IRIS Pol. Torinohttps://iris.polito.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Mon, 21 Jun 2021 01:21:30 GMT2021-06-21T01:21:30Z101271Effetcs of class B site on the seismic reliability of base-isolated steel systemshttp://hdl.handle.net/11583/2694046Titolo: Effetcs of class B site on the seismic reliability of base-isolated steel systems
Abstract: Seismic reliability of steel structures isolated using the frictional pendulum
system bearings and subjected to artificial earthquake ground motions is studied herein. The
superstructure is idealised as a linear shear-type flexible building as well as the FPS devices
are described by adopting a widespread model which considers the variation of the friction
coefficient with the velocity. The uncertainty affecting both the seismic inputs, modelled as
non stationary random processes within the power spectral density method, and the friction
coefficient at large velocity is considered through appropriate probability density functions.
Incremental dynamic analyses are developed in order to evaluate the fragility curves related
to both superstructure and isolation level. Finally, considering the seismic hazard curve
related to a site near Sant’Angelo dei Lombardi (Italy), the seismic reliability of the overall
steel system is evaluated.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11583/26940462016-01-01T00:00:00ZSeismic performance assessment of isolated bridges for different limit stateshttp://hdl.handle.net/11583/2693790Titolo: Seismic performance assessment of isolated bridges for different limit states
Abstract: This study aims to evaluate the seismic performances
of bridges isolated by the friction pendulum system
(FPS) bearings considering the seismic hazard of
Sant’Angelo dei Lombardi site (Italy), to provide useful
and preliminary recommendations in terms of health
assessment for design or retrofit of new or existing bridges,
respectively. Single- and two-degree-of-freedom models
are considered to describe the isolated bridge behavior
taking into account an infinitely rigid deck and the isolated
bridge behavior having an infinitely rigid deck with the
elastic pier, respectively. In both models, a velocity-dependent
rule for the FPS isolators is assumed. Seismic
excitations are properly modeled as non-stationary
stochastic processes having different intensities corresponding
to different limit states and with frequency contents
related to the medium soil condition, representative of
the soil type in Sant’Angelo dei Lombardi site (Italy). The
statistics of deck and pier responses of the isolated bridge
are evaluated for different system parameters such as mass
ratio, isolation period, pier period and friction coefficient of
the FPS considering both Life Safety and Collapse
Prevention limit states according to Italian seismic codes.
The results, deriving mainly from the two-degree-of-freedom
(2dof) model analyses, show that particular values of
the friction coefficient allow to minimize the response of
the pier depending on the different system properties and
the different limit states. In particular, the optimum friction
coefficient of the FPS ranges from 0.01 to 0.04 and from
0.01 to 0.05 for Life Safety and for Collapse Prevention
limit state, respectively, depending on the structural
properties.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/11583/26937902018-01-01T00:00:00ZProbabilistic assessment of groundwater leakage in diaphragm wall joints for deep excavationshttp://hdl.handle.net/11583/2693789Titolo: Probabilistic assessment of groundwater leakage in diaphragm wall joints for deep excavations
Abstract: A probabilistic method is proposed for conducting groundwater-related hazard assessments that are useful for
the risk management of deep excavations in saturated soils in urban areas. The design of deep excavations,
construction procedures and execution methods aimed at realizing underground infrastructure are characterized
by major uncertainties related to soil properties, construction imperfections and hydrogeological site conditions.
During the construction stages, geometrical imperfections and ineffective technologies to control wall seepage
can strongly affect the level of risk to the adjacent built environment, leading to severe damages. The aim of this
study is to provide an assessment of the leakage probability in reinforced concrete (RC) retaining walls. We
model the main geo-structural factors that influence trench stability and the key geometric and technological
parameters that affect construction imperfections as relevant random variables. Moreover, through Bayesian
updating, useful recommendations are provided regarding the effectiveness and influence of the monitoring
phase on reducing the failure probability.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/11583/26937892018-01-01T00:00:00ZInfluence of ground motion characteristics on the optimal single concave sliding bearing properties for base-isolated structureshttp://hdl.handle.net/11583/2693792Titolo: Influence of ground motion characteristics on the optimal single concave sliding bearing properties for base-isolated structures
Abstract: This study examines the influence of ground motion characteristics on the optimal friction properties of single
concave sliding bearings employed for the seismic isolation of structural systems. The evaluation of the optimal
properties is carried out by considering a non-dimensional formulation which employs the peak ground acceleration
(PGA) and the peak ground acceleration-to-velocity (PGA/PGV) ratio as ground motion parameters. A
two-degree-of-freedom (2dof) model is employed to describe the isolated system and two different families of
records representative respectively of near fault and far field seismic inputs are considered. Following the
nondimensionalization of the equation of motion for the proposed ground motion parameters, it is shown that
the non-dimensional responses obtained for the two types of seismic inputs are similar. This result confirms that
PGA/PGV is a good indicator of the frequency content and of other characteristics of ground motion records,
helping to reduce the scatter in the response. Regression expressions are also obtained for the optimal values of
the friction coefficient that minimizes the superstructure displacements relative to the base as a function of the
abovementioned ground motion parameter and of the dimensionless system parameters. These expressions can
be used for the preliminary estimation of the optimal properties of isolation bearings with a single concave
sliding surface or double concave sliding surfaces with equal friction coefficient.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/11583/26937922018-01-01T00:00:00ZFem simulations of a new hysteretic damper: The dissipative columnhttp://hdl.handle.net/11583/2694050Titolo: Fem simulations of a new hysteretic damper: The dissipative column
Abstract: A new replaceable hysteretic damper to better control seismic building damage,
consisting of two adjacent steel vertical elements connected to each other with continuous Xshaped
mild/low strength steel shear links, is investigated in this study. New Dampers, called
Dissipative Columns (DC), provide additional stiffness and damping to a lateral system by
using a basic and minimally invasive construction element: the column. The Dissipative
Column has been conceived or as a device installed within a frame either external damper to
provide macro-dissipation. In fact, considering different configurations, a parametric analysis,
based on FEM simulations, is developed in order to evaluate the effect of the main geometrical
and structural parameters as well as provide the design capacity curves of this new damper.
In particular, non-linear pushover and cyclic analyses have been carried out in ABAQUS in
order to characterize the local and global behaviour of the device also considering different
steel grades.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11583/26940502016-01-01T00:00:00ZFramework for definition of design formulations from empirical and semi-empirical resistance modelshttp://hdl.handle.net/11583/2709680Titolo: Framework for definition of design formulations from empirical and semi-empirical resistance models
Abstract: The study proposes a framework based on the Monte Carlo method for the probabilistic
calibration of empirical and semi-empirical resisting models. The resisting
models adopted in engineering practice may be based both on physical laws, such
as equilibrium of forces, and on semi-empirical or empirical formulations. Precisely,
empirical or semi-empirical resisting models are calibrated in order to fit
experimental data and the direct application of partial safety factors to material
properties does not allow a proper estimation of the structural reliability. For this
reason, a probabilistic definition of design expressions from empirical or semiempirical
resisting models should be preferred to define a final formulation in
agreement with a specific level of reliability. After a detailed description of the
framework, its application to the probabilistic calibration of the semi-empirical
model proposed by fib Model Code 2010 for the estimation of tensile strength of
laps and anchorages in reinforced concrete structures is proposed.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/11583/27096802018-01-01T00:00:00ZResponse spectrum analysis of frame structures: reliability-based comparison between complete quadratic combination and damping-adjusted combinationhttp://hdl.handle.net/11583/2731385Titolo: Response spectrum analysis of frame structures: reliability-based comparison between complete quadratic combination and damping-adjusted combination
Abstract: In the framework of seismic design of structures, response spectrum analysis (RSA) is the
most commonly used approach in practice. The most popular combination rule is the complete
quadratic combination (CQC) which is also prescribed by the most of seismic design
codes and is based on the assumptions that the seismic acceleration is a white noise process
and the peak factor ratios associated to the total and modal responses are unitary. Recently,
the damping adjusted combination (DAC) rule has been developed for base-isolated structures
to overcome the aforementioned simplified assumptions. Although it has been proved
that the simplifications about peak factors lead to noticeable errors in the case of baseisolated
structures, the accuracy gain of DAC with respect to CQC in the case of fixed-base
structures is still unknown. Therefore, the paper presents an in-depth study on the RSA of
three-dimensional frame structures, aimed to evaluate the accuracy of the above methods.
Two reference classes of frame structures having different degree of complexity are considered.
Average interstorey drift and floor torsion responses, obtained from a set of Time
History Analyses are compared with those of the modal combination rules. Lognormal
joint probability density functions of the predictive errors from CQC and DAC are finally
evaluated for a reliability assessment of the two combination rules under bidirectional seismic
excitations.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/11583/27313852019-01-01T00:00:00ZRobustness analysis of 3D base-isolated systemshttp://hdl.handle.net/11583/2731389Titolo: Robustness analysis of 3D base-isolated systems
Abstract: The aim of the study consists of evaluating the seismic robustness of a 3D r.c. structure equipped with single-concave friction pendulum system (FPS) devices in reliability terms considering differ-ent models related to different malfunctions of the seismic isolators. The elastic response pseudo-acceleration corresponding to the isolated period is assumed as the relevant random variable and, by means of the Latin Hypercube Sampling technique, the input data have been defined in order to perform 3D inelastic time-history analyses. In this way, bivariate structural performance curves at each level of the r.c. structural system as well as seismic reliability-based design abacuses for the FP devices have been computed and compared in order to evaluate the robustness of the r.c. system considering different models related to the different failure cases analysed. Contextually, the seismic robustness of the abovementioned r.c. structural system has also been ex-amined by considering both a configuration equipped with beams connecting the substructure columns and a configuration without these connecting beams in order to demonstrate their effectiveness in improving the seismic robustness for a malfunction of a seismic device and provide very useful design recommendations for base-isolated structures equipped with FPS.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/11583/27313892019-01-01T00:00:00ZSeismic Reliability of Structural Systems Isolated by FPShttp://hdl.handle.net/11583/2664990Titolo: Seismic Reliability of Structural Systems Isolated by FPS
Abstract: The paper deals with the seismic reliability of structural systems equipped with friction pendulum isolators (FPS). The behavior of these systems is analysed by employing a two-degree-of-freedom model accounting for the superstructure flexibility, whereas the FPS device behaviour is described by adopting a widespread model which considers the variation of the friction coefficient with the velocity. The uncertainty in the seismic inputs is taken into account by considering a set of artificial records, obtained through the power spectral density method, with different characteristics depending on soil dynamic parameters, and scaled to increasing intensity levels. The friction coefficient at large velocity is considered as random variable modeled through a uniform probability density function. Within incremental dynamic analysis, Monte Carlo simulations are developed in order to evaluate the probabilities exceeding different limit states related to both superstructure and isolation level defining the seismic fragility curves through an extensive parametric study carried out for different structural system properties. Finally, considering the seismic hazard curve related to L’Aquila site (Italy), reliability-based abacuses and regression expressions are derived with the aim to design the radius in plan of the friction pendulum devices in function of the structural system properties and reliability level expected.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11583/26649902015-01-01T00:00:00ZLifetime axial-bending capacity of a r.c. bridge pier cross-section subjected to corrosionhttp://hdl.handle.net/11583/2665002Titolo: Lifetime axial-bending capacity of a r.c. bridge pier cross-section subjected to corrosion
Abstract: Reinforced concrete structures in service may be affected by aging, which may include changes in strength and stiffness
assumed in structural design, in particular when the concrete is exposed to an aggressive environment. In this context, this paper
provides a computational probabilistic approach to predict the time-evolution of the mechanical and geometrical properties of a
statically determinate r.c. structural system (i.e. bridge pier) subjected to corrosion-induced deterioration, due to diffusive attack of
chlorides, in order to evaluate its service life. Adopting appropriate degradation models of the material properties, concrete and reinforcing
steel, as well as assuming appropriate probability density functions related to mechanical and deterioration parameters, the
proposed model is based on Monte Carlo simulations in order to evaluate time variant axial force-bending moment resistance domains,
with the aim to estimate the time-variant reliability index. Finally, an application to estimate the expected lifetime of a r.c.
bridge pier is described.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11583/26650022016-01-01T00:00:00Z