it. It does suggest in the commentary to 7.10.3 that the EOR may require an erection bracing drawing if desired.

In 7.10.3 the Erector is responsible to "determine, furnish and install all temporary supports..."

So from an AISC/steel viewpoint, the EOR clearly should communicate/educate the contractor in how the structure works, both laterally and vertically, and provide any necessary shoring loading that is anticipated on the shoring points (per ASCE 37).

The Erector determines and designs the temporary shoring necessary for the steel erection and the EOR should provide any special loads that are non-steel that might apply.

The General Contractor would oversee the temp shoring as well.

 

[kslee1000]

The above references are in line with many have spoken here - the EOR is not responsible for the physical means, nor review, of the construction support system, however, he is responsible for providing information on loads (vert, horiz, static, dynamic...) and areas need special attentions/cares.

The engineer's involvement is needed more in remodelling works than new constructions though.

 

[DRC1]

JAE,
In response to your question about my post, I would say for a simple strucure, esp. one that has no live load, I would probably calulate that myself. For a portion of a shear wall in a basement that might have several floors framing into it, that may be a different story. The EOR has probably spent a lot of time researching and modeling the structure to determine loads. As the contractor's engineer, we generally do not get all the information, have a resticted time frame to develop the design, will probably run some numbers on loads anyway, but it is good to see the struct eng numbers. As I said, despite what the contract says, we are all in this together and the beast way to win a lawsuit is to avoid it.