Nasir Malhi

Welcome aboard Nasir.
 
Thanks.

Salam all...i have graduated from NED khi in dec 2005 and from pieas isb in oct 2008 and now working as rcc designer since 2008 in a public sector organization...while surfing net for problem i got to know this plateform...i also encountered sefindia...but i think and like to join this group asap...my basic interests before starting engineering were programming gaming and electronics but fate made structures my destiny and dont know future where it will take me..hope for the best while trying ur fullest...my expertise till now will try to guide newcomers and straighten my concepts through senior guidance...like makhzumi sb and rana waseem sb....

Wa-alaikum-assalam,
 
Dear Mubeen,
 
Selection of the structural system for a building would generally depend upon the seismic zone or category of the area where building is to be constructed and the preferred material of construction.
 
For a B+G+5 building with Reinforced Concrete as preferred material of construction, my obvious choice would be a Concrete 'moment resisting system (MRF).
 
Which MRF (IMRF, SMRF etc) would actually be used, will depend upon the selected 'Lateral Force Resisting (LFR) System' corresponding to the seismic design category (or seismic zone) of the area, and the code (UBC-97 in the present case)  requirements / restrictions applicable for that area.
 
Value of overstrength factor 'R', would correspond to the 'LFR System', adopted for the building.
 
Types of various Building Systems, LFR Systems, their corresponding R values and restrictions on the use of these building / LFR systems are available in Table 16-N of UBC-97.
 
 
BTW... Where is you building located? And, what is your preferred material of construction.
 
 
Regards.

R factor is used to account for expected ductility of building in earthquake loading. There is no R in non-linear analysis.
 
Lesser R means less post-yield ductility and hence more base shear and vice versa.
 
If a building is ductile (more R) we design for less base shear because in reality building has considerable ductility even after yielding (energy dissipation in non linear range) so in simple words lets say the actual seismic force in reality is 100kn then in linear elastic code based design we design it for only 50kn (hypothetical) and for the remaining 50kn we assume based on structural framing system that building will resist by post-yield ductility.
 
Most common lateral resisting systems are moment frame system, shear wall system, building frame system, flat slabs (not in higher seismic zones) etc.
 
You first determine seismic design category and see limitations on type of lateral system you can "assume" to find R.

For seismic zone 2B and RCC, you may adopt Concrete 'Intermediate Moment Resisting Frame (IMRF)' for your building, with an R value of 5.5.
 
This would require RCC member detailing as per section 21.3 of ACI 318-08.
 
Alternately, you may also adopt 'Special Moment Resisting Frame (SMRF)' system for you structure. However, it would require a more stringent detailing, in accordance with ACI code Sections 21.5 onwards.
 
Regards.