Comparison of different approaches for seismic assessment of existing buildings

The present study consists of a commented application of the three major guidance documents on the assessment of existing buildings currently available, the New Zealand Recommendations, the US ASCE-FEMA 356 and the Japanese Standard, to three structures (two 2D and one 3D frames) which have been constructed at a large scale. The main purpose of the study is the checking of the practical applicability of the methods, the relative ease of use, and of course the degree of agreement on the results. The theoretical framework on which each document is based as well as the proposed methods are outlined and commented. Differences of conceptual nature existing between the various approaches are noted. From the small number of cases examined is not possible to systematically trace the differences in the results produced by the different approaches. The large difference in the way the shear capacities of members and joints are evaluated has been a decisive factor in some cases for the determination of the ultimate capacity of the entire building. However, even if this source of discrepancy of the results from the various approaches was eliminated, the present exploration indicates that significant differences would remain, linked to the criteria used to relate the capacity curve to the response spectrum, or to the use of elastic analysis combined with local ductility factors, as in the US FEMA 356, instead of the global mechanism analysis of New Zealand.