Proof Testing of a Shear Deficient Bent Cap

Abstract

An existing 58-year-old viaduct was removed and replaced between 2020 and 2021. Many of the bent caps supporting this viaduct exhibited wide shear cracking. Although the viaduct’s performance had been satisfactory throughout its lifetime, concerns were raised that construction disturbances required for the staged construction of the new roadway might compromise its safety. Given that this highway carries approximately 145,000 vehicles per day, closing it completely to effect these changes was an extremely undesirable solution. In response, the design-builder decided to proof test the bent cap that caused the greatest concern and use these results to improve the certainty of the calculated capacity of all the bent caps. This paper presents the results of the proof test, how those results compared with current shear models, and how they were used to assess the capacity of the other bent caps supporting the viaduct. The structure was loaded by placing ballasted trucks over the bent cap in question. The change in width of the widest shear crack, deflection, and strain at the bottom of the cap were monitored during testing. On conclusion of the test, the capacity of the bent cap was determined to be greater than the required demand. The results were used to show that most bents supporting the viaduct had adequate strength. For the small number needing strengthening, the results were used to develop a simpler and more straightforward repair procedure than would have been required without the findings of the proof test.