Developing accurate seismic load testing for Kingston University in London

By James McNally | Case Studies

load testing setup

To test the behaviour of structural elements such as reinforced concrete frames under load, civil engineering researchers at London’s Kingston University need to gather accurate data from their test equipment.

But the testing equipment used for this kind of experiment wasn’t working as effectively as it should. The university’s actuators (the devices that operate the test equipment) were controlled manually rather than by a computer, data collection was being affected by noise interference, and the system was complicated and time-consuming for researchers and students to set up.

I helped them by developing a better, simpler, more accurate system.

Background

I was contacted by George Hopartean, a postgraduate researcher and senior technician in Kingston University’s Department of Civil Engineering, Surveying and Construction Management, who needed help with a couple of problems.      

He was researching the strength of concrete structures reinforced with fiberglass. Using a large steel frame test rig and equally large actuator, the concrete was submitted to reversed quasi static cyclic loading to simulate seismic loading situations (such as earthquakes). By creating forces and stresses of up to 150kN, the researchers were able to see how the new structures behave in terms of crack propagation and pattern, stiffness and maximum load capacity.

Photos and measurements are taken during the test cycles to help the researchers to see exactly what’s happening.

The university had a logger to capture the data produced. But they also had two major problems to overcome:

  • Problem one – the actuator created a lot of noise, which was so bad it created interference that rendered the data being produced useless.
  • Problem two – the system was complicated and time-consuming to set up.

The general-purpose data logger didn’t control the actuator – a person, George, had to set up the system. This was complex to learn, time-consuming to run and potentially inaccurate. The data logger also had lots of screens and parameters that had to be configured before testing could begin.

While George had enough experience to be able to do this quickly, other researchers and students in the department didn’t. It could take a student a couple of weeks to become familiar with the system – far too long for a test that only has a few weeks to be completed.   

Example of a specimen undamaged (left) and after failure (right)

Creating the right solution

Talking with George, it quickly became clear that designing a new system would solve many of their problems. The system I developed is based on a CompactRIO industrial controller (made by National Instruments) with NI C Series acquisition modules and a LabVIEW Real-Time operating system.

This platform allowed us to measure strain gauges linear variable differential transformers (LVDT) directly with in-built signal conditioning (the circuitry required to convert a sensor signal into something easier to read and understand).  

But all of this is useless if the person doing the testing doesn’t know how to use it. So I also established some best practices for using shielded cables and made it really easy to connect sensors up the right way, further removing the risk of user error and reducing the volume of noise created.

Time to look at the software

In addition to improving the hardware, I redesigned the software to enhance the quality of the signals being received. After exploring various filter settings, we were able to remove some of the background noise that wasn’t relevant to the test being conducted. This got nice stable, smooth values that can be used to analyse the system.

The choice of LabVIEW Real-Time as an embedded operating system meant we could make sure the system is highly reliable throughout the lifetime of the tests. The tests could take several days to complete, and often resulted in the structure being destroyed in the process – making each test critical. Once testing began, it couldn’t be restarted. It was essential that the system didn’t crash during the test and reliably controlled the actuator throughout.

“I wasn’t sure if the connection from the software to the actuator would work without interfering with the live data.

In the end… it worked perfectly.”

George

Replacing George as the actuator controller    

We also needed to remove the manual element of actuator control. Before, George had to manually instruct the actuator to move forward or backward, stopping when the position appeared correct on the screen.    

My design meant that the system could do this automatically, stopping and re-starting at exactly the right time and position, which in turn generated accurate, repeatable measurements. 

Make it simple stupid

The user interface was a critical piece of the jigsaw. George and the other researchers are civil engineers. They shouldn’t have to go through a complex software set-up every time they want to take measurements. They just needed data in a format that’s useful to them.

Working closely with George, I designed and built a user interface that gives them the information and live readings they need, in a format they understand, so they can oversee and control the test. For example, at different points during the tests they need to be able to stop and take pictures of the structure being tested. These stopping points could now be programmed in, with the software ensuring the test stops between cycles at the right time to capture images, without the risk of the test moving.  

The user interface design

Safer, quicker and better. By design.

Ultimately this means they can now get reliable data with less effort. Tests can be conducted safely, quickly and accurately. The researchers and students don’t need to learn a complex system, instead focussing their time on developing ideas and analysing the data, ultimately doing more high quality research.

“The new data logger in place helps in the delivery of projects for students which it was almost impossible to do before.”

George

Delivery

The whole project was completed in under two months, in time for George to generate data to present at a conference looking specifically at Fibre Reinforced Polymers (FRP) in the construction industry. The presentation was well received, with delegates commenting on the repeatability and reliability of the experiment conducted. The university as a whole is now much more confident in the system, with more researchers and students able to use it and in turn make better use of the other facilities on offer.    

 “If there is something you would like achieve, Wiresmith Technology will find technical ways to deliver it.”

George

Images courtesy of Kingston University. 

Find out more about undergraduate and postgraduate courses in Kingston University’s Faculty of Science, Engineering and Computing.

About Wiresmith Technology:

Wiresmith Technology is a software development consultancy that specialises in developing automated data acquisition systems to help engineers realise their ideas.

If you want to find out more, here are a few pages that might be interesting:

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About the Author

I founded Wiresmith Technology to help engineers improve their systems and products with quality measurement systems. I'm a Certified LabVIEW Architect, Certified LabVIEW Embedded Developer and LabVIEW Champion.

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