Imetrum's Dynamic Monitoring System Provides Accurate and Repeatable Results in Earthquake Shaking Table Tests

Top Quote Imetrum's Dynamic Monitoring Station is used to look at the dynamic safety of single-layer spherical lattice shell for buildings. End Quote
  • (1888PressRelease) September 16, 2015 - Bristol, UK : In light of recent earthquakes, researchers in China have been looking at the safety of using of single-layer spherical lattice shell for buildings. The structural concept is favoured as it is both lightweight and has an elegant appearance, but concerns have been raised about its dynamic safety.

    In a paper published from the Spatial Structures Research Centre at the Beijing University of Technology in China, researchers have been using a unique system developed by UK-based measurement company Imetrum to study dynamic failure criterion. The researchers set out to verify the validity of a proposed failure criterion by setting up a test of a structural model that simulates the process of collapse of single-layer spherical lattice shell.

    The model was constructed on a "shaking table", a well-known and verifiable technique widely used by researchers studying the response of structures due to seismic activity. This involved installing solid spheres on spherical joints and applying a vertical harmonic load to enhance vibration.

    Imetrum's Dynamic Monitoring System (DMS) was used to record dynamic displacements for structural analysis. The non-contact video measurement system, powered by sophisticated Video Gauge™ software, used a high-speed camera to record the process of collapse. The videos were then analysed using Video Gauge™ to measure the displacement of all the nodes.

    The DMS has many advantages for structural researchers using shaking table tests. One of the key benefits is that because it is video based, key events can be captured as a simple visual record but also the video can be replayed for re-analysis of additional data points offline. This is particularly important in tests where the models are shaken to the point of failure. Additionally, using video reduces the test setup time (often including a substructure to support LVDTs), and eliminates any effects caused by additional weight or resistive forces of sensors. With Imetrum's DMS, the user simply defines points of interest in a video captured using the camera. As long as there is some pattern on the item under test, the system will be able to generate measurements. These patterns are then tracked frame by frame, to generate the required measurements, which can then be stored locally or fed into a test machine or data logger.

    Imetrum's systems are highly versatile. As 'virtual' LVDTs, tilt sensors and strain gauges are applied to the specimen simply by clicking the image, measurement ranges and gauge lengths can vary from microns to metres and multiple measurements can be quickly and easily applied at any orientation and location. This means complex configurations are easily achievable and over 100 simultaneous measurements can be made in real time tests, with a greater number achievable in post process mode. To add to its versatility, the DMS can be used with most high-speed cameras, not just those supplied by Imetrum.

    Normally, for a complex geometry like this then a 3D measurement system would be used. However, because of the modelling work already done and the careful setup used, in this case the researchers Beijing University of Technology, were able to use a 2D setup. The research project is still ongoing, however this early work suggests that the researchers can, using the proposed failure criterion, accurately identify the failure moment of single-layer spherical lattice shells damaged either by strength or stability fracture.

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