Dr. Adam Crewe is a Reader in Earthquake Engineering in the Department of Civil Engineering. His research interests are to develop a better understanding of how various types of structure respond to earthquake and other types of dynamic loading, in many cases using large scale laboratory tests to validate his theories. Particular research areas of interest are:
· Full-Scale Testing
· Shaking Table Modelling
· Earthquake Resistant Design and Construction
In an upcoming paper for 17WCEE Adam describes the design and manufacture of a very high performance 6 DoF Hexapod.
The seismic design of the power station structures and all the mechanical and electrical components is a key aspect of the whole design process….
….For assembly testing the test spectra has a peak spectral acceleration of 6g and a ZPA value of 1.2g and this level of shake is achievable on many shaking tables worldwide. However, the component testing spectra is particularly onerous with a peak spectral acceleration of 35g and a ZPA value of 7g, and this level of testing is well beyond that achievable on normal shaking tables that operate at the low frequencies (0-100Hz) needed for seismic testing.
Therefore, in order to meet the very high test levels defined for component testing, Bristol University has worked with Servotest Systems to design and manufacture a very high performance 6 DoF Hexapod shaking table that can deliver the required performance levels.
Here Adam talks about his experience of partnering with Servotest on this critical part of the project.
We had to be confident that the supplier had the expertise to deliver a shaking table with a rather unusual specification and past performance and design of similar tables was key to having that confidence. Other suppliers pushed toward a standard solution. However, Servotest listened and delivered what the University wanted. In the case of the Hexapod, the budget was tight yet we wanted a high specification table – and it was tough to find the right compromise between performance and cost. Even for our large biaxial table, which was a more standard product, Servotest developed customised solutions with the features and performance we needed, which ultimately provided better value for money than other suppliers.
In both cases, we trusted Servotest because the table specifications were high but the budgets were limited. For the high performance table there was, of course, some concern that we might be asking for the impossible, but we believed that if it were possible to build the table within our budget then Servotest would be able to do it.
Our relationship with Servotest goes back 35 years when we built our original shaking table with Glen Wardrop, so we have worked with Servotest for a long time. Since then we have used other suppliers, but we have tended to come back to Servotest. The technical expertise they have within their company shows. They have engineers who have actually used shaking tables as research tools and know how tables need to perform. Having this experience is very valuable – especially relating to the design of the table operating software – their software does what the operator wants – rather than what a programmer thinks is a good idea. The flexibility in software customisation was also important to us and some competitors were not such good value in this regard.
The project was delivered on time and on budget and we were kept in the loop throughout the design phase. For the factory & onsite acceptance - if Servotest, especially Glen Wardrop, was not satisfied with the details of the table performance – Servotest would make time & put in the effort to optimise the system to improve the performance. These are complex customised systems so you cannot expect everything to run perfectly first time – but Servotest were able to tune the system to get the best possible performance.
Changes and modifications to the design were done in a sensible way and only if there were good reasons for changes. For example Servotest highlighted limitations with the hydraulics in laboratory the table would initially be located in. So good, constructive discussions were had to reach the right performance compromises in the short term.
Flexibility was a key requirement as changes were made to the specification while the project was live. If changes are needed it is essential to have this flexibility and to agree to scope changes via a reasonable process – rather than having to renegotiate contracts.
We trusted Servotest as they offered several alternative solutions to make sure we were getting the one that best suited our needs. For the high performance table there were several options – e.g. hexapod or orthogonal tables – but we preferred a self-reacting, small footprint system. It was very useful to see all the options and talk through pros and cons, before choosing, so we got something that suited us best.
Servotest have always been very responsive and seem willing to go above and beyond what I would expect from most suppliers. We have subsequently ordered additional equipment from Servotest based on our positive experiences to date.
Servotest exceeded our expectations, and I would be happy to recommend them to other people interested in ordering shaking tables. There are currently challenges related to our latest system upgrade which Servotest are doing for us, due to factors not connected to Servotest, but this is another example where we are working together as efficiently and quickly as possible to get the best possible outcome.
