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Month: July 2010
Simple considerations of liquefaction due to earthquakes and flow failures of slopes in sandy soil
This paper summarizes briefly the existing methods for the analysis and presents simple considerations of liquefaction potential due to earthquakes and flow failures of slopes made of sandy soil for eight case histories in order to indicate the accuracy and usefulness of the simple considerations in routine engineering practice. Simple consideration of liquefaction potential of slopes in sandy soil during earthquakes is based on calculation of factor of safety of slope stability before liquefaction using pseudo-static limit equilibrium method, the shear to axial stress ratio defined using the equivalent sliding block method and the empirical charts used for assessment of liquefaction potential of level ground. Simple consideration of flow failure of sandy slopes is based on Bernoulli’s equation for conservation of energy along a flow line of incompressible fluid.
Base Isolated Building with Hybrid Base Isolation System (HDRB & FS in parallel): Linear vs. Nonlinear Dynamic Analysis
In this work, the base isolation system for a multi-storey reinforced concrete building, highly irregular in plan, has been considered. The hybrid base isolation system consists in High Damping Rubber Bearings (HDRB) in parallel with Friction Sliders (FS) with low coefficient of friction at the interface steel-PTFE. In particular the HDN.E 500 and AlgaPot PNm devices are adopted. The seismic analysis has been performed with all possible linear and nonlinear dynamic analysis according to Eu- ropean seismic code (EC8) and according to the new Italian seismic code (NTC 2008). The results of the seismic analysis have been compared closely, in terms of stresses on the main elements of the superstructure (bending mo- ment and shear force for the beams; biaxial bending moment, the axial and shear force for columns) and in terms of deformation of the superstructure (interstorey drift). In this work, has been evaluated the influence of the accidental eccentricity in the non linear dynamic analysis in order to account for uncertainties in the location of masses and in the spatial variation of the seismic motion. Con- sidering the accidental eccentricity in a nonlinear dynamic analysis, the number of tests to be performed increases substantially, so it is important to understand how the accidental eccentricity influences the seismic response of base-isolated structure.
For this paper is available an extended abstract after the text in Italian
Out-of-Plane Seismic Response of Masonry Façades Some Comparisons Among Full Dynamic and Pushover Analysis
Within the framework of the seismic risk assessment of monumental masonry buildings, we focus on the analysis of out–of–plane mechanisms which actually represent the most recurrent collapse mode for the façade of churches or basilicas. A full non-linear dynamic analysis is performed by adopting a rigid body and spring model (RBSM), where damage is entirely ascribed to the out-of-plane flexural behaviour. A phenomenological description of the cyclic response of the masonry material is provided in the definition of the constitutive prescriptions, including plastic energy dissipation and mechanical damage. Then, a comparison is made with a non-linear static pushover analysis, which is performed by means of the same RBSM under quasi-static loading, incrementally applied. The generalized force–displacement curve and the ultimate limit displacement capacity are evaluated, comparing them with the seismic displacement demand. As a case study, the church of Rosario in Guastalla was chosen, that was damaged by the Emilia Romagna Earthquake in 1987. A number of analyses have been performed, by adopting artificially generated accelerograms with different destroying potential, in order to investigate the correlation between the damage indicators obtained with the two procedures. The two methodologies showed a good agreement in the evaluation of the seismic response for low-medium seismic demands, even if NSPs tends to overestimate the damage, especially for high seismic levels.
For this paper is available an extended abstract after the text in Italian
Seismic Demand Analysis of Inelastic SDOF Systems Designed According to the NTC 2008 for L’Aquila Earthquake
he study investigates on the inelastic response of equivalent Simple Degree Of Freedom systems (SDOF) to some L’Aquila earthquake accelerograms recorded in the epicentral area. According to recent statistical analysis, L’Aquila earthquake is considered as a seismic event having a return period of about 475 years. The aim of the paper is to give a first interpretation to the high damage levels (IX-X MCS) due to the earthquake, in spite of its moderate magnitudo (ML = 5.8) and the correct historical seismic classification of the stroked area. The study thus analyzes the inelastic seismic demand of a SDOF, designed according to the NTC08, to four near-fault accelerograms recorded during the L’Aquila earthquake main shock, by varying SDOF capacity in terms of strength, ductility and viscous damping, in order to assess the performance targets imposed by the same NTC08. Two well- known damage indices have been used to estimate seismic effects on built environment: Park & Ang and low-cycle fatigue indices. The results highlight the high seismic inelastic demand, well beyond the limit specified in NTC08, both for the design of new buildings and for seismic upgrading of existing ones. This clearly shows the need for a revision of the actual seismic hazard map taking into account the near-fault and site amplification effects, which are not considered within the seismic hazard methods adopted by the NTC08.
For this paper is available an extended abstract after the text in Italian
GPS Measurements in Central-Northern Italy for Deterministic Estimate of Seismic Hazard
The recognition of the Italian seismic zones most prone to next strong earthquakes could make eco- nomically feasible a gradual restoration of the building heritage in our country. Recent advancements of research suggest that achieving such information is not anymore impossible. The proposed approach is based on the study of the strain perturbation triggered by strong earthquakes. The hypothesis that such phenomenon can produce sig- nificant increase of earthquake probability in seismic zones undergoing particular conditions is suggested by the peculiar distribution of major historical earthquakes in some periAdriatic zones and by the quantification of post seismic visco-elastic relaxation in that area. The possibility of recognizing the propagation of the above phenomenon and its possible implications on earthquake probability in some zones can considerably be strengthened by the use of geodetic measurements. In this work, we describe the information that has been obtained by the analysis of the geodetic data acquired by a fairly dense network of 202 permanent GPS stations in Central and Northern Italy.
For this paper is available an extended abstract after the text in Italian.