PSEUDO-DYNAMIC SEISMIC TESTING OF STRUCTURAL TIMBER ELEMENTS

The best method of determining the seismic capacity of a bracing element is to test it by racking it with cycles of increasing displacement. The maximum mass it can restrain is then assessed analytically but this requires verification with a dynamic test. The pseudo-dynamic test method is now well established as an alternative to shake table testing. It provides increased accuracy and enables much larger specimens to be tested. Currently, the most common method of conducting the dynamic simulation is by applying an incremental displacement to the specimen, pausing while measuring its response and calculating the subsequent displacement increment. Two significant modelling errors are introduced because relaxation reduces the load after the displacement increment is applied and the specimen is subjected to high acceleration pulses at the beginning and end of the displacement increment. A continuous test system, which keeps the specimen moving while the computation for the subsequent increment takes place, has been developed at BRANZ to overcome these errors. The BRANZ test facility is described and a proposed research programme is briefly outlined. The effect of time scale (or loading rate) on the measured loads is also discussed.