How to Calculate strength of embedded beams

[knandwana]

Hi All :

I need to calculate the strength of a W 8 X 24 beam embedded in the concrete of 8" and which is 240" long .How should I proceed to solve this problem. Is there any reference to which I can look into which talks about the strength of embedded beams ?

Basically, the reason why I need this is because I am currently working on a project where I have designed a test fixture for doors. The base of the test fixture will be welded on to the W 8 X 24 beam embedded in the concrete. FE Analysis predicts that the test fixture will be pulling up the embedded beam with a force of 20,000 lbf .

Is the embedded beam able to resist that force without any failure to concrete/beam ?

Your suggestions and help in answering this question is highly appreciated.

Thanks,

Kapil
Structural Engineer, EWI

 

[ishvaaag]

Yes, there is; in the AISC LRFD 1993 code Commentary to chapter I you have guide enough to design both encased beams and beamcolumns.

I attach a rendition of a Mathcad worksheet I made on this; I plan to add the worksheet itself with many others of the LRFD 1993 this weekend to AISC's SteelTOOLS.org site

 

[knandwana]

Hi :

Just to clarify, the W 8 X 24 beam is not a column, but a beam laid horizontally on the ground and has an 8" concrete all around it. I hope it clear doubts regarding my previious post.

Thanks,

Kapil
Structural Engineer, EWI

 

[ishvaaag]

In any case a beamcolumn covers the case. Just Pu=0.

 

[knandwana]

HI ishvaaag :

Sorry to bother again, but when I checked the reference for encased beam, they say that in order to assume a beam without shear studs to act as a composite beam, the top of the beam should be atleast 1.5" below the top slab. However, for my case, the top of the surface of the beam is visible and therefore, it is 0".

 

[BAretired]

The span is 20' with a concentrated load at midspan of 20,000# so the steel beam cannot carry the load by itself.

A conservative approach would be to design the concrete beam to carry the entire moment, taking care to provide ties each side of the concentrated load adequate to transfer the load into the compression face of the concrete.

BA

 

[ishvaaag]

Well, the AISC code took effective measures to ensure that those wanting to use its provisions comply with the specifications so some apparent composite beam wouldn't be protected by such provisions even if we would find some way the provided calculation amenable to our case.

In any case, you can proceed as BAretired says or if not counting the shape strength is not acceptable devise a way of combining the extant strengths in such way that there is compatibility of deformations. To ensure that you will have to ascertain as best as you can the stresses at the interface between steel and concrete; this is simple for some cases, say a shape being pulled out of a footing, or sharing straight bending action in the whole of both steel and concrete, both taking its share; but for more complex situations and sets of hypotheses it can become unpractical.

So maybe looking for alternatives maybe positive for these cases.

 

[paddingtongreen]

Has it been established that the beam is actually tied down to anything? or is it simply embedded in the concrete slab? Does it have any legitimate anchors to the concrete (I realize there is a mechanical interlock where the concrete goes between the flanges) to force the concrete to hold the beam down.

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

 

[knandwana]

It is simply embedded in the concrete slab and is not tied down with anything (anchors) .

Can it carry any load. How to do those calcs ?

 

[ishvaaag]

Place an sketch on the loading it is assumed to support and we can think about if there's a practical by hand or otherwise good calculation for this.

 

[BAretired]

How can you pull up with a force of 20,000# if the beam is not tied down anywhere?

BA

 

[civilperson]

Bonding friction will approximate 50 pounds per square inch for pull out, assuming unpainted smooth steel in 4000 psi concrete. If the top half of the beam is in tension due to the moment, then a amount of area at the tension flange can be approximated. (Moment/beam depth = tension)