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Dims - Structural Engineering
Laboratories, Research Themes and Publications |
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Page last updated: 12/08/2005
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Laboratories |
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Laboratories that can be used are those of the Departments involved in the Ph.D. programme.
Facilities can be used at research centers, industries or other Universities,
on the basis of agreements between these and the Faculty.
List of External Laboratories
• Institute for Systems, Informatics and Safety, Joint Research Centre, Ispra, EU.
• Brennero Highway S.p.A., Trento.
• Research Center for the Preservation and the Restoration of Architectural and Environmental Assets, Università di Brescia.
• Public Works and Civil Protection Department, Provincia Autonoma di Trento.
• Geological Service, Provincia Autonoma di Trento.
• Water Department, Provincia Autonoma di Bolzano.
• Earthquake Engineering Research Center, University of Bristol, Bristol, UK.
• International Center for Mechanical Sciences, Udine.
• Technological Research Institute for Ceramics, Consiglio Nazionale delle Ricerche, Faenza.
• Institute for Timber Technology, Consiglio Nazionale delle Ricerche, Trento.
• Istituto Trentino di Cultura, Center for Technological and Scientific Research, Trento.
• The Specialization School for “Monument Restoration”, History and Architecture Conservation Department., Politecnico di Milano.
• Provveditorato delle Opere Pubbliche di Trento.
• Rose School; European School for Advanced Studies in Reduction of Seismic Risk, Pavia.
• National Dam Service, Presidenza del Consiglio dei Ministri, Roma.
• Architectural and Monumental Assets Office, Provincia Autonoma di Trento.
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Research Themes: Mechanics of Materials and Structures |
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Current swift technological progress calls for
advanced research on the mechanical behaviour of solids and structural elements. On
one hand, the design and modelling of mechanical behaviour has been extended from
classical structural elements used in civil, naval and aeronautical engineering to a
broad class of new materials, used for instance in microelectronics, bioengineering,
mining and off-shore engineering. On the other, simulation of the behaviour of structural
elements is nowadays analyzed far beyond the linear field, including geometric and
constitutive non-linearity, defects and fractures. Engineers must be able to deal
with problems in which a sophisticated modelling phase requires advanced knowledge.
The objective of the curriculum in “Mechanics of Materials and Structures” is the
formation of professional personnel who can work in public and private research
institutions with knowledge of the instruments required for advanced modelling of
solids and structures.
The main research topics of this area involve the following targets.
Topic 1: Numerical methods for solids and structural mechanics. Enhanced Finite Element plate models using asymmetric stresses. Boundary Element Method procedures in linear and non-linear elasticity. Fast Multipole Method for large-scale Boundary Element analysis.
Topic 2: Constitutive relations and homogenization theory. Extrema of elastic moduli in anisotropic elasticity. Elastoplasticity for granular materials.
Topic 3: Wave propagation and dynamics. Dynamics of taut cables on an elastic foundation. Dynamic Finite Element simulation of rock impact against catch fences. Boundary element techniques for wave propagation analysis.
Topic 4: Non-linear theory for solid materials, stability and bifurcation. Non-linear elasticity, elastoplasticity at large strains. Bifurcation theory for elastic ad plastic solids.
Topic 5: Fracture and damage mechanics. Crack propagation in elastic-plastic materials. Asymptotic solutions for linear and non-linear elastic materials. Strain localization and progressive damage of geomaterials.
Topic 6: Thermo-electro-opto-chemio-mechanical coupling. Multifield approaches to elastoplasticity. Piezo-elasticity. Photo-elasticity. Shear banding in thermo-plasticity. Chemical interaction in poroplasticity.
Topic 7: Multi-phase materials. Poroelasticity and poroplasticity. Crack propagation in porous, fluid-saturated materials.
Topic 8: Interfaces in solids and contact mechanics. Effect of linear interfaces in problems of fracture and homogenization. Non-linear interfaces in biomechanics. Non-linear constitutive laws in contact between solids.
Topic 9: Experimental characterization of hydro-mechanical behaviour of porous media. Measurement and control of soil water tension, experimental investigation of stress state variables, shear strength under suction and water controlled conditions.
Topic 10: Modelling of hydro-chemo-mechanical coupling in multi-phase materials. Experimental analysis of the mechanical behaviour of sand. Constitutive modelling of soil behaviour. Strain localization in elastoplasticity. Electro-chemo mechanical and thermo-hydro-mechanical coupling in porous media.
Topic 11: Stability Modelling for soil structures. Slope stability analysis using boundary methods, modelling of landslide evolution, management of in situ monitoring systems, effects of rainfall on landslide triggering mechanisms.
Results:
Topic 1: Numerical methods for solids and structural mechanics
Enhanced Finite Element plate models using non-symmetric stresses: Reissner-Mindlin plates are considered and it is assumed that in-plane shear stresses are not a priori symmetric. This choice allows decoupling the equilibrium equations and involves introducing an in-plane infinitesimal rotation field corresponding to drilling degrees of freedoms (dofs). Out of plane shear stresses are then obtained such that equilibrium equations are exactly satisfied. The element does not exhibit locking effects and the exact thin plate limit is reached.
The Boundary Element Method has been studied extensively as an analysis tool for solid and structural mechanics problems.
The symmetric Galerkin version of the method is a variational formulation (entailing double integration) recovering symmetry and sign-definiteness properties, which are otherwise lost using collocation approaches. Interesting results have been obtained with reference to various computational aspects concerning the symmetric approach, both in two-dimensional and three-dimensional situations.
The symmetric formulation has been applied to linear elastic fracture mechanics problems; the necessary BE discretization being required only for the displacement discontinuity surface and for the domain boundary. The procedure has been extended to allow for the presence of cohesive cracks (in which displacement discontinuities are related to traction on the cracks surfaces through a softening constitutive law).
Three-dimensional problems have also been dealt with using the same approach. The evaluation of the double surface-integrals involved in the formulation poses serious problems when the kernel singularity is activated. This aspect has been studied in detail and special algorithms have been developed and implemented to tackle the singular integration over adjacent or coinciding elements.
Three-dimensional fracture mechanics problems have been solved by means of the computer code developed on the basis of the above-described formulation. Stress intensity factors have been evaluated by extrapolation from displacement discontinuities.
Plane strain, elastic deformations superimposed upon a given, homogeneous and finite strain are solved using a boundary element technique developed on the basis of an ad hoc Green’s function.
One of the main disadvantages of the Boundary Element Method in its classical formulation is its lack of scalability and its substantial inefficiency for the analysis of complex 3D problems. One of the most important frontiers in BEM research nowadays is directed towards the development of fast algorithms (such as the Fast Multipole Method) able to overcome the limitations of the standard approach, thus freeing the effective power of BEM for the solution of three-dimensional large-scale, external problems with moving boundaries. At the same time, fast algorithms allow an optimal coupling with the Finite Element Method, without affecting it with the severe performance loss imposed by classical BEM approaches.
Several codes have been developed to address different problems, from elastostatics to wave propagation.
Topic 2: Constitutive relations and homogenization theory
Extrema have been found of Young's modulus within several classes of anisotropic elastic materials. Constitutive equations have been formulated for granular materials subject to large strains. These are based on a new yield function and plastic potential surface. Cold forming of ceramics is addressed.
Topic 3: Wave propagation and dynamics
Closed form solutions for the dynamic of taut cables on elastic foundations have been found, which can be usefully adopted to study the motion of contact wires.
A complete simulation in the dynamic range of the behaviour of flexible interceptive devices during the impact produced by falling rocks has been performed.
Flutter instability in Mandel sense has been addressed for elastoplastic continuum with non-associative flow law. Dynamic behaviour of periodic structural interfaces has been analyzed to produce sharp filters for elastic waves.
A Boundary Element code has been developed and implemented for the analysis of three-dimensional wave propagation problems.
Topic 4: Nonlinear theories for solid materials, stability and bifurcation
Bifurcation of various elastic structures has been solved using the Trefftz criterion. A general theory of bifurcation and stability for large elastoplastic deformation has been extended to nth-order bifurcation. Strain localization has been thoroughly considered for broad classes of materials, including anisotropic-elastic, plastic solids and damaging materials.
Topic 5: Fracture and damage mechanics
Asymptotic fields for steady-state crack propagation in various elastoplastic materials have been obtained. In particular, geomaterials and porous plastic metals have been considered. Crack trajectories in elastic-brittle materials resulting from interaction of fracture with defects and inclusion have been derived under plane strain and stress assumption.
Effect of pre-stress on crack tip fields in elastic, incompressible solids has been systematically investigated.
Topic 6: Thermo-electro-opto-chemio mechanic coupling
Photoelasticity techniques are under development for masonry structures. Strain localization is under investigation in multifield theories of inelastic behaviour of materials.
Topic 7: Multi-phase materials
Steady-state crack propagation has been analyzed in porous, fluid saturated materials. Strain localization in fluid saturated geomaterials is currently under investigation.
Topic 8: Interfaces in solids and contact mechanics
Linear interfaces have been analyzed in different problems, including loss of uniqueness of incremental response, crack deflection and homogenization of linear composites. Non-linear interface constitutive equations have been formulated for modelling the mechanical response of periodontal ligament (connecting teeth to the alveolar bone).
Topic 9: Experimental characterization of hydro-mechanical behaviour of porous media
Many natural and artificial materials are porous, with one or more fluids filling the pore space. Soil mechanics, rock mechanics, hydrogeology, geophysics, environmental geotechnics as well as biomechanics deal with porous media. The research has mainly focused on a special class of multiphase material, i.e. unsaturated soils. A number of experimental techniques have been developed to investigate the hydraulic and mechanical behaviour of these materials.
A new apparatus was developed to investigate the stress variables suitable to model the mechanical behaviour of unsaturated soils.
Experimental evidence has been provided in support of the validity of the world-wide used axis-translation technique.
A new instrument has been designed to measure soil water tension up to 2 MPa.
Innovative experimental procedures for tensiometer measurement as well as models to explain cavitation in tensiometer measurement have been proposed.
A new apparatus for testing unsaturated soils under 1-D condition has been presented. It implements the osmotic technique to control soil matric suction.
Experimental procedures for measuring total suction using transistor psychrometer have been proposed.
The filter paper technique for total and matric suction measurement has been investigated and a modification of the ASTM standard is being proposed.
Topic 10: Modelling of hydro-chemo-mechanical coupling in multi-phase materials
Modelling hydro-chemo-mechanical coupling of saturated and unsaturated soils is of great importance in many engineering problems. For example, slope stability in clay soils, design of clay barriers for nuclear and municipal solid waste, soil amelioration.
By using a new apparatus developed in the geotechnics laboratory, the factors affecting the onset of unstable behaviour in saturated loose sand were analyzed in detail.
A constitutive model for the simulation of the mechanical behaviour of natural and reconstituted clays has been developed.
The theoretical analysis of onset of localization and of post-localization behaviour has been performed and compared with experimental results with particular emphasis on elastic anisotropy.
A theoretical framework and a constitutive model for the analysis of chemo-mechanical coupling in expansive saturated clays subjected to changes of ion content in pore water has been developed.
An analytical solution and a finite element model for non-isothermal dynamic analysis of saturated soils were presented.
Topic 11: Modelling of stability of soil structures
Laboratory testing and theoretical models have been applied to investigate engineering problems involving geomaterials.
Emphasis has been put on the stability of slopes both artificial (earth dams, embankments, earth banks) and natural.
Bound methods have been applied to analyze slope stability in dry, saturated and unsaturated geomaterials.
A viscous-elastic plastic constitutive relationship has been implemented in a landslide evolution model.
Numerical techniques for processing in-situ monitored data have been used to define alarm thresholds for landslide movements.
Moving from unsaturated soil concepts, a model has been proposed to define rainfall thresholds for landslide triggering.
The hydrological effects of vegetation on slope stability have been investigated. |
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Research Themes: Design, Preservation and Control of Structures |
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The research of this area focuses on
- the behaviour of structures;
- the safety evaluation of structures using experimental analyses based on non-destructive testing techniques and comparison with computer models;
- durability and restoration which have to be considered during design;
- the monitoring, analysis, diagnosis and strengthening of historical buildings taking into account soil-structure interaction phenomena.
The main research topics involve the following scopes:
Topic 1: Steel and Steel-Concrete Composite Structures
Innovations in seismic design and damage control of steel and steel-concrete composite structures.
Topic 2: Timber Structures
Static and seismic behaviour of traditional and innovative connections for timber elements, mechanical characterization of timber elements (with particular regard to those belonging to historic heritage buildings), parametric analysis of non-constant depth timber beams and of timber-based composite beams with non-linear shear connection. Timber-concrete composite elements for floors and bridges. Resistance of timber elements and joints to fire.
Topic 3: Racks and Scaffold Systems
Experimental and numerical analysis of racks and scaffold systems with reference to single components and to the overall response. Development and validation of design methods.
Topic 4: Smart Structures
Experimental modal testing of large-scale civil structures. Advanced signal processing. Methods for vibration based damage detection and localization. Sensors and data acquisition. Long term monitoring and control systems. In-field application to historical and monumental structures.
Results:
Topic 1: Steel and Steel-Concrete Composite Structures
1a) the knowledge of the cyclic performance of seismic-resisting steel joints and composite members and joints has been broadened;
1b) innovative concepts and details, like composite beams with partial shear connection and dissipation zones and semi-rigid partial-strength beam-to-column joints have been introduced;
1c) general criteria and specific rules for the design of earthquake-resistant composite sway frames and braced frames have been established;
1d) issues related to experimental and numerical methods in earthquake engineering have been explored, such as: time integration of materially non-linear dynamic equations; time integration of geometrically non-linear dynamic equations; on-line computer controlled testing techniques devoted to the evaluation of structures subjected to dynamic and earthquake loads.
Topic 2: Timber Structures
2a) The availability of a wooden queen post truss of the early nineteen century (from the “Teatro Sociale" in Trento) has provided a unique opportunity to evaluate the performance and the restoration needs of these structures, and to assess the possible intervention procedures, resorting to both traditional and innovative (glued in steel bars) methods. The damage was identified using non destructive test methods, and the actual performance of each timber element of the truss was assessed by means of full scale loading tests in the elastic field.
2b) The static behaviour of traditional and innovative connections for timber elements has been identified by means of full-scale experimental tests and numerical analysis. Specifically, the following joint mechanisms were exploited: (i) moment-rotation behaviour of joints usually modeled as pin joints; (ii) the splitting strength of timber beams loaded by dowel-type connections; (iii) the behaviour of glued-in bars acting parallel and perpendicular to the grain.
2c) The experimental program, on full-scale timber-concrete composite floors and push-out specimens, allowed for evaluation of the mechanical performance (strength, stiffness and ductility) of different types of connections, as well as of the influence of the connections on the global behaviour of the composite structure. As a possible application, research has been focused on the use of timber-concrete composite structure for building bridges and pedestrian bridges.
2d) The study of degradation of the mechanical properties of timber exposed to fire has been deepened. Protective materials and design detailing have been identified, capable of improving the fire resistance of timber elements and joints.
2e) The parametric analysis of pitched cambered, double tapered and curved glulam beams has allowed the exploitation of the influence of the geometric parameters, of the type of load, and of the orthotropic modules of elasticity on the maximum stress values (parallel and perpendicular to grain) and on deformations. The results were compared with results in the literature and with the design rules of the main structural codes.
2f) The numerical analysis performed on simply-supported timber-based composite beams with constant load, has outlined the influence of the main parameters of shear connection (the elastic stiffness, the strength degree, the ductility, the spacing – constant or uneven) on the overall behaviour of beams. As a result, the non-linear behaviour of the composite beam is quite easily predictable up to failure as a function of connection and of section parameters.
Topic 3: Racks and Scaffold Systems
Pallet racks:
3a) Equipment was developed for testing the behaviour of beam-to-column joints, short columns in compression (stub-column tests),and base-plate joints have been developed.
3b) A wide database of beam-to-column joints and stub-columns has been developed, based on an extensive experimental program.
3c) A study on the influence of the beam-to-column joint modelling on the structural behaviour of commercial steel storage pallets racks have been carried out.
3d) Appraisal of the influence of different buckling modes (local, global and distortional) on the design by means of testing procedures has been exploited.
3e) A draft design recommendations document for steel storage pallets racks has been proposed.
Scaffolds structures:
3f) Preliminary studies on the influence of the second order effects on the structural behaviour of prefabricated steel scaffolds have been completed.
3g) Simplified second-order analysis methods have been proposed and experimentally validated.
Topic 4: Smart Structures
4a) A modal testing methodology (encompassing sensors selection and location, excitation techniques, data acquisition, signal processing) has been developed, which specifically applies to full-scale civil structures. The methodology has been validated on a number of case studies, including: historical heritage building, bridges, experimental buildings, testing facilities and subassemblies.
4b) New dynamic response features for vibration-based damage detection have been experimentally identified and theoretically investigated. These include (i) the Coulomb friction damping signature and (ii) the appearance of dispersion phenomena of the 'frequency splitting' type in the free response of structures. Results have been implemented in novel damage detection techniques.
4c) Web-based remote monitoring and control concepts, for the real-time safety assessment of civil structures, have been developed and employed into demonstrative set-ups.
4d) A pilot monitoring system has been permanently installed on the Dome of the San Gaudenzio Basilica in Novara, consisting of 124 sensors (extensometers, distance gauges, load cells, level transducers and a pendulum, and thermocouples), 17 field-point a PC based data acquisition station. The system is remotely controlled via modem connection.
4e) Prototype of web-based monitoring system for real-time assessment of civil structures.
4f) Data-set relevant to the dynamic characterization of the Portogruaro Bell Tower. |
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