Lion06
Structural
- Nov 17, 2006
- 4,238
When you are using a STM with concrete strength greater than 6,000 psi, ACI 318 requires that the tie force in the bottle-shaped strut be designed (it is not automatically satisfied by equation A-4.
App. A states that you can assume the strut fans out at 2:1 (longitudinal to transverse).
I feel like there is a piece of information that's missing.
If I design the reinforcement to resist the splitting force, I would use the following equation to get the total steel perpendicular to the strut (crossing the splitting crack)) - Asv*b/sv + Ash*b/sh
where
Asv is the area of vertical steel
sv is the spacing of vertical bars
Ash is the area of horizontal steel
sh is the spacing of horizontal bars
b is the width of the strut.
b is what I think is missing.
It seems very conservative to use b at the node for a bottle-shaped strut and I don't think that is the intent of App. A. However, no guidance is provided for how long you can fan out the strut at the 2:1. This would provide a maximum width of strut if you carry the 2:1 slope all the way to the center of the strut, but that also doesn't appear to be the intent based on the graphic Fig. RA.1.8.
Does anyone have any literature or information on this? I haven't come across any good design example of a STM for anything other than the most simplistic (and unrealistic) case.
App. A states that you can assume the strut fans out at 2:1 (longitudinal to transverse).
I feel like there is a piece of information that's missing.
If I design the reinforcement to resist the splitting force, I would use the following equation to get the total steel perpendicular to the strut (crossing the splitting crack)) - Asv*b/sv + Ash*b/sh
where
Asv is the area of vertical steel
sv is the spacing of vertical bars
Ash is the area of horizontal steel
sh is the spacing of horizontal bars
b is the width of the strut.
b is what I think is missing.
It seems very conservative to use b at the node for a bottle-shaped strut and I don't think that is the intent of App. A. However, no guidance is provided for how long you can fan out the strut at the 2:1. This would provide a maximum width of strut if you carry the 2:1 slope all the way to the center of the strut, but that also doesn't appear to be the intent based on the graphic Fig. RA.1.8.
Does anyone have any literature or information on this? I haven't come across any good design example of a STM for anything other than the most simplistic (and unrealistic) case.
