Bearing capacity of reinforced foundation subjected to pull-out loading in 2D and 3D conditions

Steel-framed structures like electricity transmission towers are subjected to great pull-out forces under strong wind conditions. This paper analyses how caisson foundations with reinforcement bars can increase the uplift bearing capacity of those structures. Model tests and numerical analyses in 2D and 3D are used to investigate how the bars' position and direction affect the behavior of the foundation under different load conditions. The test results show that reinforcements stemming diagonally downward from the bottom of the foundation are the most effective against uplift loading because they increase the structure's bearing capacity. However, this gain is less significant when inclined uplift forces are applied to the foundation. The higher the force inclination angle, the less efficient the design becomes. In that case, reinforcements that stem from the foundation's bottom are more effective than those stemming from the foundation's side. The numerical results accurately describe the experimental findings, since the simulations accounted appropriately for both the mechanical behaviors of the soil and the reinforcement as well as the frictional behavior between them. Furthermore, the results from the model tests and analyses carried out in 3D and 2D conditions are compatible. (C) 2009 Elsevier Ltd. All rights reserved.