Journal of Earthquake Engineering

We use the record of earthquakes in central Greece since 1694 to estimate the seismically-released strain in that region over the last 300 years. The highest strain rate is seen in the Gulf of Corinth, an extensional graben which is the most prominent active geological structure. Over the 300-year period, the earthquakes account for an average extension rate of about 11 mm/yr between the Peloponnese and the island of Evvia, of which about 10 mm/yr occurs in the Gulf of Corinth. The earthquakes occurring in shorter time periods, perhaps as little as 100 years, account for extensional velocities similar to the 300 year average, though the 20th Century has been relatively quiescent. We are not confident that the historical record can be used to assess seismic strain release in areas smaller than the Gulf of Corinth as a whole. The similarity between the average rate of seismic strain release over 300 years and the short-term strain rates measured geodetically suggests that the bulk of the tectonic strain in this region is released by seismic slip on faults, and that aseismic creep is relatively unimportant. An apparent deficit in seismic strain release over a short period (as is observed for the 20th Century) is thus likely to be remedied by future earthquakes.

The effects of masonry infills on the global seismic response of reinforced concrete structures is studied through numerical analyses. Response spectra of elastic SDOF frames with nonlinear infills show that, despite their apparent stiffening effect on the system, infills reduce spectral displacements and forces mainly through their high damping in the first large post-cracking excursion. Parametric analyses on a large variety of multi-storey infilled reinforced concrete structures show that, due to the hysteretic energy dissipation in the infills, if the infilling is uniform in all storeys, drifts and structural damage are dramatically reduced, without an increase in the seismic force demands. Soft-storey effects due to the absence of infills in the bottom storey are not so important for seismic motions at the design intensity, but may be very large at higher motion intensities, if the ultimate strength of the infills amounts to a large percentage of the building weight. The Eurocode 8 provisions for designing the weak storey elements against the effects of infill irregularity are found to be quite effective, in general, for the columns, but unnecessary and often counterproductive for the beams.

The Hyogo-ken Nanbu Earthquake of 17 January 1995, caused destructive damage to highway bridges. Obviously, this was the first experience of such destructive damage since the Great Kanto Earthquake of 1923. Various tentative measures were taken for seismic design of repair and reconstruction of highway bridges which were damaged due to the earthquake. This paper summarises the damage feature of highway bridges and a series of actions taken for seismic design and seismic strengthening of highway bridges about half a year following the earthquake.

It is accepted that failure criteria for earthquake-resistant structures should be based on energy dissipation as well as on maximum ductility. Even though rational procedures to include low-cycle fatigue in the definition of the design spectra have been derived, major difficulties arise in the definition of the cyclic damageability of the structure. The work conducted so far was mainly based on cyclic tests conducted on simple structural elements, therefore, the extension to the complete structure is not an easy task. A final cyclic test was conducted at the ELSA reaction wall facility on a four-storey full-scale reinforced concrete frame designed according to Eurocode 8, at the end of a series of pseudodynamic tests. The results allow the performance during the pseudodynamic tests to be assessed and the cyclic damageability of a complete structure to be investigated. The effects of low-cycle fatigue on a high-ductility structure turned out to be more important than expected.

The earthquake response of shallow foundations is studied by a simple method that incorporates nonlinear behaviour at the soil-foundation interface and, unlike other simplified approaches, directly takes into account the coupling between the soil-foundation system and the superstructure. The proposed model consists of a four degrees-of-freedom (dof) oscillator, namely one dof for the superstructure and three for the foundation, and introduces nonlinear effects in the calculation of soil reactions through a failure criterion and plastic flow-rule calibrated through previous experimental work. Comparing the results of an application to granular soils with those of more sophisticated finite element analyses, a satisfactory agreement is found, suggesting that the main features of this complicated nonlinear problem can be captured without resorting to an accurate description of the soil behaviour.

In 1995, a swarm of earthquakes affected the city of Dinar, Turkey, which is located in Southwest Anatolia and has a population of 35 000. The mainshock having a local magnitude of 5.9 occurred on 1 October 1995. It was preceded by foreshocks in the previous four days, the largest one with a magnitude of 4.7. These foreshocks initiated structural damage in many buildings, which was then severely aggravated by the mainshock and a strong aftershock two hours later, with a magnitude of 5.0. Numerous aftershocks were recorded throughout the following three months. Strong ground motions were recorded within the city. The mainshock produced peak horizontal accelerations of 0.28 g and 0.29 g. The Dinar earthquake caused a death toll of 92 and more than 200 injuries. The economic losses due to structural damage alone are estimated at 250 million USD.