AISC 9th vs AISC 14th steel manual

[ENGINEER92]

I am checking another engineer and we are getting different column sizes. The reason we are getting different column sizes is due to the drift of the structure. My deflection is higher since the 14th edition decreases the stiffness of the member, as specified in section C2.3.1 of the steel manual. From looking at the two designs, my drift is higher but the majority of is members have a higher stress on them.

I would like to hear peoples opinions on using the 9th vs 14th edition steel manual for design.

 

[EngineerEIT]

You should design based on the building code adopted by the state/locality the project is located in.

C2.3.1 is related to the "Direct Analysis Method" which you would use to design your structure for strength considerations. The 20% stiffness reduction does not need to be taken for serviceability (ie drift).

 

[JoshPlumSE]

As EngineerEIT said, the stiffness reduction factor need not be used for drift calculations.

9th and 14th edition should not be expected to produce identical results. We're comparing ASD code provisions from 1989 to ultimate strength based code provisions from 2010. That's 21 years between the two codes and a fundamental change in how the capacity of the member is calculated.

 

[ENGINEER92]

Thank you EngineerEIT, I didn't see that in the steel manual. Since that is the case for drift, I am more conservative to use the 9th edition since the 9th seems to give a higher stress value on the members vs the 14th.

 

[TehMightyEngineer]

Since that is the case for drift, I am more conservative to use the 9th edition since the 9th seems to give a higher stress value on the members vs the 14th.

Possibly, but if you don't know exactly why it's giving you more conservative numbers you may not identify when it's not being conservative any longer. Easier to just design to the correct code in my mind. Plus the equivalent length method can have some fairly un-conservative extremes.

I wonder when the 9th edition will stop being used regularly? Not saying it's better or worse but it's crazy how many practicing engineers still utilize it.

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[CCox]

Well, it works for simple member calcs. But it is very outdated when it comes to stability analysis. I guess back then they were looking for simplified ways to address stability without creating 3D models.

 

[ENGINEER92]

The engineers I know who still use 9th are mainly the ones who still do all their calculations by hand or they just have a 2D software they use.

 

[SlideRuleEra]

When modifying or repurposing many existing structures from the late 20th century (and all structures before LRFD was introduced in 1986), the 9th Edition (Allowable Stress Design) allows fairly modern calcs that are more or less consistent with the original design method. Especially true if existing beams sizes were discontinued before LRFD and modern Allowable Strength Design (ASD).

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[WARose]

I would like to hear peoples opinions on using the 9th vs 14th edition steel manual for design.

I haven't used the 14th yet.....but comparing the 9th to the 13th....(ASD vs. ASD) you can generally get a bit more capacity with the 13 edition. (Especially with prying action.)

Where I have really been able to get more capacity with something that was originally done by the green book.....is checking it via LRFD in the 13th edition if the live loads are low.