Strut and Tie Model

[slickdeals]

Folks,
I have a notched cantilever wall that I need to analyse. There is a bearing connection at the tip of the notch.

I have never used the STM method before and wanted some pointers on creating the truss model.

I used the reverse of a dapped beam as my starting point.

Thanks

 

[civilperson]

Prof. Kutchma(sp?) of U of Illinois has good website for S & T method.

 

[slickdeals]

@Civilperson,
Thanks, I was going over it to familiarize myself.

 

[youngstructural]

You can't have such long, unbroken, struts... You need to mesh them in with ties. Pay close attention to your minimum and maximum permitted angles.

What code are you using? The NZS 3101 methodology is what I am familiar with, and is very similar to ACI 318. Might be able to help out if you have any specific questions.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[slickdeals]

@YoungStr:
I am using ACI 318. I looked for requirements on the angles between the strut and tie and the code limits me to a minimum of 25 degree (to avoid shallow struts)

However, I cannot find any reference regarding the length of the struts.

I would much appreciate it if you could provide an alternate to how you would do the same for me to understand. Like I said, I have never done one before and want to make sure that all things are accounted for.

Many thanks

 

[Teguci]

The PCI manual has the "Potential Failure Modes and Required Reinforcement in Dapped End Connections".

From this sketch you can see that the anticipated compression struts (parallel to the cracks) are in line with your red compression struts (usually shown on a 1 to 1 slope). However, I would make the following change to your STM:
- From the bottom right node - remove the element going up and to the left

The only other issue that puzzles me is how the end of the middle horizontal tie is terminated. In a dapped end, this tie is developed past the crossing compression strut and then terminated.

 

[slickdeals]

@Teguci,
Thanks a bunch.
What I have is really an inverted condition of a dapped end beam. However, i think I should be able to use a similar STM model. Agree?

Yes, The middle horizontal tie is going to be developed past the compression strut.

Any other suggestions, corrections are welcome.

 

[WillisV]

http://cee.uiuc.edu/kuchma/strut_and_tie/STM/examples/corbel/corbel.htm

 

[slickdeals]

@WillisV,
Thanks. I will be conservative if I take it as a corbel below the notch, but are there alternate STM models to account for the notch?

 

[civilperson]

It is a corbel below the notch, however, there are many S & T models that can represent this loading and reinforcement in the wall. The theory says that all of the models are producing stresses greater than the actual condition. There is no upper limit on strut dimension, if the strut is not confined by ties then it is derated for compressive stress. If the wall has soil forces at right angle to the plane of the wall, then this model needs three dimensional model with the tension face having the ties and the compression face having both soil forces and corbel loads.

 

[Buzzer]

try this link, scroll down to the "Strut and Tie model" and click on this. It is a very good discussion and at the end you can take a short multiple choice for pdh's

http://www.gostructural.com/pg.asp?id=20