NONLINEAR FE MODELING AND CHARACTERIZATION OF GUYED TOWERS UNDER SEVERE LOADING
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Author: yanburak
Last Post: gulilero
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NONLINEAR FE MODELING AND CHARACTERIZATION OF GUYED TOWERS UNDER SEVERE LOADING
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NONLINEAR FINITE ELEMENT MODELING AND CHARACTERIZATION OF GUYED TOWERS UNDER SEVERE LOADING

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Guyed towers have been widely employed in the telecommunication industry. However, in current building codes, there is still no comprehensive specification for their nonlinear response under severe loads, which includes large static loads, seismic loads and impulsive loads. This study thus intends to improve the understanding and analysis of guyed towers that undergo not only large deformation, but also large strain. Impulsive loads are potential threat to the safety of guyed towers besides wind load, earthquake, and ice storm. No methodology or related research has been conducted in this area so far. This research explores the area using an already developed P-I diagram method and nonlinear finite element modeling to provide an efficient and effective way for structural integrity evaluation for guyed towers.
The mechanical characteristics of basic components of guyed towers are investigated first. Geometric nonlinearity is of the main concern for the impact of large deflection. The modified Riks scheme has been applied in nonlinear static analysis and the Newmark beta method for dynamic analysis. To investigate the efficiency and effectiveness of linear analysis methods, several corresponding examples are studied. It is found that linear static analysis works only when the deformation is small. The equivalent inertia force method and the large additional stiffness method for guyed towers under seismic loads are compared and validated. Their results are very similar.
Because guyed towers with large defection also have large strain in some parts, material nonlinearity is introduced by improving the existing FEM codes for trusses and cables. Isotropic hardening is employed in nonlinear static analysis. Dynamic hardening is used in dynamic analysis. Some specific examples have been conducted to verify the improvements. It is found that the improved methodology can well predict the performance of structures and tremendous difference exists between elastic analysis and inelastic analysis. Under seismic loading condition, inelasticity in material can help dissipate the inputted seismic energy and reduce the intensity of structural response.
The combined application of nonlinear finite elements and algorithm enables the nonlinear analysis for guyed towers. A 50 ft guyed tower with taut cables and a 100 m guyed tower with sagged cables were studied for their response under large static loads and seismic loads. The nonlinear static and dynamic response was accurately traced. It is found that equivalent static analysis works well when deflection is small. In sagged guyed tower, the structure is relatively soft at the beginning of static loading. With the increase of deflection, the structure is gradually stiffened. The consideration of inelasticity greatly improves the accuracy of analysis.
To evaluate the guyed tower’s safety under impulsive loads, relative P-I formulas have been derived based on existing transverse velocity profiles of rigid plastic beams under impulsive loads. Two failure modes (shear failure and bending failure) were differentiated. The impact of boundary condition and load types on the response is investigated. It is found under certain conditions only one failure mode is possible. But shear failure and bending failure can coexist under very severe impulsive loads. One specific example has been used to demonstrate the combined application of the P-I diagram method and FEM. Most guyed towers are expected to survive light or medium impulsive loads due to their high redundancy and small loading area.



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