Thesis: Ojaghi, M. (Makhzan Ojaghi, S. M.)

Doctor of Philosophy, New College, University of Oxford, Michaelmas Term 2010

The Development of Real-Time Distributed Hybrid Testing for Earthquake Engineering

Real-time distributed hybrid testing is a new testing technique which applies the latest advances in Internet technologies to share the resources of geographically distributed laboratories. The technique combines distributed components of a structural system both physical and numerical, via a common numerical part. By doing so, it enables realistic large scale seismic simulations beyond the capabilities of any one lab. Therefore, it promises to be one answer to the call to extend current capabilities for realistic large scale seismic simulation, particularly in cases where rate effects are important and time-scaling must be avoided.

In this thesis the architecture of the UK-NEES (UK Network for Earthquake Engineering Simulation) distributed hybrid testing (DHT) system is presented. It is applied to combine the individual components of a testing system developed to conduct what are believed to be the world’s first robust (stable and accurate), repeatable and continuous real-time geographically distributed hybrid tests. New control strategies, algorithms, systems and software are presented and have been developed to form the testing system. While the architecture is scalable, it has been developed with the pre-existing hardware environments between the three UK-NEES sites at Oxford, Bristol and Cambridge universities in mind. However, the primary focus here is to describe real-time DHT with realistic physical substructures between Bristol and Oxford.

Extensive experimental results are shown. First, these are from early development work describing the issues that were overcome in enabling testing in this new environment. This is then extended to include later, local and distributed equivalent, real-time hybrid tests in a variety of challenging test configurations. This includes, demonstrating single axis real-time distributed control of a predominantly linear physical substructure. However, results are also presented of testing with highly nonlinear, stiff, hardening and degrading metallic energy dissipation devices and, with multiple local and distributed physical substructures, including with coupled nonlinear physical components. These tests prove that real-time DHT is possible with existing legacy hardware systems. They also show that these tests can be conducted under realistic, low damping conditions with large scale structural components and, that tests may be conducted independent of network conditions.

The work includes development of a new large time-step, large delay compensation algorithm which can far exceed prediction capabilities of existing algorithms. A novel test rig accommodating height reduction due to shear is also presented together with a new control system for conducting low cycle fatigue testing of a shear type metallic damper manufactured using a variety of materials. The controller is later adapted to enable variable delay, variable amplitude compensation in real-time hybrid testing. Some previously unobserved and interesting features of device dynamic response behaviour are also briefly introduced.