Galvanized steel elastic modulus

[nj86]

Hi guys,

I was just wondering what effects galvanising has on the elastic modulus of 'ordinary' steel? I assume it increases but by how much?

I need to know this as I'm trying to calculate a deflection for a galvanized steel beam.

Thanks!

 

[kelowna]

Increases it?

I have to confess I have never thought about this, but I would have guessed it is unaffected. Galvanization is supperficial, is it not? affecting only to the outer layer of a section. The heat from the galvanization bath is too low to change the properties of the steel (in most cases for most types of steel), and it would only affect strength or toughness, not elastic modulus.

When designing galvanized elements I have always assumed (maybe incorrectly) the same elastic modulus as for black steel.

I would be curious to hear other people's opinion.

 

[dik]

I would suggest that the coating thickness is so thin that it would be negligible. There may, however, be a slight reduction with deck...

Good question, I'll see what I can shake out.

Dik

 

[asixth]

I have never changed the E-modulus of steel if it were galvanized, nor have I increased the I-value, I think it would be unreasonable to do so in a beneficial way so to increase the efficiency of your beam.

I would however consider the additional self weight.

 

[hokie66]

No change. If you are trying to be that precise about deflection calculations, you are wasting your time.

 

[paddingtongreen]

I'm with hokie on this one, the variation from the standard shape will have much more influence, the beam's shape may even change slightly over it's length.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[ToadJones]

The only possible change to the material properties would be from the heat from the galvanizing bath. But, even heat treating processes, such as annealing, have no affect on the elastic modulus of steel.

 

[bridgebuster]

"If you are trying to be that precise about deflection calculations, you are wasting your time"

Or you have too much time on your hands.

Don't forget - there are also mill tolerances with steel. I've never met anyone who took into account the possible variations in dimensions.

 

[nj86]

Thanks for the replies guys, much appreciated!

 

[Lion06]

There are so many assumptions made with respect to loading conditions, actual section properties, level of composite behavior, end fixity, etc, how could you possibly expect that changing E by some nominal amount will get you any closer to the "real" deflection? That's on par with considering shear deformations for a W8 spanning 30' - It's not going to make a hill of beans....... and quite frankly you are "wasting your time".

 

[apsix]

SEIT
Your apology is accepted.

 

[Lion06]

I can't make heads or tails of this thread anymore. Did I apologize for something?

 

[paddingtongreen]

SEIT, I think nj86 did but on one of those multiple universes we hear about but only glimpse.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[hokie66]

SEIT,

The thread has obviously been trimmed due to someone redflagging some comments. I think the comments were in the sarcastic vein about your contribution, which was judged to be repetitive.

 

[rowingengineer]

boy you got to be fast around here, I just thought Apsix was being Dry (possibly sarcastic) and pretending to be a client complaining about too much deflection.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[apsix]

Hokie is on the money.

RE is half right, I wasn't pretending to be a client.

 

[CTSeng]

Not to bring this one back on point but I've seen the heat of galvanizing take camber out of a beam. nj86, Are you having a deflection problem? It would seem possible for residual mill stress to cause some unexpected camber or sag after hot-dip galvanizing.

As for bridgebuster's comment: "I've never met anyone who took into account the possible variations in dimensions." Don't read chapter C of AISC 13th it'll make you sick.

 

[bridgebuster]

CTSeng - We don't use AISC in bridge design - AASHTO LRFD is more than enough agony.

Question: What is the practice if one is following AISC? Is a designer expected to compute multiple values of S? In looking at the spec, it looks like it could be argued both ways. A few months ago, I attended a short AISC seminar that didn't make any reference to different values of S.