Beam Splice Deflection Question 1

[Berniedog]

I designed a beam to be erected under a floor in an existing office building to hold up storage units above. Deflection is the critical item. I requested splices to be designed by the Fabricator's Engineer for the full moment capacity of the beam. What I got developed the moment due to the area of the flanges.


My question is this, wouldn't this splice that is designed as described above reduce the moment of inertia, thus increasing deflection?

 

[kslee1000]

If the beam segament is not full-pen welded, you have developed a spring at the splice. Not an easy task to evaluate stiffness of the spring though.

 

[Lion06]

It might have a reduced I, but only at that one particular section which is literally almost non-existent in length compared to the overall member. I wouldn't worry about it.

 

[kslee1000]

Yes, you don't need to worry too much about it. But keep an eye on the detail provided. On top of flanges, there should be splice plates (2 preferred) on the web to transfer shear. The splice plates would stablize the section, and eliminate the tendency for add'l displacement due to loss in member rigidity.

It would be better to ask the connection design engineer to develop strength capable of resisting "full anticipated reactions", rather than just moment. Also, if the splice can be made in the shop, a full-pen weld over the joint is the most easy way to handle this type situation.

 

[BAretired]

The answer to your question is yes. It will increase the deflection marginally. The amount may be calculated using a concentrated angle change at the splice point accounting for the discontinuity of the web.



BA

 

[BAretired]

You could calculate the moment carried by the web by itself, say Mw. Then apply equal and opposite moments Mw each side of the splice point. The change in deflection should be Mw*a*b/3EI where I is the moment of inertia of the beam, including web.

BA

 

[kslee1000]

BA:

Beautiful. Delight to see the solution. The deflection could be small, but is there. Nice to have a simple method to check on it.

 

[Berniedog]

Thanks

 

[BAretired]

You are welcome.

BA