Overlapping Struts STM

[Trenno]

Currently refreshing myself in the world of STM with the current situation: a transfer wall with two columns and beam framing into the top of it. The reactions from the columns and beams are roughly similar in magnitude.

What advice would you give for dealing with the overlapping struts from the right hand side column/beam?

Ideally the STM would be a simple truss like so, however it gets tricky setting up the nodal regions and the longitudinal axis of the struts.

 

[KootK]

Finally... we're so overdue for an STM thread. I favor the model shown below. I feel that, one you adjust the flexural and shear depth appropriately to deal with that notch, the overlapping strut issue is self resolving.

 

[KootK]

I also think that you could use this very simple model conservatively and without sacrificing much efficiency. Your limiting factor may well come down to that node where the two struts meet up anyhow.
Obviously, you'd have to also not be ridiculous about discontinuing intelligent bar detailing beneath the beam etc.

 

[jayrod12]

So would you design the struts that end up overlapping as the vector sum of the two and apply the appropriate conservative assumptions to strut size?

 

[KootK]

Modelled properly, I don't feel that the struts do overlap. I haven't fully thought through the nodal geometry below but the gist of it is apparent I think.

For the simplified model that I posted above, I don't feel that any vector summing is necessary. Just the straight up moving of the load as I illustrated. As I mentioned earlier, though, one still needs to keep their wits about them with the detailing. If the final answer is just stirrups, tie bar, and skin bars, AOK. On the other hand, if each load needs a diagonal, mini-column cage to make it go, then that's different and you'd still need that under the beam.

 

[rowingengineer]

I don't know, without the numbers it is very hard to be helpful, but my gut says a dropper and tie would be best.

 

[KootK]

What's a dropper? Slab thickening?

 

[Brad805]

It might be interesting to work thru this example. I find it difficult many times to finally land on a layout and most examples I seem to find do not have many complexities. I read a recent study for a beam with openings where the engineer did 4 STM analysis and then found another solution as well.

 

[Trenno]

@KootK - I agree with most of your sketches above - however, do you have a good reference that assists setting up the proper STM geometry. For example, best way to define strut/tie axe between centres of bearing, what the nodal angles should be? How to deal with multi-strut nodes? I find most examples are very simplistic.

@Brad - what software are you using there? We've recently got our hands on Idea Statica and I've just started exploring a solution to this problem. The stress diagrams are very similar.

@RE - as per the OP, the reactions from each column and the beam are similar in magnitude. For arguments sake, let's say 2500kN SLS with a wall thickness of 500mm. This wall is bearing down onto a transverse beam at either end.

 

[KootK]

I'd have to go hunting for nodal geometry recommendations myself which is why I mentioned that I was just ballparking the nodal setup in my sketch. This stuff is spread out all over. Codes, Schlaich, ACI SP pubs, DOT guides...all the euro stuff. And there's often more than one right-ish way.

 

[Brad805]

That is output from AStruttie and IDEA Statica Detail. I am in the midst of evaluating Idea Statica for our office so I setup a quickie model. If you have not gotten a copy of the Idea Statica CSFM book I suggest it Link. It goes thru the material models and theory in good detail and explains the focus on creating a tool that is useful for everyday applications.

 

[KootK]

@Brad805: with respect to that CSFM book:

1) Is it Eurocentric or does it cover North American stuff too?

2) What's the DRM security like? Is it one of these things that you can't move from one device to another without a bunch or rigmarole?

 

[Brad805]

Koot, they cover code requirements related to ACI-14 in the book and one of the verification problems is out of the Schlaich documents you referenced. Possibly not to the level you might like Some of the anchorage options in the program are limited in the ACI code options compared to the EN code, but I asked if they are planning to make any changes. Tech support from the Canadian re-seller is not stellar since they are focused on steel, but they are trying. The DRM is a floating license, but I am still in the trial mode, so I have not seen if there are any complications. I know what you mean about the EU license issues. Tekla uses a borrow tool that is endlessly frustrating.

A couple of good videos:
1. Shear wall model: EN code Link
2. Precast Beam with openings: EN code as well: Link

 

[Brad805]

Koot, re-reading some sections of the book mentioned last night I would should refine my comment about the level of discussion for ACI code issues. The ACI code application in the book are mainly limited to the verification problems. You have the ability to change the material models within the parameter of their modeling, but the various nuances between EN and ACI-14 are not discussed in great detail in the book. I included a paragraph out of the introduction that sums up their intent of the book. I would be interested in your comments if you do look into this. I find it exhausting on projects how many different tools you must use to solve some problems and this has potential in my mind. Openings are the bane of my designs, and nobody seems to say no to architects about the sizes they can have or the proximity to other openings.

 

[KootK]

Thanks for all of the info on this Brad805. I'm still trying to decide if I want to buy the book through the link that you provided. I'd be happy to pay the $88 CAD but only if I have pretty free reign with how I use the PDF file. If it's going to be tethered to just my desktop, I'd not be interested. I've been trying to ascertain the DRM situation through their support chat but with no luck so far. They do a weird thing where, instead of just letting me ask a question, they force me to answer theirs before continuing. And most of theirs are irrelevant. I might actually have to phone somebody. You know, like it was 2019.

 

[Brad805]

I thought you meant the DRM for the software. There is nothing special for the book. I have it on my tablet, office computer, and home computer.

 

[Trenno]

@Brad - how did you get along with your Idea Statica trial? We had a call with a few of their technical reps to go through this example. They were quite helpful. Seems like a handy bit of software.

 

[Brad805]

We did purchase a license for this year. We are trying to model individual precast wall segments within a wall line (in plane forces), and the mapping of forces between SAP models and Idea Statica takes a little time. It has proven to work very well to understand the flow of forces in the panel. It has also been excellent to model small details where the parts are subjected to localized stresses. Our experience with tech support for the concrete side was quite different than yours. The re-seller in Canada is great with steel connections, but they do not have anyone for the concrete side. Getting in touch with someone in CZ proved a challenge, but that seemed largely a reality of the timing around a holiday. I used the steel connection module to design a number of connections for a small project, and that aspect is very efficient and provides a level of understanding for the connections one cannot achieve without unrealistic modeling time in FEA software that only spits our stresses that ends up with unrealistic peak forces without careful meshing.