Analysis and Behavior of Composite Transmission Towers

Abstract

A study on the behavior and design of composite transmission towers was carried out using the finite element software ABAQUS. The finite element models were validated against experimental results done by other researchers for various configurations of composite columns and tapered transmission poles. The specimens considered for verification purposes include simple composite columns consisting of steel case and core concrete, composite columns with embedded shear studs, composite columns with embedded steel section and shear studs, double skin filled steel columns and twelve-sided tapered transmission poles. The validation was achieved by comparing the axial load vs. axial strain, axial load vs. mid-span deflection, bond stresses vs. slip for composite columns and applied force vs. tip displacement curves for tapered transmission poles. An investigation and calibration of the Concrete Damage Plasticity (CDP) material model’s parameters was performed to achieve the most accurate results using such model for this application. An analysis was performed on twelve-sided composite columns (dodecagonal) under four- point bending test based on ASTM standards in order to investigate their behavior. The parameters considered for this stage were: number of studs (2, four, six, and twelve) and interaction type (fully restrained, and composite). The effect of these parameters was studied in terms of: load vs. deflection, moment vs. curvature, moment vs. slip, shear stresses in studs, and bond stresses vs. slip curves. Furthermore, a parametric study was performed on the behavior of tapered composite transmission towers in a bending test. The variables considered for this study were: cross-section shapes, composition percentages, number of studs in cross-section, arrangement of studs in cross-section, and studs dimensions. The effect of these parameters was studied in terms of: load vs. deflection, moment vs. curvature, moment vs. slip, shear stresses in studs, and bond stresses vs. slip curves. P-M interaction diagrams were developed for composite columns with various polygonal shapes and different diameter to steel thickness (D/t) ratios which intends to highlight and extend beyond the limitations of AISC code provisions (higher than 120 which is the AISC code limit). To achieve this, the concrete reduction factor for the studied geometrical shapes was investigated using multiple methods to confirm the resulted factor values. Non-dimensional version of the P-M interaction diagram was developed, and the studs’ effect on these equations was studied to provide a better understanding and prediction of these structures’ behavior. Finally, a design procedure was developed for composite transmission towers exposed to real case loading including wind load based on AISC code, Finite Element Analysis (FEA) and previously constructed P-M diagrams and load-deflection curves. A comparison was carried out between the proposed composite and steel truss transmission towers in order to emphasize the economic benefits of the proposed structures.