Matthew Stehman

Direct Acceleration Feedback Control of Shake Tables with Force Stabilization

This study presents a new strategy for shake table control that uses direct acceleration feedback without need for displacement feedback. To ensure stability against table drift, force feedback is incorporated. The proposed control strategy was experimentally validated using the shake table at the Johns Hopkins University. Experimental results showed that the proposed control strategy produced more accurate acceleration tracking than conventional displacement-controlled strategies. This article provides the control architecture, details of the controller design, and experimental results. Furthermore, the impact of input errors in shake table testing on the structural response is also discussed.

Experimental Seismic Response of a Full-Scale Cold-Formed Steel-Framed Building. II: Subsystem-Level Response

AbstractThe objective of this paper is to employ the results from the extensive instrumentation installed on recently tested full-scale cold-formed steel (CFS)-framed buildings to reveal a deeper understanding of the behavior of the building under seismic excitations. In particular, this paper complements a companion paper that focuses on system-level design and response. Here, utilizing strategically located string potentiometers, strain gauges, and accelerometers, the responses of the walls and diaphragms are isolated from the overall building response and studied. The interaction of shear walls along a wall line, as well as across stories is studied through measured data on strains in hold-down anchors, strains on floor-to-floor strap connecting shear-wall chord studs, and displacements across shear-wall sheathing and openings. The behavior of the floor diaphragm is studied through displacements measured perpendicular to the plane of one wall of the building and accelerometers throughout the floor of t...

IIR Compensation in Real-Time Hybrid Simulation using Shake Tables with Complex Control-Structure-Interaction

This article considers the use of actuator compensation in real-time hybrid simulation (RTHS) containing experimental substructures with complex control-structure-interaction (CSI). The existence of CSI in shake table testing is derived using theoretical relations. An infinite-impulse-response (IIR) compensator is developed to compensate for the shake table time delay as well as the effects of CSI. The efficacy of the IIR compensator is verified through numerical and experimental investigations of substructure shake table testing completed at Johns Hopkins University. IIR compensation is not limited to substructure shake table testing, and the concept is applicable to any RTHS that suffers from complex CSI.

Mixed Force and Displacement Control for Testing Base-Isolated Bearings in Real-Time Hybrid Simulation

ABSTRACT This paper presents a robust mixed force and displacement control strategy for testing of base isolation bearings in real-time hybrid simulation. The mixed-mode control is a critical experimental technique to impose accurate loading conditions on the base isolation bearings. The proposed mixed-mode control strategy consists of loop-shaping and proportional-integral-differential controllers. Following experimental validation, the mixed-mode control was demonstrated through a series of real-time hybrid simulation. The experimental results showed that the developed mixed-mode control enables accurate control of dynamic vertical force on the base isolation bearings during real-time hybrid simulation.

Substructure Shake Table Testing with Force Controlled Actuators

Real-time hybrid simulation (RTHS) has emerged as a feasible and economical means for seismic performance assessment of structural systems. It has been successfully applied to study the system-level response, combining experimental and computational substructures. However, existing substructure techniques are limited to interface boundaries where the influence of unbalanced forces are not significant. Because existing formulation procedures and experimental loading are both displacement-based, unbalanced forces are inevitable in conventional RTHS. In some cases (e.g., testing of extremely rigid specimens, soil-structure boundaries), force equilibrium becomes more critical than displacement compatibility. To accommodate such conditions, a force-based approach is essential and has to be developed in RTHS. This study presents substructure shake table testing as a case study of force-based RTHS. A four-story shear structure is divided into two substructures. The first story is tested on a shake table while the rest of the structure is computationally simulated. The interaction between the experimental and computational substructures is addressed such that the measured acceleration at the top floor in the experimental substructure is used as the base input to the computational structure while computed base shear in the computational substructure is fed back to the experimental substructure through a force-controlled actuator. As such, the overall simulation is performed at real-time with force-controlled actuators. This study presents the underlying theories of the substructure shake table test method, centralized actuator control and preliminary numerical simulations.

Mixed Force and Displacement Control for Base-Isolation Bearings in RTHS

This study presents a real-time hybrid simulation of a base-isolated building. In this study, the base isolation layer is experimentally tested while the entire structure is computationally simulated. To impose the earthquake induced lateral displacement as well as the vertical gravitational force, a mixed force and displacement control strategy is developed and implemented in the experimental system. The mixed force and displacement control strategy in this study is a decentralized approach that consists of a loop shaping and the conventional PID controllers. Following a thorough experimental verification of the mixed control, hybrid simulation of a base isolated building was performed using a series of recorded earthquake ground motions. The experimental results showed that the mixed control provided accurate loading in both lateral and vertical directions. This study presents the implementation of the mixed force and displacement control as well as the results in real-time hybrid simulation.

A New Approach For Acceleration Tracking of Shake Tables Using Combined Acceleration and Force Feedback Control

This presentation introduces a new acceleration control method for shake tables that provides high-performance and robustness. Unlike the conventional displacement feedback control that is used in most servo hydraulic shake tables, the proposed control method adopts direct acceleration feedback control. While acceleration feedback is not practically employed due to stability issues associated with table drift, the proposed method allows the use of acceleration feedback by adding force feedback loop for stabilization. In this study, controllers for the acceleration and force feedback loops are designed using loop shaping techniques incorporating control-structure interaction. The proposed control method was experimentally investigated at the Johns Hopkins University under two loading conditions: without payload and with payload close to the capacity of the shake table. Experimental results showed that the proposed acceleration control method combining acceleration and force feedback provides better acceleration tracking and wider controllable frequency range than the conventional displacement feedback control in both loading conditions. This presentation will cover basic theory of the proposed method, experimental results, and requirements to upgrade existing shake tables with the proposed control method.