Factored load or un-factored load in deflection calcs? 1

[RobertEIT]

I would like to double check with you guys, that in deflection calculation we should use un-factored load no matter it is a concrete beam or a steel beam, am I right?

Thanks a lot!

 

[Ussuri]

Deflection is a servicibility limit state so should be assessed using unfactored loading.

 

[Lion06]

Correct, you should use service loads (unfactored loads) for all serviceability checks regardless of the system and the method of strength checks.

 

[csd72]

You are trying to predict how much it deflects, not a multiple of how much it deflects.

 

[JoshPlumSE]

It's a servicability considereation.... as long as you're not talking about seismic drift.

Also, remember that if this is a concrete beam then you should take into account some level of cracking. That applies even when you look at servicability deflections.

 

[apsix]

It does depend on which code in which country.
Creep effects in concrete and timber are dealt with by factoring the load in my experience.

 

[youngstructural]

And apsix has it...

A star for your post, apsix.

That said, it is NEARLY always unfactored for SLS, factored (check what factors, etc) for ULS.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[kslee1000]

Note that creep is a time dependent deformation, the factor is the time rate of increase in strain (non-linear), which is different from load factors for strength concerns.

 

[rapt]

I'll throw a spanner in the works on this one as most modern codes (bad luck US designers) now use factored loads for serviceability design for concrete but the factors are less than 1! The factors depend on building function and can vary from about .5 for residential to 1 for storage.

 

[Lion06]

apsix-

What code deals with concrete creep effects by factoring loads? ACI deals with it by factoring the service deflection by a TIME-dependent factor, not by factoring the loads. That makes more sense since deflections are a serviceability consideration. If you use factored loads then you're also including additional cracking in the calculations. Maybe the procedure has been normalized to account for this, but the idea, in principal, doesn't seem intuitive.

 

[nicam]

In Australia under AS3600
we normally use factored loads for concrete
2.4G + 1.26Q

 

[Lion06]

factored loads for serviceability checks like deflection?

 

[vandede427]

Correction.

If in AUS and US during am hours of the summer solstice, the deflection load factors are < 1.0. However, if in UK and CAN during pm hours of the winter solstice, the deflection load factors are > 1.0.









just kidding.

 

[structurebeton]

What about P-Delta effects, do you use factored loads or UN-factored loads?

 

[JrStructuralEng]

young structural,
hows the work in new zealand.

I always thought it would be need to do a year there.

 

[youngstructural]

The work here is very good... But the economy at the moment is not. Our firm recently laid off approximately 10%. I would be guessing at another round in a month or two if stimuli packages don't kick in rapidly enough...

All the negative economy stuff aside, I love living here. Professionally it has been very good, given that the focus in Structural Engineering here and in Canada are so different. This has meant training with a focus on timber and steel, with vibration and snow being major concentrations while I worked in Canada, and practicing in predominantly concrete and cold formed steel with earthquakes as the (typically) governing seismic case. I feel it has made me a stronger, much more well rounded engineer.

Back to the topic at hand: In NZ practice we use a weighted live load to dead load balanced load check to simulate long term deflection under NZS 3101, and it is surprisingly accurate. I'll scan and post the appropriate section.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...