strut and tie modelling
strut and tie modelling
(OP)
Hello,
I am studying the concept of strut and tie method and modelled an rc wall and try to figure out the correct truss model for the STM.
I have the following questions;
1. How do you normally size the strut? looking at some examples, if the point load is coming from the column, it is quite easy just simply relate it to the size of the column, but how about if you have a "line load", I've just converted the line load to a point load(pls. see attached.
2. When you have a line load, and you intent to convert it to 2 point loads on top of the rc wall, normally, you just take half & half approach(pls. see attachment, in the line load diagram, I enclosed in "red" line load converted in to point loads). But how about the other "halves" outside the "red zone" do I need to include them as well?or just simply leave it according to my model?
3. Based on the result that I've got(Black (Tension), Green(Comp), Red(Reactions)). How do you provide "matching" reinforcement for this?
Any ideas/suggestions are highly appreciated.
I am studying the concept of strut and tie method and modelled an rc wall and try to figure out the correct truss model for the STM.
I have the following questions;
1. How do you normally size the strut? looking at some examples, if the point load is coming from the column, it is quite easy just simply relate it to the size of the column, but how about if you have a "line load", I've just converted the line load to a point load(pls. see attached.
2. When you have a line load, and you intent to convert it to 2 point loads on top of the rc wall, normally, you just take half & half approach(pls. see attachment, in the line load diagram, I enclosed in "red" line load converted in to point loads). But how about the other "halves" outside the "red zone" do I need to include them as well?or just simply leave it according to my model?
3. Based on the result that I've got(Black (Tension), Green(Comp), Red(Reactions)). How do you provide "matching" reinforcement for this?
Any ideas/suggestions are highly appreciated.






RE: strut and tie modelling
2. Do not just take half and half. Loads should be proportioned based on the nodes tributary width (half the distance between adjacent nodes - add left and right nodes).
3. You are working backwards. Pick where you want reinforcing first. Then create a strut and tie model with the ties matching your reinforcement locations. In your case, the right side reinforcement would probably placed horizontal with a hanger/corbel bracket at the dapped end. The STM will need more nodes here to include this flow of tension. In concrete, it is usually cost effective to benefit ease of construction over less material (concrete and rebar).
RE: strut and tie modelling
I'd assign the distributed loads to the nodes as I've shown below. With the uniform loads at the far ends, you just want to set things up so that those loads are accounted for in the nodal and bearing checks at the reaction points. What I've shown will be a little conservative for moment and shear but will prevent you from having to deal with the complex C-C-T nodes at the bearing points that you'll end up with if you add extra members to the ends of the truss.
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.
RE: strut and tie modelling
1. struts run parallel with cracks. If you know or expect where a crack will appear, run your struts parallel with that expected crack. In this case, we know how dapped ends crack so we don't put a strut running from the top node down and to the left in the dapped area.
2. Corollary, struts do not run across cracks. Ties will need to cross cracks.
3. Corollary to corollary - struts and ties can't be in line next to each other. Struts shrink and ties stretch and concrete's shear capacity is finite.
4. Sum of external forces and moments will be exactly resisted by the internal forces and moments at every section along an STM. This can help locate nodes in tricky areas.
RE: strut and tie modelling
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.
RE: strut and tie modelling
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.
RE: strut and tie modelling
Were I to attempt to reinforce your STM, I'd do something like what I've shown below. I do think that there are more advantageous models for you to use however (we've covered them above).
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.
RE: strut and tie modelling
This is what I'm praying for, a no-nonsense site that provide practical and carefully thought out answer to an amateur like me.
Thanks guys, the info that you gave me is far better than a week of useless reading to all the reference books that I could find on the internet.
Probably, it will take me a while to decipher all the informations that you guys have given me but I will have my comments/queries if I have internalise all of this information.
Again, my sincere appreciation(there's still people that really cares..)
Thank you very much.
RE: strut and tie modelling
Pls. see attachment.
I am checking the stress at the node to eurocode but I do not know what is the size(area) of the node.
Normally, where do you based the size of the nodes?
RE: strut and tie modelling
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.
RE: strut and tie modelling
Pls. see STM result attachment with my comments on it.
I have this situation where this rc wall is supported by intersecting wall at the corner(200mm thk rc wall), the reason for the dapped end. The bearing area is only 200x200. Doing the calculation for the stress in strut/nodes against the allowable (Eurocode), it fails.
Is there any other options to correct it(ie, change the truss model, providing steel plates etc...)
Again, any ideas are highly appreciated.
RE: strut and tie modelling
1) Check bearing stress at the reaction and report back.
2) Post a sketch of the note under consideration so that we can review what you've done there.
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.
RE: strut and tie modelling
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.
RE: strut and tie modelling
These intersecting walls are precast walls and they are supported by 200x200x16SHS via steel capping plates.The reason for the dapped end connection.
Pls. see attachment.
RE: strut and tie modelling