wood beam + steel (bolted together) 3

[n3jc]

I have a wood beam reinforced with steel, connected by steel bolts.
The load is applied on wood beam only.
The load is transfered through bolts (2 shear planes) to steel.
Friction between wood/steel is not considered.
I also assumed, that the whole load is transfered to the steel sections (I did not calculate the load transfering to steel - by ratio of the stiffness).

Im wondering if this calculation is OK?
I was expecting bolts closer to each other. I do not think bolts that far apart are sufficient connection for this to be a composite (one element)?
What am I missing?

 

[molibden]

You need to consider also the stiffness of bolts (K_ser and K_u in Eurocode 5). Using gamma method in EC5 you could then calculate distribution of stresses, deflection (using effective stiffness (EI)_eff) and shear force per bolt. Never tried this for timber-steel beam but have used it with timber-timber beam.

 

[n3jc]

Yes, i know... gamma = 1 means that there is an absolute connection between elemetnts, and gamma = 0 means there is none. So there is an option to use gamma = 0 and use I as a sum: I of wood element + 2x I of steel element, but thats conservative value, but you cant be wrong.

 

[KootK]

But when you are calculating shear force (tau) you are using I and Q for an actual cross section (wood + steel), not on transformed section, right?

I'd do it on the transformed cross section. Otherwise, you would need to find another means of accounting for the fact that the channels' greater material stiffness will draw more stress towards the channels. Basically, you'd need to base I and Q on areas multiplied by respective E values. No big deal but no easier than transformed sections.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dik]

For steel to wood attachment, I almost always use LePages PL Premium adhesive... it almost glues anything to anything, and I would treat it as a composite assembly and preload the joists to remove much of the deflection.

Dik

 

[KootK]

@Dik: is that adhesive in addition to bolts or on its own?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

I always treat the glue as a belt and suspenders. Design the bolts to do what you need, spec the adhesive, go to bed sleeping easy that it's twice as likely to work properly.

 

[dik]

KootK:
The adhesive is in addition... it's really good, and, I've been using it for a decade or two... I just don't have the confidence that the adhesive is good 'forever'. I design the fasteners for limit conditions, and, I almost never design other fasteners for even approaching limit.

Dik