Structures laboratory

Portable 35kg vibration shaker with additional reaction masses driven by APS 114 EP extended power amplifier. Suitable for testing medium size full-scale civil engineering structures to which the shaker is attached.

The shaker has been successfully used in testing of long-span concrete floors and footbridges in open space conditions weighing up to 1,500 tonnes. The test structures may be empty or occupied by stationary or moving people, giving an opportunity to assess the effects of human-structure dynamic interaction.

The shaker can also be used for direct drive with a stinger. The moving mass is 17.6 kg and the shaker can generate up to 100 N harmonic force amplitude

These shakers have reaction mass assemblies suitable for reaction mode excitation of large civil engineering structures. Also, custom-built horizontal reaction mass assemblies have been acquired so that the rated harmonic force can be applied horizontal to frequencies as low as 0.5 Hz, which is particularly important for structures with low horizontal natural frequencies, such as long-span bridges and sports stadia.

All four available shakers can be controlled using the newly-acquired Mobilizer II spectrum analyser suitable for advanced multi-input and multi-output (MIMO) testing of structures. The shaker can also be used for direct drive with a stinger. The moving mass is 30.1 kg and the shaker can generate up to 450 N harmonic force amplitude.

With slightly reduced moving mass and friction connection with the structure, these shakers can be used to shake with full 450N force characteristic down to 2Hz.

Horizontal rig with linear bearings, the shaker operates as a uni-axial shaking table. The same platform can be used to mount up 500kg of masses to allow the shakers to generate full 450N force characteristic down to 0.5Hz.

Able to run in voltage or current mode to drive APS113 and APS400 long stroke shakers

Portable and manually operated instrumented impact hammer for the application of transient loading on full-scale structures in the low frequency range; weight 5.4kg; max. peak force 22kN.

Used in conjunction with the Diagnostic Instruments DI2200 portable spectrum analyser for quick and cheap modal testing of small and medium size Civil Engineering structures. Battery-powered signal conditioner.

IEPE accelerometers for vibration and seismic measurements of full-scale Civil Engineering structures; robust and highly sensitive (approx. 1000mV/g) providing results with micro-g resolution.

We have measured noise floor at about 0.5mg/ÖHz and excellent characteristics in low-frequency range (near-DC frequency response) as required for Civil Engineering field dynamic testing applications, with mains-powered signal conditioners.

This accelerometer does not measure to DC (there is low frequency drift), and we use with good quality cables with XLR connectors instead of BNC/microdot combinations for best results. For field testing we use these sensors to measure shaker force via armature acceleration.

Formerly supplied by Sundstrand and Allie Signal, and (in different grades) used in applications such as missile guidance, directional drilling and monitoring of the International Space Station (ISS), these sensors have a range of +/-30g and can resolve accelerations as low as 1 micro-g across a bandwidth from DC (0Hz) to 300Hz.

The Vibration Engineering Research Group deploy these as uniaxial sensors on lightweight mountings and connected to simple power supply units via fool-proof and rugged connectors and colour-coded cables. The QAs develop current proportional to acceleration result in no EMI problems and the ability to change sensitivity simply by switching load resistor in the power supply. We have measured noise floor and found it to be in the range 0.1mg/ÖHz.

A relatively low-cost single axis capacitive accelerometer for measuring static acceleration or low-level, low-frequency vibration. Featuring 1.3μg @ <10 Hz resolution (slightly inferior to the QA performance), excellent frequency response and insensitivity to thermal transients and transverse acceleration. We have found their noise floor to be about 0.5 mg/ÖHz.

Codamotion’s measurement technology uses miniature infra-red ‘active’ markers, each with their own unique identity, to track the three-dimensional (3D) positions of the human body in real time.

‘Active’ markers are those which generate their own light, they flash (as opposed to reflect). The Vibration Engineering Section (VES) have 56 tracking markers at their disposal in the laboratory.

The motion of active markers is recorded using CODA sensors (also called CX1 units). A single sensor is a stand-alone measurement unit, capable of tracking 3D marker positions in real time.

Multiple CODAs can be easily aligned as a single framework to extend the measurement volume covered.

Force plates, also known as force platforms, are devices designed to measure forces (loads) generated by people standing and moving on them or moving across them. VES has an AMTI strain gage force plate.

In 3D space the resultant force and moment vectors can be resolved into six components acting along three-axial orthogonal coordinate system – three forces Fx, Fy, Fz and three moments Mx, My and Mz.= When designing structures which are predominantly occupied by active humans, civil structural engineers typically need only vertical Fz and/or lateral Fx force components (e.g. in the case of footbridges).

Because of its limited size, the force plate is typically used in the Vibration Engineering Section to measure forces due to activities performed on a spot, such as jumping.

In the Vibration Engineering Section, an ADAL3D instrumented force measuring treadmill is used for continuous measuring of time-varying walking and jogging forces during a large number of successive steps and over a wide range of steady-state gait speeds.

To measure independently the left and right footfalls, double belt design splits the walking surface into two identical treadmills - left and right, placed close together. Each treadmill belt is driven by a brushless servomotor equipped with internal velocity controllers to maintain the speed as constant as possible. Velocity of treadmill belts in the range 0.1-10 km/h can be controlled and monitored remotely either with a control panel or with ADAL3D-F software, Adisoft2000 (HEF Medical Developpement 2009), run from the data acquisition PC. Similar to fitness treadmills, both the FMIT and the remote control panel are equipped with a safety stop switch.

A pair of Kistler piezoelectric force transducers on each side of the treadmill are connected to signal processing units providing one vertical and two horizontal analog force signals per side. In total six force analog signals are sent from the four sensors to the charge amplifiers, then to a 16 channel, 12 bit, A/D card in the data acquisition PC. Usual sampling rates are between 100 and 1000 Hz.

Two more channels are used to monitor the instantaneous velocity of left and right treadmill belts measured by optical transducers. Finally, Adisoft2000 stores the data. Extra channels of the A/D card could be used to synchronise measurements between the treadmill data and other third party equipment, such as Codamotion.