A Linear Brushless Direct Current Motor Design Approach for Seismic Shake Tables

The progress in material and manufacturing technologies enables the emergence of new research areas in electromagnetic actuator applications. Permanent magnet (PM) linear motors are preferred to achieve precise position control and to meet the need for high dynamic forces in the seismic shake tables that are used in analyzing reactions of structure models. The design approaches on the linear motors used in the seismic shake tables may vary depending on the desired force, stroke and acceleration values. Especially, the maximum width, the maximum depth, the maximum linear motor length in longitudinal direction and the maximum travelling distance parameters are the primary design criteria in seismic shake table drive systems. In this paper, a design approach for a linear PM brushless direct current (BLDC) motor with high force/volume, force/weight and force/input power ratios is developed. The design was analyzed using two-dimensional (2D) and three-dimensional (3D) finite element method (FEM) approaches through the ANSYS Maxwell software. The mathematically designed linear BLDC motor was manufactured and subjected to displacement, acceleration and force tests that are used in seismic analyses. The results of the experimental tests validate the convenience of the proposed design approach and the selected parameters.

Comparison of Seismic Performance of Socket and Pocket Connections for Reinforced Concrete Bridge Column Base Hinges

The goal of this study was to evaluate two connection types for reinforced concrete two-way rebar hinges and to assess their seismic performance if incorporated in accelerated bridge construction applications. Two large-scale models of bridge systems were tested on shake tables; the first utilized a pocket connection with the opening preformed in the column and the second implemented a socket connection with the opening preformed in the footing. Both bridges were subjected to multiple ground motions ranging from 30% to 225% of the design level earthquake. Rebar hinge behavior during the earthquakes including interface slippage, rotation, reinforcement strains, observed damage, and bent forces were used to evaluate the connections and their relative merit and to make recommendation for implementation in the field.

Experimental Studies on Seismic Performance of Rigid-frame Extradosed Cable-stayed Bridges

<p>With the aim of further understanding the seismic performance of extradosed cable-stayed bridges, this paper presents an experimental investigation of a three-pylon rigid-frame extradosed cable-stayed bridge by conducting 1/20 scaled longitudinal shake tables model tests at the laboratory of Tongji University, Shanghai, China. The design, construction and testing protocol of the test model are firstly introduced. Observation of the seismic damage situation and empirical data on the seismic responses of the test model are then provided. The test results show that: (1) severe seismic damage appeared at the bottom and upper parts of piers and damage at the bottom parts were much heavier; (2) no damage was observed on short pylons; (3) structural stiffness degradation occurred when PGA≥0.4g; (4) the vibration of the short pylon almost has no contribution in the displacement at the pylon top.</p>