Murty K. S. Madugula

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.

Geometric axis bending strength of double angle beams

Abstract Results of tests on 13 double-angle beams bending about the geometric axis are presented. Nine regular size and two ultra-large size angles were included in the investigation. The test failure moments were 2–32% greater than the plastic moments of resistance and 55–95% greater than the nominal flexural strengths calculated as per the American Institute of Steel Construction ‘Specification for Load and Resistance Factor Design of Single-angle Members’ issued in 1993. For the angles tested, the deflections at 1.5 times the yield moment were only 1.53–1.74 times the deflections at first yield. Failure strains in compression exceeded the yield strain even for a specimen with a width-to-thickness ratio of 19.0. It is concluded that the nominal resistances for angle members bending about the geometric axis computed using the current AISC-LRFD Specification for Single Angles are highly conservative and there is need to revise the pertinent clauses in the specification in the interest of design economy.

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.

Geometric non-linear analysis of three-dimensional guyed towers

Abstract Three-dimensional geometric non-linear analysis of guyed towers using linear isoparametric formulation within an updated Lagrangian coordinate framework is presented. The complex non-linear behaviour of the guy cables is simplified by the equivalent modulus approach. Shear locking of the two-noded beam element is corrected by reduced order of integration and altering the elastic coefficient for the transverse shear. The formulation is general enough to include transverse shear effects, eccentricity of the centroidal axes from the beam shear centre and the product of inertia of the beam cross-section. A typical guyed tower example is solved and results are compared with the published work.

Analysis/Design of Reinforced Concrete Circular Cross Sections

Using the strength theory of ACI 318-83, a numerical procedure along with a computer program was developed for the analysis/design of reinforced concrete circular cross sections subjected to axial loads (compression or tension) and bending moments. In the analysis mode, the computer program calculates the design flexural strength of a given reinforced concrete circular cross section subjected to a given axial load or eccentricity. In the design mode, the program solves for all possible combinations of reinforcing bars to satisfy the given loading cases, thus leading to an optimal cost solution. An unique feature of the program is the determination of design strength without exceeding the tensile strain in the reinforcement specified by the designer. The program is most useful to determine optimal reinforcement for any given size of circular cross section or an optimal combination of reinforcement and diameter of circular cross section, based on cost. Using the computer program, optimization can easily be extended to consider different grades of steel and concrete. Comparisons with other existing anlysis methods are also included to demonstrate the effectiveness and generality of the program.

Geometric properties of schifflerized angles

Abstract Latticed triangular-base steel towers have been used as communication structures for a long time. Since these towers are economical, they are also being increasingly used as electrical transmission line towers. The legs of these towers generally consist of ‘schifferized’ angles (equal leg 90° hot-rolled angles bent to 60°). Since the properties of these schifflerized angles are not available in published literature, they are presented in the paper for ready use of design engineers.

Computer program for the design of laterally unsupported angle beams

Abstract Based on the theory developed by Leigh, Thomas and Lay, a FORTRAN77 computer program for the design of laterally unsupported steel angle beams is developed. The program can be used for any span length and superimposed load. All available angle sections may be built into the database of the program. For a given set of input data, the program prints out a complete list of available sections that are safe against the bending and shear stresses. To make the program more useful, the deflection due to the superimposed load is also calculated and the sections are checked against the allowable deflections. For the convenience of the users, the input to this program is in the form of DATA statements and, therefore, is free from formats. The computer program has been tested extensively and a good correlation with the published work has been obtained.

Behavior of bolted circular flange connections subject to tensile loading

This paper presents the tensile behavior of bolted circular flange connections that represent typical connectivity of leg members in a steel guyed lattice communication tower. A total of twelve specimens have been tested to failure under increasing monotonic tension. Each test specimen consists of a pair of circular flange plates (Φ178 mm), where each plate is welded to a solid circular bar. The flanges are bolted back-to-back using two high-strength bolts located 180º apart. The focus of the experiment includes the development of gaps between the upper and lower flanges connected with ASTM A325 bolts (Φ16 mm), increase in bolt forces, and prying action. The development of gaps between the flanges is significantly influenced by the size of leg members. The increase in the bolt force at failure is approximately 40%, relative to the initial preload of 110 kN. The maximum prying force is observed at the preload level and the prying force decreases gradually as the flanges are further loaded, indicating a complete separation of the upper and lower flanges. The widely used T-stub design equations conservatively predict the behavior of bolted circular flange connections. The proposed predictive equations agree well with the test data, especially near the failure of the bolts.

Flexural Strength of Laterally Unsupported Angle Beams

Publisher Summary This chapter discusses that in nuclear power industry, angles are extensively used as beams to support pipes. In latticed towers, angles are subjected to axial forces and bending moments. Thus, it is necessary to be able to accurately determine the bending strength of angle members for use in their design as beams and beam-columns. This chapter experimentally determines the strength of laterally unsupported angle beams and assesses the magnitude of conservatism, if any, in the 1993 edition of the American Institute of Steel Constructions “Specification for Load and Resistance Factor Design of Single-Angle Members.” The chapter presents the results of tests on eight laterally unsupported angle beams ranging in size from 75 x 75 x 9 to 150 x 90 x 9 mm. The maximum compressive and tensile strains at the tips of the legs for all the specimens far exceeded the yield strains. It discusses the evaluation of the interaction equation for bending about both of the principal axes based on the assumption of the development of the plastic moment of resistance yielded results, which are in agreement with the tests. Specification for Load and Resistance Factor Design of Single-Angle Members was highly conservative regarding the bending strength of laterally unsupported angle beams.