Natural Hazards Engineering Research Infrastructure: Upgrade of the Large High Performance Outdoor Shake Table to Six Degrees of Freedom

点击翻译按钮获取中文摘要

The large, high-performance, outdoor shake table (LHPOST) experimental facility at the University of California, San Diego, is the largest facility of its kind in the United States for conducting earthquake engineering research on civil infrastructure, and has the world's largest payload capacity (20 MN). Because there are no overhead height restrictions, this facility can accommodate the tallest structures ever tested on any shake table. The LHPOST, originally designed to accommodate six degrees of freedom (6DOF), was supported for construction during 2002-2004 as a single degree of freedom (SDOF) system, by the National Science Foundation (NSF), Network for Earthquake Engineering Simulation (NEES), Major Research Equipment and Facilities Construction account, due to budgetary constraints. As an SDOF system and a multi-user national research facility, the LHPOST has been supported by NSF for operations and maintenance under the NEES (FY 2005-FY 2014) and the Natural Hazards Engineering Research Infrastructure (NHERI) (FY 2015 to date) programs. This award will upgrade the LHPOST from its current SDOF configuration to a full 6DOF capability. In its upgraded configuration, the LHPOST will be able to reproduce all six components of motion (two horizontal and vertical translational components, as well as pitch, roll, and yaw rotational components) experienced by the ground during earthquakes. It will provide a one-of-a-kind facility to test large to full size civil infrastructure, such as structural, nonstructural, geo-structural and soil-foundation-structural systems, under strong earthquake excitation. The ability to test infrastructure under the full range of combined horizontal, vertical, and rotational seismic input motion is critical for research that can lead to effective, economical,and practical new infrastructure designs, as well as seismic rehabilitation and retrofit strategies for existing infrastructure, to improve the seismic performance for post-earthquake resilience, public safety, and national welfare. The 6DOF LHPOST will provide critical landmark datasets to support the development, calibration, and validation of high-fidelity, physics-based computational models of civil infrastructure systems that will progressively shift the current reliance on physical testing to model-based simulation for the seismic design and performance assessment of such systems. The experimental capabilities provided by the 6DOF LHPOST will support U.S. leadership in earthquake engineering research. The upgraded shake table will also provide a unique tool to educate graduate, undergraduate, and K-12 students, as well as the news media, policy makers, infrastructure owners, insurance providers, and the public, about natural disasters and the national need to develop effective technologies and policies to prevent earthquakes from becoming societal disasters. This award supports the National Earthquake Hazards Reduction Program (NEHRP). The upgrade of the LHPOST to 6DOF will be achieved by adding two horizontal actuators and reconfiguring all four horizontal actuators into a V-shape at both longitudinal ends of the shake table's 12.2 meter long by 7.6 meter wide platen to provide bi-axial horizontal motions, as well as the yaw motion capabilities. Each of the existing six pressure balanced vertical actuators/bearings will be equipped with a high-flow servovalve to enable vertical, pitch, and roll motion capabilities. To operate the 6DOF table, the number of hydraulic power units will be increased from two to four and the total size of the accumulator banks will be increased from 9,500 to 37,800 liters. A new piping system will be installed between the accumulator banks, the horizontal and vertical actuators, and the surge tank. A third nitrogen-filled hold-down strut will be installed between the bottom of the platen and the bottom of the reaction block to increase the overturning moment capacity of the table. The existing SDOF shake table controller (both hardware and software) will be replaced by a controller with 6DOF capabilities. A new hydraulic distribution system controller will also be provided to handle the safety interlocks, control of the hydraulic power units, and control of the accumulator charging and blowdown. Additionally, the height of the existing four safety towers will be doubled to protect the hydraulic power building from potential specimen collapse. During the upgrade, operations of the shake table under NHERI will cease for a period of 14 months between mid-2020 and mid-2021. Before reopening the facility for operations and research, commissioning of the facility, including acceptance and characterization tests, will be performed.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.