Strut and Tie Design

[PEinVA]

See attached images.

We have an existing building which is changing occupancies and we have to verify if the slab can handle assembly load.

We're trying to make this detail work for strut and tie, something we haven't spent much time on, and wondered if there was a requirement for horizontal ties. In ACI 318-11 11.8.4 requires ties and its explained in 11.8.3.5 commentary. However in Appendix A there is no explicit requirement for these bars. The reinforcing shown in the attached sections easily handles the tension in the top tie (AB in most corbel truss models). The thickened slab shown in the section is a spandrel beam that runs parallel to the slab edge. At alternating columns we have the plan detail shown. This only impacts 1 column for this analysis.

Any insight would be helpful. Don't get me started on how awful an original detail this is.

http://files.engineering.com/getfil...e-4556-91ee-3c4b2d540b8c&file=SectionView.JPG

http://files.engineering.com/getfil...3b4a-463e-822c-784a3e4bfd60&file=PlanView.JPG

RC

 

[rapt]

From the details provided, how does Strut and Tie apply to this design? It looks like a flexural design to me!

 

[KootK]

As Rapt has suggested, it's unusual to treat this kind of connection as strut and tie. I recommend reviewing ACI 352.1. It contains guidance for just these kind of situations. Obviously, punching shear and moment transfer are your big issues.

To answer your specific question, there are situations where I disregard the distributed reinforcement requirements. And this would probably be one of them were I to tackle it with strut and tie. That being said, I don't know of a code clause that provides an out for distributed reinforcement.

Depending on what your strut and tie model looks like, your column ties and column compressive stress may be able to effectively satisfy the distributed reinforcement requirements. For what it's worth, I would consider this to be more of a closing joint than a corbel per se.

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.