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Refer to FEMA 350 guidelines - it is a free download.

Yes, you have to use positional couplers. Generally positional couplers cost 1.5 to 2 times than a standard coupler.

DesconWin and DesconBrace are undoubtedly the best available in the market.

Having designed many steel buildings in USA (SDC D and above) and currently doing designs in India, I personally feel the IS 800 is very vague & inadequate, especially for Zones 4 and higher. We have convinced the owners and the India city officials to approve use of AISC/FEMA recommendations on...

We have been using DESCON BRACE and DESCONWIN for the last 3 years and it is an extremely good tool for designing connections. The design calculations and the details generated are quite complete. Go for it!

Post your ETABS model

While using R=3, it is not required to design the connections for overstrength factor. The connections are designed for forces resulting from the governing member designs.

An easier & economical way to deal with uplift is dropping the spread footing. This way you can count on the weight of soil (go at 45 degree angle from the edge of footing) and the slab on grade. This along with a grade beam (if needed to tranfer horizontal shear) may solve your problem...

OMRF is not an acceptable system in SDC "D" or higher. The actual forces on a structure during a real seismic event are much higher than the code specified values. The code forces are minimum required to maintain life safety. ACI requires special detailing to enable significant energy absorption...

Completely agree with structuresguy. ETABS design for core walls (box) would be much more efficient than the code approach of using effective flange widths.

The most optimal design is to assign a single label for the entire core wall. Effective flange width is an approximate method and shall be used when no better tool is available. ETABS has an advanced design module which would look at the 3D section. In some cases the reduction in reinforcement...

www.seaofsc.org -- alex's corner www.engineering-international.com

Slikdeals You will have different scaling factor for X & Y directions. I usually scale the spectra so that the dynamic effect would be scaled in all aspects. I will post a sample calculation regarding this.

Dynamic analysis captures the torsional behavior of the building. If a building is poorly laid out, the shear in Y for X-direction spectral analysis could be as high as 90%. YOU MUST INCLUDE BOTH X & Y COMPONENTS. Follow thread 487-204481 for scaling info. LET ME KNOW IF YOU NEED MORE INFO.

slickdeals: We do a number of ETABS models for highrise structures. We only do a finer meshing of slabs where we expect the slab to crack significantly. Rest of the slab is modeled with minimal number of elements. 50000 elements sounds way out of range. Just as a quick check you can model the...

Is there a way to capture torsional mode shapes? No. Will there be modal correlation between the 3D model and a simplified model? Probably not. Has anyone done such an exercise before? What is the rationale behind your study? Is this for a quick and dirty analysis?

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.

Stiffness of the frames would also play role in the magnitude of base shear. Stiffness directly influences the building period which in turn will play a role on base shear.

Follow thread487-204481 we had this discussion before.

I disagree with haynep. The kickers need not be detailed as an EBF. I would use an R=3 and no special detailing is required. R value used for Mechanical platform would have no impact on the R value used for the building.