Comportamiento sísmico de estructuras con forjados reticulares y disipadores de energía bajo acción simultánea de dos componentes horizontales del terremoto

Abstract

This Thesis investigates the seismic behavior of reinforced concrete structures consisting of waffle-flat plates supported on isolated columns, without and with hysteretic dampers, subjected to the simultaneous action of two components of the ground motion caused by an earthquake. The methodology applied involves two approaches: the experimental approach (dynamic shaking table tests), and the numerical approach (nonlinear response history analyses with a refined 3D finite element model). The study addresses the response of the structure from the initial elastic stages until collapse. Different parameters are used to characterize the seismic action and to evaluate the response and particular attention is given to the energy.Within the experimental approach, a prototype structure with waffle-flat plates and square columns was first designed following the Spanish structural codes. The structure was assumed to be located in Granada. A portion of this prototype was selected, scaled and built in the Laboratory of Structures of the University of Granada (test specimen). The specimen was tested with a biaxial shaking table using the horizontal components of a far field ground motion. These two components were applied simultaneously, scaled in amplitude to increasing values, until collapse. The analyses of the results allowed to describe in detail the evolution of the response in terms of drifts, rotations in column, forces, local deformations and energy that contributes to damage. Damage concentrated at column bases and at the exterior plate-column connection. The energy input in the structure until collapse under the biaxial seismic action was found very close to that obtained in past tests conducted with a similar specimen subjected to unidirectional seismic loadings. Further, based on the results of the tests, it is proposed to adopt the value = 2 as spectrum reduction factor in force-based seismic design methods.The numerical approach had two parts. The first part consisted on developing a refined 3D finite element model that represented the specimen tested with the shaking table. The model was calibrated with the experimental results to obtain a satisfactory fit between tests results and numerical prediction in terms of displacements and energies. This model was used to conduct a parametric study consisting on nonlinear response history analyses with a large set of ground motions. As a result, the ultimate energy dissipation capacity of this type of structures was evaluated, under uniaxial and under biaxial seismic loadings. In the second part of the numerical study, the model was equipped with displacement-dependent (hysteretic) dampers. A second parametric study was conducted with the new model to evaluate the response and the ultimate energy dissipation capacity of the mixed system. As a global result of the numerical approach, it is concluded that the ultimate energy dissipation capacity of the structure (without or with hysteretic dampers) is a relatively stable amount, scarcely influenced by the characteristic...