SUMMARYResearch engineers use two types of energy equations to study single-degree-of-freedom (SDOF) systems subject to earthquake induced ground motions. The first method uses an absolute energy formulation; the second method uses a relative energy formulation. While the relative energy formulation has been used in the majority of previous investigations, this study shows that the absolute energy equation is physically more meaningful. For a given ductility ratio, the input energy demands calculated by both methods are significantly different for both the short and long period ranges although the results are similar in the intermediate period range. A comparison between the analytically predicted absolute input energy of a SDOF system with the experimentally measured input energy of a six-storey braced steel frame shows good correlation.

Strength reduction factors which permit estimation of inelastic strength demands from elastic strength demands are evaluated. Results from various investigations of strength reduction factors carried out over the last 30 years are reviewed, and their results are presented in a common format which facilitates their comparison. The main parameters that affect the magnitude of strength reductions are discussed. The evaluation of the results indicates that strength reductions are primarily influenced by the maximum tolerable displacement ductility demand, the period of the system and the soil conditions at the site. Simplified expressions of strength reduction factors to estimate inelastic design spectra as functions of these primary-influencing parameters are presented.

Near‐fault records of the 1971 San Fernando earthquake contain severe, long duration acceleration pulses which result in unusually large ground velocity increments. A review of these records along with the results of available theoretical studies of near‐fault ground motions indicates that such acceleration pulses may be characteristic of near‐fault sites in general. The results of an analytical study of a building severely damaged during the San Fernando earthquake indicate that such severe, long duration acceleration pulses were the cause of the main features of the observed structural damage. The implications of such pulses on current aseismic design methods, particularly those used to establish design earthquakes, are examined for buildings located near potential earthquake faults. Analytical studies of the non‐linear dynamic response of single and multiple degree‐of‐freedom systems to several near‐fault records, as well as to a more standard accelerogram, indicate that at near‐fault sites: (a) very large displacement ductilities may result for current levels of code design forces; (b) smoothed elastic design response spectra should reflect the larger ground velocities that may occur; and (c) peak inelastic response cannot reliably be inferred from elastic response predictions.

SUMMARYThe main objectives of this paper are: (i) to review brie y as to what is understood by performancebased engineering, performance-based seismic engineering, and performance-based seismic design (PBSD); (ii) to discuss the main requirements that a reliable PBSD should satisfy and why some approaches that have been proposed fail in satisfying those requirements; (iii) to focus on what is considered a promising probabilistic PBSD approach; and (iv) to present a conceptual comprehensive numerical procedure for the PBSD of buildings.It is shown that to satisfy the objectives of a reliable PBSD philosophy and procedure it is necessary to start with a multi-level seismic design criteria, to consider a probabilistic design approach, to consider local structural and non-structural damage and therefore design spectra for buildings (n degrees of freedom), to take into account the cumulative damage, and to control not only displacements but also ductility (minimum strength) to limit damage. Finally, it is concluded that a transparent and conceptual comprehensive preliminary design approach is necessary.

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