EQUALS shaking table

The EQUALS shaking table of the University of Bristol

The Earthquake and Large Structures Laboratory (EQUALS) is part of the Bristol Laboratories for Advanced Dynamics Engineering (BLADE) in the Faculty of Engineering at the University of Bristol, UK. It houses a 15t capacity, 6 DoF earthquake shaking table surrounded by a strong floor and adjacent strong walls up to 15m high.

The shaking table consists of a stiff 3mx3m platform, weighing 3.8 tonnes, with a regular grid of M12 bolt holes for attaching to the platform body and for mounting of specimens. The platform can accelerate horizontally up to 3.7g with no payload and 1.6g with a 10t payload. Corresponding vertical accelerations are 5.6g and 1.2g respectively. Peak velocities are 1 m/s in all translational axes, with peak displacements of ±0.15 m.

The shaking table is accompanied by a set of 40 servo-hydraulic actuators that can be configured to operate in conjunction with the shaking table, strong floor and reaction walls, providing a highly adaptable dynamic test facility that can be used for a variety of earthquake and dynamic load tests.

Hydraulic power for the shaking table is provided by a set of six shared, variable volume hydraulic pumps, providing up to 900 lt/min at a working pressure of 205 bar. The maximum flow capacity can be increased to around 1200 lt/min for up to 16 seconds at times of peak demand with the addition of extra hydraulic accumulators.

A special feature of the EQUALS facility is its digital control system, with world leading features, including a ‘hybrid test’ capability (also known as ‘dynamic sub-structuring’) in which part of the structural system of interest can be emulated by a numerical model embedded in the digital control system, while only a sub-component need be tested physically. Extensive instrumentation is available, including 256 data acquisition channels.

EQUALS has particular expertise in seismic testing of geotechnical problems. The facility is equipped with two lamellar, flexible, shear boxes for geomechanics testing. One of these is 6m-long, 1.5m-deep and 1m-wide; the other is 1.5m-long, 1m-deep and 1m-wide.

The EQUALS facility is supported by a multi-disciplinary group of academics specialising in advanced dynamics and materials from across the Civil, Aerospace, Mechanical Engineering, and Non-linear Dynamics fields, providing to users day-to-day support, specimen fabrication and manufacturing, as well as shaking table operation, electronics and instrumentation support. The Faculty has an extensive manufacturing workshop equipped with numerically controlled machines, etc.

The research based on the EQUALS shaking table includes the response of cable-stayed bridges, soil-structure interaction, the use of discrete damping elements in building structures, base isolation systems, torsional response of buildings, masonry structures, steel and concrete buildings, multiple-support excitation, travelling earthquake wave effects, non-linear self-aligning structures, dams, reservoir intake towers, retaining walls and strengthening systems with advanced composites.

EQUALS is particularly suited to testing of small- to medium-sized specimens in order to investigate fundamental dynamic and seismic phenomena. EQUALS is sometimes used to develop a large-scale experimental campaign that will be executed on a bigger shaking table, such as those at CEA Saclay or LNEC Lisbon. The shaking table can be augmented by additional actuators, to enable multiple-support excitation or travelling wave effects to be explored.



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  Joint with US-NEES "Earthquake Engineering Research Infrastructures

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