Eccentric punching tests on column bases – New insights into the inner concrete strain development

Abstract

In the past, the punching shear behavior of centrically loaded column bases has been predominantly investigated even though eccentric loads frequently occur in engineering practice. To consider this corresponding uneven shear stress distributions around the column, many design approaches define coefficients to increase the acting load. Due to the limited test data for eccentric punching tests, an assessment of the design approaches is not reliably possible. To fill this gap of experimental test results, four centrically loaded and fourteen eccentrically loaded punching tests were conducted to analyze the effects of systematically graded load eccentricities.The tests reveal a significant influence of load eccentricity on the punching shear capacity and the load-bearing behavior. With increasing eccentricity, the crack formation shifts to the higher loaded side going along with an incompletely developed punching cone. Innovative measurements of the strains in the slab allow to analyze the circumferential multi-axial stress state inside the concrete. In contrast to centrically loaded column bases, this compression ring does not fully develop under eccentric loads. Based on these measured tangential strains, an experimental approach for describing the influence of the load eccentricity on the punching shear strength is derived and compared with the design approaches of Eurocode 2, Model Code 2010 and the stable version of the next generation of Eurocode 2. Overall, the results indicate optimization potential for more advanced design provisions of column bases with eccentric loads.