Confinement, Stirrups stresses, transverse reinfocement

[n39]

Hello
I was modelling a pile to pile cap connection with a stirups of D4-120.
Later on, I try to decrease the spacing of the stirrups to D4-30.
What I get was, the stress that occur in the stirrups increased.

I would argue that, by using the lateral confining pressure formula, we know that low spacing means more lateral confining pressure, which mean the confinement will become more effective. Therefore by using a lower spacing I obtain a greater stress in the stirrups, which means the stirrups was effectively confined the core concrete.

Is my argument correct? Or should the stress that occur in the stirrups decrease if I use a low spacing (say 30 mm)rather than a high spacing (say 120 mm)?
I would be very helpful if you can provide me with additional paper or journal. I've been looking all over for it but didn't find a great writing that highlighted the stress occuring on the stirrups

Thank youa

 

[bkal]

The following paper might give you some guidance, but not a ready-made solution:
Theoretical Stress-Strain Model for Confined Concrete, J. B. Mander, M. J. N. Priestley and R. Park, Journal of Structural Engineering, August, 1988, ASCE

 

[driftLimiter]

Definatley the mander paper. But the force in the stirrups is based on the confining pressure as well as the spacing because its like a tributary width. So even if you have lower confinement pressure, a higher spacing attracts more load per bar.