Failure mechanisms of anisotropic pentamode-based bridge bearings: A dynamic analysis

Abstract

Pentamodes are known for their almost zero shear modulus while providing high compression stiffness; a characteristic, which renders pentamodes suitable for application in seismic isolation. The current study focuses on bearings composed of alternating layers of pentamode crystals of an elastoplastic material with rigid steel plates. Pushover analyses are conducted, and plastic inges are gradually created. The failure mechanisms of the bearing are discussed and compared to those without stiffening plates. The influence of the directionality of an induced earthquake is also investigated. Since pentamode unit cells and pentamode modules are only symmetrical with respect to a vertical level, their structural response is anisotropic. Consequently, a bearing symmetric with respect to its diagonal is not expected to have an isotropic response. Depending on the formulation the ability to withstand the induced shear loading can be increased up to 30–50%. The cells, modules and bearings are proven to feature a weak direction defined by their lowest nodes, which specify how they are connected to the ground. It is proposed that a bearing composed of rotated instead of justified layers would be more isotropic. Positive and negative aspects of such a structure are discussed. The dynamic behavior of layered pentamode bearings is also discussed. Eigenfrequency and dynamic analyses of real-life bridge bearings under harmonic and real time histories showed that stiffening plates may improve a bearing’s response up to 115%.