Rana

Etabs Load Combinations

14 posts in this topic

ETABS Load Combo Creation


Have a look at it...may be u find it useful...its for manually creating combos in excel and then importing back to etabs..as it allows the flexibility to create combinations in table format and less chances for errors as compared with that of ETABS unfriendly load combo interface...Report back any bugs or suggestions...thanks

To download click on the link above with blue color
or
www.4shared.com/file/THoXlkzv/ETABS_Load_Combo.html

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one can use default combo

Default have a lot of issues unless you know what you are doing. Make sure you configure them properly with dead load multipliers for seismic. How many load cased do you define for your seismic case?

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i have experience in making load combinations in etabs at quite complex level...believe it or not for some buildings i have made 200 ultimate and 200 service combinations...i really hate the etabs combination dialogue box which cannot be resized...unlike SAFE! where you can export it into excel! anyway this sheets i just designed for my own custom application...thought to share with you guyz if you find it helping..

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look! first you need to study code for proper load combinations. This is very very critical. All the design results and serviceability criteria is based on it.

You need to understand which load combination to use and when to use.

Read chapter 9 of ACI and PCA Notes..Read its commentary..Read UBC...Try to know what is the difference between 1.3W of UBC and 1.6W of ACI.
Get to know why the factor in E is 1.0 in strength load combinations. Know why omega factor is used.

2nd...Research what are the options in softwares which affect automatic load combination creation. For example in ETABS what is the impact of code you select for concrete or steel design and the seismic design category? Why there is SPECIAL SEISMIC LOADS option in ETABS under define menu?

I would recommend you to print the page of ACI where load combinations are defined and also for UBC and keep it in front of you!..Take a paper and write all the appplicable load combinations based on your load cases. Then compare ACI vs UBC

I would say you dont use automatic load combinations rather make your own combinations.

Once you are done and confident about your understanding of load combinations then use the AUTOMATIC load combinations.

You should know which combination is appropriate for Seismic drift limit or wind drift limit. What is the meaning of probability or exceedence of seismic or wind forces?

If still this all stuff seem boring to you! do this

Goto options in ETABS> define design code to be ACI 2008..Select appropriate seismic design category. If you are not familiar with SDC open chapter 1 of ACI and see what is the equivalent SDC of UBC in Table 1.1 of ACI

Then goto define menu>Special seismic forces.

If your SDC is C or less it will not have an impact. So you select it or not...doesnt matter

then create automatic load combinations and verify them one by one..Do this atleast in your first few models.

There is a trick to make service load combinations automatic too...if you are interested i will tell you later! :P

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thanks alot for your response.........let me study it first

its good that you said that you want to study it first, rather following it blindly.

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Rana bhai where is the trick??

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@Rana sir the load combination creation file is missing ..... kindly upload it again, i need it......

 

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Dear friends

what are the most critical load combinations(service and strength) for zone 2B please.

Regards

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Posted (edited)

2 hours ago, waqar saleem said:

what are the most critical load combinations(service and strength) for zone 2B please.

it would depend upon the material of construction being used. In general, load combinations involving seismic (earthquake) effects will be critical for RC structures. Whereas, for steel structures, those involving wind effects will be more critical.

In practice however we check the structures for structural safety against the load combinations (specified by applicable material design / loading codes) involving all type of loads that are expected to be resisted by the structure during its entire design life. 

Regards.

Edited by EngrUzair

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