Abstract

VALENCIA RESTREPO, Doralba  and  VALENCIA CLEMENT, Gabriel. Evaluating response modification factor (R) for some types of steel structure. Ing. Investig. [online]. 2008, vol.28, n.1, pp.41-49. ISSN 0120-5609.

In this paper the use of the response modification factor, R, as tabulated in the Colombian Design Code, NSR-98, and many other design codes, in the evaluation of the internal member forces generated for the action of the design earthquakes in steel structures and the inconsistencies that are present when designing structures when it is necessary to comply drift limits of 1% are questioned. The design of 45 frames corresponding to the seismic resistance system of 5 buildings, that is, 15 special moment frames (PRM), 15 special concentrically braced frames (PAC) and 15 eccentrically braced frames (PAE are presented). The external load evaluation and their combination used in estimating internal loads, as well as rigidity demands (1% drift) were made according to NSR-98 requirements, on the other hand, member strength requirements was evaluated using the seismic provisions for structural steel buildings, AISC-2005. The response modification factor of the 45 frames to different structural performance levels is evaluated, by means of modal pushover analysis. It has been found that this factor is not constant for any of the three structural systems (PRM, PAC and PAE) as NSR-98 suggest and additionally the values of the response modification factor found in the present investigation, are smaller to those tabulated in this design code, which govern the common practice of the structural design; leading to significant errors in the evaluation of the design forces, not only in the structure but on the support elements (base plates, foundations, shear walls) and structures attached to the seismic resistance system.

Keywords : response modification factor; ductulity; the strong-column weak-beam concept; elastic respose; inelastic response; plastic mechanism.

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