Abstract of Dissertation Presented to the Graduate School
 of the University of Florida in Partial Fulfillment of the
 Requirements for the Degree of Doctor of Philosophy

 RELIABILITY-BASED STRUCTURAL OPTIMIZATION USINTG RESPONSE
 SURFACE APPROXIMATIONS AND PROBABLISTIC SUFFICIENCY FACTOR

 By

 Xueyong Qu

 August 2004

Chair: Raphael T. Haftka
Major Department: Mechanical and Aerospace Engineering

 Uncertainties exist practically everywhere from structural design to manufacturing,

product life-time service, and maintenance. Uncertainties can be introduced by errors in

modeling and simulation; by manufacturing imperfections (such as variability in material

properties and structural geometric dimensions); and by variability in loading. Structural

design by safety factors using nominal values without considering uncertainties may lead

to designs that are either unsafe, or too conservative and thus not efficient.

 The focus of this dissertation is reliability-based design optimization (RBDO) of

composite structures. Uncertainties are modeled by the probabilistic distributions of

random variables. Structural reliability is evaluated in term of the probability of failure.

RBDO minimizes cost such as structural weight subj ect to reliability constraints.

 Since engineering structures usually have multiple failure modes, Monte Carlo

simulation (MCS) was used to calculate the system probability of failure. Response

surface (RS) approximation techniques were used to solve the difficulties associated with