Shear Wall Transfer Beam
Shear Wall Transfer Beam
(OP)
I currently have a shear wall that has to transfer the load to the columns.
I have looked at systems that use a beam (in the same plane as the wall) to
transfer the loads from the wall to the column. The problem that I do a
finite element analysis it shows that the bottom part of my wall or beam if
I had one will be in tension. What advantage will I gain from using a beam
and not just put my wall down on the columns with column heads?
I have looked at systems that use a beam (in the same plane as the wall) to
transfer the loads from the wall to the column. The problem that I do a
finite element analysis it shows that the bottom part of my wall or beam if
I had one will be in tension. What advantage will I gain from using a beam
and not just put my wall down on the columns with column heads?






RE: Shear Wall Transfer Beam
I have looked at systems that use a beam (in the same plane as the wall) to
transfer the loads from the wall to the column. The problem that I do a
finite element analysis it shows that the bottom part of my wall or beam if
I had one will be in tension. What advantage will I gain from using a beam
and not just put my wall down on the columns with column heads?
RE: Shear Wall Transfer Beam
1) Your wall flexural compression block may not fall entirely within the columns. Column heads may well be able to deal with this.
2) If the slab is thin it may well be difficult to make the shear friction between wall and slab work. A beam/thickening helps with that.
If possible, I prefer to run the columns up to overlap with the wall by a story. There can also be all kinds of seismic implications to this if that is a big concern for the project.
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.
RE: Shear Wall Transfer Beam
coming down in the wall. The load arcs to the columns and creates
a triangle tension zone above the spanning wall with the maximum tension
in the bottom and gradually decreasing as you move up the wall, it should
therefore be scheduled appropriately. But I am looking a maximum tensile
stress of 12 MPa that has to be carried by the reinforcement. This maximum tensile
stress is basically in the slab.
1. Can I just increase my reinforcement in my slab to handle the maximum stress?
2. How many stories of the wall do you use as a "deap beam"?
Kind regards
RE: Shear Wall Transfer Beam
RE: Shear Wall Transfer Beam
load in any case.
Sounds like the wall is acting as a Deep beam and should be designed by Strut-tie action. You will need to make sure there is a mechanism to transfer the load from the wall to the columns, but all a beam will be doing is give you some extra concrete to house the tension tie reinforcement at the bottom.
RE: Shear Wall Transfer Beam
Q1) You bet. That's just what I'd do.
Q2) As others have mentioned, it's probably better to think of this in strut and tie terms as apposed to deep beam. That said, for gravity loads, I've seen recommendations similar to below. That essentially establishes an effective beam depth which can be used to proportion your tie. A quite different model would apply under lateral load, of course, and would depend on whether or not you have net overturning etc.
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.
RE: Shear Wall Transfer Beam
Q1R) I believe it better to place your tie in the bottom of your wall rather than in your slab. That way you don't wind up with a cold joint crossing your diagonal struts at an oblique angle. I'm not sure how critical this is but it's what I'd do.
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.
RE: Shear Wall Transfer Beam
RE: Shear Wall Transfer Beam
The cold joint can easily be handled by the vertical reinforcement your should be supplying in the wall and fully tying around the tension tie reinforcement so that it is fully developed by the time it reaches the cold joint.
RE: Shear Wall Transfer Beam
Correct me if I'm wrong but it sounds as though you are thinking of using the entire cold joint connecting the wall to the slab. The cold joint that I'm concerned with occurs over only distance X in the sketch below. It's certainly not impossible to make it work via shear friction but it's no slam dunk. It warrants careful designer attention in my opinion. And, if you wind up needing extra localized roughening or shear friction reinforcing, that's just one more thing that requires additional attention and inspection on site.
Why? In something that is many times taller than it is wide, it seems to me that you'll end up with exactly the same quantity of tie reinforcing regardless of whether you place it low or really low. And nearly identical performance.
@SteynvW: I found something in print. See the clip below. Everyone prefers a reference over some stranger's advice, right?
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.
RE: Shear Wall Transfer Beam
And how is the whole connection going to work with the tension tie above the top of the slab?
I did suggest that there should be a downturn which would have the compression strut coming into the side of the column! There is no way I would detail it as you have shown. Why, because it feels better to me. But that is just my opinion.
RE: Shear Wall Transfer Beam
And how is the whole connection going to work with the tension tie above the top of the slab?
I did suggest that there should be a downturn which would have the compression strut coming into the side of the column! There is no way I would detail it as you have shown. Why, because it feels better to me. But that is just my opinion.
RE: Shear Wall Transfer Beam
RE: Shear Wall Transfer Beam
If I understand you correctly, if I do install a beam right under the slab with a increased width, I will have my highest zone inside my beam. In bending this will not have a advantage, but if I use the tie and stud method and I have to use shear to transfer the tension to the reinforcement an increase in width wil be an advantage?
Kind regards
RE: Shear Wall Transfer Beam
Not having a beam obviously simplifies formwork. My first stop would be to see if it can be made to works without the beam.
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.
RE: Shear Wall Transfer Beam
My load is more or less 1000kN per meter.
Kind regards
RE: Shear Wall Transfer Beam
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.
RE: Shear Wall Transfer Beam
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.
RE: Shear Wall Transfer Beam
It does not work with 40MPa concrete, but with a slight widining
in terms of a column head and a bit of steel it works.
Thank you very much for you time. This type of system has only been used a couple of times in South Africa so the experience and literature is quite scarce.
RE: Shear Wall Transfer Beam
No sweat. Helping each other is our thing here.
Thanks. I asked because the code that you're using will impact your assumptions regarding transfer of lateral shear from the wall into the slab. As rapt mentioned, the detail would be vertical u-bars extending into the slab and wrapping around some longitudinal steel. Personally, I feel that's sufficient to develop the u-bars on either side of the horizontal cold joint. However, in the US and Canada, there is no provision explicitly allowing you to consider a u-bar like this to be developed any better that a straight bar with a standard hook would be. And regular hook bar development in a 200 slab will be a challenge for most u-bar diameters. For this reason alone, you might want some manner of thickening below the wall if not a full blown beam.
As shown below for the gravity case. If you envision the bit of slab sandwiched above the column as simply an extension of the column, the detail become that of any simple span, column supported deep beam.
Sure. And the preference that I've expressed here is simply my opinion. I believe that both details can be made to work and, in truth, my preference for placing the tie in the wall is slight. Certainly, placing the tie in slab facilitates a very appealing tie anchorage scenario.
No matter which approach is selected, the diagonal compression force needs to be "turned" vertical before it passes into the column. As a matter of general philosophy, I find it preferable to affect that change prior to the strut crossing the cold joint. One less thing to worry about in my estimation. I, like many other engineers, have reservations regarding shear friction. And, as the application gets more critical and veers further from the simple mechanisms tested, the more reservations I have.
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.
RE: Shear Wall Transfer Beam
If the wall is taking sway loadings of any sort (wind or earthquake) then the loads are going to be at the ends any and the ends have to be designed to take those loads anyway. Those loads may be higher than the averaged gravity loads
Only the bottom few floors worth of load will transfer across in strut tie action.
PS hate the detail with the tie above the slab. If you have to have a tension tie extend it below and make it the width of the column at least. Maybe even make the first floor height of the wall the width of the column, 300 as well. The column bars will have to extend through the slab anyway and they will provide the horizontal shear required.
RE: Shear Wall Transfer Beam
I caluclated the forces and required reinforcing according to our code using your proposed strut and tie layout.
(Please see attached). The first one is with a 2/1 ratio and the second one is
with a 3/1 ratio. The increase in angle has significant influence on the tension
reaction in the strut and tie model.
1. Is it fair to use a 3/1 ratio or even a 4/1 ratio considering my wall is 16 stories high and will in actual fact increase ration if the wall height increases?
2. The transfer from compression to tension has to be done through shear at the node, is the shear just in the marked area at the bottom of the pdf or is it continuous through
out the bottom of the wall?
RE: Shear Wall Transfer Beam
The 2:1 is based on research and shows up a few places in various standards which gives it some credibililty in my opinion. And this is a situation where I wouldn't skimp on reinforcing. 7000 mm^2 seems reasonable to me. Assuming a single mat in the wall, I might install 12-30M at 100 in a band at the bottom of the wall. It's a fairly narrow wall for the application and getting good concrete compaction aroumd the bars will be critical.
2) Refering to my sketch, all you need to do for shear transfer is develop the tie bars to the left of where they first pass into the strut. You'll have nearly four feet to develop the bars here which should be plenty.
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.
RE: Shear Wall Transfer Beam
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.
RE: Shear Wall Transfer Beam
Ignoring the above - I don't see any problem with placing it above the slab in the base of the wall and tend to agree on it's merits. I also agree that this is no place to skimp on steel. Even if you placed the required steel in the base of wall and then placed that same amount distributed in the slab (i.e. 2x the required) you're not talking about a lot of steel.
Stey - You have not asked about other issues with this so maybe you've already thought through them but: you should check your code for any penalties for this system/irregularity, you'll need to analyze/design your diaphragm to take that shear elsewhere (make sure software isn't using rigid diaph), if you are getting net uplift you'll need to check/develop that tension through this joint and also account for the reduced/cracked stiffness of the column.
RE: Shear Wall Transfer Beam
Exactly right. It would be better but not good enough. I don't believe it for a second but that's how it's presented in the code.
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.
RE: Shear Wall Transfer Beam
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.
RE: Shear Wall Transfer Beam
RE: Shear Wall Transfer Beam
According to my FEA the transverse forces above this beam is about 30% of the maximum at the wall slab connection.
What are your thoughts?
RE: Shear Wall Transfer Beam
Have a look at the enclosed article regarding the design of deep beams. You will want to provide additional horizontal reinforcement distributed through the bottom several feet to prevent the vertical cracks caused by the near vertical compression struts (the refined model in KootK's second post is more appropriate than the 2 to 1 compression struts).
As for your original question, and as it regards to vertical loads only, I do not see any advantage for providing a beam below the wall except to relieve potential reinforcement congestion. A beam below the slab should just be treated as an insignificant additional height to your 15 story deep beam.
RE: Shear Wall Transfer Beam
I like the beam idea as it allows you to increase the width of your node and reduce the stress on the diagonal strut. That said, I'd personally still put the tie above the cold joint, even with the beam.
I've got a couple of strut and tie models floating around in my head for the beam scenario. Let us know if that's something that you'd like to explore further.
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.
RE: Shear Wall Transfer Beam
But there are more or 50 of these walls, so over-designing a repetitive member is not going to be that economical.
But I think just because of the increase of the transition zone between the wall (increase in node size) is almost enough reason to use a beam or rather a column head.