Reliability Analysis Of Bearing Capacity And Reliability-Design Optimaization Of Piles

Pile foundation is one of important structural style in civil engineering. Consideringthe influences of uncertainties is an important topic when studying reliability of bearingcapacity and reliability-design optimaization of piles. Though a large number of researcheshave been conducted to investigate the reiliability of bearing capacity and settlement forpiles, the influences of uncertainties on reliability analysis need to be further studied.Additionally, reliability-based optimization design and reliability analysis of pile grouphave rarely been reported till now. In order to overcome these deficiencies, systemicresearches are carried out in this dissertation to analyze reliability-based optimizationdesign and reliability of bearing capacity of piles.A modified method for calculating reliability index was put forward based onmaximum entropy principle. To achieve this goal, the maximum entropy principle was usedto transform iterative calculation of reliability index into a maximum entropy densityfunction calculation. Newton iteration method was utilized to calculate entropy densityfunction and its local convergence was proved. The convergence of iteration was ensuredwhen calculating reliability index. To promote calculation efficiency, Newton down-hillalgorithm was incorporated into calculating entropy density function and Monte Carlosimulations were performed to assess the efficiency of the presented method. Finally, twonumerical examples had been presented to verify the validation of the presented methodAccording to the mathematical statistics theory and Bayesian technique, a method fordata processing and optimization in pile foundation engineering was put forward to solvethe problem caused by model uncertainty due to lack of enough accurate field data. Thepresented method was employed to classify and optimize the field data of the driven pilesand the bored piles. The first order second moment method, the advanced first order secondmoment method and the Monte Carlo simulation were employed to calculate the reliabilityof the bearing capacity, the recommended values of resistance factors were suggestedaccording to the calculated results and American specifications for load and resistancefactor design. Meanwhile, the effects of parameter uncertainties and model uncertainties on bearing capacity of piles were studied, a modification factor was introduced to calibrate thebias factors and coefficients of variance for bearing capacity, and the modified calculationformula of reliability was presented.Based on probability theory, a systematic method was proposed to estimate theoccurrence probability of defective piles from a site according to non-destructive integrityinspection. The factors influencing on sampling inspection were analyzed based onprobability theory and engineers’ experiences, and the occurrence probability of defectivepiles from a site was suggested to be as the criterion to evaluate the performance of a pilefoundation. To estimate occurrence probability of defective piles, its prior distribution andupdating distribution were deduced to follow Beta distributions, and a dynamic estimationmodel was established based on the relationship between prior mean and variance andupdating mean and variance to calibrate the occurrence probability of defective piles. Thereliability-control method dealing with uncertainties arising from quality assurance ininspection was formalized to judge whether all the bored piles from a site can be accepted,and uniform quality criterion for construction and design in pile foundation engineeringwas established.A method was presented to evaluate the reliability of pile group considering theintegrity of pile. Based on the Bayesian Statistical Theory, the probability distribution ofdefected piles was deduced. Meanwhile, the calculation formulas of reliability for defectedpile group(DPG) and intact pile group(IPG) were obtained according to the reduction factorand the pile group effect. Finally, the failure probability of the pile group containingdefected piles was formulated using the total probability theory. Additionally, the differentfailure criteria from various countries were examined, and a bias factor defined with respectto s-lgt criterion widely used in China was introduced. Meanwhile, the calculation methodof reliability of pile group considering different criteria was presented using the bias factorsand pile group effect, which provided a theoretical basis to calibrate the reliability levels ofpile foundation associated with various failure criteria. The calculation formula of targetreliability index of bearing capacity of single piles and factor of safety was presented using bias factor.Currently, deterministic optimization design recommended in prevailing codes for pilefoundations cannot take the uncertainties of design parameters into account. To overcomethis deficiency, based on reliability theory and the existing research achievements ofoptimization design, the reliability-based optimization design of piles was presented, andthe detailed optimization procedures of pile under axial load were established. A modifiedreliability optimization method was put forward to improve the design of piles under axialload, which greatly enhanced the computational efficiency. Finally, the adopted method wasvalidated by a case study.