Marialaura Malena

Analytical Modeling of Composite-to-Masonry Prisms Bond

The composite-to-substrate interfacial stresses transfer mechanism is one of the critical issues in externally-bonded structural strengthening by means of composite fabrics. In this work, an analytical approach for modeling the debonding process of a composite on a non-homogeneous substrate is developed and applied to simulate the loss of bond of FRP on brick masonry. The analytical formulation is based on the experimental outcomes of bond shear tests, which are part of a Round Robin activity involving several laboratories. The experimental work is the follow up of a previous one [1], and comprises 12 single-lap shear tests of four kinds of unidirectional reinforcement, i.e., glass, carbon, basalt and steel, applied with epoxy resin to masonry prisms composed by five clay bricks and four mortar joints. The analytical simulations of the experimental tests rely upon a bi-linear non-homogeneous bond-slip law that was calibrated using the experimental population. Eventually, the analytical results are compared to experimental ones both, in terms of global (load to displacement curve) and local behavior (strain profile on the reinforcement for increasing load values).

A Closed-Form Analytical Solution to the Debonding of SRG on Curved Masonry Substrate

Steel Reinforced Grout composites have become a popular technique for strengthening masonry arches and vaults. The SRG composites are Ultra High Tensile Strength Steel unidirectional textiles applied to masonry substrate by mean of inorganic mortar. The weakness of SRG-masonry joints is the debonding at the matrix fibers interface during the stresses transfer process. In the case of arches and vaults the interface bond properties are also affected by the curved geometry of the substrate. In this work, a closed-form analytical solution to the debonding process of a thin plate bonded on a rigid substrate with constant curvature is proposed. The work provides an upgrade of the model previous prosed by the authors (Malena and de Felice 2014). In the present work the substrate curvature is such that the normal stresses arising at the interface are tensile, as in the case of reinforcing systems applied to the intrados of a masonry arch (Malena and de Felice 2014), or compressive as for reinforcing systems applied to the extrados of a masonry arch. The proposed model describes the interfacial stresses transfer mechanism in the framework of fracture mechanics by two laws describing the behavior in normal (pure opening mode: Mode I) and in tangential (in plane shear mode: Mode II) directions. The coupling deriving from curvature is introduced directly in the cohesive laws describing the bond properties. The outcomes of the proposed predictive model are validated by comparing them with the results derived from an experimental campaign of bond tests on straight and curved substrates made of bricks assembled with mortar and strengthened with SRG.

Refined and Simplified Numerical Models of an Isolated Old Highway Bridge for PsD Testing

RETRO’ project aims at studying the seismic behaviour of existing reinforced concrete (RC) bridges and the effectiveness of retrofitting systems based on seismic isolation of the deck of the viaduct. The research program focuses on a typical non-compliant bridge system for earthquake loading, designed for gravity loads only. The prototype structure is the Rio Torto bridge system, which is located in a region of medium seismic hazard in Italy. The seismic vulnerability of the as-built framed pier bridge is first assessed. A typical seismic isolation system, employing slide spherical bearings, is then designed as a passive control retrofitting measure. The present chapter discusses the non-linear response of the Rio-Torto viaduct in the “as-built” and “isolated” configurations. The seismic performance assessment is carried out by utilizing refined non-linear structural models implemented in an advanced and reliable computer platform. The earthquake behaviour of refined models used for the sample structure accounts for non-linear phenomena of the viaduct, e.g. strain penetration of plain bars, shear deformation of transverse beams, flexural deformations in columns and beams. The finite element models are calibrated on the basis of experimental tests results. The assessment of the seismic response system is investigated in terms of local and global response parameters. In addition, the effectiveness of the isolation systems used as a retrofitting system is also investigated numerically. The outcomes of the comprehensive nonlinear analyses are used to simulate the seismic response of the viaduct in the as-built and isolated configurations during Pseudo-dynamic testing, which is illustrated in a companion chapter.

Three-Dimensional Numerical Modelling of Historical Masonry Structures Affected by Tunnelling-Induced Settlements

This paper focuses on the interaction between tunnelling and historical masonry structures. These latter often characterise the centre of many cities and should be preserved from possible tunnelling-induced damage. In recent years the Authors of this contribution have adopted an advanced numerical approach to investigate this issue in the two-dimensional domain, schematising the block masonry structure as a homogenised anisotropic medium [1, 2]. This study extends the approach to three-dimensional conditions. The behaviour of masonry is described by a modified version of the Jointed Rock model, named hereafter as Jointed Masonry model, an anisotropic elastic perfectly plastic constitutive model implemented in the code Plaxis 3D. This model takes into account the directional properties of the medium, identifying the orientation of three planes along which the Mohr-Coulomb yield criterion applies. The paper first briefly describes how the original Jointed Rock model was modified to more realistically account for some specific features of the nonlinear mechanics of masonry. This is followed by the 3D analysis of a tunnelling-structure interaction problem, aimed at highlighting the key features of the proposed masonry model.

Non-Linear Modeling of Masonry Arches Strengthened with FRCM

Recent seismic events, such as the Central Italy (2016), the Emilia (2012) and L’Aquila (2009) earthquake, have demonstrated the high vulnerability of cultural heritage represented by historical and monumental buildings. These structures are often characterized by the presence of elements with a curved geometry such as arches and vaults, which interact with the vertical elements (walls or columns) during the earthquake motion, producing a significant effect on the seismic response of the entire structure. Aiming at the reduction of the seismic vulnerability of curved masonry elements, several techniques of reinforcing based on composite fiber materials, have been recently developed and widely investigated by means of experimental tests and numerical simulations. The using of fiber reinforced systems, applied through cementitious mortar (FRCM), is becoming a very common technique of retrofitting for historical and monumental masonry buildings. This technique, if compared to the using of fiber polymeric materials (FRP), is more compatible with the mechanical properties of the masonry and more appropriate with the preservation needs of cultural heritage, associated to the historical constructions. A discrete macro-modeling approach, already available in the literature for modeling masonry structures with plane and curved geometry, is here employed to predict the non-linear behaviour of masonry arches strengthened with FRCM. In that approach the reinforcement is explicitly modeled by using a rigid plate, while the interaction between the reinforcement and the masonry support is governed by a discrete zero thickness interface. In this paper the interfacial behavior is updated with a more sophisticated bond-slip constitutive law specifically conceived for FRCM reinforcement within the framework of fracture mechanics; in particular the proposed calibration takes into account both the pure opening mode (mode I) and the in plane shear mode (mode II). The obtained numerical results are compared with an analytical closed form solution of the problem and validated by mean of experimental tests on prototypes, available in the literature.

Seismic design and characterization of a new isolation system for high voltage circuit breakers based on wire-rope devices

This paper briefly describes the design and the characterization of a new base isolation system for the seismic protection of HV ceramics circuit breakers, in order to be qualified according to the standard CEI 62271-207. The solution adopted is based on the use of Wire Ropes. Accurate numerical analyses and experimental tests performed on a typical HV breaker upon a shaking table demonstrated the effectiveness of the proposed solution. An on-site installation in several Italian substations of this system has permitted to verify the simplicity and rapidity of the intervention necessary for the seismic upgrading of the circuit breaker.Copyright