COMPARISON OF DIFFERENT CODES FOR DETERMINATION OF THE AXIAL BEARING CAPACITY OF PILES

Despite recent developments in proposing a scientific method in pile design, determination of the capacity of piles is still complicated due to the importance of soilstructure interaction in piles. Dierent codes have proposed various methods for the axial capacity of piles; however, these methods are based on assumptions that are not applicable in all situations. Traditionally, engineers use safety factors to compensate for the uncertainties and balance between reliability and economy. This traditional method is called deterministic. However, deterministic methods are very subjective and are generally not based on a systematic assessment of reliability. Therefore, these methods may produce structures with some overdesigned components. For elimination of these deficiencies, reliability-based methods have been developed. The load resistance factor design (LRFD) is one of the most applicable reliability-based methods. Its advantage is consideration of the uncertainties in strengths and loads separately. In this article, design philosophies and safety factors in difierent codes are first explained. By comparison of load factors of the LRFD in 8 difierent codes, it can be concluded that o- shore and bridge codes have wider ranges for load factors than building codes. Then, the axial design of piles, in accordance with the API code, Eurocode 7, and Canadian codes, is discussed. API proposes both LRFD and working stress design (WSD) methods for the design of oshore structures. A numerical example for the design of axially loaded pile following API is conducted to compare LRFD (reliability-based) and WSD (deterministic) methods of API. Results show that the required penetration depth computed in the LRFD method is a little higher, however; this conclusion is not generalized to other situations. The Eurocode suggests three approaches for the design of piles. The difierence between these approaches is related to the way they use load and resistance factors. A numerical example for design of axially loaded pile, according to three approaches of the Eurocode, indicates that these three approaches give approximately similar answers; however, the third approach is rather more conservative.