1,720,968 research outputs found
Determinazione dello smorzamento mediante misure di tipo sismico in camera di calibrazione su terreni granulari ricostituiti
No full text
ONDA: Computer Code for Nonlinear Seismic Response Analyses of Soil Deposits
No full textThis paper describes a newly developed computer code for performing one-dimensional nonlinear dynamic analysis (ONDA) of soil deposits. The code has been developed by revisiting the 1982 work by Ohsaki with the purpose of simulating the ground response to an earthquake of moderate intensity (i.e., values of peak ground acceleration on stiff soil on the order of 0.15 to 0.25g, which are typical of many sites in Italy). In the Ohsaki model a horizontally stratified soil deposit is idealized as a discrete mechanical system composed of a finite number of lumped masses connected with a series of springs and dashpots. Nonlinearity is modeled by assuming a “backbone” curve that describes the initial monotonic loading of the stress-strain curve, and a “rule” that simulates the unloading-reloading paths and stiffness degradation undergone by soil as seismic excitation progresses. Typically, the backbone curve is obtained from conventional cyclic undrained loading laboratory tests. The rule generally used is the so-called Masing criterion, which assumes that the unload-reload branches of the stress-strain curve have the same shape as the initial loading curve but are affected by a scale factor (n) equal to 2. In this work, the Masing criterion has been modified by assuming a scale factor (n) not necessarily equal to 2. It turns out that a factor n greater than 2 allows the simulation of cyclic hardening, while cyclic softening can be modeled by assuming decreasing values of n even smaller than 2. Pyke proposed in 1979 to use a scale factor (n) lower than 2 to simulate cyclic degradation. According to Pyke, the n parameter is a function of the mobilization factor. The generalization of the Masing criterion allows ONDA to properly simulate the phenomena of soil hardening and soil degradation, giving it the capability to compute the permanent strains developed during a seismic event. The procedure required to evaluate the model parameters is also described in the paper. Note that the laboratory tests examined gave values of n between 2 and 6 for a strain level not greater than 0.3%. In ONDA the numerical solution of the nonlinear equations of motion is obtained using the unconditionally stable Wilson θ algorithm (with θ ≥ 1.37). The new method has been used to predict the seismic response at two sites in Italy. For these case studies, the maximum input acceleration was not greater than 0.3g and the computed shear strains were less than 0.2%. The ONDA results have been compared with those computed with SHAKE, EERA (equivalent-linear analysis), and NERA (nonlinear analysis)
ONDA: Computer Code for Nonlinear Seismic Response Anlyses of Soil Deposits
No full textAbstract: This paper describes a newly developed computer code for performing one-dimensional nonlinear dynamic analysis ONDA
of soil deposits. The code has been developed by revisiting the 1982 work by Ohsaki with the purpose of simulating the ground response
to an earthquake of moderate intensity i.e., values of peak ground acceleration on stiff soil on the order of 0.15 to 0.25g, which are typical
of many sites in Italy. In the Ohsaki model a horizontally stratified soil deposit is idealized as a discrete mechanical system composed of
a finite number of lumped masses connected with a series of springs and dashpots. Nonlinearity is modeled by assuming 1 a “backbone”
curve that describes the initial monotonic loading of the stress-strain curve, and 2 a “rule” that simulates the unloading-reloading paths
and stiffness degradation undergone by soil as seismic excitation progresses. Typically, the backbone curve is obtained from conventional
cyclic undrained loading laboratory tests. The rule generally used is the so-called Masing criterion, which assumes that the unload-reload
branches of the stress-strain curve have the same shape as the initial loading curve but are affected by a scale factor n equal to 2. In this
work, the Masing criterion has been modified by assuming a scale factor n not necessarily equal to 2. It turns out that a factor n greater
than 2 allows the simulation of cyclic hardening, while cyclic softening can be modeled by assuming decreasing values of n even smaller
than 2. Pyke proposed in 1979 to use a scale factor n lower than 2 to simulate cyclic degradation. According to Pyke, the n parameter
is a function of the mobilization factor. The generalization of the Masing criterion allows ONDA to properly simulate the phenomena of
soil hardening and soil degradation, giving it the capability to compute the permanent strains developed during a seismic event. The
procedure required to evaluate the model parameters is also described in the paper. Note that the laboratory tests examined gave values
of n between 2 and 6 for a strain level not greater than 0.3%. In ONDA the numerical solution of the nonlinear equations of motion is
obtained using the unconditionally stable Wilson algorithm with 1.37. The new method has been used to predict the seismic
response at two sites in Italy. For these case studies, the maximum input acceleration was not greater than 0.3g and the computed shear
strains were less than 0.2%. The ONDA results have been compared with those computed with SHAKE, EERA equivalent-linear
analysis, and NERA nonlinear analysis
A Modified Commercial Triaxial Testing System for Small Strain Measurements: Preliminary Results on Pisa Clay
No full textExperimental Laboratory Determination of the Steady State of Sands" Soils and Foundations, Vol. 40, No. 1, pp: 113-122
No full textSome experimental problems encountered when determining Steady-State (SS) or Phase Transformation (PT) envelopes and their projections in the state diagram are studied; 1) accurate assessment of the void ratio (e) at the end of the consolidation process; 2) the effects due to the membrane compliance; 3) effectiveness of lubrication ends and 4) influence of specimen slenderness on the lateral strain uniformity.
The specimen's dimensions after its formation were continuously monitored by measuring axial and radial strains locally. Both conventional undrained triaxial tests and constant volume tests with continuous correction for the membrane penetration effects were performed at constant cell pressure using loose saturated Toyoura sand.
The adopted lubrication system worked effectively up to an axial strain of 4 % for specimens with a height to diameter ratio of H/D=2, while for H/D=1 lateral strains were uniform until the end of the tests ( 25%).
The SS and PT envelope and their projection in the state diagram (SS or PT line) were established based on results from 29 tests. The condition which triggers the softening behaviour, i.e. the so called Critical Stress Ratio (CSR) envelope was also determined. The test results showed the importance of careful control of the test factors mentioned above determining the undrained behaviour of saturated very loose sand under truly constant conditions
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
- …
