Evaluation of the environmental effects on the behaviour of GFRP composite tubes for new sustainable building and urban infrastructure applications
SubjectArmé en PRF
The advantages of fiber-reinforced polymer (FRP) composite material have attracted structural and architectural engineers as alternative construction materials of the traditional wood, steel and concrete. Concrete-filled FRP tubes (CFFTs) system is one of the most promising applications of the FRP composit material. This innovative integrated system can protect RC structures from aggressive environmental conditions; sequentially expand the service life of structures. Nevertheless, limited knowledge is available on the CFFT system at extreme service environments. Data related to durability of the CFFT as integrated system comparing with conventional ones is one of the major challenges that need to be addressed. These data are moer required prior to the widespread acceptance and implementation of FRP materials in civil infrastructure. Farther, comprehensive databases in this specific are critical to provide designers and practicing engineers with the knowledge to select the best solution toward achieving a sustainable built environment. This thesis focuses on evaluating the short and long term effect of freze-thaw cycles on the mechanical behavior of the filament wound glass-FRP (GFRP) tubes. In addition, the thesis evaluating the axial performances of reinforced and unreinforced CFFT columns through experimental and theoretical study. To fulfill the objectives of this research, an experimental program has been designed to examine three main parts. (I) Mechanical properties of the GFRP tubes; (II) The axial behavior of CFFT cylinders; (III) The axial behavior of CFFT reinforced and unreinforced columns. The effect of five parameters and their interactions were investigated; namely, the effect of different freze-thaw cycles (in dry air, frsh and/or salt water), number of cycles (100 and/or 300 cycles), two different thicknesses (2.65 mm and 6.4 mm) of the GFRP tube. The influence of using different types of internal longitudinal reinforcement (steel, GFRP, and carbon FRP bars) and the type of transverse reinforcements (spiral steel or FRP tubes) are included in the test variables. Based on the finding of experimental investigation regarding mechanical properties of the GFRP tubes (part I), neither the type nor the number of freze--thaw cycles affect the strength of GFRP tube used in this study. However, increasing in the stiffness, reductions in the strains and transition in failure mechanisms are identified after 300 freze-thaw cycles. The experimental results of axial compression tests on CFFT cylinders (part II) indicated low influence of the freze-thaw cycles on the average ultimate strength of CFFT tube with the large thickness. While, significant and sever degradation was reflected on the behavior of CFFT cylinders with the small thickness after 300 freze-thaw cycles. Based on the experimental test results of (part II) environmental reduction factors were proposed to consider the effect freze/thaw cycles on the strength capacity of CFFT cylinders. Also, the regression analysis was used to predict the service life environmental reduction Factors to design CFFT member for up to 75 years. In addition, an assessment of selected FRP-confined models has been presented to predict the ultimate strength of CFFT cylinders based on the test results of (part I). Finally, comparisons between the experimental results and those predicted by the selected models were presented. The experimental investigation on the performance of reinforced CFFT columns (part III) indicated that the freze-thaw exposure brings about individual degradation, in different levels, in the component of the CFFT (GFRP tube, concrete and reinforcement) as integrated systems. This degradation resulted in reduction in the axial carrying capacities of the conditioned columns. Nevertheless, an increase in compressive strength of the CFFT columns was evident over the RC conventional columns. Based on the test results of this (part III), environmental reduction factors were proposed to account for the effect of freze/thaw cycles on the axial load capacity of reinforced and unreinforced CFFT columns. The data obtained from the test results of (part I), predicted confined compressive strength optained from (part II) and the proposed environmental reduction factors from (part III) were used in the ACI440-2R-08 and CAN/CSA S806-08 design equations to predict the nominal capacity of CFFT columns in sever environmental condition.
- Génie – Thèses