Rigid Diaphragm Issue

[dcarr82775]

I have a very poor layout of concrete shearwalls below a podium slab that is giving me no end of trouble. I have a couple of 19' long walls and an 80' long wall. The 80' long wall takes most of the load, which is a problem for various reasons (I don't feel like writing a dissertation on the problem definition).

Without placing openings in the wall, does anyone have idea on how to make the 80' wall less stiff so I can get some load out of it and into the shorter walls? I could place a series of vertical joints in the wall., but this is problematice for waterproofing(above water table).

 

[rowingengineer]

you could put a slip joint on top of it or under it, but without the dissertation it is very hard to help

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[dcarr82775]

Yeah, I understand tough to do without the full blown description. I ended up deciding the wall/footing will slide and when it slides (if the big earthquake ever happens) the loads will re-distribute to the other walls.

 

[steellion]

You haven't gone into the reasons why you are concerned that the long wall is taking most of the load. If this load distribution will not cause issues with your structural performance, you could conservatively design the short walls for more load than the analysis suggests and the long wall for the analysis loads. You end up with more than 100% of your lateral load for your system design, but the short walls should be designed for a reasonable percentage of the load. This is required under certain seismic provisions.

 

[dcarr82775]

There is no reasonable way to make the long wall work in sliding at the full load.

 

[InDepth]

Send a plan. You could probably use grade beams or shear keys to obtain greater passive pressure. You could also provide a teflon horizontal joint where the slab is cast over the teflon joint (two plates with coating one on top of wall, one on bottom of slab) for say whatever length of slab and then keep a certain length for shear. Or just cutoff the vertical steel of the wall conneecting to the slab.

Alternativeely,
0) Increase the concrete strength of the shorter walls to increase stiffness
1) or Calculate the stiffness of the shear wall accounting for reinforcing steel (not just elastic stiffness)
2) or you could design a whole bunch of seperate walls and at the joints provide a few #4 horizontal bars, such that under a significant event a vertical crack develops and seperates the walls.
3) Or provide diaphragm to shear wall reinforcement just enough for a limited force. Once the diaphragm steel yields (ensure gravity capacity is maintained) the diaphragmn redistributes.

If you allow the large wall to slide you may have more issues with ensuring diaphragm strength.

 

[Teguci]

slide bearing between the wall and the slab (you'll need a ledge). Had to do this for a PT slab. Still provided reinforcement between the wall and slab by sleeving the bars with pipe insulation for some distance from the wall. You get some lateral slop, but no normal movement.

 

[wannabeSE]

Have you considered making the 19' walls stiifer so they attract more of the load? Is it possible to make the shorter walls thick enough to make a difference?