Gerard R. Monforton

EVALUATION OF NON-LINEAR ANALYSIS OF GUYED ANTENNA TOWERS

Abstract This paper discusses two different finite element models used in the analysis of guyed antenna towers. In the first approach, three dimensional truss elements are used to model the latticed mast of the tower and non-linear cable elements are used for the guys; this results in a large number of elements and degrees-of-freedom. In the second approach, the mast is modelled using beam–column elements and non-linear cable elements for the guys. The two computer models were evaluated using six existing towers subjected to a variety of load combinations involving dead, wind and ice loads. The results are compared to a simple, but widely used, model in which the tower is modelled as a beam on non-linear elastic supports. Structural response comparisons include guy tensions, member axial forces, face shears, mast displacements and mast rotations.

Dynamic response of guyed masts

Natural frequencies of guyed masts were determined by modelling the mast as truss elements in one model and as beam-column elements in another model. Guys were modelled as cable elements in both cases. The natural frequencies from the two models agreed closely with each other. For the purpose of verification of the finite element modelling, two triangular steel latticed scale-modelled guyed masts were fabricated and tested on a shake table specially designed to test guyed masts. The experimental results were in good agreement with the results from the finite element analysis. The finite element modelling was then applied to six existing towers which are representative of the design practices in Canada. Based on the results of these analyses, the influence of ice accretion, guy initial tensions and torsion resistors on the dynamic characteristics of the guyed masts is discussed.

Analysis of truss-cable structures

Abstract The energy search method is applied to the analysis of general pin-ended truss and cable structures. Geometric and material nonlinearities are directly incorporated within the formulation, thereby accounting for large strains and displacements as well as configuration changes due to the structural response. The principle of minimum total potential energy forms the basis of the analysis procedure and analytic strain energy expressions are presented for the individual elements of truss-cable structures. The total potential energy is obtained by summing the energy contributions from each member and solutions are generated using the conjugate gradient method. Examples illustrate the ease and versatility of the method which avoids the inherent problems associated with solving large systems of nonlinear equations.

Finite element failure analysis of schifflerized angles

Abstract Angles are extensively used in latticed triangular-base communication structures and electrical transmission towers. The legs of these towers consist of 60° equal leg angles. A finite element model designed to estimate the ultimate strength of such angles is discussed. The analytical problem has been solved under geometric and material nonlinearity. A Newtonian approach with eight-node shell elements was employed for the nonlinear solution using the commercially available software ABAQUS. Residual stress variations along the cross-section and through-the-thickness are included. Results of experimental investigation on equal-leg schifflerized angles (90° angles bent to 60°) under concentric axial compressive loading with hinge-hinge end conditions are presented. Five sizes of angles, namely 127 × 127 × 7.9, 102 × 102 × 6.4, 89 × 89 × 7.9, 76 × 76 × 6.4mm ( 5 × 5 × 5 16 4 × 4 × 1 4 , 3.5 × 3.5 × 5 16 , 3 × 3 ×; , 3 × 3 × 1 4 in) with slenderness ratios varying between 50 and 100 are included in the investigation. The loads computed using the finite element model are found to be in good agreement with experimental failure loads.

Stiffness matrix for sandwich beams with thick anisotropic laminated faces

Abstract A finite element capability is described for the analysis of sandwich beams with thick unbalanced laminated faces. Particular attention is focused on the effects of bending-membrane coupling in the faces. The stiffness matrix is developed using displacement functions generated from explicit solution of the governing differential equations.

Analysis of flexible frames by energy search

Abstract A geometrically nonlinear finite element formulation based on a moving Eulerian coordinate system is used to predict the structural response of flexible planar frames. The total potential energy of the system is expressed in terms of the strain inducing displacements and parameters that reflect the coupling between axial (tension or compression) and bending effects. A conjugate gradient energy search procedure is employed to minimize directly the total potential energy of the structural system. The method includes the effects of prestressing and prescribing displacements in addition to abrupt changes in geometric configuration due to buckling of compression members and slackening of tension elements. Numerical examples illustrate and verify the accuracy of the technique presented.