Accelerometer and displacement transducer are two common sensors used for structural displacement measurement. Due to their incapability of measuring static deflection of a structure, Global Positioning System (GPS) is developed as a novel sensor for measuring and monitoring both static and dynamic displacement responses of large civil engineering structures under gust winds. However, the accuracy of dynamic displacement measurement with GPS at the sub-centimeter to millimeter level depends on many factors such as required data update rate, satellite coverage, atmospheric effect, multi-path effect, and GPS data processing methods. Therefore, this paper focuses on the assessment of dynamic displacement measurement accuracy of GPS in two orthogonal directions. A 2-D motion simulation table is first developed as a test bed simulating various types of two perpendicular translational motions of tall buildings. The 2-D motion simulation table was then used to assess the performance of GPS through a series of field measurements in an open area. A band-pass filtering scheme is finally designed and applied to the table motion data recorded by the GPS. The comparison of the table motion recorded by the GPS with the original motion generated by the table shows that the GPS can measure sinusoidal or circular dynamic displacements accurately within certain amplitude and frequency ranges. The comparative results also demonstrate that the GPS can trace wind-induced dynamic responses of tall buildings satisfactorily.
Global Positioning System (GPS) is an emerging tool for measuring and monitoring both static and dynamic displacement responses of long span cable-supported bridges under gust winds. Since vertical vibration of a long span cable-supported bridge is more significant than its lateral vibration, this paper focuses on the assessment of dynamic displacement measurement accuracy of GPS in vertical direction. In the first phase of work, the accuracy of GPS in measuring vertical sinusoidal displacement motions is examined by using a motion simulation table. The comparison of the table motion recorded by the GPS with the original motion generated by the table shows that the GPS can measure accurately sinusoidal dynamic displacements within certain frequency and amplitude ranges. In the second phase of work, the capability of the GPS in tracking the measured wind-induced bridge deck motion of Tsing Ma Bridge during Typhoon Victor is examined. To reduce multi-path effects on GPS measurements, an adaptive filter based on the recursive least-squares (RLS) algorithm is used to enhance the measurement accuracy of GPS. The comparative results demonstrate that the GPS can trace wind-induced dynamic response of long span cable-supported bridges satisfactorily.
Hybrid control platform is investigated in this paper for mitigating microvibration of a batch of high tech equipment installed in a high tech facility (building) subject to nearby road vehicle-induced horizontal and vertical ground motions. Hybrid control platform, on which high tech equipment is installed, is mounted on the building floor through a series of passive mounts and controlled by hydraulic actuators in both horizontal and vertical directions. The hybrid control platform is taken as an elastic body with significant bending modes of vibration, and a sub-optimal control algorithm is used to manipulate the hydraulic actuators with the actuator dynamics included. The governing equations of motion of the coupled platform-building system are established in the absolute coordinate to facilitate the feedback control and performance evaluation of the platform. The horizontal and vertical ground motions at the base of the building induced by nearby moving road vehicles are assumed to be random and statistically stationary processes. A typical three-story high tech building is selected as a case study. The case study shows that the ground motion and vibration of the high tech building are higher in the vertical direction than in the horizontal direction. The use of hybrid control platform can effectively reduce both horizontal and vertical microvibrations of a vast quantity of high tech equipment to the level satisfying the most stringent microscale velocity requirement specified in the BBN criteria.
KEYWORDS: Buildings, Control systems, Earthquakes, Electroluminescence, Logic, Feedback control, Matrices, Actuators, Control systems design, Connectors
Mitigating seismic responses of adjacent buildings by using control devices linked the two buildings has been recognized as a feasible alternative control scheme in past decade. A numbers of research studies have been undertaken in revealing and comparing the control capability among passive, active and semi-active control strategies employed in the coupled building system. The general interest and intention for the coupling control approach are mainly placed on the adjacent high-rise structures, and the LQ control algorithm relying on feedback with multiple measurement points is also the major design preference. This paper will focus on evaluating the effectiveness of controllable friction dampers as coupling devices that are implemented with semi-active control strategy based on local response feedback for a coupled podium structure and medium-rise building system. The effect of the height, mass and stiffness of two semi-actively controlled structures is one of the investigations. A comparison on control performance by a proposed semi-active control strategy with passive and clipped optimal control strategy is also presented. It is shown that control strategy with local response feedback can provide increased control performance over the passive strategy, and it is also of similar efficiency compared to the clipped optimal control strategy.
Experimental studies have been carried out to employ GPS to measure the vibrations of the 384 m tall Di Wang building in Shenzhen, China. Two GPS receivers were employed in the experiment with one set on the top of the building and the other on a reference station on the ground near-by. The GPS data were collected at a rate of 4 sets per second. The experiment was conducted under different weather conditions over two 24-hour periods. This paper describes the GPS equipment used, the field operations, the data processing and analysis strategies, and the results obtained from the study. It is shown from the study that GPS can be successfully applied for monitoring structural vibrations. However cautions have to be exercised in analyzing GPS data to remove biases such as the so-called GPS multi-path errors. Besides, some practical issues still need resolved before GPS can be applied routinely for this type of applications.
A long suspension bridge is usually located in a unique wind environment and accordingly strong winds at the site seldom attack the bridge at a right angle to its longitudinal axis. However, the buffeting response prediction often assumes that the wind approaches the bridge at a right angle to its longitudinal axis. This paper thus intends to investigate this subject to some extent. The conventional buffeting analysis method in the frequency domain is refined first to take into account the effects of wind inclination and yaw angle. The field measurement data, which were recorded during Typhoon Sam in 1999 by the `Wind And Structural Health Monitoring System' (WASHMS) installed on the Tsing Ma Bridge, are then analyzed to obtain both wind characteristics and structural responses. Finally, the aerodynamic and aeroelastic coefficients of the Tsing Ma bridge deck under yawed and inclined winds, which are required in the analytical prediction, are measured through wind tunnel tests and reported in this paper. The detailed comparison of the field measurement data with the analytical results, however, is still under the way, which cannot be reported in this paper.
A new procedure is presented for determining dynamic characteristics and seismic response of adjacent buildings linked by active tendon devices. Dynamic characteristics of active tendon-linked adjacent buildings are obtained by a generalized modal analysis approach. Random seismic response of adjacent buildings linked by active tendon devices is determined by a combination of the generalized modal analysis approach and a pseudo-excitation method. Based on the derived formula, a computer program is written and extensive parametric studies are performed to assess the effectiveness of active tendon devices and to identify optimal type of sensor and beneficial parameters of devices. It is showed that using active tendon devices of proper sensors and parameters to link adjacent buildings can increase the modal damping ratios and reduce the seismic response of both buildings significantly.
Tuned liquid column damper (TLCD) was developed mainly for the purpose of suppressing horizontal motion of structures. No relevant research has been found on the suppression of structural pitching vibration by using TLCD. This paper thus conducts a series of TLCD experiments with different configurations and parameters to investigate the possibility and effectiveness of applying TLCD to reduce pitching motion of structures. A theoretical model of TLCD-structure interaction under pitching motion is also developed to guide the experiments and verified by the experimental results on the other hand. In this study, the influence of variable TLCD parameters on control effectiveness are determined. It is concluded that TLCD can efficiently reduce structural pitching motion.
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