AS3600-2018 CL14.6.7 hooked horizontal lap bars

[BentEng]

Hi all,

Looking at the CL 14.6.7 requirement for "all horizontal lapped bars within the central two-thirds region of the wall shall be provided with minimum 135degree hooks and lapped with a full-strength splice (figure 14.6.7(D).

1. What is the central two-thirds region? Is this meant to be the middle third region?
2. If lapping outside of this zone, but not in the boundary element, is a standard lap acceptable?
3. Why is this detail necessary, when CL14.6.6 already dictates the design shear to be increased to the (full) elastic shear force. If treating the walls as non-ductile, the shear force is possibly the same as limited ductility, but not the detailing. Further, if the wind shear force is greater than the full, elastic seismic shear force, would the hooked detailing still apply?
4. Is a "full-strength splice" just a tension lap splice? The term "full-strength splice" isn't used anywhere else on the code that I can see.

Appreciate any thoughts or help on this.

 

[rapt]

1 central 2/3 would tend to mean middle 2/3. Why would 2/3 be 1/3?

It is necessary because the cover reinforcement tends to spall off in an earthquake and if the lap is in the cover it loses most of its effect.

The diagram shows the splice length as Lsy.t which is a full tension splice.

 

[Agent666]

rapt, can you shed any light on why a lap in the outer 1/6 of the wall length wouldn't require hooks into the core concrete? I'd say in the end regions you are more likely to lose the cover concrete in a ductile hinge. In NZ irrespective of the location we require the lap with hooks to horizontal bars in the cover layer.

Or is it supposed to mean, if you're going to (or need to) lap the horizontal bars, then lap in the central 2/3rd's using hooks as specified? I find it odd that you don't need to the hooks in the outermost 1/6 of the length otherwise.

Further, if the wind shear force is greater than the full, elastic seismic shear force, would the hooked detailing still apply?

My opinion is the seismic detailing is still required irrespective of the governing load case. Larger than code earthquakes occur all the time for example.

https://engineervsheep.com

 

[Retrograde]

Further, if the wind shear force is greater than the full, elastic seismic shear force, would the hooked detailing still apply?

The hooked detail only applies to limited (and moderately) ductile walls. If you design as non-ductile you don't need it.

 

[BentEng]

To me "central two thirds" is a confusing way of saying dividing a wall into 4 sections, but thanks for the clarification. Unfortunately I've seen other firms use this interpretation to get away from the detailing.

I assume that a wall goes beyond the elastic limit is more likely to have cover blown off towards the centre of the wall? As opposed to an elastic behaving wall, even under the same shear magnitude?

Agent666
I understand that certain detailing is still required, but my point is that if you adopt mu and sp as 1, then you don't need the hooked horizontal bars. But CL14.6.6 makes you design to the mu=1, sp=1 shear force anyways. And says your wind load is 3 times greater than the elastic earthquake load, is the hooked bard detailing still required? Is it because the cover concrete has also blown off under elastic behaviour? If so, that detailing should be in the main body of section 11, not section 14.

 

[rapt]

Agent666,

https://www.eng-tips.com/viewthread.cfm?qid=485461

The outer 1/3 is probably into the boundary elements (.15Lw at each end) and it is required there also in (ii) which has other requirements added for the boundary element detailing.

Not sure why it was worded this way but it basically covers the whole wall, unless someone wants to get really stupid and put it in the .015Lw length between the middle 2/3 and the .15Lw boundary elements at each end and not provide the hooks, because the code "allows it".

I do not know how many times I have to say this, but good engineering is not about "interpretations to get away from special detailing". Engineers who think that is their job description should get out of the industry. Trying to avoid good design and good detailing based on semantics is just stupid.