Francesco Fabbrocino

OPTIMAL DESIGN AND ADDITIVE MANUFACTURING OF NOVEL REINFORCING ELEMENTS FOR COMPOSITE MATERIALS

We experimentally investigate on the use of additive manufacturing technologies for the design and fabrication of innovative reinforcing elements of novel composite materials. We perform short-beam shear tests on cement mortar specimens reinforced with additively manufactured reinforcing fibers made of photopolymers or a titanium alloy. The fracture toughness, shear capacity and first crack strength of the examined materials are estimated based on the provisions of different international standards for construction materials. We also characterize the surface morphology of the examined fibers through microscopy analyses before and after testing. The given results highlight that the microscopic or macroscopic nature of the surface roughness of the analyzed fibers greatly influences the energy absorption capacity of the final materials, while the nature of the fibers’ material (metallic/polymeric) is of central importance in terms of strength properties. The present study represents a first step in the direction of designing reinforcing elements with hierarchical structure to form fabrics, fibers and coatings of groundbreaking reinforcements for next generation composites, profiting from the rapid prototyping capabilities of additive manufacturing technologies at different scales. Fabbrocino, I. Farina, A. Amendola, L Feo, F.Fraternali

ON THE FORCED VIBRATION TEST BY VIBRODYNE

Abstract. In civil engineering, Experimental Modal Analysis (EMA) dynamic tests are powerful aids to the seismic design of new structures, and useful tools for the structural identification of existing structures. EMA tests require to accurately evaluate the harmonic forcing function that is applied to the structure under testing, in order to correctly apply “model updating” procedures. The present work experimentally investigates on the nature of the forcing function applied by a vibrodyne, and its influence on the results of simulations on the dynamics of a single degree of freedom system . By using wireless accelerometers attached to a vibrodyne, we were able to measure the applied accelerations in the time domain, and the applied forcing function under different frequencies. Such an identification procedure was applied both in presence of 3+3 keyed masses, and in presence of 5+5 keyed masses, considering different angular speeds. In both cases, the forcing function applied by the vibrodyne was accurately determined as a function of time. We found out that the actual forcing function is slightly different from the theoretical sinusoidal profile, featuring marked oscillations.The work is completed by the analysis of the dynamic response a simple degree of freedom system under the action of smooth and oscillating sinusoidal forcing functions. A comparison between the results of the analyzed systems highlights marked mismatches in terms of predicted displacements, velocities, and accelerations. We therefore conclude that an accurate knowledge of the applied forcing function in EMA tests is essential in order to correctly identify the properties of the tested structures.

Minimal mass design of strengthening techniques for planar and curved masonry structures

We present a discrete element model of a masonry structure strengthened through the application of reinforcing elements designed to work in tension. We describe the reinforced masonry structure as a tensegrity network of masonry rods, mainly working in compression, and tension elements corresponding to fiber-reinforced composite reinforcements, which are assumed to behave as elastic-perfectly-plastic members. We optimize a background structure connecting each node of the discrete model of the structure with all the neighbors lying inside a sphere of prescribed radius, in order to determine a minimal mass resisting structure under the given loading conditions and prescribed yielding constraints. Fiber-reinforced composite reinforcements can be naturally replaced by any other reinforcements that are strong in tension (e.g., timber or steel beams/ties). Some numerical examples illustrate the potential of the proposed strategy in designing tensile reinforcements of a three-dimensional structure composed of a masonry vault and supporting walls.

Repair of Clay Brick Walls for out of Plane Loads by Means of FRCM

Aim of this work is the evaluation of FRCM capacity in repairing pre-damaged clay brick walls under out of plane loads. Full scale experimental tests have been performed damaging clay brick walls subjected to out of plane loads; then, tests are performed on damaged walls repaired with innovative composite grids with inorganic matrix (FRCM). The boundary constraints of the walls (two adjacent edges constrained and the other two free) allowed to simulate a non-uniform out of plane behaviour of the wall subjected to a pointwise normal load applied at the free corner. The aim of this study was to assess the potentiality of FRCM to recover stiffness after significant damage and to improve the lateral (out-of-plane) capacity of the repaired wall. Experimental evidences demonstrated that the externally bonded strengthening was not strongly affected by debonding and it was able to prevent a flexural failure; the collapse of the wall occurred at almost double load with respect to the unreinforced configuration, despite previous significant damage, and that the failure was governed by shear sliding. Future developments include experimental tests of strengthened walls not previously damaged, to investigate on the effect of pre-damage on out of plane strengthening capacity of FRCM.

ON THE OPTIMAL DESIGN OF CABLE-STAYED BRIDGES

This paper studies cable-stayed bridges (CBSs), with special focus on the initial force distributions in cables during construction phases. An algorithm for the optimal design of the pre-tensioning sequence of cables is presented. A procedure for the optimization of cable forces is developed, according to a given objective function. Particular attention is given to the choice of the parameters to be optimized, and numeric examples are provided. The proposed method is employed to study the At Tannumah bridge in Basrah, Iraq; and is suitable for the optimization of the pre-tensioning sequence of arbitrary cable-stayed bridges. We show in the rest of the paper that an initial design (named S0 configuration) that does not include any pre-tensioning forces in cables can lead to a highly non uniform bending moment distribution over the deck; which is not ideal for an optimal structure. Fort that reason we develop an “optimal design” (named Sd configuration), that corresponds to pre-tensioning forces inducing an “optimal” bending moment distribution over the deck.

Numerical Investigation of Masonry Strengthened with Composites

In this work, two main fiber strengthening systems typically applied in masonry structures have been investigated: composites made of basalt and hemp fibers, coupled with inorganic matrix. Starting from the experimental results on composites, the out-of-plane behavior of the strengthened masonry was assessed according to several numerical analyses. In a first step, the ultimate behavior was assessed in terms of P (axial load)-M (bending moment) domain (i.e., failure surface), changing several mechanical parameters. In order to assess the ductility capacity of the strengthened masonry elements, the P-M domain was estimated starting from the bending moment-curvature diagrams. Key information about the impact of several mechanical parameters on both the capacity and the ductility was considered. Furthermore, the numerical analyses allow the assessment of the efficiency of the strengthening system, changing the main mechanical properties. Basalt fibers had lower efficiency when applied to weak masonry. In this case, the elastic properties of the masonry did not influence the structural behavior under a no tension assumption for the masonry. Conversely, their impact became non-negligible, especially for higher values of the compressive strength of the masonry. The stress-strain curve used to model the composite impacted the flexural strength. Natural fibers provided similar outcomes, but a first difference regards the higher mechanical compatibility of the strengthening system with the substrate. In this case, the ultimate condition is due to the failure mode of the composite. The stress-strain curves used to model the strengthening system are crucial in the ductility estimation of the strengthened masonry. However, the behavior of the composite strongly influences the curvature ductility in the case of higher compressive strength for masonry. The numerical results discussed in this paper provide the base to develop normalized capacity models able to provide important information on the out-of-plane behavior of masonry elements strengthened with inorganic matrix and several kinds of fibers, both synthetic and natural.

Corrosion effects on seismic capacity of reinforced concrete structures

Abstract Recently, corrosion prevention and monitoring of reinforced concrete (RC) structures became an important issue for seismic assessment of such kind of structures. Therefore, it is important to develop adequate models to represent material degradation into seismic behavior simulation of RC structures. Because of its effects, corrosion represents the most important form of degradation for materials and structures, both for wide diffusion and the amount of danger it presents. To understand the corrosion process is critical in order to design RC structures that are able to guarantee the required service life and in order to understand the residual service life and strength of an existing structure. The seismic behavior of a corroded framed RC structure is analyzed by means of push-over analyses, which allow understanding the development of the global behavior of the structure. Three different degrees of corrosion penetration were simulated, by means of the reduction of bars and stirrups’ diameters and concrete cover cracking and spalling, and three different configurations of corrosion, depending on the number of corroded frames and sides of the structural elements.

Numerical Modelling of Masonry Barrel Vaults Reinforced with Textile Reinforced Mortars

Among masonry buildings characterized by a complex architecture, a significant portion is represented by heritage buildings. A significant seismic vulnerability is due to the presence of thrusting elements like as arches and vaults. Their ultimate capacity can be improved by means of several strengthening techniques. However the advantages of using Textile Reinforced Mortars (TRM) are well highlighted in the scientific literature.The present work focuses on ultimate behaviour of masonry barrel vaults, in the framework of incremental analysis, including the strengthening effect. The analytical model is compared in terms of ultimate capacity and failure mode with a full scale masonry barrel vault dynamically tested. After the first tests, the vault has been strengthened with Textile Reinforced Mortar (TRM) and tested again.

ACCURATE NUMERICAL METHODS FOR STUDYING THE NONLINEAR WAVE-DYNAMICS OF TENSEGRITY METAMATERIALS

This paper presents presents an effective numerical approach to the nonlinear dynamics of columns of tensegrity prisms subject to impulsive compressive loading. The equations of motions of the analyzed structures are formulated in vector form, by modeling the cables as deformable members and the bars as rigid bodies. The given numerical results investigate the wave dynamics of tensegrity columns, with focus on the propagation of compression solitary waves with variable size and amplitude throughout the system, as a function of the applied impact velocity and the state of prestress of the structure. The engineering potential of the examined structures as tunable acoustic actuators is discussed. 3911 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 3911-3922