Large High Performance Outdoor Shake Table (LHPOST)
LHPOST is a unique outdoor shake table facility that can accurately reproduce far- and near-field ground motions for the seismic testing of large structural, geotechnical or geostructural systems, or soil-foundation-structural (SFS) systems, up to a weight of 20 MN. A schematic of the LHPOST mechanical and servo-hydraulic components is shown in the accompanying figure.
Component 1 is the 12.2 m long by 7.6 m wide by 2.2 m deep honeycomb steel platen with a grid of multi-purpose, high-capacity, tie-down points spaced at 610 mm o.c.
Component 2 is the reinforced concrete reaction mass and the service tunnel that connects to the Hydraulic Power System Building. The reaction mass also has a grid of multi-purpose, high-capacity vertical tie-downs for the deployment of safety or measurement frames or for the deployment of reaction frames as needed for hybrid testing.
Component 3 consists of the set of two ±750 mm stroke servo-controlled dynamic horizontal (longitudinal) actuators with a combined maximum force of 680 tons. Each actuator is equipped with two four-stage servo-valves (each rated for a flow of 10,000 liter/min @ 7 MPa pressure drop).
Component 4 comprises the six vertical actuators, currently acting as passive hydrostatic pressure-balanced bearings, which support the shake table platen.
Component 5 is a set of two nitrogen-filled hold-down struts that passively pre-compress the platen against the sliding bearings and, consequently, provide overturning moment resistance.
Component 6 is a yaw restraint system (consisting of two pairs of transversal actuators, one at each end of the platen, with each pair consisting of two coupled actuators, one at each side of the platen) to prevent the platen from undesirable yaw in the current single axis configuration. Finally,
Component 7 is a weatherproofing system consisting of removable concrete planks. The performance characteristics of the LHPOST in its current single axis configuration are shown in the Table.
The LHPOST can be used in combination with either a 3 m wide by 6.7 m long by 4.7 m high large laminar soil box, funded by Caltrans, or a 4.6 m or 5.8 m wide by 10 m long by 7.6 m high large soil confinement box (LSCB), funded by NSF. Both soil boxes are modular and can be configured to a given height. The soil confinement box can be configured in two different widths. These large soil boxes enable large-scale seismic experiments on geotechnical and SFS systems.
The LHPOST includes software and hardware equipment to support real-time dynamic hybrid testing in combination with shake-table substructures. To this end, the EF has available: a 500 kN MTS model 244.41S dynamic actuator with ±200 mm stroke and three-stage servo-valve rated at 950 liter/min, a portable hydraulic power system consisting of a 35 MPa accumulator bank (475 liters capacity) chargeable by a small diesel engine driven pump. The control equipment consist of a multi-channel MTS FlexTest controller able to control up to four external hydraulic actuators simultaneously, and a SCRAMNet ring for real-time communication and synchronization of data flow between the shake-table controller, the FlexTest controller, and the real-time target PC running the user programmable hybrid simulation algorithms.