Target reliability index for serviceability limit state of single piles

BIAN Xiao-ya(边晓亚)¹, ZHENG Jun-jie(郑俊杰)¹, XU Zhi-jun(徐志军)², ZHANG Rong-jun(章荣军)¹

(1. School of Civil Engineering & Mechanics, Huazhong University of Science and Technology, Wuhan 430074, China;
2. School of Civil Engineering and Architecture, Henan University of Technology, Zhengzhou 450052, China)

Abstract:The objective is to develop an approach for the determination of the target reliability index for serviceability limit state (SLS) of single piles. This contributes to conducting the SLS reliability-based design (RBD) of piles. Based on a two-parameter, hyperbolic curve-fitting equation describing the load-settlement relation of piles, the SLS model factor is defined. Then, taking into account the uncertainties of load-settlement model, load and bearing capacity of piles, the formula for computing the SLS reliability index (β_sls) is obtained using the mean value first order second moment (MVFOSM) method. Meanwhile, the limit state function for conducting the SLS reliability analysis by the Monte Carlo simulation (MCS) method is established. These two methods are finally applied to determine the SLS target reliability index. Herein, the limiting tolerable settlement (s_lt) is treated as a random variable. For illustration, four load test databases from South Africa are compiled again to conduct reliability analysis and present the recommended target reliability indices. The results indicate that the MVFOSM method overestimates β_sls compared to that computed by the MCS method. Besides, both factor of safety (FS) and s_lt are key factors influencing β_sls, so the combination of FS and β_sls is welcome to be used for the SLS reliability analysis of piles when s_lt is determined. For smaller s_lt, pile types and soils conditions have significant influence on the SLS target reliability indices; for larger s_lt, s_lt is the major factor having influence on the SLS target reliability indices. This proves that s_lt is the most key parameter for the determination of the SLS target reliability index.

Key words:single pile; serviceability limit state; target reliability index; mean value first order second moment method; Monte Carlo simulation