F.G.A. Al-Bermani

Geometric and material nonlinear analysis of structures comprising rectangular hollow sections

This paper presents a nonlinear finite element analysis of structures comprising thin-walled rectangular hollow sections. Nonlinearities due to both the change of geometry and material yielding are included, incorporating also the effects of strain-unloading. The geometry and the stiffness of the elements are modified and used to update the structure tangent stiffness matrix. An iterative numerical procedure combining the arc-length and the work methods is employed for the solution of the incremental equation of equilibrium. The method has been applied successfully to predict the nonlinear load-deflection behaviour of isolated cold-formed SHS columns, fabricated RHS parabolic fixed end arches, and double chord SHS trusses having different joint configurations.

Modelling of cold-formed purlin-sheeting systems. Part 2. Simplified model

A number of theoretical and experimental investigations have been made into the nature of purlin-sheeting systems over the past 30 years. These systems commonly consist of cold-formed zed or channel section purlins, connected to corrugated sheeting. They have proven difficult to model due to the complexity of both the purlin deformation and the restraint provided to the purlin by the sheeting. Part 1 of this paper presented a non-linear elasto plastic finite element model which, by incorporating both the purlin and the sheeting in the analysis, allowed the interaction between the two components of the system to be modelled. This paper presents a simplified version of the first model which has considerably decreased requirements in terms of computer memory, running time and data preparation. The Simplified Model includes only the purlin but allows for the sheetings shear and rotational restraints by modelling these effects as springs located at the purlin-sheeting connections. Two accompanying programs determine the stiffness of these springs numerically. As in the Full Model, the Simplified Model is able to account for the cross-sectional distortion of the purlin, the shear and rotational restraining effects of the sheeting, and failure of the purlin by local buckling or yielding. The model requires no experimental or empirical input and its validity is shown by its goon con elation with experimental results

Free vibration of cantilevered arbitrary triangular Mindlin plates

This paper presents a free vibration analysis of thick cantilevered arbitrary triangular plates based on the Mindlin shear deformation theory. The solutions are computed using the recently developed pb-2 Rayleigh-Ritz method. The actual triangular plate is first mapped onto a basic square plate, and the deflections and rotations of the plate are approximated by Ritz functions defined as products of two-dimensional polynomials in the basic square plate domain and a basic function. The basic function satisfies the geometric boundary conditions at the outset and is chosen as the boundary expression of the cantilevered edge. Stiffness and mass matrices are integrated numerically over the domain of the basic square plate using Gaussian quadrature. Wherever possible, the present results are verified by comparison with existing analytical and experimental values from the open literature. To the authors knowledge, first known results of natural frequencies for cantilevered arbitrary triangular Mindlin plates are presented for a wide range of geometries and thicknesses. These results are valuable to design engineers for checking their natural frequency calculations and may also serve as benchmark values for future numerical techniques and software packages for thick plate analysis. The influence of shear deformation and rotary inertia on the natural frequency parameters are examined.

Single-equation yield surfaces for monosymmetric and asymmetric sections

Single-equation yield surfaces are presented for channel, tee, single-and double-angle sections under combined axial force and biaxial moments. The equations give very good approximations to the accurate yield surfaces while maintaining smoothness, convexity and continuity requirements in three-dimensional space. The equations derived may be implemented in an elasto-plastic analysis program for modelling the nonlinear global behaviour of steel frame structures comprising one or more of these types of section.

Kinematic and non-linear analysis of foldable barrel vaults

Kinematic analysis is conducted to derive the geometric constraints for the geometric design of foldable barrel vaults (FBV) composed of polar or angulated scissor units. Non-linear structural analysis is followed to determine the structural response of FBVs in the fully deployed configuration under static loading. Two load cases are considered: cross wind and longitudinal wind. The effect of varying member sizes, depth-to-span ratio and geometric imperfections is examined.

Nonlinear elastoplastic analysis of spatial structures under dynamic loading using kinematic hardening models

A method is presented for the elastoplastic nonlinear analysis of spatial structures under dynamic loading using an updated Lagrangian formulation and a radial return predictor/corrector solution strategy. A bounding-surface kinematic hardening plasticity model is employed to simulate the hardening and hysteretic material response. This model is used in conjunction with the lumped plasticity assumption coupled with the concept of a yield surface in force space. A hardening coefficient matrix, which is a function of the plastic strain and the elastic stiffness operator, is introduced while the vectorial nature of the material memory parameters is maintained. Several examples are presented to demonstrate the accuracy of the method.

Some practical aspects of modeling lattiice towers

Publisher Summary The chapter proposes a finite element model (FEM), in which member continuity, asymmetrical sectional properties of members, the eccentricity of connections, and geometrical and material nonlinearities are considered. The proposed finite element analysis (FEA) model is verified using experimental results. Some practical aspects of lattice towers are analyzed with the proposed FEA model. Recommendations on the design of transmission tower systems are discussed in the chapter. The connection rigidity of main bracings should be considered in practical terms, because connection rigidity greatly affects the buckling capacity and inappropriate modeling of connection rigidity may overestimate or underestimate the buckling capacity. Although secondary bracings are subjected to very small axial forces, they greatly enhance the buckling capacity of a structure. Nonlinear analysis without consideration of secondary bracing members may lead to unreliable results.

Lattice Transmission Tower Analysis: Beyond Simple Truss Model

The advances in the transmission line analysis tools were discussed. These advances gave the designer the ability to better define the structural performance of transmission line towers. The advanced tools were used to determine a transmission tower failure mechanism and member loads. Computer programs attempted to model the non-linear behavior, post-buckling performance and capacity variation of the transmission tower variation system.

Full Scale Testing of Transmission and Telecommunication Towers Using Numerical Simulation Techniques

A compact and practical nonlinear analytical method for simulating the global structural response of transmission and telecommunication towers is described. The tower is modelled as an assembly of beam-column elements. Linear, geometric and deformation stiffness matrices are used to describe the behaviour of a general thin-walled beam-column element in an updated Lagrangian framework. The formulation reduces greatly the number of elements required for accurate modelling of the nonlinear structural response. A lumped plasticity approach coupled with the concept of the yield surface in force space is adopted for modelling material nonlinearity. A former configuration formulation of the towers is used for automatic generation of data necessary for the analysis. The proposed numerical simulation technique has been used to investigate the ultimate structural behaviour of several latticed and guyed transmission and telecommunication towers under different loading conditions. The technique has now been accepted by many power supply authorities as a tool for replacing the current practice of full-scale tower testing.