MS13.5 - Hybrid analyses, experimental tests and numerical modeling in earthquake engineering

Through the centuries, earthquakes represent one of the main causes of damage and loss of cultural heritage, monumental buildings, and historic centers, affecting the development of many countries worldwide. These kinds of constructions are usually constituted by structural masonry and have shown evidence of good behavior under vertical static loads, however, given the mechanical properties of this heterogeneous material, such as the high specific mass, low tensile/shear strength, and reduced ductility, makes its use unsuitable in seismic prone areas. This paper conducts a comprehensive study regarding the seismic assessment of existing ma-sonry structures considering the variability in the geometry, material properties, and seismic action. For this purpose, various sets of ground motions are selected and fitted to the target elastic response spectrum according to the Eurocode 8 provisions. The compliant seismic ac-tion will be used to compute the nonlinear response of masonry structures. Results are compre-hensively analyzed, and fragility curves are derived.

In this study the effects of an energy dissipation device in a real reinforced concrete building are presented. The investigated damper belongs to the passive energy dissipation systems and absorbs the seismic energy through yielding in bending and frictional forces occur in the metallic elements of the damper. It can be used on new or existing structures and can be easily adapted to the particular demands of structures. It can be installed in a variety of ways such as in single or X diagonal bracing in building frames. Moreover the use of this device may result in improving (i) the increase of stiffness (ii) the absorption of seismic energy, (iii) as well as control of the axial forces that are developed at the diagonal steel braces. The first step of this study is to present the dynamic response of this dampers, testing it experimentally under cyclic loading. Based on these experimental results, a numerical model has been created using 3D solid finite elements. The study is based to a set of systematic procedures for finite element model calibration and parametric evaluation that enable robust simulation of this damper under cyclic loading with high fidelity using explicit time-stepping time-history analysis methods. In addition, a real 2 stories reinforced concrete building, located in Greece, is used in this analyses. It is being analyzed using the pushover analysis and time history analysis, as regards three different cases, the initial pure r/c building without strengthening, the simple strengthening building with steel diagonal braces and the strengthening building with the investigated damper. The effects of each strengthening solution are presented, and from this comparison based to optimal design, further useful results are observed.

Unreinforced masonry (URM) buildings show high vulnerability to seismic loading. The performance of such buildings during past earthquakes has highlighted that wall collapse in the out-of-plane direction represents a major source of concern. Depending on the connection of a wall with diaphragms and transversal walls, different resisting mechanisms to the out-of-plane loading can develop and, hence, different configurations are commonly distinguished. Two-way spanning walls are characterized by effective restraints at least at one lateral side of the wall. The capacity of a two-way spanning unreinforced masonry wall with a single opening under seismic loading has been investigated in several reported studies by means of experiments and further derivation of analytical formulations. However, two-way spanning walls with more than one opening lack both experimental data and analytical formulations proposed to predict the out-of-plane capacity. This study presents an engineering approach to calculate the out-of-plane capacity of four-sided supported walls with two openings. The proposed methodology involves dividing the wall into simple components, whose performance may be assessed separately by means of available formulations, such as those recommended in the Dutch guidelines for the assessment of structural safety under earthquakes, NPR-9998:2020. The division into components is based on simple geometrical considerations. The first two components are defined as the wall portions comprised between side support and one opening. These components are analyzed as equivalent three-sided supported walls. The length of such components is increased fictitiously to account for the presence of the openings which is calibrated based on consolidated expressions defined for walls with a single opening. The second component corresponds to the wall portion between the two openings and is analyzed as a one-way spanning wall. The remaining components corresponding to the portions above and below the openings are analyzed both as cantilever walls and three-sided supported walls. This is dependent on whether the failure of the adjacent components is expected to occur or not and, consequently, whether lateral restraints can be provided. The applied seismic demand used for the analysis of the components is based on the natural frequency of the original wall with two openings and not on that of the components themselves. The adequacy of the proposed approach is evaluated by cross-comparing the outcomes of predictions computed based on both analytical calculations and finite element analyses. By investigating a number of practical configurations, it is shown that the presented engineering approach is conservative and efficient awaiting further validation.