Construction Joint in STM Designed Transfer Beam 1

[KootK]

Please refer to the PDF sketch attached.

A construction joint has been constructed that crosses a major concrete transfer beam that we've designed using strut and tie methods. The joint cannot be relocated to a more favourable position.

For a non-STM designed beam, I would address this issue using shear friction provisions. Additionally, I would count on my flexural tension reinforcement to pull double duty as flexural / shear friction steel. If any additional shear friction reinforcement was required, I'd add it to the beam tension steel per ACI recommendations.

Because the girder under consideration was designed using STM methods, I'm wondering if the procedure described in the previous paragraph is still valid. To be consistent with my STM design, I feel that:

1) I should be able to use the horizontal component of the compression strut crossing the joint as an effective clamping force for shear friction computations.

2) I should concentrate any additional reinforcement required for shear friction over the calculated height of the compression strut.

3) I should calculate the maximum permitted shear stress using the vertically projected area of the compression strut rather than the area of the entire beam.

On the one hand, I feel that my shear friction design should be consistent with my STM design, as described above. On the other hand, I feel that the "right" answer should be the same for both STM and sectional design methods.

Please advise.

KootK

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[hokie66]

I agree with CEL, so guess I am off the list as well. I don't think either of us is giving up on understanding structural behaviour, but we realise our limitations.

 

[KootK]

@Hokie: Please refer to the attached sketch. With regard to the term "inclined plane", you seem to be thinking of physical discontinuities such as cold joints, cracks, and perhaps interfaces between dissimilar materials. And that makes sense as made up stuff is much less satisfying to discuss.

In the context that I've used the term, an "inclined plane" is just an arbitrarily chosen plane of study. It's a stroke of a pen. It is still, however, a plane upon which shear slip must be resisted. And that's the crux of my point. Whether a particular shear slip plane is a physical discontinuity or a hypothetical construct within a monolith, a real mechanism of shear resistance must be present along that plane.

A cold joint on a particular plane just transforms that plane form being a hypothetical construct to being a true physical discontinuity.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[KootK]

Sorry Hokie, I posted my latest comment before I read your post extricating yourself from this one.

I was just giving CEL a hard time. And you were never on the Christmas card list. I've got other plans for you. My wife and I are planning a trip to Australia in the near future. Itinerary item #89:

89) Find Hokie. Ply with alcohol. Convert to shear friction lover.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[CELinOttawa]

Hahahaa.... Ah, the fun never ends on Eng-Tips...

And Hokkie said it perfectly.