Thermal and structural properties of a hemp–lime biocomposite

Abstract The need to reduce greenhouse gases emission produced by the building sector leads to the research of renewable and less impacting materials that can replace traditional ones. This subject has encouraged new researches on biocomposite concretes with the aim to exploit renewable resources like vegetal fibres intended as materials whose production processes are generally characterized by low costs and energy demand. This biocomposite is obviously much lighter than concrete and, therefore, can be suitably used in such cases where a structure cannot be overloaded, for instance in the realization of a green covering on top of a preexistent building. In this work, a first analysis of the…

I Telamoni del Tempio di Zeus ad Agrigento: rilievi, disegni e ricostruzioni

Oggetto dello studio qui presentato è la ricostruzione di un intercolumnio del fronte esterno del Tempio di Zeus ad Agrigento, basata sul rilievo del Telamone oggi custodito presso il Museo Archeologico, sugli studi e i numerosi saggi di ricostruzione proposti dagli studiosi dal XVIII secolo fino alla metà dello scorso secolo e sulla analisi strutturale del Telamone ricostruito nel Museo. The drawings of the telamones, the giant statues placed the front of the Temple of Zeus in the archaeological area of Agrigento, have fascinated some of the most famous neoclassical architects in Europe. The virtual reconstruction of one intercolumnial of the Temple, based both on the range-based survey of…

A new design problem in the formulation of a special moment resisting connection device for preventing local buckling

In the present paper an improved formulation devoted to the optimal design problem of a special moment resisting connection device for steel frames is proposed. This innovative device is called a Limited Resistance Plastic Device (LRPD) and it has been recently proposed and patented by some of the authors. It is thought to be preferably located at the extremes of the beam, connecting the beam end cross section with the relevant column. The typical device is a steel element characterized by symmetry with respect to three orthogonal barycentric planes and constituted by a sequence of three portions with abrupt cross section changes. The main novelty of the present proposal is related to the d…

Optimal Design of New Steel Connections

The Limited Resistance Rigid Perfectly Plastic Hinge (LRPH) are special steel connections mainly usable to join beam elements of plane or spatial steel frames. The fundamental characteristics of these devices are the mutual independence of their own resistance and stiffness features as well as the respect of assigned constraints related to the elastic and limit behaviour of the joined elements. Within the frame structural scheme, the device plays the role of a rigid perfectly plastic hinge, constituted by a suitably sized sandwich section. The efficient use of the LRPH in the relevant frame depends on the appropriate design of the device geometry. In the present paper, a new approach devote…

Numerical and experimental verification of a technique for locating a fatigue crack on beams vibrating under Gaussian excitation

The stationary vibrations of a beam excited by Gaussian noise are strongly affected by the presence of a fatigue crack. Indeed, as soon as the crack arises the system response becomes non-linear due to crack breathing and a non-Gaussian behaviour is encountered. The paper presents both numerical and experimental investigations in order to assess the capability of the non-Gaussianity measures to detect crack presence and position. Monte Carlo method is applied to evaluate in time domain the higher order statistics of a cantilever beam modelled by finite elements. The skewness coefficient of the rotational degrees of freedom appears the most suitable quantity for identification purpose being …

Analisi del comportamento flessionale del legno attraverso la interferometria Speckle

Nel lavoro vengono presentati i risultati di uno studio sperimentale effettuato sul comportamento flessionale di due differenti essenze di legno: l’abete rosso ed il ciliegio. L’analisi viene effettuata sottoponendo il provino al test di flessione a quattro punti ed utilizzando la interferometria speckle, una tecnica di misura non a contatto ed a campo intero, che consente di ottenere i campi di spostamento e di deformazione sulla superficie del provino. Al fine di mettere in evidenza le peculiarità del comportamento flessionale del legno i risultati ottenuti vengono confrontati con quelli di un provino di Plexiglas nelle stesse condizioni. Tale confronto conferma la complessità del comport…

Pseudo-force method for a stochastic analysis of nonlinear systems

Nonlinear systems, driven by external white noise input processes and handled by means of pseudo-force theory, are transformed through simple coordinate transformation to quasi-linear systems. By means of Itô stochastic differential calculus for parametric processes, a finite hierarchy for the moment equations of these systems can be exactly obtained. Applications of this procedure to the first-order differential equation with cubic nonlinearity and to the Duffing oscillator show the versatility of the proposed method. The accuracy of the proposed procedure improves by making use of the classical equivalent linearization technique.

Probabilistic Evaluation of the Adaptation Time for Structures under Seismic Loads

Abstract In this paper, a probabilistic approach for the evaluation of the adaptation time for elastic perfectly plastic frames is proposed. The considered load history acting on the structure is defined as a suitable combination of quasi-statical loads and seismic actions. The proposed approach utilizes the Monte Carlo method in order to generate a suitable large number of seismic acceleration histories and for each one the related load combination is defined. Furthermore, for each load combination the related adaptation time is determined, if any, as the optimal one for which the structure is able to shakedown under the unamplified applied actions. A known generalized Ceradini's theorem i…

Optimal design of steel frames accounting for buckling

A formulation of a special design problem devoted to elastic perfectly plastic steel frame structures subjected to different combinations of static and dynamic loads is presented. In particular, a minimum volume design problem formulation is presented and the structure is designed to be able to elastically behave for the assigned fixed loads, to elastically shakedown in presence of serviceability load conditions and to prevent the instantaneous collapse for suitably chosen combinations of fixed and ultimate seismic loadings as well as of fixed and wind actions. The actions that the structure must suffer are evaluated by making reference to the actual Italian seismic code. The dynamic respon…

Bòvedas tabicadas: experimental and numerical analysis

A class of thin vaults, the so-called “bovedas tabicadas”, which represent one of the most common Spanish traditional building techniques at the end of XIX century are studied here, treating the relevant analysis problem through a numerical, as well as an experimental, approach. At first the problem is studied by searching for the behaviour of the material effecting suitable experiments. Once the constitutive behaviour of the materials and the structural elements are experimentally characterized, a semi inverse method for the identification of the optimum mechanical parameters to assign to an equivalent homogeneous ideal material through analysis reproducing the executed experimental tests …

Multicriterion design of frames with constraints on buckling

The present paper is devoted to the optimal design of frame structures subjected to static and dynamic loading assuming the material behaviour as elastic perfectly plastic. The relevant optimal design problem is formulated as a minimum volume search problem. The minimum volume structure is determined under suitable constraints on the design variables as well as accounting for different resistance limits: the elastic shakedown limit and the instantaneous collapse limit, considering for each limit condition suitably chosen amplified load combinations. The effects of the dynamic actions are studied on the grounds of the dynamic features of the structure taking into account the structural perio…

Experimental characterization of dacron 360 woven constitutive behavior

In the present paper some experimental analyses of Dacron© 360 woven aimed to characterize its constitutive behavior are presented. This woven, widely adopted in sail manufacturing, is obtained by weaving polyethylene terephthalate (PET) yarn and it shows some peculiar features due to the manufacturing process. The experimental tests, in terms of tensile tests and cyclic tests, clearly show the orthotropy features of the material, its high strength and deformability. Finally, the examination with optical microscope of the tested specimens allows to evidence how the warp and weft yarns interact.

A case study of the structural behavior of a catalan bricks masonry vault

Seismic shakedown design of frames based on a probabilistic approach

The present study concerns the optimal design of elastic perfectly plastic structures subjected to a combination of fixed and seismic loads. In particular, plane frames are considered and suitable measures of the beam element cross sections are chosen as design variables. The optimal design is required to behave in a purely elastic manner when subjected just to the fixed load and to have the capability to eventually shakedown when simultaneously subjected to fixed and seismic loads. Due to the natural uncertainness related to the definition of the seismic load history, a new probabilistic approach is proposed, consisting into two subsequent search steps. At first a suitably chosen large num…

Dynamics analysis of distributed parameter system subjected to a moving oscillator with random mass, velocity and acceleration

Abstract The problem of calculating the response of a distributed parameter system excited by a moving oscillator with random mass, velocity and acceleration is investigated. The system response is a stochastic process although its characteristics are assumed to be deterministic. In this paper, the distributed parameter system is assumed as a beam with Bernoulli–Euler type analytical behaviour. By adopting the Galerkin's method, a set of approximate governing equations of motion possessing time-dependent uncertain coefficients and forcing function is obtained. The statistical characteristics of the deflection of the beam are computed by using an improved perturbation approach with respect t…

Sul progetto di telai metallici ad elevata dissipazione plastica

Modellazione numerica del comportamento meccanico delle volte catalane

Il presente lavoro riguarda la modellazione numerica del comportamento costitutivo delle cosiddette volte in foglio (le bóvedas tabicadas) che rappresentano una delle tecniche edilizie tradizionali catalane più diffusamente impiegate da alcuni tra i più grandi architetti spagnoli (primo fra tutti Gaudí) alla fine del XIX secolo [1-3]. Tali volte risultano fondamentalmente costituite da strati alternati di spessore in generale pressoché uguale di mattoni e di malta. Questa particolare caratteristica viene studiata in questo lavoro nel quale si vuole confrontare la modellazione del comportamento costitutivo considerando il materiale come ideale omogeneo con quella ottenuta modellando il mater…

On the Post-Elastic Behavior of LRPH Connections

The paper concerns the study of the post-elastic behavior of a recently proposed innovative device, named Limited Resistance Rigid Perfectly Plastic Hinge (LRPH). In particular, LRPH is a steel device of finite length realizing a moment connection between beam elements of a steel frame; it is designed in order to possess two main and independent requirements: its bending moment resistance must be suitably lower than the one of the connected beam element and its overall bending stiffness must be equal to that of the connected beam element characterized by the same length. In order to make the proposed device reliable, LRPH must be capable of realizing a full plastic hinge for the assigned be…

Identification of multi degree of freedom civil systems under base lateral random forces by using potential models

Optimal design of structures equipped with different seismic protecting devices

Comparison between unrestricted dynamic shakedown design and a new probabilistic approach for structures under seismic loadings

The paper concerns a study related to the comparison between two different approaches utilized for the formulation of an optimal shakedown design problem for elastic plastic frame structures subjected to a combination of fixed and seismic loading. The first formulation utilizes the unrestricted dynamic shakedown theory, while the second one is based on a new probabilistic approach. The comparison is effected in terms of mathematical formulations, in terms of adopted loading models and in terms of numerical results. The performed applications are related to plane steel frames.

Analisi numerica e sperimentale sul comportamento meccanico delle volte catalane

Targeted steel frames by means of innovative moment resisting connections

Abstract The present paper proposes the use of stepped cross section devices on steel frames aiming at reproducing a pre-established target push-over curve. To this aim a Limited Resistance Plastic Device (LRPD) to be inserted along selected structural members is proposed. The following two main specific features for LRPD are required: any elastic flexural stiffness variation of the original selected member must be avoided; an ultimate plastic bending moment value equal to an assigned percentage of the original limit resistance value must be ensured. Steel frames equipped with LRPD are modeled by means of an extension of a recently proposed Fibre Smart Displacement Based (FSDB) beam element…

Mode-superposition correction method for deterministic and stochastic analysis of structural systems

The role played by the modal analysis in the framework of structural dynamics is fundamental from both deterministic and stochastic point of view. However the accuracy obtained by means of the classical modal analysis is not always satisfactory. Therefore it is clear the importance of methods able to correct the modal response in such a way to obtain the required accuracy. Many methods have been proposed in the last years but they are meaningful only when the forcing function is expressed by an analytical function. Moreover in stochastic analysis they fail for white noise excitation. In the paper a method able to give a very accurate response for both deterministic and stochastic input is p…

A perturbation approach for the response of dynamically modified structural systems

The problem of the structural analysis under changes of dynamical parameters is of particular interest. This is due to the fact that often the real structures are different from the predicted ones. In this paper, an unconditionally stable step-by-step procedure, able to evaluate the deterministic response of linear structures with modifications, is presented. The proposed procedure requires the evaluation of the transition matrix, which is the fundamental operator of the step-by-step solution, by means of a perturbation approach. This technique overcomes the difficulties connected with the evaluation of the eigenproperties of the modified structures usually required to obtain the transition…

Case Study of the Structural Behavior of a Catalan Bricks Masonry Vault

Catalan vaults are a peculiar type of low thickness vaulted brick masonry structure. Knowledge of load-deflection response and load bearing capacity are important aspects to consider with the aim of preserving these structural members as part of the cultural heritage. In order to investigate these aspects, complete knowledge of the constituent materials and geometry (dimension, thickness, constructive section) is necessary in such a way as to predict the load-deflection response and the effective load-carrying capacity; the latter can be determined utilizing simplified models (limit analysis) or by means of a numerical analysis (finite element method). With this aim, the structural behaviou…

P-Delta effect in structural optimization

The present paper is devoted to the optimal design of structures constituted by elastic perfectly plastic material. In particular, reference will be made to the minimum volume design of multi-storey steel frames taking into account the P-Delta effect. For the sake of generality, the structure is thought as discretized into compatible finite elements and subjected to fixed and quasi-statically acting (wind) loads as well as to dynamic (seismic) loads. The effects of the dynamic actions are studied by utilizing a classical modal technique. The relevant optimal design problem is formulated on the grounds of a statical approach and different resistance limits are considered: in particular, it i…

Evaluation of the bending behaviour of laminated glass beams via electronic speckle pattern interferometry

The paper is devoted to the experimental analysis of the kinematical and mechanical behaviour of laminated glass beam structures. In particular, the utilized laminated glass specimens are composed of two glass layers bonded by a polymer layer constituted by Ethylene-vinyl acetate whose thickness has been nominally considered as constant for all the specimens. The experimental behaviour of the analyzed specimens is deduced by applying Electronic Speckle- Pattern Interferometry technique; actually, among optical methods this technique (handled by phase-stepping technique) is very effective to obtain a full-field displacement map and to numerically achieve the longitudinal strain. In particula…

On the optimal design of base isolation devices

The paper deals with the optimal design of a base isolation system for a given structure subjected to seismic loads. In particular, an appropriate minimum displacement seismic protection device optimal design formulation is proposed for an assigned elastic perfectly plastic steel frame constrained to behave in conditions of elastic shakedown. The chosen base isolation device is constituted by elastomeric isolators. Suitable combinations of fixed and seismic loads are considered. According to the unrestricted shakedown theory, the seismic input is given as any load history appertaining to a suitably defined seismic load admissibility domain. The relevant dynamic structural response is obtain…

Il rumore ambientale e l’affidabilità strutturale: il caso della chiesa di N. S. dell’Itria a Castelvetrano

Discrete variable design of frames subjected to seismic actions accounting for element slenderness

An optimal design problem formulation of elastic plastic frames under different combinations of fixed and seismic loads is presented. The optimal structure must behave elastically for the fixed loads, shakedown for serviceability conditions and prevent instantaneous collapse for fixed and high seismic loads. P-Delta effects and element buckling are considered. An appropriate modal technique is utilized. The design variables can have components in a continuous field or, alternatively, in chosen discrete sets or, yet, both kind of variables can be present. The design problem is formulated on the ground of a statical approach. The applications are related to steel frames.

Shakedown design of structures under dynamic loading

The optimal (minimum volume) design of elastic plastic structures under static and dynamic loads is studied. The minimum volume design is reached accounting for different resistance limits: it is required that the optimal structure simultaneously satisfies the elastic shakedown limit and the instantaneous collapse limit, or alternatively the elastic and the plastic shakedown limits, adopting for each limit condition a suitably chosen load combination and some appropriate load amplifiers. The load combinations are characterized by the presence of fixed loads, quasi-statical cyclic loads and dynamic (seismic) loads. Reference is made to the Italian Code related to structural analysis and desi…

Analisi numerica e sperimentale sul comportamento meccanico delle volte catalane

TRADITION AND MODERNITY OF CATALAN VAULTS: HISTORICAL AND STRUCTURAL ANALYSIS

Il lavoro analizza da diversi punti di vista un particolare tipo di strutture voltate noto come volte catalane (bóveda tabicada) e la tecnica costruttiva correlata. Le volte catalane sono volte realizzate da strati alterni di mattoni e malta, caratterizzate da un esiguo spessore in relazione alle altre dimensioni. Il primo passo presentato nel lavoro è quello di investigare tutti gli aspetti storici al fine di inquadrare sia la tipologia che la tecnica costruttiva correlata all'interno della storia dell'architettura e di individuare le ragioni di un così grande successo lungo i secoli. Successivamente, è stata effettuata una campagna di indagini sperimentali, che completa una precedente, su…

Analisi limite elastica di strutture con resistenze aleatorie sotto azioni dinamiche campionate

Optimal design of structures under dynamic loading

Approccio cinematico per la analisi limite di strutture reticolari con resistenze aleatorie

Evaluation of continuous filament mat influence on the bending behaviour of GFRP pultruded material via Electronic Speckle Pattern Interferometry

Abstract Pultrusion is a process allowing the production of unidirectional (roving) fibre-reinforced polymer (FRP) structural elements with constant cross section. Recently, also civil engineers focused their attention on pultruded composite materials as alternative to traditional ones (e.g., concrete, steel). Furthermore, to improve the transverse strength and stiffness with respect to the fibres direction, continuous filament mat (CFM) is often placed within the stacking sequence. The CFM influence on the global mechanical behaviour is not considered by appropriate actual international standards. In this paper, the influence of the CFM layers on the mechanical behaviour of glass fibres pu…

Minimum displacement design of base isolation devices

On the analysis of Catalan thin vaults

This paper is concerned with the identification, modelling and analysis of thin layered vaults, typical in the Catalan constructions of the XIX century. These special structures, also known as bovedas tabicadas, are characterized by very low thickness with respect to the medium surface dimensions and by the presence of different superimposed layers of bricks tied with mortar, are studied in order to individuate a coherent mechanical model for describing the material behaviour, to recognize the structural response utilizing as comparison adequate experimental results, and to extend the obtained results for the analysis of new vaults or for the restoration design of existing vaults. Firstly, …

Smart Beam Element Approach for LRPH Device

LRPH (Limited Resistance Rigid Perfectly Plastic Hinge) device is a special steel device mainly usable to join beam elements of plane or spatial steel frames covered by patent n. 102017000088597 at the Italian Ministry of Economic Development and identified in the International Patent System with the number PCT/IB2018/055766. In the framework of moment (rigid) connection, the main fundamental innovation of LRPH consists in the mutual independence of its own resistance and stiffness features. The device is constituted by a sequence of three steel elements of limited length bounded by two parallel steel plates joined up with the connected structure elements. The cross-sections of the three st…

An optimal design of FE structures with limited ductility

The minimum volume design of elastic perfectly plastic FE structures subjected to quasi-static fixed and cyclic loads is searched in such a way that the structure remains into the elastic field in serviceability conditions, while it is subjected to alternating plasticity under very strong cyclic actions, incremental and instantaneous collapse being prevented. In order to take into account the limited ductility of the material, suitable chosen limits on the plastic deformations related to the initial transient phase and/or to the subsequent steady-state phase are considered for the structure subjected to very strong cyclic actions. A numerical application confirm the theoretical expectations…

Materiali naturali in edilizia: analisi sperimentali e primi risultati.

Speckle Interferometry Analysis of Full-bending Behavior of GFRP Pultruded Material

Abstract The use of Glass Fiber Reinforced Polymer materials (GFRP) has increased in the last years even among civil structural engineering due to their high specific strength, lightweight and excellent corrosion resistance. With application of the pultrusion method, the manufacture of large-scale profiles with various cross-section forms became potentially possible with relatively low costs. Usually two different technological approaches are available to realize the element: in the first one a mat-roving-mat sequence is adopted, in the second one only roving is present. Continuous filament mat (CFM, fibers distributed randomly in all directions) is often used to build up laminate thickness…

A plastic shakedown design of FE structures with constraints on deformations

Limited Resistance Rigid Perfectly Plastic Hinges for Steel Frames

The paper concerns the proposal of a new special device for steel frames that can be utilized as external constraint as well as internal one connecting the structure beam elements. The device is designed as a rigid perfectly plastic hinge characterized by suitably chosen stiffness and resistance. Its constituting material is steel. The elastic stiffness and the limit resistance, treated as independent of each other, are fixed with the aim of satisfying special features required to the structure. The proposed device is thought as a sandwich section with wing thickness appropriately variable. Its dimensions are designed so that it can exhibit the fixed independent stiffness and limit resistan…

Bounds on transient phase plastic deformations in optimal design of steel frames subjected to cyclic loads

A minimum volume multicriterion design of elastic perfectly plastic steel frames subjected to a combination of quasi-static fixed and cyclic loads, bounding the transient phase plastic deformations, is proposed. The problem is formulated according to a plastic shakedown criterion, so that incremental and instantaneous collapse are certainly prevented when the frame is subjected to very strongly amplified cyclic loads. The further condition that the structure must also behave elastically in serviceability conditions is imposed. Since the steady-state loading history is known it is possible to directly bound the steady-state plastic deformations. By applying a suitable own bounding theorem, i…

Durability assessment of basalt fiber polymer as reinforcement to expanded clay concrete in harsh environment

Basalt fiber-reinforced polymer composites are receiving considerable attention as they represent a low-cost green source of raw materials. In most cases, fiber-reinforced polymer composites face harsh environments, such as chloride ions in coastal marine environments or cold regions with salt deicing. The resistance of fiber-reinforced polymers subjected to the above environments is critical for the safe design and application of such composites. This research aims to develop a framework to investigate the durability properties of the lightweight expanded clay basalt fiber polymer reinforced concrete exposed to the NaCl environment. The specified quantity of concrete structural elements wa…

DACRON© 360 WOVEN: EXPERIMENTAL CHARACTERIZATION AND COMPUTATIONAL ASPECTS

In this paper a first experimental study on Dacron© 360 woven constitutive behavior is presented. This woven is widely adopted in sail manufacturing, it is obtained by weaving polyethylene terephthalate (PET) yarn and it shows some peculiar features due to its own manufacturing process. The experimental tests, in terms of tensile tests and cyclic tests, clearly show the orthotropy features of the material, its high strength and deformability. The examination with optical microscope of the tested specimen allows to evidence the interaction between warp and weft yarns. The obtained results represent a first step for the definition of a correct computational approach to such materials.

Flexural behavior of laminated glass beams with T cross-sections

Reliable measures of plastic deformations for elastic plastic structures in shakedown conditions

A new formulation for evaluating reliable measures of the plastic deformations occurring in the transient phase of a structure in shakedown conditions is proposed. The structure is thought as constituted by elastic perfectly plastic material and subjected to a combination of fixed and cyclic loads. The proposed formulation consists in the search for the optimal plastic strain field that minimize a suitable objective function defining a strain energy measure related to the plastic strains at the shakedown limit. The typical self-stress field can be obtained as the elastic structural response to an assigned plastic strain field respecting appropriate ductility limits for the material. Without…

The restoration of the North-East corner columns of Santa Maria La Nova the cloister in Monreale, Italy

Lo scopo della presente ricerca è quello di descrivere i risultati dello studio, con la rappresentazione tramite scanner laser 3D, e del restauro scientifico, che ha previsto anche una reintegrazione, del gruppo di colonne posto nell'angolo Nord-Est del famoso chiostro dell'Abbazia di Santa Maria La Nova in Monreale, vicino Palermo, Italia (ultimo quarto del XII secolo) The purpose of the present research is to describe the results of the study, with 3D laser scanner representation, and scientific restoration, which also included reintegration, of the group of columns located in the northeast corner of the famous cloister of the Abbey of Santa Maria La Nova in Monreale, near Palermo, Italy …

A multicriterion design of steel frames with shakedown constraints

The minimum volume design of elastic perfectly plastic steel frames subjected to fixed and cyclic loads is searched in such a way that the structure remains in elastic field in serviceability conditions, while it is subjected to alternating plasticity under very strong cyclic actions, incremental and instantaneous collapse being prevented. The problem is faced on the grounds of a statical and a kinematical approach. The Kuhn-Tucker conditions of the two problems prove that they are each one the dual of the other and provide useful pieces of information about the structural behaviour. Numerical applications confirm the theoretical expectations: optimal designs turn out to be quite light, wit…

Optimization of structures with unrestricted dynamic shakedown constraints

The unrestricted dynamic shakedown theory is here utilized with the aim to formulate different optimal design problems for structures mainly subjected to seismic loads. In particular, reference is made to plane frame structures constituted by elastic perfectly plastic material subjected to load combinations characterized by the presence of simultaneous fixed and seismic actions. The design problems, formulated on the ground of a statical approach, are devoted to structures with and without seismic protection devices, with special emphasis to seismic isolators. For the proposed design problem formulations different constraints are utilized; actually, for structures without protection devices…

Experimental analysis of "bovedas tabicadas"

A particular type of vaulted structures, known as bóvedas tabicadas (Catalan vaults), made with alternate layers of bricks and mortar and characterized by a very low thickness in comparison to the other two dimensions, are studied. The research has been faced under the historical aspect as well as under the mechanical one, developing experimental and numerical analysis regarding real existing structures. In particular, the experimental analysis, performed by effecting compression and bending tests on samples taken from a real structure, has been devoted to the constitutive material identification and the characterization is made by considering the material as an ideal homogeneous; further e…

On the Limit Behaviour of Moment Resisting Connections Under Uncertainties

Abstract Moment resisting connections are mainly designed to transfer bending moments and shear forces. Generally speaking, the design strength of a moment resisting connection can be classified as full-strength (moment capacity of the connection equal to or greater than that of the connected member) or partial-strength (the moment capacity of the connection less than that of the connected member). Similar remarks can be made regarding the stiffness defining connection rigid or semi-rigid if compared to the stiffness of the connected member. In the past, full-strength connections have been widely adopted especially in moment resisting frames and their structural performance relied on the pr…

Discrete variables structural design of frames safe against buckling

On the structural optimization in presence of base isolating devices

The minimum volume design of plane frames constituted by elastic perfectly plastic material and subjected to appropriate combinations of fixed, cyclic and dynamic loads is studied. The influence on the design, in terms of cost (volume) and behavioural features, of seismic protecting devices is particularly focused. The considered protecting device is a lead rubber bearing base isolation system. Two optimal design problem formulations are proposed for the structure with or without the protecting device, both based on the so-called statical approach. The minimum volume frame is reached accounting for three different resistance limits: the purely elastic limit, the (elastic) shakedown limit an…

Alterazioni delle caratteristiche fisico-chimiche e meccaniche dei paletti di castagno in ambiente mediterraneo

Identification of stiffness, dissipation and input parameters of multi degree of freedom civil systems under unmeasured base excitations

A time domain dynamic identification technique based on a statistical moment approach has been formulated for civil systems under base random excitations in the linear state. This technique is based on the use of classically damped models characterized by a mass proportional damping. By applying the Itô stochastic calculus, special algebraic equations that depend on the statistical moments of the response can be obtained. These equations can be used for the dynamic identification of the mechanical parameters that define the structural model, in the case of unmeasured input as well, and the identification of the input itself. Furthermore, the above equations demonstrate the possibility of id…

Progetto ad adattamento plastico di strutture ad elementi finiti

L'isolamento dalle vibrazioni

Crack identification in a beam by measure of the responce to white noise

Identificazione dinamica di una struttura complessa in muratura attraverso rumore ambientale: problematiche e strategie

Experimental analysis of flexural behaviour of glued lamellar wood by speckle interferometry

EFFECT OF SURFACE FINISH ON THE TENSILE BEHAVIOR OF DACRON© 360 WOVEN

Nel presente lavoro vengono presentate alcune indagini sperimentali mirate alla caratterizzazione dell’effetto del trattamento superficiale sul comportamento costitutivo di un tessuto in Dacron© 360. Tale tessuto, largamente utilizzato nella realizzazione di vele, è ottenuto dalla tessitura di fili di polietilene tereftalato (PET) e presenta alcune peculiarità dovute al processo manifatturiero. Le prove di trazione realizzate evidenziano le caratteristiche di ortotropia del materiale e l’effetto del trattamento superficiale che si manifesta principalmente in un comportamento più rigido nella direzione dell’ordito ed in quella inclinata e in un aumento della resistenza ultima in tutte le dir…

Influence of protecting devices on the optimal design of elastic plastic structures

The paper concerns the minimum volume design of structures constituted by elastic perfectly plastic material. The relevant optimal design problem is formulated on the grounds of a statical approach and two different resistance limits are considered: in particular, it is required that the optimal structure satisfies the elastic shakedown limit and the instantaneous collapse limit, imposing for each different condition a suitably chosen safety factor. For sake of generality, the structure is thought as discretized into compatible finite elements and subjected to loads quasi-statically acting as well as to dynamic (seismic) loads. The effects of the dynamic actions are studied on the grounds o…

LRPH device optimization for axial and shear stresses

The paper concerns an in-depth study of a special connection for steel structures and the formulation of the related optimal design problem. The connection is called Limited Resistance Rigid Perfectly Plastic Hinge (LRPH) and it represents an innovative device devoted to join steel beam elements of frame structures. The device consists in a sequence of steel cross sections constituted by two parallel flanges with suitably different thickness connected by as many webs with constant and equal thickness. The fundamental innovation of the device is the possibility of designing special connections with elastic stiffness and limit strength independent of each other. Such a special characteristic …

Stochastic response of MDOF wind-excited structures by means of Volterra series approach

Abstract The role played by the quadratic term of the forcing function in the response statistics of multi-degree-of-freedom (MDOF) wind-excited linear-elastic structures is investigated. This is accomplished by modeling the structural response as a Volterra series up to the second order and neglecting the wind-structure interaction. In order to reduce the computational effort due to the calculation of a large number of multiple integrals, required by the used approach, a recent model of the wind stochastic field is adopted.

Analysis of mechanical behaviour of wood species by speckle interferometry

The understanding of the mechanical behaviour of wood is a very important task in modern structural engineering. This is due to the increasing role played by wood structures in modern architecture as well as to its use in the restoration of ancient buildings. However, solid mechanics of wood is very difficult since it is a complex, polymer-based, cellular, inhomogeneous material. Moreover, at the cellular scale wood is not a continuum due to the presence of vascular vacuums and it can be regarded as an anisotropic material. Conversely, at a macroscopic scale when the analysis is carried out on a structural member which is large in comparison to the size of cell, wood is usually considered a…

An optimal design of elastic plastic structures with bounds on transient and steady-state plastic deformations

Effect of surface finish on the mechanical behaviour of Dacron© 360 woven

Abstract In the present paper some experimental analyses of Dacron© 360 woven with and without surface treatment are presented to evaluate the effect of this treatment on the constitutive behaviour. This woven, widely adopted in sail manufacturing, is obtained by weaving polyethylene terephthalate (PET) yarn and it shows some peculiar features due to the manufacturing process. The experimental tensile tests, clearly show the orthotropy behaviour of the material. The effect of the treatment results in a stiffer behaviour especially along the warp and bias direction and in an increment of ultimate strength in all directions.

Gaussian and non-Gaussian stochastic sensitivity analysis of discrete structural systems

Abstract The derivatives of the response of a structural system with respect to the system parameters are termed sensitivities. They play an important role in assessing the effect of uncertainties in the mathematical model of the system and in predicting changes of the response due to changes of the design parameters. In this paper, a time domain approach for evaluating the sensitivity of discrete structural systems to deterministic, as well as to Gaussian or non-Gaussian stochastic input is presented. In particular, in the latter case, the stochastic input has been assumed to be a delta-correlated process and, by using Kronecker algebra extensively, cumulant sensitivities of order higher t…

Evaluation of the shakedown limit load multiplier for stochastic seismic actions

A new approach for the evaluation of the shakedown limit load multiplier for structures subjected to a combination of quasi-statically variable loads and seismic actions is presented. The common case of frame structures constituted by elastic perfectly plastic material is considered. The acting load history during the lifetime of the structure will be defined as a suitable combination of never ending quasi-statical loads, variable within an appropriate given domain, and stochastic seismic actions occurring for limited time interval. The proposed approach utilizes the Monte Carlo method in order to generate a suitable large number of seismic acceleration histories and the corresponding shake…

Welded section defence by LRPD devices

The present paper concerns a special application of some recently proposed structural devices, called LRPD, able to protect the welded sections of frame steel structures from undesired brittle collapse ensuring the good expected ductile behaviour. Standard I-shaped cross-sections are treated, and the proposed devices are suitably considered as moment resisting connections between beams and columns. At first the domain representing the brittle safe conditions is defined in the N,V,M space; then a sample plane frame subjected to seismic load conditions is studied and it is proved that, equipping the structure with the proposed devices suitably designed, the generalized stresses at the welded …

Influence of the quadratic term in the alongwind stochastic response of SDOF structures

A parametric study, regarding the influence of the quadratic pressure term, which is often neglected in the literature, on the stochastic alongwind response of a single-degree-of-freedom (SDOF) structure subjected to wind action, is presented. The results are reported in terms of percentages of difference in the evaluation of the response, by considering and neglecting the quadratic pressure term. The changing parameters considered are: the terrain drag coefficient, the structure height, the structure natural radian frequency, the structure damping coefficient and the wind reference mean velocity. The response stochastic analysis has been carried out in the time domain, by means of the mome…

Il comportamento sismico dei telai tamponati

Experimental and numerical analysis of flexural behaviour of GFRP pultruded material

L'uso di elementi in acciaio per la messa a punto di un set-up di prova per lastre di vetro strutturale di grandi dimensioni

Flexural behaviour of glass panels under dead load and uniform lateral pressure

Abstract In the present paper the experimental results relative to flexural tests on out-of-plane loaded large scale panels made of laminated structural glass are presented and discussed. Glass panels are parts of the structural facade of the Fontanarossa International Airport of Catania (Italy). Panels are mounted on a rigid testing frame and loaded with an uniformly distributed lateral pressure. Two different kinds of tests were carried-out, cyclic and monotonic, able to reproduce the serviceability and the ultimate conditions of the glass panels when subjected to the coupled effects of dead load and horizontal forces, the latter reproducing the wind action. Results obtained focused the h…

Filter approach to the stochastic analysis of MDOF wind-excited structures

Abstract In this paper, an approach useful for stochastic analysis of the Gaussian and non-Gaussian behavior of the response of multi-degree-of-freedom (MDOF) wind-excited structures is presented. This approach is based on a particular model of the multivariate stochastic wind field based upon a particular diagonalization of the power spectral density (PSD) matrix of the fluctuating part of wind velocity. This diagonalization is performed in the space of eigenvectors and eigenvalues that are called here wind-eigenvalues and wind-eigenvectors, respectively. From the examination of these quantities it can be recognized that the wind-eigenvectors change slowly with frequency while the first wi…

Electronic speckle pattern interferometry for the analysis of wood bending behaviour

Optimal design of elastic plastic frames accounting for seismic protection devices

The optimal design of elastic perfectly plastic steel frames with or without suitable protection devices and subjected to static as well as seismic loadings is studied. Two minimum volume problem formulations are proposed, on the grounds of the so-called statical approach, accounting for three different resistance limits: the purely elastic limit, the (elastic) shakedown limit and the instantaneous collapse limit. The adopted load combinations are characterized by the presence of fixed loads, of quasi-static perfect cyclic loads and dynamic (seismic) loads. The linear elastic effects of the dynamic actions are studied by utilizing a modal technique. The proposed treatment is referred to the…

Optimal shakedown design of base isolated structures

The optimal design problem of finite element discretized elastic perfectly plastic structures is studied. In particular, a minimum volume formulation is developed, based on a statical approach, and two different resistance limits are considered: the elastic shakedown limit and the instantaneous collapse limit, imposing for each a suitably chosen safety factor. The structure is thought as subjected to quasi-static loads as well as to dynamic actions. The dynamic features of the relevant structure are determined taking also into account an appropriate base isolation system in order to reduce the seismic effects. According with the Italian code related to the structural analysis and design, th…

Testing mechanical characteristics of chestnut stakes used in bed sills for stream restoration

Using of wood elements for constructing bed sills in Mediterranean streams, where the banks are not protected by tree vegetation, needs an evaluation of biological and mechanical characteristics for evaluating both the wood durability and the effectiveness of the stream restoration project. Very few studies have dealt both with the decay of mechanical characteristics of wood elements employed for stream restoration works and with the changes over time of physical and chemical wood characters. In this paper, for a wood and stone bed sill located in a stream having no shaded banks, the changes of physical and chemical characters detected after 12, 18, 24, 30, 36, 42 and 48 months on chestnut …