- 311 - Reliability Analysis of Static Pile Capacity for Concrete and Steel in Cohesionless Soils J.O. Afolayan Department of Civil Engineering, Federal University of Technology, PMB 704, Akure, Nigeria. e-mail: joafol@yahoo.com D. A. Opeyemi Department of Civil Engineering Technology, Rufus Giwa Polytechnic, PMB 1019, Owo, Ondo State, Nigeria e- mail: da_opeyemi@yahoo.com ABSTRACT The reliability assessment of the carrying capacities of piles based on static approach with special consideration to pre-cast concrete and steel as pile types in cohesionless soils is reported in this paper. The static carrying capacity is often made up of the ultimate point capacity and the skin resistance of the pile. In this report, the skin resistance is based on β- method. Uncertainties are common phenomena in engineering, therefore all the interrelated variables in the carrying capacities are treated as random variables with assumed practical probability density functions. The concept of the First-Order Reliability Method (FORM) is a powerful tool for estimating nominal probability level of failure associated with uncertainties and it is the method invoked for the reliability estimations. Generally, piling reliability decreases as pile length increases but the rate of decrease is more rapid for concrete than steel. For concrete piling, pile length greater than 30 m will result in catastrophe while much longer steel piles that economy will permit are admissible. Hence, steel piles are recommended as alternate materials in cohesionless soils. KEYWORDS: Reliability analysis, static pile capacity, concrete piles, steel piles, cohesionless soils. INTRODUCTION Pile capacity determination is very difficult. A large number of different equations are used, and seldom will any two give the same computed capacity. Organizations which have been using a particular equation tend to stick to it especially when successful data base has been established. It is for this reason that a number of what are believed to be the most widely used (or currently accepted) equations are included in most literature. Also, the technical literature provides very little information on the structural aspects of pile foundation design, which is a sharp contrast to the mountains of information on the geotechnical aspects. Building codes present design criteria, but they often are inconsistent with criteria for the super structure, and sometimes are incomplete or ambiguous. In many ways this is an orphan topic that neither structural engineers nor geotechnical engineers have claimed as their own (Coduto, 2001).