Temporary Shoring? 5

[SteelPE]

I recently designed a rather tall masonry bearing building (you can find threads on this somewhere in the forum). Now the client is beginning to plan out the construction process. During a job meeting (which I did not attend, not was I required to or contract to attend) the architect volunteered for the structural engineer (me) to review the shoring plans for the masonry wall during construction.

This make me a little cross. On our drawings we specifically state that shoring of the wall is up to the GC, and that shoring should only be removed once the walls are in place. I am not really qualified to review their plan for shoring (as I have never done shoring design in my life). While I am happy they actually have a plan, I do not want to include any type of standard “reviewed” shop drawing stamp on the plan as I do not want to attract any liability on my end. I am wondering if anyone else takes a similar stance in that shoring of such walls is the responsibility of others or if I am just being obtuse?

 

[phamENG]

I think there was another thread on this type of issue recently.

I'm guessing you didn't require the GC to have the shoring plan analyzed and approved by a PE? If yes, just reject it when it comes in without a certification letter. If no, then look at it to make sure there is a reasonable load path. If there is a load path and nothing screams "I'm going to collapse" at you, return it saying you performed a cursory review of load paths and that the GC retains all responsibility and liability for the adequacy of the shoring.

 

[r13]

I consider this is a courteous review, which does not concern the ways and means of the contractor, nor the strength of the shoring material. But you shall be able to tell if the setup fits the purpose, and any notion that the setup might interfere with activities of other design features. You shall change your stamp to "Accepted with, or without, notes", and accompanied with a transmittal letter that states the nature of the review, and indicates if it is acceptable or not.

 

[oldestguy]

You've been around long enough to stand firm and refer to the documents on this. What are you paid for anyhow?

 

[miningman]

A daily rate of about half a million dollars would quickly evaporate somebody's desire for your involvement on this matter.

 

[BAretired]

I don't think shoring or bracing of tall walls can be removed as soon as the walls are in place. Tall walls, in most cases, rely on roof diaphragms or other elements to brace them against collapse due to wind forces. Usually, it is the responsibility of the contractor to provide bracing until it is safe to remove it, but there may be exceptions. It is prudent to specify the party responsible for the design of such bracing, but it may not always be done in practice.

The architect is not at liberty to volunteer the services of the structural engineer to check wall bracing who has not been specifically retained to do so. However, if a wall falls down and causes injury or death, you can be sure all parties will be involved at the courtroom or the coroner's inquest. Been there, done that.

BA

 

[SteelPE]

BA, I'm sorry, the note says to remove shoring once the floor/roof is in place.

 

[oldestguy]

One can tell by their comments as to who has been involved these sort of things as claims. This one in particular. Pay attention.
The architect is not at liberty to volunteer the services of the structural engineer to check wall bracing who has not been specifically retained to do so.

 

[r13]

It is a good question why the contractor decided to submit shoring plan for review, which normally does not require. However, if the drawing states "the contractor to shore...", then that's another story, because to me, it is a specification.

 

[BAretired]

BA, I'm sorry, the note says to remove shoring once the floor/roof is in place.

That's good; you seem to be a diligent and competent engineer, but I believe there are many engineers who don't specify responsibility for design of bracing and shoring on every project. Sad to say, I was one of them. Most of the time, it is agreed that the contractor is responsible, most of the time, but not always.

BA

 

[atrizzy]

Do you have a general note on your drawings indicating that all temporary/ancillary works are the responsibility of the contractor? And that you as the engineer are not responsible for the means and methods used by the Contractor? If not, now you know.

EDIT: I've now fully read your original post. I stand corrected, carry on.

 

[r13]

Construction shoring is rarely call out on the drawing, or addressed in the note. Now the contractor is guessing/worried that you know something hidden they won't easily know. Don't do it, unless you meant something, then, IMO, you have the obligation to review the plan, so get over with it.

Because of the duration is almost as long as the project, pay attention to potential interference, as simple as the brace is beyond the wall high, will it in the way of beams/trusts installation? If it will, how the contractor purposed to do? Identify potential problems and ask questions, as these problems might come back to bite you, or make you look bad. Be careful.

 

[bones206]

Some resources:

https://ncma.org/resource/bracing-concrete-masonry-walls-under-construction/

http://imiweb.org/wp-content/uploads/2015/11/IMIInternalBracingGuide.pdf

What can go wrong:

https://www.osha.gov/sites/default/files/2019-12/2013_r_03.pdf

 

[BAretired]

The last reference of bones206 is interesting. It reports on a masonry wall which collapsed under a 33 mph wind including gusts. As a result of the wall collapse, two employees were killed and one was injured. All calculations were based on a 33 mph wind velocity and their conclusion was that, for various reasons, the wall as braced, could not withstand the corresponding pressure.

What is a reasonable design pressure for a wall during construction? I can remember projects where wind gusts were much stronger than 33 mph with no roof diaphragm in place. And yet, to design for full building code wind pressure would seem overkill and is never done in practice.

As things stand, masonry contractors know they are taking a chance; they know that, prior to installation of roof diaphragm, their walls are not braced to withstand building code winds. They also know they can and usually do collect from their insurance policies in the case of collapse. At the very least, they should be following minimum NCMA standards, but that does not appear to be the case in many projects.

BA

 

[r13]

BA,

I think the failure cases are the reason most engineers don't want to deal with construction issues with high uncertainty, such as shoring. But I think the contractors in North America in general know the risks, and obey the rules, otherwise we may hear much more failure cases. Occasionally, for tall wall, and consideration of its setting (in city along populated street), we do require review the shoring plan and calculation to ensure the contractor has done the job, and accompany with inspection to confirm compliance.

 

[human909]

And yet, to design for full building code wind pressure would seem overkill and is never done in practice.

Unless you had great weather forecasts and a short time frame, it would be foolish and negligent not to design it to withstand significant winds.

The AUS code specifies wind strengths of 1 in 100 year winds for props and construction equipment. If I'm designing temporary props or restraints that is what I work to if I'm going to be putting my name to anything... (Sure there is no 'right' answer, it is all statistics. But if I'm walking around a site then I'd want to know that a decent gust isn't going to blow a wall onto me.

 

[Lomarandil]

Even for active construction operations, I never really go under 30-40mph in most locales.

For something that might stand in a temporary condition for a few days or weeks, there's more specific guidance in ASCE 37, but generally speaking (from memory), it comes out to 60-70mph in the Midwest US.

----
just call me Lo.

 

[SteelPE]

Just so everyone is clear, the architect volunteered my services for the review. My response back to the architect was that I was not qualified to do the review (as I have never done one before). I'm sure I could take a stab at it, but they wouldn't want me creating the plan as it would be overkill.

Also, with the current events of the world, who knows if these things may get 1/2 way up before construction stops. Then what happens? How long does it stay that way? In terms of life safety, it's an issue I am concerned about, but the project is in the middle of a forest in a small industrial park, so it's not like it's int he city with people walking below.

 

[FloydLloyd]

I believe the standard of practice is defined by Standard Practice for Bracing Masonry Walls Under Construction, Council for Masonry Wall Bracing. This is ref 1 in the first link that bones206 gave above.

Contractually speaking, I've done a few of these with my client always being the masonry contractor, who has to submit a "bracing plan" as required by the Specifications, generally a school or other government project, and the product is similar to a shop drawing submittal. So I guess, to answer the original question of liability, depending on how your specs or notes are written, its the same as a component design like roof trusses. Require the contractor to submit a stamped bracing plan.

In the above referenced link, and the good articles that bones206 referenced, the contractor is required to have a gal on site that can judge the wind speed. This skill is taken from sailors' tradition. And the contractor is responsible for stopping work and clearing the site, based on wind speed conditions.

 

[r13]

Just so everyone is clear, the architect volunteered my services for the review. My response back to the architect was that I was not qualified to do the review (as I have never done one before).

I think the architect leads the project, and trust your judgement on structural issues. If you feel strongly on "I must have done/been taught, something before, otherwise I don't want touch it, then point out the liability issues, see if he/she will back off and retract the offer. I just wish you have a reasonable lead, and understandable owner.