9.3.2 Biaxial testing
For each series of tests, the two time-histories are applied simultaneously along two of the preferred testing axes of the specimen. If the time-histories are not independent, each test is repeated with a relative phase angle of 0° first and then 180°.
NOTE When biaxial testing is specified, testing may be carried out in a single inclined axis installation but the movements along the two axes will always be dependent. The test response spectrum for each axis should be adjusted to envelop the required response spectrum in that axis.