AS3600 Cl 10.8 Transmission of Axial Force Formula 1

[T9809]

I noticed based on the AS3600 formula, f'ce decreases with increasing joint depth (h)

This appears to be counter intuitive, does anyone know what the underlying reason is? Or if this is an error?

See example graph below for (65MPa column, 40MPa slab, y=fce and = h/D

Thanks in advance

 

[Retrograde]

It seems logical to me that increasing the joint depth (ie. increasing the depth of the zone of weaker concrete) would decrease the effective strength.

Note the limit on h/Dc

 

[Just Some Nerd]

The intention is definitely that increasing depth results in a lower effective strength.


An abstract way I think of it is that a shallower joint is better confined when sandwiched primarily between the column above and below, and the sides of the sandwich being confined by weaker slab concrete is kept relatively low. The analogy also works for being sandwiched by wider columns (larger Dc) too.

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Why yes, I do in fact have no idea what I'm talking about

 

[KootK]

I feel that the key to this is to recognize that, normally, it is only the bottom of the slab that confines the interstitial volume. As such, if the yellow struts are allowed to get too steep, they will be prone to longitudinal splitting much as unconfined concrete is.