Integrated implementation system for pseudodynamic testing
The pseudodynamic test method is a tool for obtaining the non-linear response of structures to transient ground acceleration. The modelling technique relies on representing the inertial and viscous damping components of the equation of motion computationally, while obtaining a measure of the non-linear elastic restoring forces experimentally. A pseudodynamic implementation system is presented, displaying innovations within both the computational and experimental domains. A SDOF pseudodynamic test facility has been designed and manufactured employing a computer controlled servo-hydraulic actuator system. The experimental facility enables displacements of up to 50mm under forces of up to 50kN with all required instrumentation. The experimental apparatus is controlled by algorithms running in the LabView environment, fully integrated within the execution system, rendering the requirement for a hardware controller obsolete. The execution system allows interactive control of the experiments, and offers a large range options with respect to both control and time integration. The execution routine incorporates both the time integration and control algorithms, and combines these such that they effectively execute as an integrated system. This enables semi-continuous implementation of the pseudodynamic tests with very limited resources. A novel, integral form time stepping scheme is proposed, based on an explicit integral form algorithm (Chang et al. 1998) and the Newmark Implicit scheme. The proposed formulation offers an implicit, and thus unconditionally stable alternative to Chang's algorithm without introducing further approximations. This yields improved dissipation and accuracy properties in addition to enabling combination of the integral form schemes' advantages of representing non-linear force variations during a time step with an unlimited time step size. The improvements have been shown both through analytical analyses and numerical examples in linear and non-linear systems. Implementation of the implicit integral form algorithm has been enabled by coding parts of the algorithm directly into the digital controller.