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Re: Fw: PROBLEM ON USING CORRECT Rw FACTORS

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Fuat
Of course this is a structure and should be classified as a structure and NOT a nonstructural component. The Rw value should correspond to the type of  structural system used in the design in your case a braced frame. Nonstructural components are those components that do not usually participate  in the seismic resistant system and although their masses are included in the design of main structure their stiffnesses are ignored. These components are connected to the main structure by means of anchorage systems which should be capable of sustaining much higher seismic loads than the structure itself due to the amplified component's oscillation. The damping and ductility of the structure in earthquake motions is built up of all the structural elements that form the structure and as such is normally much larger as compared to an individual  nonstructural component. Last point to consider is  in calculating the seismic force on a nonstructural component normally there are two factors regarding the ductility to be considered, ie Rw and ap and because one is in the nominator and the other in the denominator they can easily balance/counter balance each other.

GAMA Factory wrote:

 
----- Original Message ----- To: SEAINTSent: Wednesday, January 17, 2001 6:38 PMSubject: PROBLEM ON USING CORRECT Rw FACTORS
 I am in hesitation to decide on correct clasification type and consequently correct Rw factor of high steel structure in one petroleum refinery. This steel structure is 77 m tall and and it has 5 columns on one alignment and 3 columns on the other alignment (therefore, there are 15 columns). The width of structure is 30.4 m where 5 columns are and 12 m in the other direction (where 3 columns are). The structure is eccentrically braced with vertical bracing in all directions. There are 18 platforms on different levels which are composed of steel beams and horizontal bracing covered with grating. These platforms are for supporting some equipment and for reaching different levels of reactor (long vertical vessel) inside the structure. (The reactor is not supported by the steel structure). Structure is not covered with any cladding material (open structure). There is a stair tower and elevator in the structure. What should be the correct clasification type for this structure? Can it be accepted as steel building frame system with eccentrical bracing or should it be considered as trussed tower nonbuilding structure? If it is accepted as steel building frame with eccentrical bracing, Rw factor is 10 according to UBC-1994. However, if it is considered as nonbuilding trussed tower structure, Rw factor is 4 according to UBC-1994, regardless of whether eccentrically braced or not. What is the reason having so much different Rw factors in building and nonbuilding structures? Any comments on this topic will be highly appreciated. Best Regards,Fuat TINIS