The NSEL Reaction Wall consists of a 1.5 m (5 ft) thick and 8.7 m (28.5 ft) high L-shaped structure that is post-tensioned to a 0.6 m (2 ft) thick Testing Floor. The wall was built in 2004 as a part of the Network Engineering for Earthquake Simulation (NEES). This experimental research program was sponsored by the National Science Foundation.