Journal of Earthquake Engineering

In this paper we address two problems: (a) the estimation of the total moment release for the calculation of average strain rates and (b) the assessment of the contribution to the total moment of earthquakes smaller than those available in regional or global catalogues. We also examine the bias associated with the different methods currently in use to estimate earthquake recurrence and total rate of seismic moment release, which are important considerations in engineering seismology and tectonics.

A method is demonstrated using Monte Carlo simulation (stochastic modelling) techniques that allows the extraction of information about design earthquakes that constitute the most likely combinations of earthquake magnitude/epicentral distance that would actually generate the computed hazard ground motion at a site of interest, taking into account the log-normal scatter in the attenuation relationship. A worked example, at three different return periods, is shown for a realistic case in Greece. The results demonstrate the range of events that may contribute to the hazard, from which median or modal values can be derived. This method should be very useful in cases where it is desired to select earthquake time series representing the hazard for engineering analyses. In the example shown, the most probable magnitude/distance pairs are those that would produce predicted deterministic acceleration values of about half the design ground motion.

A seismic hazard analysis of Florence city was performed in the frame of a project concerning the dynamic behaviour of cable-stayed bridges. Both a probabilistic approach and a methodology based on the use of a local macroseismic catalogue were applied. A local catalogue was expressly compiled for this purpose, to collect the macroseismic intensities actually observed at the site as a result of past earthquakes. This sort of catalogue is an independent tool to verify the assumptions of the probabilistic approach (seismic zoning, earthquake recurrence relation, attenuation model), though it can supply results in terms of macroseismic intensity only and reflects the effective seismic history at the site, without taking into account any variability. The Cornell's methodology was used to assess probabilistic hazard in terms of macroseismic intensity, peak ground acceleration, peak ground velocity, and pseudovelocity uniform response spectra. The local catalogue points out level VII of the Mercalli–Cancani–Sieberg scale (MCS) as the maximum intensity historically observed in Florence. The probabilistic approach leads to the consideration of intensity VIII MCS as the maximum credible for the city. The probabilistic analysis in terms of ground motion was performed using attenuation relations estimated for alluvium sites, since the geology of Florence area is represented by fluvial and lacustrine deposits of various thickness. Peak ground acceleration values with 90% non exceedence probability in 50 and 500 years are respectively 145 and 219 cm/s*s for a shallow alluvium site, and 95 and 157 cm/s*s for a deep alluvium site; the corresponding peak ground velocity values for sites located on alluvium are 6.41 and 11.76 cm/s. Uniform response spectra are provided for shallow and deep alluvium sites, according to frequency-dependent attenuation relations estimated from strong Italian earthquakes.

A procedure for deformation-controlled, or displacement-based, seismic design of multi-storey RC buildings is proposed, implemented and applied for the full design of a four-storey RC structure. It is integrated into the overall structural design, along with the design for the non-seismic actions and consists of a ULS verification against the conventional strain limits for a frequent "serviceability" earthquake and of proportioning the compression reinforcement and the transverse reinforcement of critical regions of members to meet the member peak inelastic chord rotation demands under the "life-safety" seismic action. Quantitative rules and expressions are proposed for the estimation of (a) mean and upper-characteristic peak inelastic chord rotation demands, through appropriate linear-elastic analyses, and (b) mean and lower-characteristic values of member ultimate chord rotations, in terms of member geometric and material data.

The present paper investigates the seismic energy demand in steel moment-resisting frames. The frames, with 3, 6 and 10 storeys, and 4 and 8 spans, are designed according to current seismic code provisions. The energy response (energy quantities and their distributions) in the frames subjected to an ensemble of six earthquake ground motions recorded on different soil conditions, is investigated by nonlinear time history analysis. The study concludes that (1) the results of energy response can be developed into a rational method of seismic evaluation and design for steel moment-resisting frames; (2) the energy concept based on the single-degree-of-freedom has limitations when extended to the realistic structural system for design purposes; and (3) it is necessary to develop the energy-based approach for seismic evaluation and design based on the seismic response of a realistic multi-degree-of-freedom structural system.

A rigorous boundary element method algorithm incorporating higher order elements and infinite boundary elements is used to analyse high-frequency response of embedded square foundations. Coupled horizontal-rocking impedance functions for dimensionless frequency factors up to ten are presented. The behaviour of high frequency damping of nearly incompressible soils validates the use of "truncated" P-wave velocity in the simple radiation damping model. Further more, the paper shows that the simple model is an excellent approximation for both surface and embedded foundations.