Structures laboratory

Contact: James Bassitt

Our facilities are the most advanced in the UK for vibration testing and analysis of large civil engineering structures. 

Our extensive range of software and hardware costs over £1million and is constantly adapted and upgraded by both the company and the University of Exeter for fundamental and applied research, as well as for commercial work.

Analysis software

We have an extensive library of commercial and bespoke software for data collection and analysis including:

ANSYS finite element code

A general purpose finite element code with powerful and well-developed structural dynamic analysis facilities. Analysis results may be exported for correlation with experimental modal analysis results.

ARTeMIS output-only modal parameter estimate software

Software for carrying out modal parameter estimation of structures where only response data are measured. Typically used for ambient testing of large structures where artificial excitation is inconvenient or impossible.

FE-Map structural pre- and post- processor by Majenta

A windows based pre- and post-processor for engineering finite element analysis. Analysis may be performed using ANSYS or the FEMAP internal solver.

FE-Model updating software

Software used to automatically update finite element models of structures using experimental data. Compatible with a range of experimental modal analysis and finite element analysis software.

ICATS

Experimental modal analysis software for extracting structural dynamic parameters from raw modal test data and finite element model correlation.

LUSAS finite element code

A general purpose finite element code with particular strengths in the analysis of Civil Engineering structures.

MATLAB and SIMULINK

Programming language for technical computing. Used primarily for development of signal processing and modal parameter estimation routines, also used for interfacing with ANSYS and for model updating.

MATHEMATICA

Mathematical software for technical computing.

ME'Scope MATLAB Modal parameter estimation software

Used extensively for analysis of field test data acquired by forced vibration testing. It caters for multi-input multi-output (MIMO) analysis of frequency domain experimental data, in the form of frequency response functions (FRFs). It recovers both mode shapes and operating deflection shapes. It has time domain analysis capabilities.

MODAL

Graphical user interface (GUI) developed in-house using MATLAB. Modal analysis software with capabilities for time and frequency domain signal analysis, modal parameter estimation and viewing and comparison of modal analyses.

NDOF

Graphical user interface (GUI) developed in-house using MATLAB. Simulation software primarily for teaching structural dynamics, but with capabilities for vibration serviceability assessment and virtual modal testing.

Plaxis

A finite element program for geotechnical applications in which soil models are used to simulate the soil behaviour. It includes a variety of soil constitutive models and a dynamics module.

VSATS

Graphical user interface (GUI) developed in-house using MATLAB. Used for a range of vibration serviceability simulations using modal solutions imported from analytical and experimental modal analysis. Incorporates all relevant design guidance on vibration serviceability of floors, footbridges and grandstand tiers.

Model test excitation

APS DYNAMICS 113 long stroke shakers

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

APS DYNAMICS 400 long stroke shakers: vertical mode

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.

APS DYNAMICS 400 long stroke shakers: horizontal mode

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.

APS DYNAMICS 400 long stroke shakers: shaking table

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.

Power amplifiers for long stroke shakers

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

DYTRAN MODEL 5803A instrumented impulse hammer

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.

Vibration transducers

Endevco Model 7754-1000 piezoelectric accelerometers (22 units)

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.

Honeywell QA700 and QA750 force balance accelerometers (24 units)

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 Section 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.

Kistler 8133A uniaxial accelerometers (16 units)

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.

Kinemetrics Episensor Model FBA ES-T triaxial and FBA-11 uniaxial force balance accelerometers

Model FBA ES-T is a triaxial surface package useful for many types of low frequency vibration applications, and comprises three EpiSensor force balance accelerometer modules mounted orthogonally in a package. Episensor has full-scale recording ranges of ± 0.25 to ± 4g (user selectable), and a maximum resolution of 10V/g. The FBA-11 is housed in a watertight cast aluminium case, and is suitable for a variety of seismic, structural and commercial applications. The maximum sensitivity of this accelerometer is 5V/g.

GURALP CMG-5TD accelerometer (2 units)

A three component accelerometer with performance similar to the QA700/750. It incorporates a 24-bit digitiser and is designed to transmit data over internet connection, with protocols for synchronisation that include use of GPS. We have used this for measuring vibrations of the Humber Bridge, and for continuous monitoring of the University of Sheffield Arts Tower.

GURALP CMG-3ESP seismometer

A three component seismometer with exceptional performance for resolving extremely low vibrations at least an order of magnitude weaker than those measured by QA700/75. We have measured the noise floor to be below 0.01mg/ÖHz. Requires delicate handling and levelling, incorporates a 24-bit digitiser.

Data acquisition

Bespoke remote data acquisition systems such as these have been created for monitoring of football stadia, chimneys, bridges and buildings, using robust, high quality acquisition and computing hardware.

Data Physics 'MOBILIZER II' Spectrum analyser

State of the art spectrum analyser used for single- and multi-shaker modal testing of structures. 32 input channels and 4 output channels with 24-bit resolution. The Mobilizer chassis connects to a laptop PC via Ethernet and runs SignalCalc software that interfaces with a range of modal analysis packages.

Data Physics 'QUATTRO' Spectrum analyser

State of the art spectrum analyser used for single- and dual-shaker modal testing of structures. 4 input channels and 2 output channels with 24-bit resolution. The Quattro analyser connects to a laptop PC via Ethernet and runs SignalCalc software that interfaces with a rannge of modal analysis packages.

National Instruments ‘COMPACT DAQ’

NI-USB 9233, NI USB-9234 and NI USB-9239 24-bit 4-channel data acquisition systems, with automatic anti-alias filtering, driving IEPE and Voltage-output accelerometers. LabVIEWirtual instruments (VIs) developed for continuous data acquisition and interfacing with modal analysis software.

GEOSIG GSR-24 Seismic recorder

This functions as a battery-powered stand-alone 24 bit data acquisition system with scheduling and GPS synchronisation. These recorders were used with units from FEUP to for measurements on the Humber Bridge in 2008. Seen here connected to a set of three QA-700 accelerometers.

Biomechanics

Codamotion 3D measurement instruments

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.

Codamotion Sensor CX1

The Codamotion CX1 unit, known as a CODA. It only weighs 5kg, so it is readily portable.

Standard Marker

The standard active marker for use with the CX1 system can be powered by any of the marker drive boxes in the standard range. Each marker is given a unique identity by the drive box it is connected to.

2-Marker Drive Box

Contains the battery and optical synchronisation for up to two markers. Markers are time-multiplexed by these boxes so that every marker has a unique identity. Boxes are usually placed mid-segment so that no marker wires should cross any joints. Boxes are self-powered and fully independent.

8-Marker Drive Box

Contains the battery and optical synchronisation to for up to eight markers

Active Hub with Quad UART

A rack-mountable industrial computer unit. Quad UART gives combined power and data connections for Cx1 units, plus sync input/output connectivity. The sync input connection can be used to control the timing of Codamotion acquisition using external devices, whilst sync output can be used to trigger external devices to run synchronously with the Codamotion system. Optional analogue and digital interfaces allow synchronous acquisition of data from other devices, and real-time triggering.

Force plates

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.

Instrumented treadmill

In VES, 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.