Maria Lippiello

A Differential Quadrature based procedure for parameter identification

In this paper, a numerical scheme for a parameter identification problem is presented. The problem here considered is the identification of the stiffness of structural elements and a new procedure to solve it is proposed. This procedure involves not only the usual Newton-like iterative algorithm for nonlinear least squares problems, but it also provides a unitary framework to calculate the solution of the equation of motion (forward problem) and the Jacobian matrix (required by minimization) by means of Differential Quadrature (DQ) rules simultaneously applied in space and time. DQ based methods are promising numerical schemes and a novel application is here proposed. Two practical example applications are discussed. The proposed method is very simple in its principle and has great potential for future applications, provided that a suitable model is adopted.

Free Vibrations of a Cantilevered SWCNT with Distributed Mass in the Presence of Nonlocal Effect

The Hamilton principle is applied to deduce the free vibration frequencies of a cantilever single-walled carbon nanotube (SWCNT) in the presence of an added mass, which can be distributed along an arbitrary part of the span. The nonlocal elasticity theory by Eringen has been employed, in order to take into account the nanoscale effects. An exact formulation leads to the equations of motion, which can be solved to give the frequencies and the corresponding vibration modes. Moreover, two approximate semianalytical methods are also illustrated, which can provide quick parametric relationships. From a more practical point of view, the problem of detecting the mass of the attached particle has been solved by calculating the relative frequency shift due to the presence of the added mass: from it, the mass value can be easily deduced. The paper ends with some numerical examples, in which the nonlocal effects are thoroughly investigated.

Restoring of timber structures: connections with timber pegs

A quite widespread methodology of restoration of ancient timber structures envisages the introduction of new timber elements, connected to the standing structure by a timber-to-timber joint. An efficient alternative to the most used jointing technologies, which employ metallic bolted plates, steel pins, or epoxy resin adhesives, could be the use of timber pegs, if reliable design formulas could be found in codes devoted to timber structures. The design rules currently available for pinned joints contemplate only steel connectors, involve mechanical characteristics of the dowel as well as of the timber elements constituting the joint and are based on Johansen’s theory. The present research has the target of verifying the applicability of this theoretical model, and of the derived design formulas, to the case of timber pegs. At this aim, an experimental research has been performed, devoting special attention to the description of timber peg behavior inside the double shear plane joint and of dowel-bearing strength of the base timber, when a timber peg substitutes the envisaged steel bolt. Obtained results were compared with theoretical ones, showing that the different nature of the material employed for the pins needs more specific evaluation of the mechanical properties to be inserted in design formulas. Moreover, as in the field of new building timber joints fastened by timber pegs are widely employed in prefabricated timber frame industry, contents of the design standard for those structures are also taken into account, especially with reference to the “effective shear” failure mode of the timber peg.

Limit Analysis for Unilateral Masonry-like Structures

Abstract: This paper is devoted to the application of unilateral models to the stress analysis of masonry structures. Some 2d applications of what we can call the simplified masonry-like model for masonry, are discussed and studied. The results here presented demonstrate that the unilateral model for masonry can be a useful tool for modeling real masonry structures. The main technique here employed for applying the No-Tension model to structures is the systematic use of singular stress and strain fields within the frame set by the theorems of Limit Analysis. A number of simple examples is discussed to illustrate the method.

Free vibration analysis of DWCNTs using CDM and Rayleigh-Schmidt based on Nonlocal Euler-Bernoulli beam theory.

The free vibration response of double-walled carbon nanotubes (DWCNTs) is investigated. The DWCNTs are modelled as two beams, interacting between them through the van der Waals forces, and the nonlocal Euler-Bernoulli beam theory is used. The governing equations of motion are derived using a variational approach and the free frequencies of vibrations are obtained employing two different approaches. In the first method, the two double-walled carbon nanotubes are discretized by means of the so-called “cell discretization method” (CDM) in which each nanotube is reduced to a set of rigid bars linked together by elastic cells. The resulting discrete system takes into account nonlocal effects, constraint elasticities, and the van der Waals forces. The second proposed approach, belonging to the semianalytical methods, is an optimized version of the classical Rayleigh quotient, as proposed originally by Schmidt. The resulting conditions are solved numerically. Numerical examples end the paper, in which the two approaches give lower-upper bounds to the true values, and some comparisons with existing results are offered. Comparisons of the present numerical results with those from the open literature show an excellent agreement.

The Influence of Dowel-Bearing Strength in Designing Timber Pegged Timber Joints

ABSTRACT The employment of timber pegs in timber structure joints is a widespread technology in the field of timber frame building in the United States, where the Timber Frame Engineering Council has published a special Standard to supplement the National Design Specification for Wood Construction. The authors have been studying the possibility of supplementing the Eurocode 5 design formulas, thought for timber joints with metal connectors, with specifications needed for a reliable design when employing timber pegs. The field of application envisaged is that of restoring timber structures and results obtained until now are quite encouraging. In this step of the research, more attention has been paid to deformation process: fir and chestnut samples have been tested to determine their dowel-bearing behavior with steel and ash timber peg while double-shear plane joints made of the same wood species, and fastened with steel as well as timber pegs, have been analyzed.

Pozzolanic Cementum of the Ancient Constructions in “Campi Flegrei” Area

In the research program concerning the heritage in the Campania region, particular attention is paid to ancient constructions of the Campi Flegrei (burning fields), which are subject to eruptive phenomena and frequent bradyseism cycles. At the beginning of the 3rd century BC, the cementum technique (concrete) had already marked a revolutionary development in construction method. The breakthrough was the discovery that a volcanic powder — pozzolana — mixed in suitable proportions with lime created a mixture that also set under river and seawater with excellent qualities of resistance and durability. This article focuses on pozzolanic concrete and its interaction with the other materials — tuff, bricks, trachyte — used in foundations, wharfs, water reservoirs. In addition, examples of buildings for which such materials were used are described in detail. Moreover, the present study considers the results of mechanical characterization of some mortars and the evaluation of the compressive strength of several specimens at the different setting times. Finally, a few hints are proposed for a correct strengthening.

Stop-Splayed Scarf-Joint Reinforcement with Timber Pegs Behaviour

Restoring ancient timber structures often involves cutting or reinforcing stop-splayed scarf-joints in beams or truss-rods. Steel nails, bolts and plates or adhesive resins and rods are commonly used, however these jointing technologies cause some disadvantages, such as moisture between steel and timber surfaces, hard reversibility of the intervention and a questionable aesthetic output in uncovered structures. The employment of timber pegs, inserted perpendicular to the grain, could be an efficient solution and is already preferred in some applications. Since no design rules for traditional timber joints or for timber pegged connections are given by European codes, investigations on scarf joint behaviour before and after reinforcement are needed aiming to reliable design procedures. In this study, the role of the fastener inside this tension resisting carpentry joint and its contribution in yield strength and stiffness have been investigated. Specific attention has been addressed to stiffness, which is positively influenced by the insertion of timber pegs. Three samples of fir scarf-joints have been tested, a total of eight specimens, with different configurations: without fasteners, with timber pegs and with steel pins. The different failure modes under tension load of the samples and their rheological behaviour have been studied and compared to trace force distribution between the resisting elements, that is the ash key and the added fasteners.

Differential quadrature solutions for the nonconservative instability of a class of single-walled carbon nanotubes

Purpose The aim of the present paper is to investigate the nonconservative instability of a single-walled carbon nanotube with an added mass through nonlocal theories. To discretize the governing equations is used the Differential Quadrature (DQ) rules, as introduced by Bellman and Casti. DQ rules have been largely used in engineering and applied sciences. Recently, they were applied to enhance some numerical schemes, such as step-by-step integration schemes and Picard-like numerical schemes. Design/methodology/approach In the present paper the Differential Quadrature (DQ) rules are employed in order to investigate the nonconservative instability of a single-walled carbon nanotube (SWCNT) through nonlocal theories. Findings In order to show the sensitivity of the SWCNT to the values of added mass and the influence of nonlocal parameter on the fundamental frequencies values, some numerical examples have been performed and discussed. Yet, the effect of the different boundary conditions on the instability be...

Non-conservative Instability of Cantilevered Nanotube Via Cell Discretization Method

Based on the nonloocal elasticity theory, this paper deals with the dynamic instability analysis of cantilevered single-walled carbon nanotube with concentrated mass, located at a generic position, and subject to a follower force at the free end. Accounting for the small scale effect, the governing equations of motion are derived using an alternative Hamilton’s variational principle and the governing equations are solved numerically employing the Cell-Discretization Method (CDM) in which the nanotube is reduced to a set of rigid bars linked together by means of elastic constraints. The resulting discrete system takes into account nonlocal effects, added mass, and position of added mass, and follower force direction. A comparative analysis is performed in order to verify the accuracy and validity of the proposed numerical method. The effects of the nonlocal parameter and dimensionless mass on the dynamic instability of single-walled carbon nanotube are shown and discussed in details. The effect of a sub-tangential follower force on the stability of cantilever single-walled carbon nanotube is studied. Finally, the validity of the proposed analysis is confirmed by comparing the present results with those obtained from the litertaure and listed in bibliography.