Design Guidelines for Steel Pole Drilled Pier Foundations

Abstract

Steel Poles are common type of structures erected to support power overhead lines of most voltage rating in the United States. Typically these poles are founded on single reinforced concrete drilled circular piers designed to resist the high bending moments of the supported poles. The principle of designing these drilled piers relies on the theory of soil resistance to the central point rotation of the pier. Soil structure interaction is simulated through a complicated system of springs acting on the circumference and base of the piers inducing a set of internal pier forces which control sizing and reinforcing these piers. Soil structure interaction is governed by several parameters, the most important of which are the soil mechanical parameters and the depth and diameter of the pier. However the design problem is further complicated by set limits on horizontal deflection and pier rotation in addition to the strength requirements. In several cases these constraints control the design of the pier rather than the loading applied. Assuming a fixed set of soil parameters the question can be narrowed down to deciding upon the best depth/diameter combination. However, currently there is no guidance on the optimum combination of depth/diameter for a particular loading and deflection constraints. This paper attempts to establish guidelines to help deciding on the optimal depth/diameter combination. The methodology adopted to define these guidelines is through parametric studies which examine the effect of varying depth and diameter on the ultimate capacity of the drilled piers and at the same time satisfy the deflection constraints under service loads. Foundation Analysis and Design (FAD) software, developed by Electric Power Research Institute (EPRI), is used in this study.