Effect of Splice Length and Creep on the Structural Response of Reinforced Concrete Columns Subjected to Pure Compressive Loading

Abstract

On June 24, 2021, the Champlain Towers South (CTS) condominiums in Surfside, Florida partially collapsed. A forensic investigation was launched by the National Institute of Standards and Technology (NIST) to determine the technical cause of the collapse and to use this understanding to recommend changes to building codes, standards, and practices. NIST contracted a structural engineering team at the University of Washington (UW) to perform multiple components of an experimental research program. This thesis focuses on the portion of the testing program aimed at determining the effect that lap splices and long-term loading have on the axial compressive response of reinforced concrete columns.Three full-scale column specimens were designed to simulate the structural elements from the CTS building. The column specimens were constructed, instrumented, and tested in axial compression at the UW Structural Engineering Testing Laboratory. One of the column specimens was loaded for 120 days prior to destructive testing to simulate the load that the building underwent for 40 years before the collapse occurred. The research program was especially important due to the limited amount of research previously conducted on concentrically loaded reinforced concrete columns with compression lap splices. None of the previous research programs included column specimens with geometry similar to what was seen in the CTS building. 6x12 in. (152x305 mm) companion cylinders were also cast and tested under sustained loading to learn more about the performance of the concrete in the column specimens. The results from the experimental tests were shared with NIST to aid in their forensic investigation. Some additional observations were made: (1) introducing a compression lap splice decreased the axial compressive strength of the reinforced concrete columns tested and (2) long-term loading did not decrease the axial compressive strength of the reinforced concrete columns tested. When comparing the experimental creep and shrinkage of the companion cylinders to the ACI 209.2R-08 creep and shrinkage prediction models, it was found that the prediction models generally underestimated the creep and shrinkage of unsealed companion cylinders. While this research program unveiled some information about the axial compressive performance of reinforced concrete columns with lap splices and long-term loading, further research is required to improve the design of compression lap splices in reinforced concrete columns.