Here are some clips from a stress report I collaborated on. The hardware was designed specifically for the ET-137 Intertank that flew with STS-133. The fixture was used during the effort to repair and qualify the tank for flight, after a fracture was found in the stringer at the rivet line.
This test fixture is designed to test a one-stringer section of STS External Tank panel under loading conditions similar to those experienced during tanking. The simulated loads are experienced when the bottom of the tank contracts under the cryogenic thermal load, but the top of the tank is at ambient temperature. This fixture uses mechanical means to deliver the simulated load without applying any actual thermal load to the test panel. The loading is intended to cause cracking in the stringers similar to that of the flight article.