Matteo Colombo | Politecnico di Milano (original) (raw)

Papers by Matteo Colombo

Engineering Structures, 2022

ABSTRACT In the last decades, the rapid expansion of the built environment has attracted interest... more ABSTRACT In the last decades, the rapid expansion of the built environment has attracted interest in the development of prefabricated components characterized by reliable structural performances, lightness, energy efficiency and durability. In the design of innovative building systems, High Performance Fiber Rein-forced Cementitious Composites (HPFRCC) and Textile Reinforced Concretes (TRC) are becoming increasingly important, since the use of fibers and textiles can easily enhance toughness and ductility of the plain materials, fitting the key issue of weight reduction and, at the same time, guaranteeing a more efficient exploitation of environmental resources. During the research program, several experimental tests were carried out in order to perform the mechanical identification of individual and coupled materials constituting an innovative multilayer roofing panel.

SP-326: Durability and Sustainability of Concrete Structures (DSCS-2018), 2018

Fibre reinforced concrete is a concrete with a diffused reinforcement based on fibre pull-out res... more Fibre reinforced concrete is a concrete with a diffused reinforcement based on fibre pull-out resistance and its toughness in tension is strongly affected by fibre distribution. The material response of a representative volume is significantly affected by the uncertainties related to fibre location and number: only a homogeneous distribution of fibres can guarantee an isotropic behaviour, but in any case its mechanical behaviour dominated by mode I failure, identified by means of a bent notched beam, shows a large standard deviation. By the way, a structure characterized by a significant capability to redistribute stresses and large fracture volume at the onset of collapse can reduce the sensitivity to the high standard deviation and exhibits a bearing capacity aligned to the average mechanical properties of the composite. In the paper several approaches to compute the coefficient that quantifies this structure ability, K Rd , are proposed, taking as a reference cases a slab on grou...

The design of detailing in discontinuity regions plays a crucial role both for the structure beha... more The design of detailing in discontinuity regions plays a crucial role both for the structure behaviour and for its safety [1,2]. The stress flow in the so-called D-regions, where the strain distribution over the cross-section is significantly non-linear, is well described by strut & tie model. In this work the behaviour of Steel Fiber Reinforced Concrete (SFRC) in a D-region has been investigated. The experimental program refers to the bottle-shaped stress field, that develops significant transverse compressive and tensile stresses, respectively in the bottle neck and far away along the vertical symmetry axis (bursting). The distribution of the high local stresses under the bearing plate causes transverse tensile stresses also along the horizontal upper border, there inducing concrete cracking (spalling). The experimental tests were performed on thin square slabs (270 x 270 x 60mm) made of either SFRC or plain concrete. One fiber type (hooked –end, low-carbon steel, lf = 60mm, df = 0.80mm) and one fiber content (25 kg/m3) were investigated. A uniform vertical displacement was imposed on the top region characterized by a variable depth. Several ratios  (1, 1.5, 2, 2.5 and 3) between the specimen size and the bearing plate width were considered for both SFRC and plain concrete specimens, with the only exception of  = 2.5 for the latter material. The analysis of crack propagation highlights some limits concerning the generally accepted assumptions for the bearing capacity design of these zones and allows us to quantify the related fiber benefits

The paper presents the technical causes of the collapse of Annone overpass, which occurred in Oct... more The paper presents the technical causes of the collapse of Annone overpass, which occurred in October 2016. The tests carried out to identify the characteristics of the materials used for the construction, the verification calculations that led to the identification of the critical mechanism in the collapse and the test on the structural element deemed critical at the time of collapse are summarized. The paper highlights the critical issues occurring concurrently with the passage of the exceptional transports, the safety coefficient in relation to the project loads at the time of construction and that at the time of the passage of the exceptional convoy. The note also highlights some critical aspects of the national infrastructural system, with particular reference to exceptional transports and the methods that could be used to prevent future accidents in the absence of macro-design mistakes. / La memoria presenta le cause tecniche del crollo del cavalcavia di Annone, avvenuto nell'ottobre del 2016. L'articolo sintetizza le prove svolte per identificare le caratteristiche dei materiali impiegati per la costruzione, i calcoli di verifica che hanno condotto alla identificazione del meccanismo di collasso e le prove sulla membratura ritenuta critica all'atto del collasso. La memoria mette in evidenza le criticità sopraggiunte in concomitanza del passaggio del trasporto eccezionale, il coefficiente di sicurezza nei confronti dei carichi di progetto all'atto della costruzione e quello all'atto del passaggio del convoglio eccezionale. Nella nota si mettono in luce anche alcune criticità del sistema infrastrutturale nazionale, con particolare riferimento al trasporto eccezionale e alle modalità che potrebbero essere impiegate per evitare futuri incidenti in assenza di macro-errori progettuali. KEYWORDS: overpass bridge collapse; identification tests; mechanical characterization; steel-bar oxidation measures; diagnostics techniques; structural robustness; safety indexes / collasso di un cavalcavia; test di identificazione; caratteristiche meccaniche; misure di ossidazione delle barre di acciaio; tecniche diagnostiche; robustezza strutturale, indici di sicurezza.

Textiles, 2021

Alkali-resistant (AR) glass textiles are used as the main reinforcement in several composite appl... more Alkali-resistant (AR) glass textiles are used as the main reinforcement in several composite applications due to their good performance-to-cost ratio. A huge variety of textiles are already present in the market; they differ on various parameters, such as, for example, the filaments’ diameters, the geometry, the type of weaving, or the nature of the impregnation coating. To orient manufacturers towards the production of efficient textiles, the most important aspect is the balance between cost and performance. In this paper, a series of different fabrics designed for textile-reinforced cementitious composites were considered. Performance was assessed by means of uniaxial tensile tests and the results are presented in terms of load vs. displacement. Then, the selected AR-glass textiles were compared in terms of fabric efficiency, targeting the effect of each parameter on the textile capacity. The research here presented is part of a comprehensive campaign aimed at the optimization of ...

Materials and Structures, 2021

In the context of the evaluation of the load-bearing capacity of a steel fibre reinforced concret... more In the context of the evaluation of the load-bearing capacity of a steel fibre reinforced concrete (SFRC) elevated slab recently built in northern Italy, this paper presents the study addressing the effects of fibre distribution and orientation. An extensive experimental programme was carried out in a collaboration between Politecnico di Milano and Universitat Politècnica de Catalunya. The programme included mechanical tests on four shallow beams and six notched standard beams. Additionally, uniaxial tensile tests (UTTs), double edge wedge splitting tests (DEWSTs) and double punching tests (DPTs) on 192 drilled core samples extracted from the shallow beams were performed. Inductive tests, measuring the self-induction change that occurs when a SFRC sample is placed inside a coil, were performed on all samples subjected to DPTs to assess fibre distribution. This paper compares direct and indirect tensile tests for the definition of the FRC post-cracking constitutive law, highlighting ...

Applied Sciences, 2019

Textile reinforced concrete (TRC) is a promising high-performance material that has been employed... more Textile reinforced concrete (TRC) is a promising high-performance material that has been employed with success in new constructions, as well as a strengthening layer of existing structural components. In this work, we document the optimisation procedure of textile-based composites for new construction and for the seismic retrofitting of under-reinforced concrete elements and masonry buildings. The study, aimed at maximising the material performances avoiding waste of economic resources, was addressed by means of a series of uniaxial tensile tests conducted on a wide set of alkali-resistant (AR) glass fabrics and TRCs. The samples differed in terms of cement-based matrices, embedded textiles and addition of dispersed microfibers. The results highlight the effects of fabric characteristics and introduction of short fibres on the mechanical behaviour, proposing novel comparison parameters based upon the load bearing capacity and the deformation response of the composites. The applicati...

Journal of Building Engineering, 2018

This paper concerns the investigation of the behaviour of sandwich beams previously tested in fou... more This paper concerns the investigation of the behaviour of sandwich beams previously tested in four point bending through analytical and numerical models. Modelling is a fundamental resource to predict the mechanical response of the element and to investigate the mechanisms that act during the evolution of the test. The sandwich beams here taken into account are characterised by external textile reinforced concrete (TRC) layers and an insulation material (expanded polystyrene, EPS) able to transfer shear stresses. Bond between the layers is obtained during production thanks to an in-pressure casting technique, and no particular device is used in order to transfer shear stresses between the layers. Two beam slenderness values are taken into account. An analytical and a numerical approach have been used in order to predict the experimental behaviour: concerning the analytical approach, a model based on the Stamm and Witte sandwich theory has been developed including material nonlinearity; concerning the numerical analysis, a finite element (FE) model has been built in ABAQUS including material and geometry non-linearity. The assumption of perfect bond is used in both cases. The non-linear analytical and finite element models have been validated, as a good agreement with experimental results has been achieved. The experimental identification of material parameters-TRC in tension, mortar in compression and EPS in tension, compression and shear-is crucial for the definition of proper constitutive laws for the models and is here presented and discussed. For both approaches, the assumptions of modelling TRC in bending as homogeneous and assuming perfect bond between TRC and EPS (even when behaviour becomes highly non-linear) have been proved to be reliable. Analytical and FEM results show that EPS non-linear behaviour and TRC membrane and bending behaviour govern the response. The FE analysis also highlights the mechanisms involved in specimen failure.

Materials and Structures, 2018

Fibre reinforced concrete shows enhanced performance in statistically redundant bi-dimensional st... more Fibre reinforced concrete shows enhanced performance in statistically redundant bi-dimensional structural elements that undergo biaxial bending. However, the lack of reinforcing rebars in fibre reinforced structural elements may affect the structural ductility which may further affect the overall load bearing capacity of these structures. To investigate the influence of fibres in such elements, six concrete plates of 2000 9 2000 9 150 mm reinforced with steel fibres and/or reinforcing rebars are tested under a central concentrated load. Two of the elements are reinforced with only 35 kg/m 3 of steel fibres, two are reinforced with 2-way conventional reinforcing rebars (35 kg/m 3 , in each direction) and two are reinforced with both steel fibres and rebars. The specimens are simply supported at the middle of each side by means of a bilateral restraint; the deflection response and cracking behaviour of all the specimens are recorded and compared. Moreover, the methodology introduced in the fib Model Code 2010 for design of steel fibre reinforced concrete is implemented to predict the ultimate load bearing capacity of these elements and its reliability is determined in comparison with the experimental values. The comparison of the behaviour of the specimens reinforced only with steel fibres, with those reinforced with steel rebars, shows the higher efficiency of steel fibres in terms of load carrying capacity, but with a lower ductility. The combination of steel fibres and rebars allows for a better exploitation of the capacity of both reinforcement solutions. Finally, the reliability of the approach implemented for the ultimate load prediction is shown and the need of rebars in providing ductility in fibre reinforced concrete members is underlined.

International Journal of Architectural Heritage, 2017

The paper presents the results of an experimental and numerical investigation on Azzone Visconti ... more The paper presents the results of an experimental and numerical investigation on Azzone Visconti bridge, a XIV century arch bridge in Lecco (northern Italy). Starting from the historical data and from an extensive mechanical characterization of both the soil constituting the riverbed and of the masonry constituting the piers, the aim of the study is to investigate the bearing capacity of the bridge. A testing loading scheme defined according to the current Italian Code is adopted to check the structural behaviour. A simplified finite element structural model was conceived and calibrated as a control tool to safely perform the experimental tests. Post-test nonlinear finite element analyses have allowed the prediction of the bridge bearing capacity and the definition of the bridge class according to the Italian regulations.

Proceedings of the 9th International Conference on Fracture Mechanics of Concrete and Concrete Structures, 2016

In the framework of the CEN Committee involved in the writing of the fiber reinforced concrete st... more In the framework of the CEN Committee involved in the writing of the fiber reinforced concrete structure standards, a strong debate has been focused on the possibility to use a stress-strain rather than a stress-crack opening constitutive relationship, even if only the second one is physically meaningful after the cracking of the matrix. The use of a stress-strain model, even if it can be regarded as an effective simplification in many cases as it is in R/C structures, can be justified by the rough choice of a unique crack spacing in the range of 125 mm. In the paper, the modeling of different FRC cross sections and in particular of a thin-walled open cross-section profile longitudinally reinforced with steel bars like a FRC box-culvert (U-channel) highlights as only the use of a correct structural characteristic length when a simplified Navier-Bernoulli plane section model is adopted prevents the overestimation of the bearing capacity in bending. A comparison with F.E. model and previous experimental tests on full-scale structures are also proposed.

In this work, a numerical procedure based on a simplified FE model for the analysis of undergroun... more In this work, a numerical procedure based on a simplified FE model for the analysis of underground tunnels subjected to internal explosion is proposed. The procedure can provide a valuable tool for designers for checking the structural tunnel safety in case of an internal blast event. The tunnel geometry considered is that adopted for the Brescia metro line. It has an inner diameter of about 8.15 m, a length of about 13.7 km and is located from about 23.1 m below the surface (distance measured from the surface to the centre of the tunnel). Six segments and a smaller key segment (6+1) compose the tunnel. The segment average length is of about 1.5 m. The FE model is firstly tested under serviceability static loads. Dynamic analyses are carried out in order to reproduce the blast scenario. Aim of this work is the pressure-impulse (p-i) diagrams generations for underground tunnel in case of internal explosion. Limit state criteria based on ultimate flexural and shear capacities are intr...

The interest in the use of high performance cement-based materials (HPC) has been recently increa... more The interest in the use of high performance cement-based materials (HPC) has been recently increased due to the need to intervene on existing buildings that do not meet the structural and seismic requirements imposed by the revised national codes. A retrofitting strategy that might be successfully applied to several precast buildings in Northern Italy is represented by the substitution of the unsafe roofing elements with innovative multilayer panels characterized by lightness and high structural performances. The significant self-weight reduction might play a positive role on both the static and the dynamic building behavior. The paper investigates the flexural behavior of three sets of prismatic specimens (400 mm long, 70 mm wide, 15 mm thick); the first set was reinforced with unoriented high carbon steel microfibers, the second one with two layers of glass fabrics and the third one with a combination of steel fibers and textiles. Performing four point bending tests, it was find o...

Existing buildings are characterized by a large energy consumption due to heating and air-conditi... more Existing buildings are characterized by a large energy consumption due to heating and air-conditioning. Hence, their energy retrofitting has to be considered with a high priority. In this perspective a multi-layer prefabricated façade sandwich panel characterized by an internal insulation layer and by two external layers of Textile Reinforced Concrete (TRC) is proposed for the application on existing building walls. Just the insulating material is used to transfer the shear between the two structural TRC layers. The main goal of the work is to provide the mechanical characterization of this panel. The research is developed at material, cross-section and full-structure level. In this paper the global sectional behaviour is investigated: results concerning bending tests on sandwich beams are proposed, together with the developed numerical simulations.