Terminology "Slab Band"; "Continuous Drop"

[ajk1]

Is a continuous drop exactly the same as a "slab band"? My opinion is that a "continuous drop" is more specific and clearer in meaning than a "slab band", if continuous drop is what is meant. To me a "continuous drop" in a span means that the drop panel extends right across the span at a location (rather the just to span/6), whereas "slab band" refers more to the width into which rebar is placed. Do you agree?

 

[KootK]

Is a continuous drop exactly the same as a "slab band"?

They're the same in my world.

To me a "continuous drop" in a span means that the drop panel extends right across the span at a location (rather the just to span/6), whereas "slab band" refers more to the width into which rebar is placed. Do you agree?

- I don't agree. I like slab band for the feature that you've described.

- My preference probably stems from the fact that everybody says "slab band" in my area. Regional thing as usual.

- Really, I don't have strong preference either way. I find both options reasonable.

- To my ears, "drop" is suggestive of "drop panels" which, since time immemorial, have been more localized elements that slab bands are.

- I get what you're saying about "slab band" suggesting a local reinforcing strip but I'd not sweat that personally. I think that usage is more common among designers discussing design that it is among contractors discussing contruction.

 

[hokie66]

My preference is for "band beam". This is what they are called here, and it seems to me that description removes the ambiguity.

 

[rapt]

Hokie

It has been called that here forever as you said, but I disagree that it removes ambiguity.

I see too many people thinking it is a "beam" because of the term, where it is really a thickened slab and is a flat slab rather than a beam and slab design. The way it is designed should be as a slab with a continuous drop panel.

Most designers put the thickening in the direction of the longer span as you would for a beam, but logically as a slab thickening it should actually go the other way, especially in more rectangular grids. The idea of a beam is that it is stiff enough to act as a continuous support. In a very rectangular grid, the "band beam" is not stiff enough to do this and should be in the short span direction as this is the direction tending towards one way action. If you look at the moment pattern for a very rectangular grid, the logical direction is the short direction where slab thickening is being placed where the much larger moments are and are in the band direction the moments are more concentrated near the column line (column strip width = length of the shorter span / 2) with a very wide middle strip.

 

[hokie66]

I agree, with shallow bands, but how do you distinguish between wide, flat beams which actually do result in a one way system, and shallow bands which are just components of a flat slab? The designer needs to know, but to the formsetter, steel fixer, and concrete, "band beam" works for things like a 600 deep x 2400 wide beam.

 

[rapt]

I was thinking in terms of terminology for the designer. On the construction side, it does not really matter as far as I am concerned.

But when you see some idiot using a band beam in a slab with an 11m * 5.5m column grid, and he puts a relatively shallow band beam in the 11m direction, you have to wonder if they understand engineering. I saw a director from a relatively large and well known consultancy do it many years ago! He said it was because beams are always used to stiffen the long span direction enough to make the short span direction a one way slab! And his band still only made the long span direction half as stiff as the short span direction!

 

[hokie66]

Yes, but I have never used those shallow drops, so never had use for that terminology. For me, it is either beams with one way slab or a flat slab.

 

[ajk1]

Maybe I am too old, having started my engineering career here in Ontario in 1964, and for sure we called them "continuous drops", never slab bands. That may not have been the practice in other parts of the world. It is possible that the terminology has shifted over the years, I don't know. Since this is a "typical detail" that is issued for construction, to the contractor, it seems to me that "continuous drop" is a little better term, as it is a fuller description of what is to be physically built than "slab band". So I think that I will stay with the terminology "continuous drop" on the typical detail sheet we issue for construction. If there is some ACI or similar publication that shows a continuous drop and labels it a "slab band" I will reconsider.
Thanks everyone for your thought and comments. Much appreciated.

 

[ajk1]

... and an additional comment: we generally use continuous drops in spans that would otherwise have excessive deflection i.e. in the long direction

 

[rapt]

Maybe if you had explained all of that (except for your age) in the first place rather than asking a general question you would not have got a general discussion on band beams!

We could have left Kootk to give you the Canadian version!

 

[KootK]

As this discussion has unfolded, I've found myself becoming less agnostic about the terminology. My preference is for "band beam". Here's why:

1) I found neither "continuous drop" nor "band beam" in my ACI terminology document. So no silver bullet there.

2) In my opinion, the that stuff we choose to show on our slab drawings should be 95% about clearly communicating intent to our contractor friends. Structural designers can, and should, fend for themselves.

3) Viewed in plan, an continuous drop sure does look like a wide beam.

4) In my market, a continuous drop will often have stirrup shear reinforcement, much like a beam and not like a drop panel.

5) In my market, a continuous drop will often have continuous, column to column top steel, much like a beam and not like a drop panel.

6) In my market, a continuous drop will often have concentrated, large diameter bottom steel running column to column, much like a beam and not like a drop panel.

In summmary, when a contractor is reading my plans and trying to identify all of their beams for pricing and planning, I like that continuous drops present like beams as that will alert the contractor to all of the beam-like features that will need to be installed in the continuous drops.

 

[rapt]

Not knowing standard Canadian drafting practice, is it necessary to name it at all if it is simply a thickened slab area, albeit looking like a continuous drop panel? if it is simply a thicker area of flat slab without any special reinforcing detailing like stirrups etc, can't it simply be shown as as a thicker area of slab on the slab layout plan?

Then if it is really meant to create one way action like a Band Beam, it is called a Band Beam.

 

[ajk1]

I agree completely with your item 2. Well put. That is why I an taking the time to solicit opinions on this in this forum.

I feel that "continuous drop" is the clearer and most descriptive term, at least to the forming trade. The continuous drop is formed by the forming contractor. I am doubtful that the forming contractor would know what a "band beam" is. In my area (Toronto), a continuous drop generally does not have stirrups like most beams do. If it did have such, I would likely assign it a beam number, design and schedule it as a beam.

In any event, I thank you for having taken the time to respond and give me your thoughts and to have looked at the ACI document on terminology and found that they do not have a term for this. That is interesting to know.

Our chief field engineer who has 40± years of site experience, prefers the term "continuous drop". I appreciate that others such as yourself may prefer the term "slab band". I will discuss it further with our other senior engineers. Thank you as always for your insight, guidance and advice. Much appreciated.

 

[ajk1]

My immediate previous post was meant for KootK
As to rapt: you make a good point. i.e just avoid the problem by not labeling it.

 

[ajk1]

Does anyone else, particularly in the southern Ontario region, or the northeast U.S., have any comment on the usage of the term "slab band" vs. "continuous drop" on the structural drawings and typical details, and which phrase they use? Note that I am not talking about design terminology, but rather the terminology they use to label a drop panel that extends from support to support.

 

[ajk1]

to Kootk - I have found that CSA A23.3 2014 does define "slab band" in the definitions at the front as "a continuous extension of a drop panel between supports or between support and another slab band".
Not a great definition because it includes the term it is defining within the definition, but the first part of the definition is valid. So you were right. I owe you an apology. This does not appear in an earlier edition from many years ago that I checked. I don't know when it was introduced into the Standard. Again, my apologies. I will do our typical detail accordingly, even though that I like "continuous drop".

I wonder if anyone has the latest ACI 318, and whether that has a definition for "slab band"?

 

[hokie66]

"Continuous drop" to me is illogical, as drop panels are often unreinforced in the bottom, while the type of band we are talking about always has bottom bars.

 

[Celt83]

we use "Continuous Drop" for drop panels that extend over multiple supports and have a companion detail for "Continuous Drops" that shows the reinforcing steel in the direction of continuity being "dropped" to the lower cover elevation.

Ultimately I'd say the terminology doesn't matter a whole lot as long as you've got documentation that clearly backs up the intent of what your trying to accomplish so the folks in the field place the reinf. as your design requires.

Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

 

[ajk1]

Agreed

 

[KootK]

I owe you an apology.

You don't but it's gracious of you to offer an apology anyhow. Just a spirited debate between colleagues.

Similar to the direction recommended in the last few posts:

1) Your drawings likely have a "definitions" page which you can control. Whether you go with continuous drop or slab band in your drawings, perhaps you could define the term in your definitions section and, there, mention the alternate term that you chose not to use on your drawings. And maybe even refer to a typical continuous drop detail if you have one.

2) So long as "continuous drop" has not been causing confusion with contractors over the last 30 yrs or whatever, I'd be inclined not to lose much sleep over it.