Journal of Seismology and Earthquake Engineering
Volume:7 Issue: 1, Spring 2005

In order to control the responses of a building, different control systems may be employed. To recognize and select a proper control system, a designer has to analyze many cases. This paper investigates the behavior of some control systems with respect to changes in different parameters of an AMD, and various combinations of masses and control forces of two or three AMDs, and also different locations of an AMD along the height of a building. In this study we used a recently proposed control algorithm, named discrete instantaneous optimal control method. A new discrete stable weighting matrix strengthens this method.

An approximate method is proposed to estimate the seismic response of nonlinear nonstructural components attached to nonlinear building structures. The method is based on a previously developed procedure for the analysis of linear secondary systems mounted on a linear primary structure, the introduction of simplifying assumptions similar to those made in the derivation of the equivalent lateral force procedure for the seismic analysis of conventional buildings, and the use of strength reduction factors to account for the nonlinear behaviour of nonstructural component and supporting structure. Its application to any given nonstructural component only requires knowing the geometric characteristics, weights, and target ductilities of the nonstructural component and the structure to which it is connected, in addition to the fundamental natural period of the structure and the elastic response spectrum specified for the design of the structure. Presented also are a numerical example that illustrates the application of the method and the results of a comparative numerical study that is carried out to assess the method''s adequacy. Based on its simplicity and rationality and the results from the comparative study, it is concluded that the proposed method represents a simple but effective procedure for the seismic design of nonstructural components in buildings.

A new method for the identification of dominant modal parameters (natural frequencies, damping ratios and participation factors) of classically damped linear structures using response to a multi-component earthquake is presented. If different components of the base acceleration of a structure are measured, the possibility of coupling between each of the six components of an earthquake and the measured absolute acceleration of the structure can be investigated. After introduction of the modal equations of motion of classically damped linear systems under multi-component earthquake, a newly proposed method for identification of the structural modal parameters is explained and, by application of the method to a model and on a real structure using artificial and real earthquake records, the accuracy of the method has been verified. The results of this verification indicate that the effect of the multi-input can be important for the identification of modal damping ratios and modal participation factors, and can improve compatibility between the recorded acceleration response and the calculated model response.

Tuned liquid column dampers (TLCD) considerably increase the effective damping of vibration prone civil engineering structures in horizontal motion. A single-degree-of-freedom (SDOF) basic system with a TLCD attached is analyzed under horizontal and vertical base excitations in order to prove its sensitivity with respect to the vertical parametrical forcing. The main result is cast in a sufficient condition for the linearized damping coefficient of the fluid motion to ensure its stability under the most critical, time harmonic forcing conditions. The output of computer simulations when varying the damping of the TLCD tuned with respect to frequency only, are verified experimentally by means of a novel model setup. The scaled Friuli 1976 earthquake is applied horizontally and vertically to an SDOF-shear frame with optimally tuned TLCD. A three-DOF-benchmark structure, equipped with two passive TLCD in parallel connection, optimally fine-tuned in state space, is analyzed by nonlinear computer modeling. Two different relevant earthquakes are alternatively applied in both, horizontal and vertical directions. In all cases it is verified, that sealed TLCD, (with the air-spring effect taken into account) are stable, since the optimal linear damping coefficient exceeds by far the required cut-off value of parametric resonance: the vertical component of the earthquake load remains ineffective. Hence, taking into account this sufficient condition with the maximum vertical ground (floor) acceleration assigned and the maximum amplitude of the fluid motion estimated, saves the consideration of the vertical seismic activation at all.