AISC - Non self supporting structures

[todousa]

A few years ago I was involved with a hi-profile project that included structural steel erection of a new parking structure over an existing precast parking structure, which incidently was being used by the public while erection of the new structure took place. During the course of erecting the new structure it was found that the new structure was a non-self supporting requiring either additional interior brace frames or for the floors to be poured in sequence with the erection.

My question is:

This structure was not identified as a non-self supporting structure on the contract drawings, so, if a catastophic incident involving the failure of this steel stucture to support itself during erection occured whose responsibility is it?

This is a real incident.

 

[JAE]

Check out AISC's Code of Standard Practice...In a number of places it outlines the issue of non-self supporting steel in that the "Owner's Representative for Design" (i.e. the Engineer of Record) is responsible for directly stating on the contract plans whether the steel is self-supporting or not.

We are just finishing up a 4 story structure that is comprised of exterior load-bearing masonry (shearwalls) and structural steel columns and beams on the interior - all supporting precast concrete hollow core planks. We have a note on the cover of our structural plans that clearly state for all to see that the interior steel cannot stand on its own, but is dependent upon the masonry walls for lateral support. The Contractor (AISC's term: Owner's Representative for Construction) is responsible for the temporary bracing.

The contractor must include the bracing, but it is the engineer's job to state WHETHER the bracing is required.

 

[todousa]

JAE,

Thanks for your coorespondence. I have grappled with the question of responsibilty for this project gone bad almost daily for the last 6-years. Have you ever seen a 24-inch long knife plate (shear lug) zipped off of a column? The structure we were working on collapsed after a resequencing of the erection to accomodate a schedule problem the general contractor had because they were behind with installation of their pin piles on a main support frame building line.

The Ironworkers were blamed for going too fast without providing enough erection bolts in the connections (2-each conn.). Somehow the media, the owner, the general contractor, and the engineer of record managed to put the focus of the investigation onto the erection bolts issue with no further discussion on where, possibly, the real responsibiliy lies.

Three men lost their lives. I am emotionally connected to this accident but, to my knowledge, it's root cause has never come to light and that is that this structure was never identified as a non-self-supporting structure. The erection team was forced to deal with the problem through RFI's and changed temporary support structures to provide the lateral support. To make matters worse the general contractor could not keep-up but were promoting getting the structure erected as fast as possible, even offering monitary incentives to the raising gang for each piece erected over 80 pieces to be divide between the raising gang. On a good day they would erect 150 pieces.

A found that after the accident no good could come out of my best efforts to help with the investigations or to provide the men's families with my own money or support. I cannot forget what I have learned nor can I stop thinking this accident was a missed opportunity for people in this industry to learn what can go bad when things are bad.

 

[JAE]

Sounds like a mess....especially when you mentioned the "media" word. They have a way of really getting the concepts twisted in a way that sounds good to the public, but makes no sense to any competent engineer.

There seems to me to be a very gray area, still, within our industry. I mentioned above that the engineer states WHEN a structure is non-self-supporting and the contractor is responsible for that bracing when it is so stated.

However, when is a contractor expected to get help from an engineer (not the engineer of record) to review, plan, and design the required bracing? The erector is responsible for all the bracing required during construction (per AISC). But the AISC Code of Standard Practice does not seem to deal with the point at which an engineer (licensed) is required to design the bracing. It's totally left up to the judgement of the erector...

 

[todousa]

JAE,

The erector did indeed have a licensed engineer on the payroll who designed the required lateral bracing to support the structure.

I think re-sequencing the erection was a primary cause of the failure because the newly imposed load conditions were not fully addressed in the bracing calculations. Basically the erector was erecting steel like they always do with no engineered plan to guide them. They were building a house of cards.

I guess the thing I've always thought was that no matter what amount of engineering analysis takes place there are other factors which can take presidence....like schedule.

Its a hard lesson to learn.