José Luis Vital de Brito

PARAMETRIC STUDY ON MULTIPLE TUNED MASS DAMPERS USING INTERCONNECTED MASSES

In this paper, the dynamic performance of a controlled high building is numerically investigated considering the effects of different numbers of mass dampers and their interconnection. The numerical analysis is conducted on a 20-story building considered as a shear frame and reduced to an SDOF system by means of the mode-superposition method. The system is subjected to harmonic load. Numerical searches are conducted based on the Min. Max. procedure in order to obtain efficient interconnected (I) multiple tuned mass dampers (MTMD). Comparisons are made among the uncontrolled system, the system controlled by non-interconnected (NI) MTMD, and the system controlled by (I) MTMD in frequency and time domain. Both (NI) and (I) MTMD reduce significantly frequency response peak amplitude. It is observed that the (I) MTMD produces great reductions on maximum displacement, rms displacement, steady-state peak response, and story displacements close to the reductions obtained by (NI) MTMD using review parameters. Mass maximum displacements analysis shows that the space required for (I) MTMD installation is smaller than (NI) MTMD.

Modal Tests and Model Updating for Vibration Analysis of Temporary Grandstand

Temporary grandstands are subjected to dynamic loading due to the movement of spectators, and problems associated with the excessive vibration of these structures have been observed. In this context, since they can be used during design stage to address such problems, reliable finite element models of the structure are needed. In this paper, a finite element model of a temporary grandstand is developed while modeling effects are investigated. To do that, a temporary grandstand for about one hundred people was assembled in a laboratory. Modal tests were conducted to calibrate the numerical models of the whole structure. These models were developed by using various degrees of refinement in order to allow comparing the effect of modeling simplifications. The results evidenced that the modeling of connections and seat planks caused significant changes in natural frequencies. The complexity of the structure, with a significant number of parameters affecting dynamic behaviour, requires that modeling ideally start from individual structural components tested in separate.

Synchronization among Pedestrians in Footbridges due to Crowd Density

AbstractCrowding is a critical condition for footbridges that are prone to vibration problems from pedestrian loads. Synchronization of pedestrian movements has been identified as the cause of the excessive lateral vibration in some footbridges. Two conditions have been named as the cause of synchronization: increase in crowd density and pedestrian-structure interaction. The former would be related to the onset of the phenomenon; the latter takes place after structural vibration reaches a certain level. This paper focuses on the former condition. A test program to investigate whether this condition occurs was carried out for a range of pedestrian densities, complementing data previously published on this subject. The head movement of pedestrians walking both in groups and in a flow was recorded by a video camera, and the examination of the video indicated no synchronization from densification. However, it was observed that the lateral sway of the pedestrians’ bodies increased with the increase of density....

Experimental study of the neighborhood effects on the mean wind loading over two equivalent high-rise buildings

This paper presents a series of results with respect to the mean values of shear, base moment and torsion acting in a building obtained through an experimental wind tunnel study using the standard building proposed by the Commonwealth Advisory Aeronautical Research Council (CAARC) as building reference. In the loading determination, the interference of a neighboring building with similar geometric characteristics to the CAARC was simulated, considering variations of positioning and spacing in relation to the reference building. It was concluded that the presence of the neighboring building increased the mean loads in the reference building for a significant number of directions considered. In the case of the considered deviations and the proposed provisions by this study, it was concluded that the vicinity factor that would contemplate the majority of the results obtained in the tests should increase the wind loads by at least 60% in relation to the values obtained for the building reference considered in isolation.

Comparative analysis of semi-active control algorithms applied to magnetorheological dampers

espanolEste documento analiza el rendimiento de tres algoritmos de control semiactivos diferentes utilizados para calcular y gestionar las fuerzas de amortiguacion optimas generadas por un par de amortiguadores magnetorreologicos (MR) instalados en un edificio de dos pisos. Los algoritmos semiactivos utilizados son el regulador lineal cuadratico (LQR) asociado con el algoritmo optimo recortado, un algoritmo basado en un modelo de prediccion y un modelo dinamico inverso que utiliza redes neuronales artificiales autoregresivas exogenas no lineales (NARX), y una decision haciendo algoritmo basado en logica difusa. Ademas, los rendimientos de los algoritmos semiactivos propuestos se comparan con los de los dispositivos de control pasivamente utilizados. Los resultados muestran reducciones del valor de respuesta superiores al 50% para todas las estrategias de control semiactivas, que superaron considerablemente al control pasivo. EnglishThis paper analyzes the performance of three different semi-active control algorithms used to calculate and manage the optimal damping forces generated by a pair of magnetorheological (MR) dampers installed in a two-story building. The semi-active algorithms used are the linear quadratic regulator (LQR) associated with the clipped optimal algorithm, an algorithm based on a prediction model and a dynamic inverse model using nonlinear autoregressive exogenous (NARX)-type artificial neural networks, and a decision-making algorithm based on fuzzy logic. Additionally, the performances of the proposed semi-active algorithms are compared to those of passively used control devices. The results show response value reductions exceeding 50% for all the semi-active control strategies, which considerably outperformed the passive control. The three control strategies are thus confirmed as interesting tools with potential applications as MR damper administrators.