This dataset contains the experimental data for two large-scale reinforced concrete U-shaped wall specimens tested at the Earthquake Engineering and Structural Dynamics Laboratory (EESD Lab), École Polytechnique Féderale de Lausanne (EPFL) in Switzerland. This dataset contains supplementary material for the journal paper titled, "Seismic Performance of Slender RC U-shaped Walls with a Single-Layer of Reinforcement", which contains some of the experimental observations and results. Thus, this dataset also contains MATLAB files associated with calculating the results presented in the journal paper and the corresponding figures and plots. The abstract for the journal paper is below: Reinforced concrete walls are typically used to resist the lateral loading induced by wind and earthquake actions. While most walls feature two vertical reinforcement layers, in some regions the use of slender reinforced concrete walls with a single vertical layer of reinforcement is current construction practice or has been in the past. The seismic performance of such elements is largely unknown given the paucity of experimental research that has been conducted on walls with a single layer of reinforcement, particularly for non-rectangular walls, such as the popular U-shaped wall. This paper presents the results of two slender reinforced concrete U-shaped walls tested at the Earthquake Engineering and Structural Dynamics Laboratory (EESD Lab), École Polytechnique Féderale de Lausanne (EPFL) in Switzerland. Both wall specimens were unconfined and detailed with a single-layer of vertical reinforcement to replicate some of the current construction practices being conducted in Colombia. Both walls reached ultimate drifts larger than 2.5-3.0% and initially failed due to buckling of the longitudinal reinforcement at the flange ends. The buckling length was 700-800 mm, which corresponded to 44-50 bar diameters.