Large-scale Experimental, Numerical, and Design Studies of Steel MRF Structures with Nonlinear Viscous Dampers under Seismic Loading.

摘要

Analytical and large-scale experimental studies on steel MRF building structures with nonlinear viscous dampers were conducted. The primary objectives of this research are to investigate the seismic response and performance of steel MRF structures with nonlinear viscous dampers and develop a simplified design procedure (SDP) for seismic design of these structures.;The prototype building for this research is an office building located on a stiff soil site in Southern California. Moment resisting frames (MRFs) and frames with nonlinear viscous dampers and associated diagonal bracing (DBFs) constitute the seismic force resisting system (SFRS). Three different strength level designs of the prototype building MRFs (i.e., D100V, D75V, and D60V) were generated by changing the seismic mass of the building. A single-bay MRF and a single-bay DBF, and the associated mass and gravity load system were extracted from the prototype buildings to serve as the prototype structure. The design calculations for the prototype building and prototype structure were based on current seismic provisions. The prototype structure was scaled down by a factor of 0.6 to develop the test structures for the analytical and experimental studies.;The dampers used in the test structures are large scale nonlinear viscous dampers with a force capacity of 600 kN and maximum stroke of 125 mm. The dampers were characterized under harmonic loading with various combinations of loading frequencies and amplitudes. A model for the damper response, called the Nonlinear Maxwell damper model, was developed. This model was validated by comparing the damper force response of the model with the measured force response from tests under harmonic loading and under earthquake-induced damper deformations.;The procedure used to select ground motions to represent the seismic hazard at the prototype building site is described. Using this procedure, three sets of 40 ground motions representing the frequently occurring earthquake (FOE), design basis earthquake (DBE), and maximum considered earthquake (MCE) hazard at the prototype building site were selected. Nonlinear numerical models of the test structures were developed using the program OpenSees. Nonlinear dynamic time history analysis (NDTHA) was performed using the nonlinear numerical models to predict the response of the test structures under the sets of ground motions.;Real-time hybrid earthquake simulations (RTHS) were conducted on the test structures. Two phases of RTHS (i.e., Phase-1 and Phase-2) were conducted. In the Phase-1 RTHS, the experimental substructure is the single-bay DBF with one damper in each story, and the analytical substructure consists of the single-bay MRF, the gravity load frames, and the seismic mass tributary to the MRF and DBF. In the Phase-2 RTHS, the experimental substructure includes the single-bay MRF and single-bay DBF, and the analytical substructure includes only the gravity load frames and the seismic mass tributary to the MRF and DBF. In the two phases of RTHS, the measured floor displacements from the experimental substructure were used as the feedback for the RTHS, and the errors between the target displacements and measured displacements due to dynamic characteristics of the servo-hydraulics controller and actuators, test fixtures, and experimental substructure were compensated appropriately. RTHS with FOE, DBE, and MCE level ground motions, along with RTHS with ground motions more intense than the MCE were conducted.;The results show the test structures achieved high performance at all level ground motion intensities. The results from the RTHS are compared with the results from NDTHA. Differences between the RTHS results and numerical simulations are discussed. Considerations for modeling structures with nonlinear viscous dampers to enable more accurate results are proposed. Based on the response of the nonlinear viscous damper in the RTHS and NDTHA, an approach for linearizing the damper response for use in design calculation was developed and assessed.;A simplified design procedure (SDP) for seismic design of steel MRF structures with nonlinear viscous dampers is presented. For selected performance objectives and associated story drift based design criteria, the SDP enables an integrated design of the MRF and damping system to be performed. The SDP requires only linear elastic analysis of a linear model of the MRF, and is consistent with the analysis procedures in ASCE 7-10 for seismic design of conventional structures without dampers. The SDP was validated using results for a 4-story example steel MRF building with nonlinear viscous dampers, and was validated in part by comparing the story drift results from the SDP with the results from real-time hybrid earthquake simulations (RTHS) for the 3-story test structures.