| Due to the need for maintenance and corrosion protection, the use of galvanized steel in the fabrication of latticed structures has become an expensive process. To avoid these problems Advanced Composite Materials (ACM), such as Fibre-Reinforced Polymers (FRP) have been introduced. A new technology developed by Cormorant Composites and University of Manitoba was used to fabricate tower segments using a specially constructed collapsible mandrel and a continuous multiple roving filament winding process. The ANSYS Finite Element Analysis Program was used to design the optimal cross sectional properties. A non-linear finite element analysis of a full scale guyed tower prototype was performed using wind loads outlined in CSA-S37-01. The dynamic response of the wind was included by using a gust factor method in which a gust factor was applied to the wind pressure of a static loading. The finite element results were validated through laboratory testing of an 8.53 m (28 ft) long tower segment. The test conditions were created to resemble actual restraints and loading conditions acting on the tower. In Phase-1, static testing of the 8.53 m (28 ft) tower segment was conducted, using a "Whiffle Tree" arrangement, to simulate a uniformly distributed wind loading. Static testing in Phase-1 provided insight into the FRP connection performance, which was significantly improved for the dynamic testing. In Phase-2, dynamic testing of 8.53 m (28 ft) tower segment in an upright position was conducted to obtain natural frequencies of vibrations, which were confirmed through a mathematical model and through ANSYS Modal and Harmonic analyses. The dynamic test results showed that the undamped natural frequency of the vibrating tower segment was 4.31 Hz. Also, the modal analysis of a full scale model was carried out in order to compare its dynamic findings with the results obtained through testing of the 8.53 m (28 ft) tower segment. The first natural frequency of vibration of full scale tower was 0.219 Hz which was lower than the natural frequency of the tested FRP tower segment by the factor of 20. A full dynamic analysis of the FRP tower was also conducted using the patch load method, recommended by CSA-S37-01 (CSA, 2001). Twelve different patch load cases were used in the FEM ANSYS 8.1 (ANSYS, 2004) program. After the dynamic analysis using the patch load method it was concluded that the gust factor method and the patch load method with the detailed scaling predict the peak response of the FRP tower well. Finally, design considerations for FRP towers were developed. The effect of fibre volume fraction on the mechanical properties of the FRP tower was illustrated through an example. It was found that by increasing the fibre volume fraction of lamina by 28.2% resulted in a reduction in the tip deflection of the FRP tower by 7.5%. The strength performance of the FRP tower was also evaluated using the Maximum Stress non interactive criterion and the Tsai-Wu interactive criterion. The maximum combined stress from static analysis was -68.22 MPa (-9.89 ksi) which was well below the compressive strength of FRP material. An estimation of the compressive buckling strength of the chord members, based on the model developed by Rosen (1964) for unidirectional composites, was obtained. The result showed that local buckling of chord members was not the critical mode of failure. |
