NCh2369 vs. ASCE 7 – Strength vs. Ductility? Industrial steel braced frames

Abstract

Earthquake-resistant design philosophies behind ASCE7-10/AISC341-10 and NCh2369.Of2003 are different. The differences make very difficult the task of satisfying simultaneously both design criteria, both from the conceptual and the practical points of view.This paper presents the comparison of the inelastic seismic response of a concentrically brace frame of an industrial structure. The structure was designed to meet independently with both American and Chilean Codes provisions. The comparison of the seismic response is made at three levels of earthquake excitations: for a standard earthquake demand, (10% of exceedance in a 50-year period), for a maximum credible demand, (2% of exceedance in 50-year period), and for an operational level earthquake, (50% of exceedance in a 30-year period). Each of these earthquake levels is represented by a set of artificial ground motions compatibles with the corresponding design spectra. Additionally, some design aspects showing the differences among the design philosophies are presented.Results of this study show that, in spite of the fact that American design base shear is 34% less than the corresponding Chilean-designed structure, seismic weight using American design is 22% larger than the Chilean design value due to design conditions not associated to seismic requirements. In spite of the fact that Chilean-designed structure has a larger lateral strength, American structure response seems to provide a better satisfaction of performance objectives defined for each level of earthquake demand.