The dependence of response spectrum on the tectonic ambient shear stress field

Introduction The acceleration response spectrum and peak ground acceleration are the necessary and im-portant parameters in earthquake-resistant design at present. They are still active research field. With the increase of digital high accurate strong motion observation data, especially the earth-quakes of Loma Prieta (M=7.0) in 1989; Landers (M=7.3) in 1992; Big Bear (M=6.4) in 1994 and Northridge (M=6.7) in 1994 in USA; Kozani (M=6.6) earthquake and afteshocks in 1995 in Greece; Dinar…     

Ground deformation of Nisyros Volcano (Greece) for the period 1995–2002: Results from DInSAR and DGPS observations

Differential GPS (DGPS) and Differential Interferometric Synthetic Aperture Radar (DInSAR) analyses were applied to the Kos-Yali-Nisyros Volcanic Field (SE Hellenic Volcanic Arc) to quantify the ground deformation of Nisyros Volcano. After intense seismic activity in 1996, a GPS network was installed in June 1997 and re-occupied annually up to 2002. A general uplift ranging from 14 to 140 mm was determined at all stations of the network. The corresponding horizontal displacements ranged from 13 to 53 mm. The displacement vectors indicate that the island is undergoing extension towards the East, West and South. A two-source “Mogi” model combined with assumed motion along the Mandraki Fault was constructed to fit the observed deformation. The best-fit model assumes sources at a depth of 5500 m NW of the centre of the island and at 6500 m offshore ESE of Yali Island. DInSAR analysis using four pairs of images taken between May 1995 and September 2000 suggests that deformation was occurring during 1995 before the start of the seismic crisis. An amplitude of at least 56 mm along the slant range appeared for the period 1996 through 1999. This deformation is consistent with the two-source model invoked in DGPS modelling. Surface evidence of ground deformation is expressed in the contemporaneous reactivation of the Mandraki Fault. In addition, a 600 m long N-S trending irregular rupture in the caldera floor was formed between 2001 and 2002. This rupture is interpreted as the release of surface stress in the consolidated epiclastic and hydrothermal sediments of the caldera floor.     

Pseudo‐dynamic seismic response of reinforced concrete frames infilled with non‐structural brick masonry

This paper presents pseudo‐dynamic test results on the in‐plane seismic behaviour of infilled frames. Thirteen single‐storey, single‐bay, half‐size‐scale, reinforced concrete‐frame specimens, most of which infilled with non‐structural masonry made of perforated bricks and cement mortar are tested. The infills are in contact with frames, without any connector; openings are not covered. The frames are different in their strength and details, reinforcement grade, and aspect ratio. Seismic input is the 1976 Tolmezzo (Friuli, Italy) ground acceleration, to which specimens are subjected two times: virgin and damaged by the previous test. The global seismic response of initially virgin infilled specimens considerably differs from that of bare specimens. This follows a dramatic change of properties: compared to a bare frame, the initial stiffness increases by one order of magnitude, and the peak strength more than doubles. The peak drift lessens; however, the displacement ductility demand does not. The energy demand is greater. Nevertheless, the influence of infill decreases as damage proceeds. Displacement time histories of damaged specimens are quite similar. At the local level, infill causes asymmetry and concentration of the frame deformation. Copyright © 2005 John Wiley & Sons, Ltd.     

Seismic response analysis of multidrum classical columns

This paper presents a numerical investigation on the seismic response of multidrum classical columns. The motivation for this study originates from the need to understand: (a) the level of ground shaking that classical multidrum columns can survive, and (b) the possible advantages or disadvantages of retrofitting multidrum columns with metallic shear links that replace the wooden poles that were installed in ancient times. The numerical study presented in this paper is conducted with the commercially available software Working Model 2D?, which can capture with fidelity the sliding, rocking, and slide‐rocking response of rigid‐body assemblies. This paper validates the software Working Model by comparing selected computed responses with scarce analytical solutions and the results from in‐house numerical codes initially developed at the University of California, Berkeley, to study the seismic response of electrical transformers and heavy laboratory equipment. The study reveals that relative sliding between drums happens even when the g‐value of the ground acceleration is less than the coefficient of friction, µ, of the sliding interfaces and concludes that: (a) typical multidrum classical columns can survive the ground shaking from strong ground motions recorded near the causative faults of earthquakes with magnitudes M_w=6.0–7.4; (b) in most cases multidrum classical columns free to dislocate at the drum interfaces exhibit more controlled seismic response than the monolithic columns with same size and slenderness; (c) the shear strength of the wooden poles has a marginal effect on the sliding response of the drums; and (d) stiff metallic shear links in‐between column drums may have an undesirable role on the seismic stability of classical columns and should be avoided. Copyright © 2005 John Wiley & Sons, Ltd.     

Evolutionary aseismic design and retrofit of structures with passive energy dissipation

A new computational framework is developed for the design and retrofit of building structures by considering aseismic design as a complex adaptive process. For the initial phase of the development within this framework, genetic algorithms are employed for the discrete optimization of passively damped structural systems. The passive elements may include metallic plate dampers, viscous fluid dampers and viscoelastic solid dampers. The primary objective is to determine robust designs, including both the non‐linearity of the structural system and the uncertainty of the seismic environment. Within the present paper, this computational design approach is applied to a series of model problems, involving sizing and placement of passive dampers for energy dissipation. In order to facilitate our investigations and provide a baseline for further study, we introduce several simplifications for these initial examples. In particular, we employ deterministic lumped parameter structural models, memoryless fitness function definitions and hypothetical seismic environments. Despite these restrictions, some interesting results are obtained from the simulations and we are able to gain an understanding of the potential for the proposed evolutionary aseismic design methodology. Copyright © 2005 John Wiley & Sons, Ltd.     

Growth response of the saltbush Atriplex nummularia L. to inoculation with the arbuscular mycorrhizal fungus Glomus intraradices

Plantlets of Atriplex nummularia were inoculated with the arbuscular mycorrhizal fungi Glomus intraradices in a pot experiment. Plants were grown in a low P soil. Highly significant growth response of a Chenopodiaceae was recorded for the first time. Mycorrhizal colonization of roots was well developed, internal hyphae and vesicles were observed, but not arbuscules. These observations suggest that arbuscules are not necessary to obtain significant growth stimulation from mycorrhizal inoculation. Atriplex nummularia is already used as forage crops, its high mycorrhizal dependency offers possibilities to develop this production and revegetation strategies.     

Influence of transducer-ground coupling on vibration measurements

Various methods of transducer mounting provide varying degrees of coupling between the transducer and the measurement surface. The influence of four of these methods on vibration measurements was studied. For this purpose, the first transducer was placed freely on a horizontal surface, the second one was 'sandbagged', the third one was 'spiked' and the fourth one was completely buried in soil. These transducers were mounted side by side and ground vibrations were monitored for 14 blasts at an opencast coal mine.

Ground vibrations in terms of peak particle velocity, peak vector sum and frequency with different mounting methods were analysed. Assuming the data of the buried transducer as the most acceptable one, relative values of other transducers were determined and plotted. For the given tolerance for instrumental and human errors, anomalous readings were found in some cases. The waveforms of the buried transducer were then compared with those of others. Clear distortion in the waveforms or a very low correlation coefficient between two waveforms was suspected poor coupling.

The results indicate that decoupling is most likely with the surface transducer. However, the sandbagged and spiked transducers are also prone to decoupling. Decoupling can result in higher or lower ground vibration. Therefore, burial should be the preferred method for mounting of transducers in soil.     

Modelling surface runoff to evaluate the effects of wildfires in multiple semi‐arid,shrubland‐dominated catchments

Wildfires change the infiltration properties of soil, reduce the amount of interception and result in increased runoff. A wildfire at Northeast Attica, Central Greece, in August 2009, destroyed approximately one third of a study area consisting of a mixture of shrublands, pastures and pines. The present study simultaneously models multiple semi‐arid, shrubland‐dominated Mediterranean catchments and assesses the hydrological response (mean annual and monthly runoff and runoff coefficients) during the first few years following wildfires. A physically based, hydrological model (MIKE SHE) was chosen. Calibration and validation results of mean monthly discharge presented very good agreement with the observed data for the pre‐wildfire and post‐wildfire period for two subcatchments (Nash–Sutcliffe Efficiency coefficient of 79.7%). The model was then used to assess the pre‐wildfire and post‐wildfire runoff responses for each of seven catchments in the study area. Mean annual surface runoff increased for the first year and after the second year following the wildfires increased by 112% and 166%, respectively. These values are within the range observed in similar cases of monitored sites. This modelling approach may provide a way of prioritizing catchment selection with respect to post‐fire remediation activities. Additionally, this modelling assessment methodology would be valuable to other semi‐arid areas because it provides an important means for comprehensively assessing post‐wildfire response over large regions and therefore attempts to address some of the scaled issues in the specific literature field of research. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of forest roads on the hydrological response of a small‐scale mountain watershed in Greece

The effects of land use changes on the ecology and hydrology of natural watersheds have long been debated. However, less attention has been given to the hydrological effects of forest roads. Although less studied, several researchers have claimed that streamflow changes related to forest roads can cause a persistent and pervasive effect on hillslope hydrology and the functioning of the channel system. The main potential direct effects of forest roads on natural watersheds hydrologic response are runoff production on roads surfaces due to reduced infiltration rates, interruption of subsurface flow by road cutslopes and rapid transfer of the produced runoff to the stream network through roadside ditches. The aforementioned effects may significantly modify the total volume and timing of the hillslope flow to the stream network. This study uses detailed field data, spatial data, hydro‐meteorological records, as well as numerical simulation to investigate the effects of forest roads on the hydrological response of a small‐scale mountain experimental watershed, which is situated in the east side of Penteli Mountain, Attica, Greece. The results of this study highlight the possible effects of forest roads on the watersheds hydrological response that may significantly influence direct runoff depths and peak flow rates. It is demonstrated that these effects can be very important in permeable watersheds and that more emphasis should be given on the impact of roads on the watersheds hydrological response. Copyright © 2014 John Wiley & Sons, Ltd.