Rule of Thumb On No. of Storeys To Consider Introducing Shear Walls

[YuleMsee]

I'm doing preliminary drawings for proposed R.C frame highrise residential towers, the towers vary in height from 8-20 storeys, no real calculations as yet at this stage as its just to enable the q.s comeup with an estimate of cost. What is the rule of thumb when it comes to introducing shear walls, above what no. of storeys do you consider prudent to have shear walls. The seismic hazard is low (PGA 0.2-0.8 m/s2).

 

[MotorCity]

One rule of thumb (not really unique to shear walls) is that for rigid diaphragms, locate your shear walls on the perimeter of the building or at least as far from the center of gravity of the diaphragm as possible. Also, if you are in the US, check ASCE 7 for building height restrictions using shear walls.

 

[Once20036]

Yule, what other options are you considering? Is this a steel building such that you're comparing the relative benefit of steel braced frames vs concrete shear walls?

 

[YuleMsee]

Once, the project is reinforced concrete frame from the get go, steel is more expensive where I'm based. I'm trying to see if there is a rule of thumb in determining above what no. of storeys shear walls become cheaper in resisting lateral loads as compared to the reinforced concrete frame resisting the same.

 

[dik]

Also, if you are in the US, check ASCE 7 for building height restrictions using shear walls.

There are restrictions on height?

Dik

 

[MrHershey]

There are restrictions on height?

In seismic regions, yes. Can't do a special shear wall building taller than 160 ft (240 ft if you meet additional requirements) in SDC D, for instance. Once you're taller than 240 feet you have to go special moment frame or dual system if you stick to the body of the code. With a performance-based approach you can keep using just shear walls but that's a whole other can of worms.

 

[dik]

MrHershey: thanks... Dik

 

[KootK]

We really need to know:

- Kind of building. Residential tower, office etc?
- High, moderate, or low seismic?
- What region?

Where I practice, moment frames are pretty much dead for the low-rise buildings for which they are generally suitable. These buildings go shear wall and, usually, the question is not when to start using shear walls but, rather, when to stop. In non-seismic country, easy bake shear walls should get you up to 30 stories or so. Beyond that you start to get into fancier systems with very thick walls, energy dissipating devices, diagrids, hybrid wall-frame, outriggers etc. For serious high rise, my understanding is that we've settled on core + mast setups as being generally the most economical. That, in a segment of construction where the economics is very regional and technology changes fast.

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.

 

[Lomarandil]

In my new neck of the woods (Cambodia, similarly low seismic) -- I observe that residential towers start incorporating shear walls around 8 stories. But I think that's primarily based on when elevators start appearing. Here, forming up a moment frame seems to be much more common (economical) than forming up a shear wall.

----
The name is a long story -- just call me Lo.

 

[KootK]

Cambodia huh? I was there in the summer of 2014. Neat place. Save the cold towel things on my neck 24/7, I'd surely be dead now from heat stroke. But, then, if I were any whiter, I'd be translucent.

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.

 

[hokie66]

In fairness to the OP, he did say they were residential towers ranging from 8 to 20 storeys, reinforced concrete, low seismicity.

In Australia, most buildings have shear walls, even low rise. Most of our buildings are concrete, and most of us don't like to depend on concrete moment frames.

 

[YuleMsee]

Region - Kenya
Use - Residential
Seismicity - Low

From what I've got so far it appears I will incorporate the shear walls.

Thanks every one, I have never done anything above 20, so I did not know that after 30 storeys or 160ft shear walls are an automatic NO!

 

[hokie66]

That is not correct. For tall concrete buildings, shear walls are a must. You can't depend on concrete moment frames. Now, as KootK says, it gets a bit more complex the higher you go, and involves not only shear walls, but outriggers to engage the big external columns...and other things.

 

[KootK]

In fairness to the OP, he did say they were residential towers ranging from 8 to 20 storeys, reinforced concrete, low seismicity.

Yup, my bad. I bounce back and forth quite a bit during the day and sometimes get threads jumbled in my head.

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.

 

[YuleMsee]

@hokie66, thanks for the correction