1,721,558 research outputs found
Un modello per l'interazione taglio-flessione in elementi in C.A. soggetti ad azioni sismiche
No full textA fiber beam-column finite element based on Timoshenko beam theory has been recently proposed by the author to model the flexure-shear interaction in reinforced concrete elements of reduced shear slenderness subjected to seismic loading. Shear resistance is obtained by modeling the principal resisting mechanisms; these are linked to the flexural behavior by means of suitable kinematics assumptions. In flexure the element differs from standard fiber beam element since, to account for the contribution to shear resistance due to arch action, fibers, which are normal to the cross-section in standard fiber elements, are here rotated. Materials non-linear behavior is taken into account by means of uniaxial and interfaces constitutive relations available in literature. The element, initially developed to model the cyclic response of the dissipative end zones of R/C bridge piers having low to intermediate shear slenderness, has been further validated in this work by reproducing some cyclic experimental results on a shear wall. The agreement with the experimental results highlights the element ability to capture the behavior of moment-resisting structural elements subjected to high shear loading
Numerical simulation of cyclic tests of R/C shear walls
No full textWithin the framework of better defining the protection level offered by the Eurocode 8 provisions, with respect to the cyclic behaviour of R/C shear walls, accurate and as simple as possible numerical models of the non-linear behaviour of shear walls are necessary to carry out a sufficient amount of parametric analyses. To assess the performance of a recent column fibre finite element some well documented experimental cyclic tests, performed on simple shear walls designed to comply with different ductility requirements, were numerically simulated. The element is based on Timoshenko’s beam theory and accounts for shear-flexure interaction, a feature which might be of some relevance for the problem at hand. Shear resistance is obtained by modelling the principal resisting mechanisms. Shear and flexural behaviour are related to each other by means of suitable kinematics assumptions. This element differs from standard fibre beam elements since the principal direction of the compressive stress (direction of the fibres) is rotated to account for the contribution to shear due to arch action. Results of the experimental-numerical comparison are given in terms of the hysteretic behaviour of the structure. The good agreement with the experimental results suggests that the element is suitable for future modelling of complete structural systems
WECS under mild wave climates
No full textToday, wave energy harvesting is considered to be economical only at oceanic scale, although the hindrance to demonstration are posed by the same harsh environment that is considered so essential. Is it reasonable to investigate the opportunity to install Wave Energy Converters (WECs) in the Mediterranean seas? Will they ever be economical in such conditions? The (many) arguments against and (the few) in favor of this eventuality are discussed, raising the issue of defining appropriate scaling laws for the cost. Some general ideas to enhance the efficiency of WECs under mild wave climates are given by observing the Italian patents. One of the Italian devices, the SeaBreath, is analyzed in greater detail. In conclusion, Italian WECs need to be coupled to other functions, such as breakwaters, to reach economic viability. They could also be associated to wind farms, where it is likely that the incident wave climate is mild: to reduce the wave impact on the piles and increase the persistence of power production
Modeling Shear-Flexure Interaction in Reinforced Concrete Elements Subjected to Cyclic Lateral Loading
No full textThis paper presents a beam-column fiber element able to describe the interaction between the bending moment and the axial and shear forces in reinforced concrete (RC) elements subjected to cyclic loading. In RC elements, shear forces are due to many complex interacting mechanisms, involving a significant part of the volume of the element; in this work, however, these are considered in an independent way and are modeled mainly at a cross section level. This strategy aims to reduce the computational effort in view of the application to seismic problems.
In the proposed enhanced fiber element, stiffness-based, which adopts the Timoshenko beam theory, shear and flexural behavior are linked by means of kinematical assumptions.
Different from standard fiber elements, the cross-sectional fibers take, for the purpose of computing the flexural sectional response, the direction of the compressive principal stress and hence are not parallel to the element longitudinal axis. This peculiar formulation accounts for the contributions to shear strength due to both the arch action and the inclined thrust-line developing in squat elements. In addition, The other important shear resisting mechanism of the so-called Mörsch’s truss is explicitly modeled by considering both a tension and a compression stress field inside the concrete below the neutral axis. These stress fields are modeled by comprising into the Mörsch’s truss analogy both a tension and a compression concrete diagonal. This modeling choice solves the problems related to the choice of the active compressive diagonal in standard Mörsch’s trusses when subjected to cyclic or seismic loading, and allows for adopting only one truss for cyclic loading. The nonlinear behavior of materials is described by means of appropriate constitutive relations for which the critical implementation issues are high-lighted.
The proposed element has been validated by comparison with selected experimental results. The overall performance shows that the element is able to reasonably represent the experimental response in test cases strongly influenced by shear. A limited number of elements is required and an outstanding computational efficiency has been detected
Numercally estimated response of two different designed dual RC systems
No full textDisplacement Based Design methods have become a possible alternative to the traditional concept
of the force based design, generally adopted in seismic codes. However, the performance
assessment for new design methods can seldom be entirely carried out through experimental
testing of real specimens. Experimental results are the base on which representative numerical
models can be set up. Once available and validated these may be employed to asses the
performance of the design method at study. This work is related to the estimation of the
performance of two reinforced concrete systems, differently designed; the first according to a
Displacement Based Design method, the other according to the force based design of Eurocode 8.
Each system is a dual structure composed of a frame part working in parallel to coupled shear
walls. A composed structure, assembled from the two dual systems working in parallel, has been
experimentally tested with the pseudodynamic technique and allowed for the calibration of a
numerical model of the global type, based on beam-column fibre elements. The model was used to
study numerically the response of two new structures, the first entirely composed of elements
designed according to the displacement based design, the second to the force based design of
Eurocode 8. Each structure has been analyzed for ten different natural accelerograms, selected to
have a mean pseudoacceleration spectrum similar to the Eurocode 8 one. The results in terms of
global and local damage indexes for the two structures are compared and constitutes the base for
the assessment of the DBD viability
MODELING AND DYNAMIC ANALYSIS OF CABLES UNDER HARMONIC AND ENVIRONMENTAL LOADING
No full textIn the paper the past and ongoing activity on the dynamic behaviour of cables, carried on by the
research group at the Dep. Of Structural Engineering of Politecnico di Milano, is reviewed. The
implications coming form the results of this activity are summarized and discussed. At some points,
the needs for future research are pointed out.
The origin of the research group interest in flexible structure can be traced to their behaviour (static
and dynamic) induced by interaction with ambient excitations of various nature, such as wind, sea
waves and current, or support motion resulting from different causes. In time, a set of structural types
characterized by slender components have been investigated by the research group: guyed masts[1],
power lines[2,3,4], cableways[5], submerged floating tunnels[6]. Emphasis however will be restricted
on cables and on structural types having cables as structural components
The behavior of reinforced concrete piers under strong seismic actions
No full textA fibre column finite element based on Timoshenko beam theory has been developed to model the
cyclical response of the end critical zones of bridge piers having low-to-intermediate shear
slenderness. Shear resistance is obtained by modelling the principal resisting mechanisms; these
are linked to the flexural behaviour by means of suitable kinematics assumptions. In flexure the
element differs from standard fibre beam element since, to account for the contribution to shear
resistance due to arch action and for the inclined trust-line which develops in squat elements
subjected to shear, the principal direction of the compressive stress, which is normal to the cross-
section in standard fibre elements, is here rotated. Non linear behaviour of material is taken into
account by means of appropriate constitutive relations. The proposed element, implemented in a
well established non linear computer code, has been tested by comparison with some experimental
results
Numerical modeling of a PSD test on a dual RC system
No full textThis work describes the setup and the performance of a numerical model pertaining to the global type. In such a model, only few elements are used to represent a complete structural element. Here, columns, shear walls, beams and coupling beams are modeled using a column fiber model previously developed. The obtained results highlight the possibility of these models to capture, with reasonable accuracy, the structural response even for a relatively complex structure as is a dual RC system having coupled shear walls
Seismic response of multi story concentrically braced steel frames including accidental torsion
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