1,720,964 research outputs found
Soft Barriers for the Mitigation of Seismic Risk
No full textThis paper gives an insight on the static and dynamic performance of soft buried barriers made of a mixture of soil and a Super Absorbing Polymer (SAP) to be used for the mitigation of seismic risk. Laboratory tests were carried out on sand-SAP mixtures at different relative percentages. The results have been interpreted with reference to the peculiar properties of the two materials (sand and SAP) at the grain scale. The results of the numerical analyses indicate that the higher the SAP content, the higher the isolating effectiveness of the barrier but the worse the overall static behaviour. A balance between the two opposite needs must be found for the most effective desig
Centrifuge modelling of the seismic performance of soft buried barriers
Full text linkThe paper presents the results of an experimental work carried out in a geotechnical centrifuge at the Schofield Centre of Cambridge University. Two reduced scale models of soft barriers in a sand layer underwent a series of ground shaking. In the first model a thin horizontal layer made of latex balloons filled with a cross-linked gel was created at about mid-height of the sand layer. In the second, the same balloons were deployed to form a V-shaped barrier aimed at isolating a relatively shallow volume of sand. The aim of the study was to get experimental evidence of the capability of such soft barriers to isolate a volume of soil thus reducing amplification of ground motion during severe seismic events. The experimental results were compared with FE numerical analyses of the same models, carried out also in free field to have a benchmark condition. By validating the FE modelling via the comparison with the experimental results, a robust model has been built, aimed at being used for carrying out a wider parametric numerical testing. The experimental results confirm the effectiveness of such soft barriers to reduce amplification in the isolated volumes during seismic events
The Effect of a Grouted Isolating Barrier on the Seismic Performance of a Reinforced Concrete Structure
No full textPassive structural systems installed at the foundation level of existing buildings are a common solution to protect them against earthquakes. However, installation procedures are expensive and not always feasible, as for instance in the case of valuable buildings. In this paper, an alternative and innovative solution for the seismic isolation of existing buildings is presented: the idea is to create a barrier buried in the ground, made of grouted soil, able to properly filter the seismic input. This can be obtained by using soft grouts, having a dynamic impedance much lower than that of the natural soil. Previous papers published by some of the authors have shown that the soft barrier can be effective, tending to filter the high frequency components of the amplitude spectrum without modifying in a significant way the low frequency ones. This implies that ground treatment has to be tuned on the characteristics of the structure to be protected, above all its natural frequencies. In this paper, the case of a simple four-story building with a reinforced concrete structure and a shallow slab foundation resting on a sandy soil is considered. Analyses are carried out with the commercial codes PLAXIS 2D and SAP2000, considering a fixed base, the foundation on the soil and finally the existence of a soft barrier. It is shown that the natural frequencies of the structure are largely influenced by the characteristics of the subsoil. Once the soft barrier is created in the soil, a sharp decrease of the first natural frequency of the structure is obtained, similarly to the effect of traditional isolators. In the paper, dynamic analyses with different input motions are considered. It is confirmed that the soft barrier, whose dynamic impedance was assigned considering some experimental results obtained by the authors and previously published, is able to filter higher frequencies, while it has a minimum or even nil effect in the case of low frequency input signals
Field trials on soft grouting barriers to mitigate vibrations effects.
No full textThe use of soft buried barriers to mitigate the effects of vibrations has been deeply analysed in literature, showing that their effectiveness depends on dynamic impedance ratio and on the barriers’ geometry. However, most times the problem of the physical and mechanical properties to be given to the barrier is by-passed. This paper proposes to deal with barriers made of an innovative material, a special kind of Super Absorbing Polymer (SAP), easy and cheap to find and environmentally friendly. In particular, a field trial test has been carried out, in which an inverted pyramid barrier and a linear barrier have been created with a 100% SAP filling. The site was fully instrumented and carefully investigated, and vibration tests were carried out. It was shown that the barriers were able to largely attenuate the vibrations, thanks to their mechanical and physical properties
Numerical Analyses of the Effectiveness of Soft Barriers into the Soil for the Mitigation of Seismic Risk
No full textAn approach to mitigate the seismic risk of existing structures by means of the creation of a continuous thin layer of grouted soil at a convenient depth is presented. A parametric numerical analysis is reported using different constitutive models with reference to two geometrical schemes. It is shown that if the grouted layer has a stiffness significantly lower than that of the surrounding soil, it may be effective in reducing the seismic demand. In the parametric analyses, the positive role of yielding is also observed, which indicates that the barrier is more effective with larger input amplitude
PARAMETRIC STUDY TO EVALUATE THE PERFORMANCE OF HORIZONTAL DRAINS AS MITIGATION TECHNIQUE AGAINST SOIL LIQUEFACTION.
No full textIn the framework of the LIQUEFACT project a series of centrifuge tests were conducted at ISMGEO (Italy) to verify the effectiveness of three mitigation techniques against soil liquefaction. This paper is focused on the study of horizontal drains as mitigation measure against liquefaction. The centrifuge layout with horizontal drains was numerically modelled and the change of boundary conditions reproduced by the FE code Plaxis 2D. Additionally, slightly different layouts from those tested in the centrifuge were also modelled to expand the scope of the experimental work. Horizontal drains were installed in the model, to analyse their effectiveness in reducing the pore pressure build up as a function of their spacing. The soil was characterized by an advanced coupled soils constitutive model implemented in the Plaxis code: PM4sand. The input parameters for the model are evaluated on the basis of both laboratory element tests and centrifuge tests
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
