MS13.3 - Hybrid analyses, experimental tests and numerical modeling in earthquake engineering

The earthquake response of bridge cranes is a very important safety issue for industrial facilities, for example, nuclear plants. During an earthquake, the bridge crane is subjected to multi-impacts and frictional contacts between trolley wheels and girders, as well as between crane wheels and runways. In order to take into account such non-linear effects in the numerical simulation of bridge cranes under earthquake, firstly, an efficient explicit time integrator for the impact and frictional contact, based on the Central Difference (CD) scheme, is presented, where the constraints are treated with Lagrange multipliers. For the purpose of reducing CPU time, the explicit time integrator is only applied in the 3D contact areas with a fine time scale satisfying the stability condition, while an implicit time integrator is adopted in the other parts with a large time step. Thanks to the proposed hybrid approach, Rayleigh viscous matrix can be adopted only in the implicit partition, without reducing the critical time step in the explicit CD partition. Finally, three-dimensional explicit/implicit multi-time step simulations of bridge cranes under earthquake are carried out using the proposed explicit/implicit heterogeneous asynchronous time integrator (HATI) for non-smooth transient dynamics to predict the non-linear earthquake response of the experimentally tested bridge crane. The comparison between experimental and numerical results gives an overall satisfactory agreement in terms of displacements, accelerations and efforts transmitted to the anchorages.

Inter-story seismic isolation has become a valuable solution for high-rise buildings to effectively separate the various parts having several functions, and thus different seismic performance requirements, with the main advantage being the interruption of the flux of energy between the upper and lower stories. The isolation layers introduced at various heights of the buildings may filter the inertial forces transmitted to the superstructure and improve the seismic behavior of the whole system. This paper proposes numerical simulations a 20-floor building and several inter-story configurations where the isolation layer is located at several heights. The mail goal is to discuss the performances of each model and to assess the best location along the height of the structure. OpenSees is performed to calculate the high non-linearities of the models and to consider the interaction between the vertical loads and the horizontal forces. The various responses are discussed in terms of shear forces, accelerations and drifts, demonstrating the potentialities of inter-story isolation as a means of base isolation.

The construction of a new industry building was stopped halfway due to the concerns about the structural quality by the developer. It is a four-storey steel frame structure with a composite floor system. Majority of structure has been accomplished besides finishing layer and internal equipment. Various technical methods can be used for quality assessment of a structure, e.g. visual inspections, radar tests, vibration tests, etc. Among them, vibration tests have gained a special interest. It is a non-destructive method and can be performed without the interruption of the construction, which is especially suitable for a half-built building. The principal of the tests is identifying the dynamic behavior of the structural element by the measurement of structure response (acceleration or velocity) under certain excitations. Artificial excitations, e.g. heel-drops, jumps, etc., are used as the excitation source for the tests. The measurements are easily performed with a relatively simple equipment. Specific elements and system elements can be assessed through the test. Any structural deviation or damage is reflected by the dynamic re-sponses, e.g. a very high/low eigenfrequency or a large deviation to theoretical estimation. In this assessment, various floor locations are chosen for the evaluation of specific structural ele-ments, e.g. main beams, secondary beams, composite floors, etc. Natural eigenfrequencies of the tested structure are extracted by the frequency analysis. For the comparison and verifica-tion purpose, numerical and analytical methods are also employed for the structural analysis. By the comparison between theoretical estimations and tested results on a referenced structure, different methods are verified each other. It shows the eigenfrequency of (complex) structural elements/systems can be estimated accurately with simple analytical formulas. Therefore, the analytical method is further used for comparison with the vibration tests. In this way, the struc-tural quality of main structure was successfully assessed.