1,721,368 research outputs found
Equipment qualification in testing the flexural resistance of bended ceramic tiles
No full textThe capability to bend in a controlled manner Grès Porcelain stoneware tiles passing by a processes of pyroplastic deformation opens up new opportunities in utilisation of this important family of ceramics. A bent tile can be used in innovative applications, such as stairs, shelves, benches and even radiators, turning this element from a simple piece of furnishing in a modern functional component. But this change in functionality requires a new and different approach to the quality control that can no longer be limited to the validation tests as specified in the regulations used for traditional ceramics (e.g. colour, porosity, hygroscopic ...). Starting from a brief description of the first and only device devised for the verification of flexural resistance of curved tiles, this paper investigates the limitations and possibilities of use of that innovative equipment for product/process quality monitoring. Thanks to a careful modelling of its mechanism of operation, accompanied by various simulations comparing the limit cases of use, it has been possible to verify the incidence of some of the potential weaknesses of the equipment as well as to carry out a sensitivity analysis of this new tool for measure
Consistency and recovery in electroelasticity. Part II: Equilibrium and mixed finite elements
No full textDeveloping finite elements for electroelastic analysis requires a special care as the coupling in the discrete equations
depends on the matching between the approximations assumed for mechanical and electrical variables. To provide a
formal basis to this intuitive remark, a notion of consistency is established and a rigorous consistency analysis is
presented for the standard finite element model based on assumed displacement and electric potential. In this way,
specific analytical requirements are obtained which serve as a guide to select the interpolation functions for primary
variables. Moreover, the analysis shows that violating consistency can be reflected as spurious outcomes upsetting the
local distributions of secondary variables. Indeed, this undesirable effect is shown to be typical of the standard approach
if stress and electric flux density are computed via the constitutive equations. To cure the trouble, an alternative recovery
procedure is devised based on the consistency analysis. The procedure is variationally correct and reconstitutes
in a consistent manner the distributions of stress and electric flux density
A simplified micro-modeling approach for Historical Stone Masonry Walls
No full textA recent study [2] has discussed the accuracy of the nodal elastic stresses of zero thickness interface elements when fictitious elastic parameters (often called penalty stiffness factors) are used. These stresses, commonly used to calculate the triggering conditions of the opening of the interface simulating a discrete crack in quasi-brittle materials, are affected by non-negligible errors if the interfaces are embedded in unstructured/irregular meshes. A procedure to avoid these errors has been proposed for homogeneous materials [2] and bi-material interfaces [3]. Accurate nodal stresses are recovered if certain geometry-dependent pre-processed coefficients are used. In this paper, the method is proposed in the analysis of Historical Stone Masonry Walls: zero-thickness interface elements represent the interaction between stones of irregular shape. The crack opening triggering conditions are calculated for two identical meshes with rigid continuous elements representing the stones and fictitiously elastic zero-thickness interfaces representing the mortar layers. This paper shows that the use of the proposed coefficients significantly changes the values of the interface stresses leading to different configurations of the cracking onset
Effects of low incoming turbulence on the flow around a 5:1 rectangular cylinder at non-null-attack angle
Full text linkThe incompressible high Reynolds number flow around the rectangular cylinder with aspect ratio 5: 1 has been extensively studied in the recent literature and became a standard benchmark in the field of bluff bodies aerodynamics. The majority of the proposed contributions focus on the simulation of the flow when a smooth inlet condition is adopted. Nevertheless, even when nominally smooth conditions are reproduced in wind tunnel tests, a low turbulence intensity is present together with environmental disturbances and model imperfections. Additionally, many turbulence models are known to be excessively dissipative in laminar-to-turbulent transition zones, generally leading to overestimation of the reattachment length. In this paper, Large Eddy Simulations are performed on a 5: 1 rectangular cylinder at non-null-attack angle aiming at studying the sensitivity of such flow to a low level of incoming disturbances and compare the performance of standard Smagorinsky-Lilly and Kinetic Energy Transport turbulence models
Non-stationary winds effects over large partially-open roofs: A CFD study regarding the role of unsteady aerodynamics
Full text linkNon -stationary winds are increasingly attracting the attention of the scientific community and, despite not being explicitly considered in current design practice, they are known to produce important damages. In particular, the non-stationarity of such events has important consequences with respect to four main aspects which affect the definition of design wind loads: (i) the design wind speed definition, (ii) the wind profiles, (iii) the calculation of the structural response and (iv) the insurgence of unsteady aerodynamics effects. While the first three aspects already received considerable attention, the last one is still largely unclear and its relevance still to be assessed. In particular, for non -stationary winds such as macro- and micro-downbursts, the ramp -up time might become so short to trigger unsteady aerodynamic effects in the overall flow arrangement, which cannot be inferred from results obtained for stationary cases. In this paper, we propose a first investigation of such matter considering a large stadium roof using Large Eddy Simulations. Results show that, for the considered case, noticeable unsteady aerodynamic effects, which leads to an amplification of wind loads, can be triggered when the wind rump -up time is in the order of 30 s, and quickly decrease in importance for higher rump -up times
Numerical study of a twin box bridge deck with increasing gap ratio by using RANS and LES approaches
No full textTwin box decks are becoming increasingly adopted in long span bridges due to their good aerodynamic performance with respect to the flutter instability. For small gaps between the decks they behave as a whole continuous body while, increasing the gap, strong dynamic interaction between the two occurs: the windward deck causes a turbulent wake that impinges on the leeward girder inducing unsteady aerodynamic forces. This complex behaviour makes the simulation of the aerodynamics of these structures a challenging task from the Computational Fluid Dynamic point of view. In this context, the present paper aims at investigating the capabilities and limitations of RANS and LES based simulations in reproducing the flow field organization around a twin box deck section. Different configurations, with increasing separation gap, are studied and compared with experimental data. Finally, the effects induced by the presence of barriers is investigated for the largest separation gap
A high performance flexibility-based GBT finite element
No full textA new 2-node finite element for the Generalized Beam Theory is developed based on the hybrid complementary energy functional, involving nodal displacements and equilibrating stresses within the element as independent variables. Assumed stresses are rationally derived basing on the stresses associated to analytical solutions of some particular cases. Displacements within the element are a posteriori recovered by shape functions based on the same solutions. Numerical results show the high performance of the proposed element: generalized displacements and stresses are accurately predicted with very rough meshes, often using only one or two finite elements
An efficient approach to the evaluation of wind effects on structures based on recorded pressure fields
No full textA well known peculiarity of the structural response to wind loading is that static, quasi-static and resonant effects are present, in general, without a clearly dominant contribution. In such conditions, the calculation of wind effects would require to consider a large number of modes due to the relevant contribution of high frequency ones. In the present paper, in order to alleviate inaccuracies in the evaluation of static and quasi-static effects, induced by the truncation of the modal base, an efficient approach to the evaluation of static and quasi-static corrections is developed. To this purpose, a new class of pressure modes, called Proper Skin Modes (PSMs), is introduced and the corrections are evaluated based on the structural response to such modes, statically applied. PSMs can be seen as a novel modal version of traditionally adopted influence coefficients and naturally arise from the adopted pressure interpolation technique. The obtained approach is compact and efficient leading to a reduced data exchange between structural and wind engineers and to an optimal organization of the software used to perform the analyses. The proposed procedure is tested on a low-rise and a high-rise building showing very good performances
An innovative numerical modeling strategy for the structural analysis of historical monumental buildings
Full text linkIn this paper, an innovative numerical modeling strategy for the structural analysis of historical monumental buildings is presented. The strategy is based on a procedure that enables the semi-automatic transformation of a three-dimensional points cloud surveyed through terrestrial laser scanner or closed range photogrammetry into a three-dimensional finite element mesh, as well as its mechanical characterization. Therefore, an increase of the level of automation in the mesh generation process is attained and a large reduction in the required time in comparison with traditional modeling procedures is achieved. In order to validate the new strategy, an application to the case study of the San Felice sul Panaro (Italy) fortress is carried out. The reliability of the proposed model is assessed through a comparison between the results of structural analyses and the crack pattern experienced by the structure during the Emilia earthquake (2012). Moreover, the vulnerability assessment of the main tower of the fortress is performed through simplified pushover analyses conducted on the generated mesh
Salt Effects in Plastered and Unplastered Outdoors Brick Masonry: Quantitative Laser Monitoring of Surface Decay Evolution
No full textIn masonry materials, the superficial decay is a widespread problem. Aggressive environmental agents such as moisture and salts trigger the damage by propagating through the material capillary pores. Although several studies have been carried out on salt crystallization and their damaging effects, additional research effort is required to better investigate this phenomenon on real cases and real weathering conditions. To this purpose, testing and monitoring tools capable of following degradation process since the early beginning are necessary. Repeated visual inspections are commonly used to monitor the superficial decay, but this is a subjective technique not capable of providing any quantitative information. In this work, an experimental campaign, carried out in Bologna, Italy, is presented. A 2-header brick wall, one main face unplastered and one plastered, was stored outdoors and exposed to weathering over two summers. Before the start of the second ageing season, moisture and salt capillary rise was simulated by low-concentrated sodium chloride solution (0.1% -wt). The aim was to favour solution evaporation and salt crystallization and to provoke material damage. The degradation process was monitored based on a contactless, rapid and accurate image diagnostic technique. In particular, high-resolution laser scanning by triangulation technique was adopted. 3D data acquisition was repeated at the end of both seasons. The proposed procedure successfully extracted quantitative information about areas of material spalling and detachment even in the initial phases of decay
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