Enercalc Warning - Errors in ASCE 7-16 Seismic Load Generation 3

[Karryn]

The company I work for reviewed Enercalc's "Seismic Base Shear per ASCE" module and found several items that we consider errors.

1. The Fa & Fv values in Tables 11.4-1 & 11.4-2 have not been updated for the ASCE 7-16 version of the code. It appears that the ASCE 7-10 values are being used in the ASCE 7-16 module. (edit - they have informed me they will be updating this)

2. The exceptions to the requirements for Site-Specific Ground Motion Procedures are not taken into account but, the module still outputs design values. Based on hand calculations, these design values are incorrect and should not be used for design.

I have brought both of these issues to Enercalc and was told that they don't plan to update the module for the exceptions because it is outside of the indented scope of the module and they have only received one request to do so.

I request that Enercalc users verify and report these issues so that Enercalc might make changes to their module. Also, please let me know if you don't note the same issues.

I am using Enercalc Build 12.19.8.30.

 

[msquared48]

Nice to know that Enercalc does not support their product.

Mike McCann, PE, SE (WA, HI)

 

[azcats]

I've had good experience with Enercalc (retainpro) updating their products for issues I found. Twice this year.

That being said, I found two mistakes this year in the software.

 

[ARPASEVAN]

... and this is why I never rely on any software for design and only use them to check my spreadsheets.
Risa 2d gives you the option of 1.5 factor per TMS 402-13/ACI 530-13 section 7.3.2.6.1.2 but does not use the correct in Plane Shear Capacity formula.
Weyerhaeuser's Forte software under the design results table gives the maximum bracing distance not for the stress ratio noted in the table, but for when the beam will be 100% stressed.
and so on...

 

[CConrad]

Karryn,

For the benefit of all of the readers, I would like to clarify two things that we have discussed through our tech support email conversation.

1. The developers are aware of the need to update the Fa and Fv values for seismic base shear calculations according to ASCE 7-16 ELFP method, as you mentioned in your edit. I have your email associated with that support case, so I can notify you when those values get updated.

2. You asked us if we planned to implement logic to handle the exceptions listed in Section 11.4.8 of ASCE 7-16. This section deals with site-specific procedures that apply to sites that fall into Site Class F. My response was that the developers recognized long ago that Site Class F imposed certain restrictions that were outside the intended scope of the ELFP Seismic Base Shear module in ENERCALC's Structural Engineering Library. As such, they have set up this module so that it doesn't even offer Site Class F on the tab where Site Class is identified. In this way, the module automatically alerts the user to the fact that it is not appropriate for that Site Class. As we discussed, this is not our area of focus, and programming these exceptions would not be a wise use of our development time.

This does not imply that we don't support the product or our users. I hope you would agree that we gave you prompt responses to your concerns, even if you didn't necessarily hear what you wanted to hear about our development intentions.

ENERCALC, Inc.

Director of Technical Services
ENERCALC, Inc.
Web:

http://www.enercalc.com

 

[sandman21]

Section 11.4.8 does not deal with only site class F. But is a general section requiring a ground motion hazard analysis for buildings in site class D, E, and F.

 

[Aesur]

We all know Enercalc has errors, but find me a program that doesn't. I have found errors in RAM Structural, RAM Concept, CFS 11, and many others, each time I reported the errors. I have found that working with CConrad has always resulted in Enercalc looking into the problem, diagnosing and fixing, I probably have some correspondence with him a few times a month, sometimes about errors, other times about a crash and backup duplication going crazy after updates. It may not always be a fast fix, programs are complicated and take time to correct, but EnerCalc typically fix or address it within a few versions. Keep in mind that many programs are not being programmed by engineers, but by programmers with little to none engineering knowledge and therefore will have errors. It is the users responsibility to know what they are doing and use the programs as a tool to ease their frustration with the ever increasing complexity of the code. I am seeing way too many engineers only relying on programs with no knowledge of the codes, just assuming the program is always right. I prefer to do something by hand before I even think about using a program to do it and other engineers should as well; this gives confidence in what you are designing, helps you understand how the calculations work, and learn what the "gotcha's" of the calculation are. We really should be focusing on finding a way to simplify the codes and/or remove these "life long professors/PHD students" on the code committee's who are making our lives as practicing engineers a living **** by increasing the complexity of the codes every few years. Our fees tend to only adjust down (as they did when BIM took off), so we end up killing ourselves to do more work with less time which is why many engineers eventually leave the field.

One suggestion I do have for EnerCalc however is create a database users can view that shows the reported errors that are being worked on so we know them and don't have to stumble across them ourselves.

 

[Agent666]

create a database users can view that shows the reported errors that are being worked on so we know them and don't have to stumble across them ourselves

I wish software people would do this.

Well said on the other stuff. You only need to head over the the ETAB/SAP2000 sub-forums here to see examples of people wholly reliant on software programs without understanding codes. If you ask how did it compare to their hand calcs you hardly ever seem to get a reply.....

 

[ThQH]

Sad to say almost 4 months later and with Oregon having officially switched to ASCE 7-16 as the governing code, this issue with the exception to section 11.4.8 has still not been addressed. CConrad, I have to disagree with your interpretation of section 11.4.8. It does not apply solely to site class F. Generally, this would not be an issue if it were not for the fact that this misinterpretation of 11.4.8 results in Enercalc producing not only incorrect design results, but un-conservative ones as well.

For the benefit of the Enercalc Development Team:

11.4.8.3 of ASCE 7-16 indicates: A ground motion hazard analysis shall be performed in accordance with Section 21.2 for the following: structures on Site Class D and E sites with S1 greater than
or equal to 0.2.

However, it is indicated that there is an exception to this requirement in exception 3 that: Structures on Site Class D sites with S1 greater than or equal to 0.2, provided the value of the seismic response coefficient Cs is determined by Eq. (12.8-2) for values of T ≤ 1.5Ts and taken as equal to 1.5 times the value computed in accordance with either Eq. (12.8-3) for TL ≥ T > 1.5Ts or Eq. (12.8-4) for T > TL.

So in short, if your commercial products are going to provide seismic design coefficients for Site Class D areas where S1 is greater than 0.2 (basically the default assumption along the west coast), then the software needs to account for these exceptions. Aesur, I agree it is up to the engineer to double check our results, and that is why this mistake was caught in the first place. However, the product is not free either. The developers have a very real obligation to produce correct results and especially more so when errors are identified and made public.

 

[jdgengineer]

Making sure I understand the condition here. Wouldn't low rise structures (say <5 stories) be generally not impacted by this as the Cs would be governed by Sds? And I'm assuming there are few people who would design a building larger than 5 stories by hand rather than using RISA, ETABS, RAM, etc?

I don't personally use the Enercalc module for seismic forces. I'm just trying to understand how often this occurs. Obviously, it would be helpful when checking output from other software, but it's also a relatively easy hand calc.

 

[JoshPlumSE]

Sandman -

I think what CConrad was trying to say is that 11.4.8 is advanced stuff and doesn't really apply to what Enercalc is doing (Equivalent Lateral Force Procedure). My guess (though I don't know for sure) is that the program flags the user when the parameters they've entered might invoke the requirements for 11.4.8's "Site-Specific Ground Motion Procedure". If the program is throwing up a flag, that is perfectly reasonable in my opinion. We know all programs have limitations and the best way to deal with them is for the program to figure out when it's pushing up against one of its limits and let the user know.

Now, in an ideal world, the OP would like the program to recognize the cases where the "exceptions" of 11.4.8 occur and adjust their calculations so that the programs seismic forces meet the requirements of the exceptions without having to necessitate a Site-Specific procedure.

 

[ThQH]

JoshPlumSE,

11.4.8 in ASCE 7-16 is a changed requirement for between 7-10 (11.4.7) and 7-16 (11.4.8) which extends the requirements for having a motion hazard analysis performed to SDC D, E, and F.

Please allow me to explain the complication that arises. Previously in 7-10, this requirement was only for site class F which made it a relatively rare and special case. If we are following this requirement as defined in 7-10, then a wholeheartedly agree with CConrad, however, in its definition in 7-16, this is commonplace (and I would argue that it should now be the default assumption).

The issue with 11.4.8 as defined in 7-16 is two-fold. Firstly, this requirement extends to SDC D, and E. This makes having a motion hazard analysis a requirement for literally all small projects along the west coast. Luckily, there is an exemption clause, which is where the second problem occurs. The exemption, specifically for site class D, is that there is a alternative requirement for calculating Cs.

Now, the problem with the Enercalc module is also two-fold. Firstly, it does not indicate that the user is required to have performed a motion hazard analysis (this should be a relatively easy flag to add) and secondly, it does not provide the user an option to check that the seismic design parameter Cs be calculated per exemption 2 of 11.4.8. Enercalc, as it is currently, is not really intended for applications in large structures and industrial projects. It's application is more for smaller projects such as residential and minor commercial applications. As such, these kinds of projects are not going to have a motion hazards analysis performed due to limited budget constraints. It is therefore borderline unreasonable for the Enercalc module to assume a motion hazard analysis was performed (at least without indicating this in some way). So while CConrad may conclude its not "a wise use of development time", not having support for 11.4.8 is not a wise decision for its target clientele.

 

[Karryn]

My guess (though I don't know for sure) is that the program flags the user when the parameters they've entered might invoke the requirements for 11.4.8's "Site-Specific Ground Motion Procedure".

Enercals does not currently flag the user if the requirement of 11.4.8 may be applicable. Though preferably I would like Enercalc to take the Exceptions of 11.4.8 into account, I have suggested adding a flag to point the user to this code section if it is potentially applicable.

 

[JoshPlumSE]

Ahhh.... If they don't have a flag, then this is certainly a little problematic. Not for the 2016 CBC (which invoked site specific requirements rarely), but for the new 2019 CBC which invokes them more frequently. Or, requires a modification to the Cs to avoid the site-specific requirements.

Got it. Thanks for the clarification Karryn and thQH!

 

[JoshPlumSE]

But, wait.... If I open the 2019 CBC, I see the following:

1613.2: Seismic Ground Motion Values: "Seismic ground motion values shall be determined in accordance with this section"

This section appears to supersede / replace ASCE 11.4. Therefore, the 11.4.8 sub-section wouldn't really apply to any structures in California. Would it? Very weird.

 

[ThQH]

It doesn't look like that statement would exempt the requirements of completing a motion hazard analysis. The CBC and OSSC provide exemptions in their building codes for determining SDC (1613.1) and seismic ground motion values (1613.2), but does not directly address the requirement of completing a motion hazard analysis. Unfortunately, the requirement for having the motion analysis is tied into determining the seismic ground motion via exception 2 in ASCE 7-16.

1613.1 also requires that conformance with ASCE 7-16 must be made as applicable. Since there are no exemptions to performing a motion hazard analysis is section 1613, the default would be to follow the exemptions in 11.4.8.

 

[chris3eb]

The Fa and Fv tables in the 2019 CBC reference you directly to Section 11.4.8 of ASCE 7 for the cases that have been mentioned above.

 

[sandman21]

Josh what everyone else said.

And to add the note B and C in the tables is a reference to 11.4.8 and the section as mention does not deal exclusively with site class F