On the design of performance-based pentamode bearings

Pentamode lattices are particular metamaterials belonging to the class of extremal materials, which feature a primitive unit cell equipped with four rods meeting at a point. The potential of confined pentamode lattices in different engineering fields, such as, e.g., structural engineering, has not been largely explored yet. In this area, what is particularly interesting is the confinement of pentamode structural "crystals" between stiffening plates for the design of novel impact or seismic protection devices. Such a research line has recently appeared in the literature, with the aim of developing performance-based, vibration-isolation devices. The present study makes use of discrete-to-continuum approaches to the elastic moduli of pentamode lattices, and investigates the feasibility of pentamode structures as innovative anti-seismic devices. Experimental results and analytic formulae are employed to understand the mechanics of pentamode structures equipped with rigid and hinged connections, and the role played by design variables characterizing the aspect ratio of the structure and the response of the junctions. The final part of the work deals with the design of pentamode bearings that feature stiffness and strength properties similar to those of a commercial rubber bearing available on the market for the seismic isolation of buildings and bridges

On the optimal design of pentamode lattices

The present work studies the mechanical response of confined pentamode lattices equipped with rigid connections, with the aim of designing innovative extreme materials that show high compression modulus and low shear modulus. Employing a computational design approach, we show that the mechanical response of pentamode lattices with rigid connections is bending-dominated, and that such structures are able to carry unidirectional compressive loads with sufficiently high stiffness, while showing markedly low stiffness against shear loads. Differently from systems equipped with hinged connections, the high ratio between effective compression and shear rigidities stems from the nonzero bending rigidity of nodes and rods, and from the confinement effect of the stiffening plates

On the mechanics of pentamode lattices

The present work illustrates results concerned with experimental tests on physical (reduced-scale) models of pentamode lattices confined between rigid plates and equipped with rigid connections. Finally, it discusses the potential use of such systems for the base isolation of existing buildings. Through experimental arguments, we show that the mechanical response of pentamode lattices with rigid connections is bending-dominated, and that such structures are able to carry unidirectional compressive loads with sufficiently high stiffness, while showing markedly low stiffness against shear loads. The high ratio between effective compression and shear rigidities derives both from the nonzero bending rigidity of nodes and rods, and from the confinement effect played by the stiffening plates. The obtained results emphasize the ability of such structures to behave as tension-capable and performance-based systems, whose mechanical properties are driven more by the geometry of the lattice microstructure (i.e., such systems behave as mechanical metamaterials) than the chemical composition of the material they are made of

Innovative devices for the base isolation of existing buildings

It is well known that pre-existing buildings are often inadequate to resist strong ground motions, and that their seismic rehabilitation is not an easy task. Several studies available in the to-date literature have shown that seismic isolation is a cost-effective and efficient method that can be employed to protect existing structures from earthquakes. A new class of performance-based seismic isolators has been proposed in recent studies, making use of pentamode lattices confined between stiffening plates. The present work illustrates experimental results concerned with shear and compression tests on physical (reduced-scale) models of pentamode bearings, and discusses the use of such systems for the base isolation of existing buildings. Given results highlight the special ability of such systems to behave as tension-capable and performance-based systems, whose mechanical properties are driven largely by the geometry of the lattice microstructure (i.e, such systems behave as mechanical metamaterials), and can be finely adjusted to the properties of the structure to be protected

Experimental testing campaign and numerical modelling of an innovative base-plate connection for pallet racking systems

The problem of the high fragility of upright frames of pallet racking systems against lateral forces raises an important question for researchers. This lack of seismic performance can be attributed to a small degree of internal overdetermination of the system, as is also acknowledged by the European Standard for adjustable pallet racking structures (EN16681), which only takes into account the low-dissipative behaviour for these structures. This paper presents an innovative base-plate connection that can provide the upright frames of pallet racking systems with a certain degree of global ductility, thus improving the seismic attitude of these structures when seismically stimulated along the cross-aisle direction. A design procedure for the specimens to be tested is proposed, which aims at guiding the system design toward localizing yielding strains in the plates of the base connections, as the principles of the capacity design posit. The proposed base-plate connection is tested under monotonic and cyclic loads to better understand its properties and, by inference, its dynamic characterization, which could be utilized in a lighter numerical model in order to study overall performance improvement. Additionally, a numerical model of the specimen, as tested in the Laboratory of Steel Structures at the National Technical University of Athens (Greece), which has been calibrated and validated in accordance with experimental tests results, is presented

Experimental testing campaign and numerical modelling of an innovative base-plate connection for pallet racking systems

The problem of the high fragility of upright frames of pallet racking systems against lateral forces raises an important question for researchers. This lack of seismic performance can be attributed to a small degree of internal overdetermination of the system, as is also acknowledged by the European Standard for adjustable pallet racking structures (EN16681), which only takes into account the low-dissipative behaviour for these structures. This paper presents an innovative base-plate connection that can provide the upright frames of pallet racking systems with a certain degree of global ductility, thus improving the seismic attitude of these structures when seismically stimulated along the cross-aisle direction. A design procedure for the specimens to be tested is proposed, which aims at guiding the system design toward localizing yielding strains in the plates of the base connections, as the principles of the capacity design posit. The proposed base-plate connection is tested under monotonic and cyclic loads to better understand its properties and, by inference, its dynamic characterization, which could be utilized in a lighter numerical model in order to study overall performance improvement. Additionally, a numerical model of the specimen, as tested in the Laboratory of Steel Structures at the National Technical University of Athens (Greece), which has been calibrated and validated in accordance with experimental tests results, is presented