Strut and tie method maximum angle of truss
Strut and tie method maximum angle of truss
(OP)
Generally the truss angle of strut and tie system is restricted to a maximum limit about 60 deg. What happen if someone goes beyond this upper bound limit. What is the concept behind max limit? I am struggling with a deep pile capping beam where the strut and tie system angle is almost about 75 degress
Thanks
Thanks






RE: Strut and tie method maximum angle of 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 method maximum angle of truss
RE: Strut and tie method maximum angle of truss
In Shear Truss analogy, the upper limit is often 60 degrees, but that is for flexural members.
For Strut Tie, the strut can technically be vertical! The maximum angle of the strut from the vertical is normally about 60 degrees. Any shallower than this and it basically becomes flexural.
RE: Strut and tie method maximum angle of truss
So the important limitation on angle is a minimum limit, not maximum.
RE: Strut and tie method maximum angle of truss
I am afraid that whether the ties at bottom of the cap will be formed. Doubt that when the strut angle is becoming more and more, the ties will become mobilized.
Other than that my another point is that even any space truss with much steeper angle, is unstable and we don't practice
@rapt
I am referring to a strut and tie system
@stickandtriangles
Thanks but your system with vertical tie is not practical in pile caps. Identifying of vertical ties in a big chunky rc volume is not practical
RE: Strut and tie method maximum angle of truss
I don't believe you understand truss behaviour. The steeper the angle of a compression member, the smaller the horizontal force.
RE: Strut and tie method maximum angle of truss
RE: Strut and tie method maximum angle of truss
RE: Strut and tie method maximum angle of 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 method maximum angle of truss
RE: Strut and tie method maximum angle of truss
I'd be curious to know more about the method of model selection based on energy principles mentioned in the clauses that you posted. Sounds like some sweet, sweet intellectual Halloween candy to me...
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 method maximum angle of truss
RE: Strut and tie method maximum angle of truss
Dik
RE: Strut and tie method maximum angle of truss
What you have printed is commentary, not code limits. The text on the right is the Code and you have not printed that. Greater than 60 is not a problem, up to 90 degrees which is a straight through compression without tie required. Less than 45 degrees is a problem as it is then too low an angle and the tie forces and strut compression stress become unmanageable as it approaches a flexural design.
RE: Strut and tie method maximum angle of 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 method maximum angle of truss
Same as a tied compression arch. There is a limit beyond which thou shall not go as the arch can easily snap through and it becomes a tension membrane structure!
RE: Strut and tie method maximum angle of truss
RE: Strut and tie method maximum angle of truss
RE: Strut and tie method maximum angle of truss
RE: Strut and tie method maximum angle of truss
It anushka's example, the D regions are at the point load at the top of the wall and the 2 supports. The compression stresses spread out from the point load down through the wall, then in the middle of the wall the compressive stresses will be fairly uniform, before the stresses concentrate to the supports.
I quick FE model would show this behaviour.
RE: Strut and tie method maximum angle of truss
Vertical stress picture (notice struts form in a way consistent with "good model"
Horizontal stress picture (notice tie where expected in "good model"
RE: Strut and tie method maximum angle of 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 method maximum angle of truss
Based on the "good model" you need horizontal tension reinforcement at about 20% of the depth from the top, at the kink from slope to vertical. Personally I think it is a waste of good reinforcement to put tension tie reinforcement there!
Yes, there may be bursting effects near the top where the compression stresses spread out. Yes some side face reinforcement over the full depth of the section if a beam. But tension tie reinforcement at 1/4 depth!!
RE: Strut and tie method maximum angle of truss
RE: Strut and tie method maximum angle of truss
Agreed, stresses do not change angle suddenly without a good reason, and I cannot see one there! Maybe a gentle curve in the compression strut, but sudden angle changes. Someone is smoking something that is not good for their logic thought processes!
RE: Strut and tie method maximum angle of 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 method maximum angle of truss
RE: Strut and tie method maximum angle of truss
Haha thanks rapt. I agree the vertical lines are questionable between the "good" and "bad" model.
The main thing that made me like the relationship between the "good" model and linear elastic FEM was the presence of horizontal tension in the FEM model (horizontal stress picture). This is not captured in the "bad" model.
RE: Strut and tie method maximum angle of truss
Agree the PT busting effect is very different. It is the dispersion of a very concentrated compression at the anchorage over the full width of the section causing transverse bursting stresses over a length of the member. It is very different to a pile cap situation.
RE: Strut and tie method maximum angle of 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.