EQUALS Shaking Table at University of Bristol  

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The Earthquake and Large Structures Laboratory (EQUALS) is part of the £20m Bristol Laboratories for Advanced Dynamics Engineering (BLADE) in the Faculty of Engineering at the University of Bristol, UK. It houses a 15t capacity, 6 degree of freedom earthquake shaking table surrounded by a strong floor and adjacent strong walls up to 15m high (Figure 1). The shaking table is accompanied by a set of 40 servohydraulic 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. A special feature of EQUALS is the digital control system. This has world leading features, including a ‘hybrid test’ capability 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. The EQUALS shaking table is one of the few earthquake shaking tables in the world with this capability. The associated control software was developed in-house.

The EQUALS laboratory is a node of the UK Network for Earthquake Engineering Simulation (UK-NEES), which forms part of the worldwide NEES. NEES enables participation of remote users in experiments via high performance video conferencing and, where appropriate, direct interactivity and control of test and data acquisition equipment, enabling senior researchers to interact remotely with their junior staff at the lab. Data and video can also be streamed in real-time to remote users for use in off-line analyses. EQUALS is also newly connected to Bristol Is Open (BIO), the University’s new living laboratory research infrastructure comprising a dedicated high performance programmable fibre optic and wireless network around the city centre, overlain by an innovative City Operating System (CityOS). BIO enables the shaking table to be coupled to full scale experiments that are embedded in the city.

The shaking table consists of a stiff 3 m x 3 m cast aluminium platform weighing 3.8 tonnes and is capable of carrying a specimen payload of 15t. 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 1.0 m/s in all translational axes, with peak-to-peak displacements of 300 mm. A large database of recorded earthquake records can be applied, or synthetic motions can be readily created. Extensive instrumentation is available, including up to 256 data acquisition channels.

Services currently offered by the infrastructure: The EQUALS facility is supported by a primary group of ten senior academics, led by Prof Colin Taylor, with very broad experience across earthquake engineering and civil engineering dynamics. They form part of a larger, multi-disciplinary group of academics specialising in advanced dynamics and materials from across the Civil, Aerospace, Mechanical Engineering, and Non-linear Dynamics fields. EQUALS users of can draw on the support of a wider academic group. The primary academic group has supported around 150 external users over the past 15 years through TNA programmes.

EQUALS is also supported by five, highly experienced, postdoctoral research assistants, who will provide day- to-day support for the users, including design of the experimental programmes. Four experienced technicians provide specimen fabrication and manufacturing as well as shaking table operation support. The Faculty has an extensive manufacturing workshop equipped with numerically controlled machines etc.

Over the past 20 years, the EQUALS shaking table based research has included 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 advanced composite strengthening systems. The facility is equipped with two lamellar, flexible, shear boxes for geomechanics testing. One of these is 6 m long, 1.5 m deep and 1 m wide; the other is 1.5 m long, 1.0 m deep and 1 m wide. EQUALS is particularly suited to testing of small to medium sized specimens in order to investigate fundamental dynamic and seismic phenomenon. EQUALS has particular expertise in seismic testing of geotechnical problems.