Journal of Earthquake Engineering

The duration of strong ground shaking during earthquakes can play an important rôle in the response of foundation materials and structures, particularly when strength or stiffness degradation is encountered. A thorough seismic hazard assessment should therefore include an estimation of the expected duration of strong motion, which first requires criteria to define the part of an accelerogram considered to represent the duration of strong ground motion. Some 30 different definitions of strong motion duration are reviewed and classified into generic groups. Problems that arise with the use of these definitions for duration are highlighted. A new definition of duration is presented using a previously unexplored option which identifies the part of the record where the main energy is contained and constrains this strong shaking phase by absolute criteria. This new definition is shown to give consistently meaningful durations for strong earthquake accelerograms from an engineering viewpoint. The correlations between the new definition of duration and magnitude, soil conditions and distance are explored as a first step towards the development of predictive equations.

For RC frame buildings with heightwise irregularities of the infills, Eurocode 8 (EC8) requires increasing the resistance of beams and columns in the less-infilled storey(s) in proportion to the deficit in infill strength there. For the columns of the less-infilled storey, a less demanding alternative rule is proposed, based on the observation that bending of the columns in the storeys above and below is often opposite to that in the less-infilled storey. It is proposed then to modify the capacity design rule at beam column-joints, in such a way that the capacity of the column of the more-infilled storey is added to that of the beams rather than to the capacity of the column of the less-infilled (or open) storey. A three-storey two-bay infilled RC test frame was designed on the basis of this concept, for pseudodynamic testing at the ELSA reaction wall facility in Ispra (I), in two configurations, each one with absence of infills from a different storey. Pre-test nonlinear dynamic analyses showing satisfactory response of the so-designed frame in comparison to the EC8-rule version, are verified by the test results. Parametric inelastic analyses for different infill-frame relative strengths verify the proposed design rule.

Experimental and analytical investigations were performed to verify an original methodology that was developed for the repair and seismic strengthening of Byzantine churches. This work was part of the long-term research project entitled Study for Seismic Strengthening, Conservation and Restoration of Churches Dating from the Byzantine Period (9th–14th century) in the Republic of Macedonia. The project was realised jointly by the Institute of Earthquake Engineering and Engineering Seismology (IZIIS) — Skopje, the Republic Institute for Protection of Cultural Monuments (RZZSK) — Skopje, and the Getty Conservation Institute (GCI) — Los Angeles, California.

A model of St. Nikita church was constructed to a scale of 1:2.75 and tested on a seismic shaking table simulating the existing and the strengthened state to investigate the linear behaviour, non linear behaviour, and behaviour in the heavily damaged state (close to failure). To investigate the non-linear dynamic response of the structure, an original trilinear model of stiffness degradation and pinching of the hysteretic loop was developed on the basis of the experimental results obtained for the original and the strengthened model as well as from the results of the quasi static testing of wall elements. This model allows successful modelling and description of the behaviour of the church structures in all phases of behaviour: elastic range, non-linear range (occurrence of cracks), sliding range, and the heavily damaged range that resulted in failure.

This work aims to provide frequency-dependent amplification factors according to a site classification system. The criterion adopted for the assignment of site-dependent amplification functions is the average shear wave velocity over the upper 30 m. The data used come from downhole surveys at different sites in Greece. From the total number of the geotechnical boreholes used, four soil classes are delimited, but only two of them are further examined due to lack of adequate data. The use of the amplification functions based on Hellenic data is justified as they result in simulated response spectra which fit reasonably well with those obtained by existing predictive empirical relationships for the Hellenic seismotectonic region.

A series of cyclic triaxial tests on clayey sands was carried out and attempts were made to evaluate the strain dependency of shear modulus and damping. Although the strain dependency of the shear modulus of clayey sands was similar to that of clay in the low strain range, G/G₀ became close to that of clean sand in the high strain range. The damping ratio was less for the clayey sand containing more fines, especially in the medium to large strain range. It was shown that the change in the effective confining stress with loading cycles in the undrained shear test needed to be considered, particularly in the large strain range. The consideration can be made by normalising G with G′₀ instead of using G₀. When an initial shear stress was applied to the specimen, the amount of residual strain, which was induced with cycles, had to be added to the normal strain amplitude in order to determine the shear modulus. If the effects of excess pore pressure and the amount of residual strain were taken into account properly, it was suggested that the shear modulus of clayey sand in irregular loading could be evaluated reasonably well by using the average G/G′₀-γ curve obtained by cyclic loading tests on isotropically-consolidated specimens.