Development of a Large-Scale 6dof Hybrid Shake Table and Application To Testing Response Modification Devices for Tall Buildings

Abstract eng:
Over the last decade, the introduction of high performance response modification devices to improve structural behavior of components and/or systems under extreme loading conditions such as earthquakes, blast, and wind has increased notably. Most of these devices, such as seismic isolation bearings, energy dissipation devices, and high performance materials, exhibit intrinsic rate dependent behavior. It is, therefore, of utter importance that experimental testing of structural systems incorporating such devices is performed at the correct loading rates. Real-time hybrid shake table testing, sometimes referred to as smart shake table testing, provides an attractive, versatile, and cost-effective method to test structural subassemblies with response modification devices by applying RTHS principles to drive a shake table. This experimental method provides means to dynamically test subassemblies of large systems in full-scale or near full-scale that could otherwise not be tested on a shake table due to size, weight, or strength limitations imposed by the simulator platform. In general, it is beneficial to perform hybrid shake table tests instead of traditional shake table tests whenever the dynamics of the test specimen significantly affects the response of the supporting structure or soil and, therefore, alters the required input to the shake table as testing progresses. In the case that the experimentally tested portion of the structure is a non-destructive specimen, such as a high performance response modification device, the hybrid shake table testing method provides the unique ability to perform efficient parameter studies by changing the properties and behavior of the numerically modeled portion of the structure. To develop the hybrid shake table capability on a multi-degree of freedom simulator platform, the Pacific Earthquake Engineering Research Center (PEER) shake table at the University of California Berkeley was upgraded and modified. The 20x20 ft. table is driven by a MTS 469D real-time digital controller. This digital control system provides closed-loop, threevariable-control (TVC) for all six degrees of motion. The existing system was upgraded with a shared memory network for fast communications and forty signal conditioner channels to directly feed force measurements back into the 469D controller. OpenFresco and OpenSees were installed on a special purpose, multi-core, high performance analysis machine to achieve the computation speeds required to solve large finite element analysis models in real time. Because hybrid shake table tests are a subset of real time hybrid simulations, where very precise control with minimal time delays is of absolute importance, advanced delay compensation techniques were employed for this testing system. A series of experimental tests were then carried out using response modification devices that consisted of a large mass isolated by triple friction pendulum bearings or lead plug rubber bearings. Both of these bearings exhibit significant nonlinear behavior. For the analytical portion of the hybrid model, various building models were investigated in two and three dimensional configurations. Control of the rotational degrees of freedom (roll and pitch) of the hybrid shake table was included for the taller building models to investigate the effects on the behavior of the isolation systems.

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