Development and control of a novel test rig for performing multiple support testing of structures

Multiple support excitation is caused when different ground inputs occur along the length of a bridge. Much research has been carried out on modelling long span bridges with multiple support excitation both numerically and analytically, however there have been few successful experimental models investigating the effect of this type of input motion on large scale bridges. This paper outlines the design and construction of a unique multiple support excitation experimental test bed. The bed comprises 5 single axis shaking tables which are independently controlled by 5 actuators. The shaking tables are steel boxes each mounted on a single 50mm diameter rod. A pair of bearings prevents each table rotating around the horizontal axis, perpendicular to the rail. To prevent rotation of the tables around the rails the actuators are hung below the tables and this keeps the tables stable and upright. To date no significant spurious motions of the tables have been observed. This paper discusses the design of the test rig in detail and also addresses the control issues associated with operating this type of experimental rig where the interaction between the test specimen and the test rig itself can have a detrimental effect on the results of the tests. The results of the testing of MSE on bridges have revealed that multiple support excitation can be a significant factor in the behaviour of bridges with moderate spans of 200m.