The effects of added manufactured viscous dampers upon shear-type structures are analytically investigated here for the class of Rayleigh damping systems. The definitions of mass proportional damping ...(MPD) and stiffness proportional damping (SPD) systems are briefly recalled and their physical counterpart is derived. From basic physics, a detailed mathematical demonstration that the first modal damping ratio of a structure equipped with the MPD system is always larger than the first modal damping ratio of a structure equipped with the SPD system is provided here. All results are derived for the class of structures characterised by constant values of lateral stiffness and storey mass, under the equal “total size” constraint. The paper also provides closed form demonstrations of other properties of modal damping ratios which further indicate that the MPD and the SPD systems are respectively characterised by the largest and the smallest damping efficiency among Rayleigh damping systems subjected to base excitation. A numerical application with realistic data corresponding to an actual seven-storey building structure is presented to illustrate and verify the theoretical findings.
Low reinforced thin concrete panels have been used for the re-construction of living buildings in the devastated zone of L’Aquila. A structural characterization of these types of panels is presented ...in this paper, paying particular attention to the fact that these panels are subjected mainly to shear forces. Refined compression-field theory (RCFT) has recently been proposed in order to better predict the behaviour of reinforced concrete members subjected to in-plane shear and axial stresses. This theory is based on continuum mechanics, i.e. satisfying compatibility, equilibrium and formulating the constitutive equations in terms of average (i.e. “smeared”) stresses and strains. The improvement of RCFT in comparison with the two most famous theories for reinforced concrete member subjected to shear i.e. the modified compression-field theory (MCFT), and the rotating-angle softened-truss model (RA-STM), deals with an embedded bar model based on the tension stiffening model in concrete. After an ad-hoc calibration procedure, the RCFT is employed in order to reproduce the envelope of the experimental load-deflection response of three full-scale thin low reinforced concrete panels subjected to cyclic loading. The predictions provided by RCFT are compared with the experimental data as well as with those provided by MCFT and RA-STM. This paper presents the necessary parameters for the design of thin low reinforced concrete panels using the RCFT. The preliminary numerical validations seem very promising. However, additional experimental data are required for calibrating and validating the parameters of the proposed RCFT theory.
The Simultaneous Medicina-Planck Experiment (SiMPlE) is aimed at observing a selected sample of 263 extragalactic and Galactic sources with the Medicina 32-m single-dish radio telescope in the same ...epoch as the Planck satellite observations.
The data, acquired with a frequency coverage down to 5 GHz and combined with Planck at frequencies above 30 GHz, will constitute a useful reference catalogue of bright sources over the whole Northern hemisphere. Furthermore, source observations performed in different epochs and comparisons with other catalogues will allow the investigation of source variabilities on different time-scales.
In this work, we describe the sample selection, the ongoing data acquisition campaign, the data reduction procedures, the developed tools and the comparison with other data sets.
We present 5 and 8.3 GHz data for the SiMPlE Northern sample, consisting of 79 sources with δ≥ 45° selected from our catalogue and observed during the first 6 months of the project. A first analysis of their spectral behaviour and long-term variability is also presented.
Structures characterized by non-coincident center of mass and center of stiffness, referred to herein as eccentric structures, develop a coupled lateral–torsional response when subjected to dynamic ...excitation. This phenomenon is particularly important for seismic isolated structures due to the potentially large deformations imposed on the seismic isolators by the earthquake ground motion.
A careful examination of the governing equations of motion of linear elastic, one-story eccentric systems sheds new light and new insight into the coupled lateral–torsional dynamic behavior of such systems and leads to the identification of a basic system parameter, the “alpha” parameter, which controls the maximum rotational response of such systems under free and forced vibrations. The “alpha” parameter is defined as the mass radius of gyration of the structure multiplied by the ratio of the maximum rotational to the maximum longitudinal displacement response developed by a one-story eccentric system under free vibration from a given initial deformation. Closed-form exact and approximate solutions for the “alpha” parameter are provided for undamped and damped eccentric systems, respectively, for a wide range of system parameters. A new basic result is that the “alpha” parameter has an upper bound of unity, thus physically limiting the maximum rotational response of an eccentric system in free vibration from an initial imposed deformation. A new physically based, simplified analysis procedure is developed, based on the “alpha” parameter to effectively estimate the maximum rotational response of a given eccentric system under seismic excitation. The extensive numerical and experimental verification of the simplified “alpha” method performed demonstrate that the proposed “alpha” method is accurate enough for design purposes, is robust and is significantly more accurate than the current International Building Code (IBC) design provisions.
The experimental verification was performed through a suite of 88 shaking table tests performed on a versatile, carefully designed, one-story small-scale building model able to represent the dynamic characteristics of a wide range of eccentric systems.
The dimensionless “alpha” parameter, bounded between zero and unity, can also be used as a formal index for the inherent property of a given structure to develop a rotational response under dynamic excitation. Sensitivities of the “alpha” parameter to various physical system characteristics are investigated and provide valuable guidance for eccentric system design.
Recent detailed simulations have shown that an insufficiently accurate characterization of the contamination of unresolved polarized extragalactic sources can seriously bias measurements of the ...primordial cosmic microwave background (CMB) power spectrum if the tensor-to-scalar ratio r ∼ 0.001, as predicted by models currently of special interest (e.g., Starobinsky’s R2 and Higgs inflation). This has motivated a reanalysis of the median polarization fraction of extragalactic sources (radio-loud AGNs and dusty galaxies) using data from the Planck polarization maps. Our approach, exploiting the intensity distribution analysis, mitigates or overcomes the most delicate aspects of earlier analyses based on stacking techniques. By means of simulations, we have shown that the residual noise bias on the median polarization fraction, Πmedian, of extragalactic sources is generally ≲0.1%. For radio sources, we have found Πmedian ≃ 2.83%, with no significant dependence on either frequency or flux density, in good agreement with the earlier estimate and with high-sensitivity measurements in the frequency range 5–40 GHz. No polarization signal is detected in the case of dusty galaxies, implying 90% confidence upper limits of Πdusty ≲ 2.2% at 353 GHz and of ≲3.9% at 217 GHz. The contamination of CMB polarization maps by unresolved point sources is discussed.
The Palazzo della Civiltà Italiana is a monumental building characterised by a reinforced concrete structure composed of parallel (cast in situ) portal frames and composite (reinforced concrete + ...hollow bricks) floors which spans between adjacent portals: a common construction technique in Italy. The floors are characterised by having a large span of about 10.0 metres. The construction took place between 1939 and 1943, most likely according to the Italian building code published in 1939. The authors have co-ordinated a comprehensive experimental campaign aimed at (a) the identification of the characteristics of the structural materials and members, and (b) the identification of eventual damages. Based upon the experimental results a number of analytical and numerical investigations have been developed in order to assess the structural reliability of the Palazzo which still remains in its 'original' configuration, as no substantial intervention of structural retrofit or rehabilitation have been implemented so far. This analysis allowed the identification of two major reliability issues: (i) the load bearing capacities of the floors do not allow the intended use, and (ii) the seismic vulnerability of the building does not satisfy the reliability standards required by current codes. On the basis of all data acquired and investigations performed, a simple (non invasive) structural retrofit solution capable of bringing the Palazzo to the level of structural safety required by current codes is identified.
Numerical simulations of the trajectory and thermal history of spherical particles injected into inductively coupled plasma torches working at atmospheric pressure have been performed taking into ...account the effects of coupling between particles and plasma and the turbulent dispersion of the particles, in the frame of a stochastic approach. The computational domain includes the torch region, as well as a region downstream the torch representing a reaction chamber.
PDF
