Braced frame and shear wall lateral load resisting system 1

[lancha2001]

I am designing 6 story building using ram structural system. My building is rectangular and satisfies the rigid diaphragm criteria. I am using braced frame and shear wall for lateral load resistance. 90% of the system is braced frame and I used service elevator shaft to the very right of the building as a shear wall. Has any body has the experience of mixing these two systems and if so on what shall I be concerned? Ram program seems distributing the shear load reasonably.

 

[csd72]

As the elevator shaft is stiffer, it will attract more than its share of load(in proportion to stiffness).

As it is at one end this will result in a twisting motion in the diaphragm.

Is this in a seismic zone?

 

[lancha2001]

The seismic zone is B and soil class of C. How do you think I can check the distribution of shear load on the shear wall other than based on their relative stiffness?

Thanks

 

[asixth]

I agree with csd72, the elevator shaft will be very stiff, and using a rigid diaphragm, load will be distributed to the lateral system depending on their relative stiffness (There are plenty of threads on this site that cover the topic).

Because your stiff element is on one side of your building, the other end of your structure will sway relative to the lift shaft, and a torsional moment will be introduced.

Try to make your lateral system as symmetric as possible. Try and get a shear wall on the side of your building opposite to the lift shaft.

 

[lancha2001]

Thanks guys for your responces. I am designing my building for R value of 6 which is SCBF and satisfy criteria of Seismic Provisions for structural Buildings. I managed to fulfill my demand by doing this. But I have to detail a couple of typical connections. It is a bit time consuming but it worth it when Architects give you a very limited location for brace.

Thanks All

 

[prsconsultant]

lancha2001

You did not mention the Seismic Design Category (SDC). If you happen to be in SDC "C" or lower, try using an OCBF. You will be spending a lot of money on meeting the detailing and brace configuration in an SCBF.

 

[Whiffle]

Look at ASCE 7-05 12.2.3.2 for R factors for horizontal combinations, which it sounds like you have. You are limited by the lowest R factor in that direction, so if you have ordinary reinforced concrete shear walls (R=4)
around your elevator shaft, you can't even take advantage of the R=6 for the steel braced frame, as I understand it.

If you are in SDC "B", I would recommend using a "steel system not specifically detailed for seismic" and take an R of 3. The higher design forces will require larger members, but usually the simpler connections will make the frame more economical.

 

[pablohenry]

hi, someone knows how to design a contention wall using SAP

 

[lancha2001]

First thanks for all your replies.

The problem of using steel system not specifically detailed for seismic in my case is having a very heavy uplift load on certain areas around 500kips. It is such a large load to be taken by anchor bolts at these column location. I am using SCBF and I am not using shear wall in conjunction with BF. It helped a lot in reducing the uplift load and the connection size was not that bad at all eventhough it was not same as the ordinary connection. Because here you desing for the member capacity instead of for the actual load.

Thanks all

 

[sreichwein]

Just be sure you look into all the detailing requirements of such a system. I suggest you read through the AISC Seismic Design manual to see what has to be done in order to benefit from the R=6 of a SCBF system.

Good Luck!

 

[gyroman10]

if you are using shear wall at one end (very right) make sure you check that the center of the Rigidity, as the building will exhibit large twist in floors.

Your center of Rigidity should be close to center of mass. When you say braced frame ? what is bracing these frames ??