Phd in STRUCTURAL AND GEOTECHNICAL ENGINEERING

Thesis title: Trave Tensairity per la realizzazione di strutture temporanee: sperimentazione e studio di una soluzione tecnologica per un ponte di piccola luce

Tensairity structures, thanks to their ability to intelligently adapt load distribution, open up new prospects in civil and aerospace engineering, offering innovative solutions. Despite this premise, the literature is strongly limited to the study of behavior under static actions. Such studies demonstrate the structure's ability to support heavy loads with a contained self-weight. From a dynamic perspective, extremely lightweight and rigid structures present significant vibration attenuation problems. A solution to this problem is proposed here, introducing hysteretic damping produced through the use of superelastic NiTiNOL alloy cables. The complexity of the problem, with strong geometric and contact nonlinearities, has led us, as often reported in the literature, towards an empirical approach to address the problem and implement the solution. A first prototype of a Tensairity beam was therefore realized, capable of managing multidirectional loads and capable of exerting control over the cable tension state. The experimental campaign was divided into two distinct phases. In the first phase, the behavior with respect to a quasi-static action was studied. The beam prototype, hinged at one end and supported at the opposite end, was subjected to an action with displacement control at the midpoint, and the response to the action was measured using a load cell. The displacement followed a non-zero mean sinusoidal law with a frequency of 0.2 Hz. The test was then conducted in relation to different possible configurations of the prototype in order to clearly demonstrate the difference in behavior in relation to the pressure with which the balloon was inflated, in relation to the tension of the cables and in relation to cables of different materials. The result, published in a first article, demonstrates how the NiTiNOL cable is able to increase the damping of the structure compared to traditionally used steel cables, without losing too much stiffness. In the second phase, the structure is mechanically characterized and the modal damping of the prototype is identified. The tests are carried out on the structure hinged at both ends, the input is generated through an automatic hammer with a load cell. Through the use of a sophisticated Polytec interferometry system, several points of the structure were measured and the data analyzed to identify natural frequencies and associated modal dampings. Each test was conducted again by varying the pressure in the pneumatic component and by varying the tension values in the NiTiNOL cable. Concurrently with the experimental tests, several finite element models were created with commercial Abaqus software using Python programming language. The models followed the evolutions first of the CAD model and then of the modifications during the construction phase of the prototype. These models were used to identify the natural frequencies of the structures and obtain a comparison with the experimental results. Despite the simplifying assumptions introduced, an error between the experimental and numerical natural frequencies of around 20% and 5% on average is obtained. Finally, given the PON nature of this doctorate, the Python calculation codes developed for the prototype were adapted to the real case for the design of a 12-meter temporary bridge and for the project of a temporary exhibition structure.