Squat RC shear wall - strut-and-tie 1

[P205]

I have a 5 storey building with concrete shear walls and steel joist + concrete floors. Low seismic area. All the walls between units are RC shear wall.

Even with the overall building height (15.6m), I get a H/L < 2.0 and so, according to CSA23.3-04 (R2010), the walls are squat.

The code requires me to design the walls for typical reinforcing (cl.14) as well as using a strut-and-tie model. (This is described in cl.14.4.1).

Does anyone have a design example of a squat shear wall designed using a strut-and-tie model? Or, does anyone have guidance/comments on how to handle this problem?

 

[P205]

Anyone?

 

[KootK]

- If you read the language closely, it says that you may use STM, not that you must. Not that it's probably not the right thing to do technically mind you.

- In Canadian practice, I've not seen much use of squat wall provisions for better or worse. Mostly laziness and ignorance I feel.

- I'd consider the simplified, suggested procedure below to be STM-ey enough for this. Basically just some detailing and a bunch of overlapping lean-tos as your STEM.

- The ACI recommendation on vertical reinforcing shown below applies to this and is prudent in my opinion.

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.

 

[P205]

Thank you KootK.

If I understanding this correctly, 11.9.9.4 suggest a reinforcement ratio of 0.0025 for vertical steel for squat shear walls. This would be above the minimum requirement of cl.14.1.8.5 which is a reinforcement ratio of 0.0015. Basically I'm providing additional vertical steel to account (sort of) for the STM truss analogy (where tension chords are provided by the additional vertical steel).

I did notice the wording of "may be design using strut-and-tie", but I was hung up on the first line of 14.4.1 which says "the following shall apply..." I think you're right.

Interestingly, the masonry code (S301.1-04, cl.10.2.8) suggests using a reduced d value in calculating the moment capacity. It also defines squat wall as H/L<1 whereas the concrete code it's H/L<2.

 

[dik]

Unless you have unusual loading conditions and/or openings... STM may not be appropriate for squat shear wallsl... best to consider them as KootK suggests.

Dik

 

[KootK]

It also defines squat wall as H/L<1 whereas the concrete code it's H/L<2.

I'm not surprised as I'd expect this to be a function of the shear stiffness to flexural stiffness ratio which I imagine is lower for block. Who knows if these guys actually talk amongst themselves though.

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.