Yunbyeong Chae

Large-Scale Real-Time Hybrid Simulation for Evaluation of Advanced Damping System Performance

AbstractAs magnetorheological (MR) control devices increase in scale for use in real-world civil engineering applications, sophisticated modeling and control techniques may be needed to exploit their unique characteristics. Here, a control algorithm that utilizes overdriving and backdriving current control to increase the efficacy of the control device is experimentally verified and evaluated at large scale. Real-time hybrid simulation (RTHS) is conducted to perform the verification experiments using the nees@Lehigh facility. The physical substructure of the RTHS is a 10-m tall planar steel frame equipped with a large-scale MR damper. Through RTHS, the test configuration is used to represent two code-compliant structures, and is evaluated under seismic excitation. The results from numerical simulation and RTHS are compared to verify the RTHS methodology. The global responses of the full system are used to assess the performance of each control algorithm. In each case, the reduction in peak and root mean s...

Large-Scale Experimental Studies of Structural Control Algorithms for Structures with Magnetorheological Dampers Using Real-Time Hybrid Simulation

AbstractReal-time hybrid simulations using large-scale magnetorheological (MR) dampers were conducted to evaluate the performance of various structural control strategies to control the seismic response of a three-story steel-frame building. Magnetorheological dampers were installed in the building to limit the story drift to less than 1.5% under the design-basis earthquake (DBE). The laboratory specimens, referred to as experimental substructures, were two individual MR dampers, with the remainder of the building modeled as a nonlinear analytical substructure. The experimental technique enables an ensemble of ground motions to be applied to the building, resulting in various levels of damage, without the need to repair the experimental substructures because the damage will be within the analytical substructure. Five different damper control algorithms, including passive and semiactive control algorithms, were selected. An ensemble of five ground motions scaled to the DBE was used for the real-time hybrid...

Real-time Hybrid Simulation Studies of Complex Large-Scale Systems Using Multi-Grid Processing

Real-time hybrid simulation combines physical testing (experimental substructuring) and numerical simulation (analytical substructuring) such that the dynamic performance of the entire structural system can be considered during the simulation. A grid-based real-time hybrid simulation technique is introduced as a means to perform real-time hybrid simulations of complex structural systems where the analytical substructure poses a large computational demand. Real-time hybrid simulations of the 9-story ASCE benchmark structure with large-scale magnetorheological (MR) dampers are performed at the Lehigh NEES Equipment Site to demonstrate the multi-grid real-time hybrid simulation procedure and illustrate the ability to significantly reduce the time to perform the state determination of the analytical substructure. The 9-story building structure is modeled as the analytical substructure, with the experimental substructure consisting of large-scale MR dampers that are located in the structure. The analytical substructure is divided into two parts and implemented onto a computational grid consisting of two parallel xPCs that run MathWorks real-time Target PC software package. The restoring force data from these two xPCs are synchronized together along with the measured damper forces from the experimental substructure, and processed in a real-time manner for each time step of the hybrid simulation. The results of real-time hybrid simulation are compared to those of numerical simulations to validate the new test methodology.

Implementation of configuration dependent stiffness proportional damping for the dynamics of rigid multi-block systems

The distinct element method (DEM) has been used successfully for the dynamic analysis of rigid block systems. One of many difficulties associated with DEM is modeling of damping. In this paper, new procedures are proposed for the damping modeling and its numerical implementation in distinct element analysis of rigid multi-block systems. The stiffness proportional damping is constructed for the prescribed damping ratio, based on the non-zero fundamental frequency effective during the time interval while the boundary conditions remain essentially constant. At this time interval, the fundamental frequency can be estimated without complete eigenvalue analysis. The damping coefficients will vary while the damping ratio remains the same throughout the entire analysis. A new numerical procedure is developed to prevent unnecessary energy loss that can occur during the separation phases. These procedures were implemented in the development of the distinct element method for the dynamic analyses of piled multi-block systems. The analysis results for the single-block and two-block systems were in a good agreement with the analytic predictions. Applications to the seismic analyses of piled fourblock systems revealed that the new procedures can make a significant difference and may lead to much-improved results.

Development of equivalent linear systems for single-degree-of-freedom structures with magneto-rheological dampers for seismic design application

Numerous studies have been conducted for magneto-rheological dampers, but the application of magneto-rheological dampers in seismic design is limited due to the lack of a systematical design procedure. In this article, a simplified analysis procedure is proposed to estimate the response of a single-degree-of-freedom structure with diagonal bracing and a magneto-rheological damper without performing the time history analysis. The proposed simplified analysis procedure is based on the equivalent linear system of a magneto-rheological damper. The equivalent damping ratio and the effective period of the single-degree-of-freedom system are determined from the loss factor and the effective stiffness of the magneto-rheological damper based on the quasi-static model. Design response spectrum is utilized to calculate the displacement of the single-degree-of-freedom system. The equivalent damping ratio and the effective stiffness of the single-degree-of-freedom system are dependent on the displacement of the system; thus, the proposed procedure is iterated until the displacement from the design response spectrum converges. The accuracy of the simplified analysis procedure is evaluated by comparing the estimated response from this procedure with the response from the time history analysis. The results show a good agreement between two methods, demonstrating the robustness of the proposed simplified analysis procedure.