Pizhong Qiao

Date of Graduation


Document Type



Considering current and future applications of composite materials in civil engineering structures, a need exists for developing a design analysis and optimization approach for FRP shapes to improve their performance efficiency and competitiveness in relation to conventional materials. An analytical approach for design of pultruded FRP shapes under bending is proposed, and based on this approach, a computer program is developed to carry out the analysis of FRP sections. This analytical approach combines micro/macromechanics analyses with the Mechanics of thin-walled Laminated composite Beam model (MLB) to evaluate the response of existing pultruded FRP beams. Based on buckling analyses of individual composite plates under axial and shear loading, the critical local buckling strength of FRP sections is predicted and appropriate design equations are proposed; the effect of the stiffness of the flange-web connection on the buckling response of component plates is considered, and an approximate coefficient of restraint for the plate analysis is proposed for use in design. An energy method combined with nonlinear elastic theory is developed for analyzing the flexural-torsional buckling behavior of FRP I-beams. Allowing for distortion of the web and using a 5th order polynomial shape function for the buckled web shape, an analysis approach for lateral-distortional buckling of I-beams is also proposed. The proposed analytical models correlate closely with experimental data and ANSYS finite element results. A global approximation method to optimize material architecture and structural shape of FRP beams is developed. For existing FRP shapes, a multiobjective design optimization formulation is proposed to optimize fiber architecture, which can greatly enhance the load carrying capacity of a section. The global approximation method is extended to concurrently optimize material architecture and cross-sectional area for new FRP beams. The proposed method can concurrently optimize the dimensions and material architecture of a given shape, and as an illustration, a new winged-box (WB) shape is optimized. It is significant that through this study, new optimal material architecture and structural shapes for FRP beams are obtained for structural applications, and the proposed method can be used to develop various innovative shapes for specific applications.