Experimental and numerical evaluation of fiber-matrix interface behaviour of different FRCM systems

Abstract Fiber Reinforced Cementitious Matrix (FRCM) composites are a relatively new strengthening system family, whose mechanical behavior is strongly affected by the wide array of possible inorganic matrices and composites fabrics that can be used and coupled together. Structural tests highlighted that global capacity of the system is strongly affected by fabric-matrix adhesion mechanism. In the present paper, the experimental results of tensile and single-lap shear tests, aimed to define mechanical properties of four FRCM types, are discussed and compared. For each system type, the failure modes for both types of test have been physically identified and clarified. The following development of detailed finite element models, carefully reproducing the mechanical behavior of the different layers of the strengthening system, allowed for the proposal of a reliable shear stress-slip relation for the fiber-matrix interface. The experimental outcomes showed the relevant dispersion of the results in terms of performance, effectiveness and failure mechanisms exhibited by the different FRCM types while the numerical interpretation allowed for a better understanding of the reasons and the parameters behind them

Structural Characterization of an Historical Building by Means of Experimental Tests on Full-Scale Elements

In order to properly design strengthening intervention of existing buildings, careful assessment of the structural behavior is certainly required. This is particularly important when dealing with historical constructions made of heterogeneous materials like masonry or stonework. In this context, this paper presents the results of knowledge process on a large monumental nineteenth century building located in Trieste. The traditional investigation approach considering a wide number of destructive tests for characterization of materials and evaluation of the structural details were not admissible due to the valuable cultural and historical importance of the building. Therefore, an alternative and not conventional investigation approach has been considered. After a wide historical research and a detailed structural survey, it has been possible to identify the main structural systems of the building. Then, to characterize the structural response, a limited number of nondestructive tests but on full-scale typological systems have been preferred to a larger number of destructive tests on specimens of the different materials. The selected experimental load tests have been conducted in order to assess the actual structural response of the main systems that constitute the building, thus allowing for a fine tuning of both the rehabilitation interventions and the numerical finite element models

Post‐earthquake estimates of different ground motion intensity measures for the 2012 Emilia earthquake

Estimates of the earthquake ground motion intensity over a geographical area have multiple uses, that is, emergency management, civil protection and seismic fragility assessment. In particular, with reference to fragility assessment, it is of interest to have estimates of the values of different ground-motion intensity measures in order to correlate them with the observed damage. To this purpose, the present paper uses a procedure recently proposed in the literature to estimate the ground-motion intensity for the 2012 Emilia mainshocks, considering different groundmotion intensity measures and directionality effects. Groundmotion prediction equations based on different site effect models, and spatial correlation models are calibrated for the Emilia earthquakes. The paper discusses the accuracy of the shakemaps obtained using the different soil effect models considered and presents the obtained shakemaps as supplementary material. The procedure presented in the paper is aimed at providing ground motion intensity values for seismic fragility assessment and is not intended as a tool to estimate shakemaps for rapid emergency assessment

Behavior factor of concrete portal frames with dissipative devices based on carbon-wrapped steel tubes

AbstractThe key element characterizing the seismic vulnerability of existing prefabricated RC structures, not designed for earthquake actions, are friction-based connections between structural members; mainly those between beams and columns and beams and roofing beams. The paper discusses the effectiveness of dissipative connectors made of carbon wrapped steel tubes. In particular, it presents the results of Incremental Dynamic Analyses on portal frames, aimed at evaluating behavior factor values to be used in design. A simplified formula for estimating the behavior factor is also proposed. Results of nonlinear IDAs suggest that the introduction of these dissipative devices in friction-based beam-column joints provides an effective connection between structural members and, in addition, reduces the forces transmitted to columns, improving the seismic behavior of the entire structure

Self-compacting concrete with recycled concrete aggregate: Study of the long-term properties

This paper investigates the shrinkage and creep of self-compacting concrete prepared with coarse and fine recycled concrete aggregates (up to 40% of total amount of aggregates). Physical properties and porosity measurements are studied and related to the mechanical properties. Results highlight that self-compacting characteristics are maintained when recycled aggregates are utilized and their good quality promotes high mechanical properties. Creep behavior and pores size distributions are more influenced by the content and assortment of recycled aggregates, although their effect is more limited compared to what occurs in traditional concrete with recycled aggregates

Experimental characterization of the mechanical behaviour of U-shaped dissipative devices

Energy dissipation devices are used in earthquake engineering in order to reduce the negative effects of ground-motions on structures, thus limiting damage to structural and non-structural components. Different technologies have been proposed to this aim, i.e. viscous fluid dampers, friction-based dampers, hysteretic dampers, etc. Among the different solutions available the present paper focuses on a specific type of hysteretic dampers, U-shaped dissipators. They were first proposed in the 70s and to date have found limited application in the design practice, mainly in buildings with structural walls, exploiting the relative displacement between adjacent walls to dissipate energy. The paper presents the results of an experimental campaign aimed at characterizing the mechanical behaviour of energy dissipators with linear movement, based on U-shaped steel plates. Different configurations were designed and tested, imposing displacement cycles of increasing amplitude. The paper discusses the observed energy dissipation capacity and the stability of the hysteretic cycles

New Solutions for the Modelling and Design of a Hand Exoskeleton System

Recently, a prototype of a hand exoskeleton for post-stroke rehabilitation purpose was proposed by the Group of Robotics, Automation and Articular Biomechanics (GRAB) at the Department of Industrial Engineering, University of Bologna. The prototype comprises five planar mechanisms (one per finger) globally actuated by two DC motors. A total of fifteen human-machine connections are needed to fasten the device to the patient hand. The moving link of the thumb mechanism is actuated by a spatial RSSR mechanism whose frame link geometry must be ad hoc regulated every time the device is fitted on the patient hand. With the future goal to build a new version of the hand exoskeleton, in this dissertation three problems arising from this prototype were tackled. The first problem regards the need to lower the number of human-machine connections needed to fasten the exoskeleton to the patient hand. A new finger mechanism that permits to lower the total number of human-machine connections from fifteen to only six was proposed. The second problem regards the synthesis of the RSSR mechanism. A novel synthesis procedure was proposed in order to guarantee the optimal motion and force transmission to the thumb mechanism once the hand exoskeleton is fitted to a new patient, i.e. for different frame link geometries of the RSSR mechanism. The third problem regards the need to approximate the finger phalange motion as a rotation about a revolute axis. In this perspective, two different joint axes identification techniques were proposed. The techniques are based on the Burmester theory (a theory generally used for the synthesis of mechanisms), here used in an original way to identify an axis of rotation. A comparison of this two technique with a more standard technique based on the finite helical axis is reported

Location-Dependent Human Osteoarthritis Cartilage Response to Realistic Cyclic Loading: Ex-Vivo Analysis on Different Knee Compartments

Objective: Osteoarthritis (OA) is a multifactorial musculoskeletal disorder affecting mostly weight-bearing joints. Chondrocyte response to load is modulated by inflammatory mediators and factors involved in extracellular cartilage matrix (ECM) maintenance, but regulatory mechanisms are not fully clarified yet. By using a recently proposed experimental model combining biomechanical data with cartilage molecular information, basally and following ex-vivo load application, we aimed at improving the understanding of human cartilage response to cyclic mechanical compressive stimuli by including cartilage original anatomical position and OA degree as independent factors. Methods: 19 mono-compartmental Knee OA patients undergoing total knee replacement were recruited. Cartilage explants from four different femoral condyles zones and with different degeneration levels were collected. The response of cartilage samples, pooled according to OA score and anatomical position was tested ex-vivo in a bioreactor. Mechanical stimulation was obtained via a 3-MPa 1-Hz sinusoidal compressive load for 45-min to replicate average knee loading during normal walking. Samples were analysed for chondrocyte gene expression and ECM factor release. Results: Non parametric univariate and multivariate (generalized linear mixed model) analysis was performed to evaluate the effect of compression and IL-1β stimulation in relationship to the anatomical position, local disease severity and clinical parameters with a level of significance set at 0.05. We observed an anti-inflammatory effect of compression inducing a significant downmodulation of IL-6 and IL-8 levels correlated to the anatomical regions, but not to OA score. Moreover, ADAMTS5, PIICP, COMP and CS were upregulated by compression, whereas COL-2CAV was downmodulated, all in relationship to the anatomical position and to the OA degree. Conclusion: While unconfined compression testing may not be fully representative of the in-vivo biomechanical situation, this study demonstrates the importance to consider the original cartilage anatomical position for a reliable biomolecular analysis of knee OA metabolism following mechanical stimulation