LRFD Resistance Factors Including the Influence of Pile Setup for Design of Steel H-Pile Using WEAP

American Association of State Highway and Transportation Officials (AASHTO) allows individual states to use regionally calibrated resistance factors based on the local soil conditions to improve the cost effectiveness of pile foundations as long as the development of these factors comply with the Load and Resistance Factor Design (LRFD) concept. This paper presents preliminary resistance factors developed for the Wave Equation Analysis Program (WEAP) using the PIle LOad Test database of the Iowa Department of Transportation (PILOT-IA). Using the pile penetration rate (blows/m) at the end of driving as the main variable, the LRFD calibrations for WEAP were conducted using 32 sites comprising the following four soil categories: clay (8 sites), mixed soil (11 sites), sand (13 sites), and all soil types (32 sites). Three different procedures, namely the Iowa DOT steel pile design chart, the DRIVEN program, and the GRLWEAP^TM SPT N-value based method (SA), were used to estimate the soil driving resistance. When compared to the AASHTO (2007) recommended LRFD resistance factors, the developed resistance factors for clay increased by 125%, while the resistance factors for the mixed, sand and all soil types improved by 50%. Among the procedures used for estimating the soil driving resistance, the resistance factor based on the SA method yielded the highest efficiency factor for mixed, sand and all soil types, while the Iowa DOT design chart led to the best efficiency factors for clay soil. In addition to using 32 data sets from PILOT-IA, data from three recently completed load tests were used to examine the effect of the pile setup on the resistance factors. Pile driving records and restrike data were used to predict the pile capacity as a function of time and establish a modified empirical pile setup equation incorporating a soil property using the Standard Penetration Test (SPT) N-value. In addition to incorporating this information, the paper demonstrates the benefits of incorporating the soil setup in resistance factor calculations.