ASCE7-02

[Djorge]

I have two engineers looking at the same problem from different angle. The design engineer for large steel girder form system at 100' elevation has presented calculations with the asce 7-02 reference for wind loads that allow the use of this with out guy systems. The reviewing engineer is using UBC 97 thus requiring additional guy systems to support he wind loads.

Which standard is correct and what is the impact on the calculation for this project.

 

[RHTPE]

Djorge: In my NTBH opinion, I would refer the reviewer to SEI/ASCE 37-02, which in 6.2 refers to ASCE 7. In 6.2.1 of SEI/ASCE 37-02 it allows a wind speed reduction factor that ranges from 0.75 (< 6 weeks duration) to 0.90 (for 2-5 year duration). Temporary works should not routinely be designed to the same requirements as permanent structures. Sometimes the requirements for temporary works far exceed that of permanent structures, but for this application I think ASCE 7 is fine. If your check of overturning with an empty form (no concrete) is okay, I'd stick with ASCE 7.

What worker is going to be on the form during an extreme wind event anyway? It is a cost vs reasonable risk evaluation that the contractor must determine.


Ralph
Structures Consulting
Northeast USA

 

[civilperson]

ASCE 7-05 and IBC latest edition.

 

[RHTPE]

ASCE 7-05 is the current. The 2003 IBC 1609.1.1 references Section 6 of ASCE 7.

But, civilperson, why should the IBC apply to temporary works such as concrete formwork IF it has been designed by the rational methobs under ASCE 37 & ASCE 7?


Ralph
Structures Consulting
Northeast USA

 

[JAE]

RHTPE - I would side with you on using ASCE 37. But one point worth making here is that the specific location of Djorge's project may have an adopted building code that may or may not refer to the IBC, or ASCE 7 for that matter.

Djorge, you need to find out what the governing code is for the project. That will determine the "legally" required code. If you choose, you can use a more conservative code, but techically,....legally, you must use the one adopted by the governing body in that location.

 

[RHTPE]

JAE: I guess my difficulty has to do with requiring that something most design professionals consider to be "means & methods" meet codes that may be more restrictive than is necessary.

Djorge's picture shows what is most likely a DOT project. Most DOT structure specifications are pretty explicit about the governing codes relating to their construction.

What I truly despise is "blanket" language in ANY project's specifications requiring that construction meet "all applicable Federal, State, or Local codes." It allows the reviewer to "pick and choose" what he/she is most comfortable applying to the specific project and not necessarily the one that is most suitable. It also does not put all bidding contractors in the same ballpark when they are determing their cost of construction.

That said, I DO believe that a single acceptable & rational specification should apply to the contractor's means & methods to provide for safe construction methods and the safety & welfare of the workers.

Yes it's a bit of a rant. But I have discussed projects with my industry peers where some agencies/reviewers have required detailed seismic analysis for concrete formwork and shoring systems that will be in place less than 30 days. Why? Did the EoR do the same kind of analysis of his/her partially constructed structure as each additional portion was completed? I think not.


Ralph
Structures Consulting
Northeast USA

 

[JAE]

Ralph,

I agree with you on buildings and such. For bridges, which this most certainly is, the "building" codes wouldn't apply at all.

Also, from the OP's original post (they haven't appeared here for a while) - it sounds like they are the formwork engineers. Thus: means and methods issues aren't really relevent here. As a formwork designer, they ARE the means and methods.

 

[Djorge]

The pictured columns continue to elevate with flared column resting on ring beam and support jacks at the high point in the bridge. The form work designer and the contractor are using the Asce 7 code to determined guy at lower column heights and forces impacting flare when attached to the concrete stem. They've determined wind loading of 90 MPH / 30# psf as a standard. The reviewing engineering (not on site) relies on the UBC which results in a load of 50PSF. The difference is significant enough when the appropriate safety factors are applied to require additional tie downs to support the form when at the peak. The form is substantial as you can see and I fear an over abundance of caution on the review engineers part is the source of the issue. Your thoughts are very enlightening. Thanks