Real-time Hybrid Simulations of a Large-scale Steel Structure with Nonlinear Viscous Dampers Subjected to the Maximum Considered Earthquake Hazard Level
The NEESR project entitled NEESR-CR: Performance-Based Design for Cost-Effective Seismic Hazard Mitigation in New Buildings Using Supplemental Passive Damper Systems (PI: Richard Sause) is currently conducting a series of large-scalereal-time hybrid simulations (RTHS) on a 3-story steel frame building at the Real-time Multi-directional (RTMD) Earthquake Simulation Facility, the Lehigh NEES Equipment Site. The goal for this NEESR project is to develop a validated, probabilistic, performance-based seismic design procedure for buildings with passive damping systems.
The RTHS will be used to experimentally validate the performance-based seismic design of the 3-story building constructed of structural steel and equipped with nonlinear rate-dependent viscous dampers. The prototype building for the study is located in Pomona, California and the steel structure is designed for 75% of the code design base shear, as permitted by the code, with supplemental viscous dampers to control drift. (Earlier in the project we tested the structure designed for 100%.) A performance based design procedure to control drift and thereby avoid damage to the building under the design earthquake.
In the RTHS the complete structure is represented as an experimental substructure and an analytical substructure. The experimental substructure consists of a large-scale 3-story steel frame with nonlinear viscous dampers and diagonal braces supporting the dampers, and the analytical substructure is comprised of the remaining parts of building, including steel SMRFs, gravity load frames, seismic mass, and the inherent damping of the building. The analytical substructure has a total of 296 DOFs, and includes nonlinear fiber elements and panel zone elements to model the members and panel zones, respectively, of the MRF and gravity load system. In addition, geometric nonlinearities are included to account for the P-delta effects of the gravity load system of the building.
The RTHS data will be used to observe and understand the interactions of the viscous dampers with the braces, beams, and columns of the experimental substructure as well as the interactions between the steel frame with the dampers and the rest of the building. The project team has developed detailed analytical (numerical simulation) models of the prototype building with nonlinear viscous dampers, and the RTHS data will be used to validate the models.
The current series of RTHS will utilize ground motions scaled to the maximum considered earthquake (MCE) level, associated with a return period of about 2500 years. Robust actuator control algorithms will be used in conjunction with a complex MDOF nonlinear analytical substructure and an unconditionally stable explicit integration algorithm. The control algorithms, nonlinear analysis tool, and integration algorithm have been developed and implemented by the Lehigh Equipment Site as tools to support large-scale RTHS. The RTHS will be the first of their kind, involving large-scale real time simulations of a multi-story steel frame subjected to MCE-level ground motions.
The project's initial RTHS at MCE level took place April 18-22. The next RTHS took place on May 1, May 2 and May 3. The next test takes place May 6, between 11 am and 3 pm EDT. The RTHS test matrix includes conducting a series of simulations using an ensemble of 16 earthquake records at the maximum considered earthquake (MCE) level. The test matrix in Table 1 (below) lists the ground motion records that will be used. Each of record will be scaled to the MCE seismic hazard level. The RTHS can be viewed by telepresence, where webcams and the Real-Time Data Viewer can be used to view video, data and animation of the response of the building acquired from the RTHS. To remotely participate, go to the following link (http://www.nees.lehigh.edu/rths-of-mrf-dbf-system-with-viscous-dampers). Result (including video) from completed tests will also be archived and available at the previous link and through the Project Warehouse on NEES.org. Also, follow us on Facebook to get up to the minute simulation updates from our research team.
Table 1. Earthquake Ensemble for Real-time Hybrid Simulations
The project is a collaborative effort that includes California State University, Northridge; California State Polytechnic University, Pomoma; Lehigh University; The Pennsylvania State University, Erie; and Tokyo Institute of Technology. Industry partners include Corry Rubber Company, Taylor Devices, Miyamoto International, Inc. and Simpson Gumpertz & Heger.
More information about the above NEESR project can be found at http://www.nees.lehigh.edu/projects/pbd-for-seismic-hazard-mitigation.
You are encouraged to visit the RTMD website (http://www.nees.lehigh.edu/) to learn about the capabilities of the Lehigh NEES Equipment Site and completed and ongoing research projects (http://www.nees.lehigh.edu/projects). Data can be accessed at NEEShub for the completed projects, in addition to data for completed phases of the above project.