How rebar quantity for Minimum Clear Spacing Layout rule calculated?

[longt61]

According to document, the Minimum Clear Spacing Rebar Layout rule will have an actual spacing value that must be greater than the value input by user. After that, the rebar quantity will be determined based on the Array Length and actual Spacing (not the value input by user). However, it seems to me that the actual spacing was choose quite arbitrarily as shown in this example:

Array Length: 2577 mm

Spacing: 100 mm

Actual spacing: 117 mm

Quantity: 23

Why does the value 117 mm was choose for actual spacing if 112 mm was perfectly fine with a quantity of 24 rebars?

How is the actual spacing was calculated?

[j.buijs]

I think you're confusing clear spacing with centre to centre distance. Depending on the diameter of your rebar, 24 stirrups would give you a clear spacing which is less than 100

[longt61]

I do believe that spacing is the distance between 2 continuous rebar in a rebar set, is it not? And I find it correct with MaximumSpacing and NumberWithSpacing rebar layout rule. 

Otherwise, could you explain what does spacing mean and how to calculate it in MinimumClearSpacing rebar layout rule in detail? Your effort is much appreciated.

[j.buijs · Accepted solution]

Yes that's true, but the clear spacing is the free distance between the bars, so the spacing minus the diameter.

[longt61]

I am afraid there are 2 things you are confusing here:

1. The "actual spacing" of a rebar layout rule is different from the "user input spacing" or the Rebar.MaxSpacing you can find in Revit Lookup tool or through API (yes, I see you did work with Revit API). The "actual spacing" is the actual distance between 2 continuous bar in a rebar set, that is calculated from rebar set Array Length and number of rebar (quantity). Depend on the rebar layout rule, the "actual spacing" may varies from the "user input spacing":

    - Maximum Spacing: the "actual spacing" is less than or equal to "user input spacing".

    - Number with spacing: the "actual spacing" is exactly the same as "user input spacing".

    - Minimum Clear Spacing: the "actual spacing" is greater than the "user input spacing"

You can look up the RebarLayoutRule enumeration in API docs for explanation. Further more, the "actual spacing" is the distance from the same point of the current rebar to the same point of the next rebar in rebar set (as you have rephrased "center to center", depend on how you define "center"). This "actual spacing" does not minus the diameter of the bar. 

Reproducable case: create a rebar set and change layout rule to "Number with spacing", then chcange the spacing to less than rebar diameter, put a linear dim between centers of 2 continuous rebar of that set, you 'll see.

2. The thing I was struggling with is not "why the user input and the actual spacing are different", but it is "I know it must be diffferent, but why choose this arbitrary value for actual spacing when there are other values that makes sense and more predictable?". I just want to find out how to calculate the actual spacing / rebar quantity for MinimumClearSpacing layout rule. I did believe you have some hints or suggestions about this, but it turned out we are both quite far from it.

Regards. 

[ovidiu_paunescu · Accepted solution]

Hi @longt61 

Like @j.buijs wrote, when the layout is Minimum Clear Spacing, the bars are distributed such that the clear distance between the bars is greater than the specified value.

This was originally intended as a way to ensure construct-ability (e.g. ensuring bars are spaced far enough apart, so concrete flows properly).

Since sets with any of these two distributions (Min clear and max spacing) are placed in elements with lengths that don't divide exactly, the remaining distance is basically distributed in the actual spacing.

For Number with spacing, the last bar in the set cannot be moved, since the length of the set is fixed.

I know there is at least one idea on Revit Ideas about having more distribution types, so I recommend you vote for that or add your own.

[longt61]

Thanks @ovidiu_paunescu  and @j.buijs for yours explanations.

Finally, I truly understand what you mean about excluding the rebar diameter. I could have used a little more time thinking and testing before jumping to conclusion. I just hoped the document could explain the "actual spacing" better.

[b_bataller5QK77]

"Since sets with any of these two distributions (Min clear and max spacing) are placed in elements with lengths that don't divide exactly, the remaining distance is basically distributed in the actual spacing.

For Number with spacing, the last bar in the set cannot be moved, since the length of the set is fixed."

In my opinion, this is pretty much useless to me. I can't use this if the space is varying when you specified actual an actual spacing for the rebar spacing. 

[jay_colcombe]

I think i am reading your point correctly and need to move a single bar in a set range?

You can use the Edit Bars Tool with Number & Spacing