P. Ansourian

Buckling of circular cylindrical shells subject to uniform lateral pressure

A theoretical investigation of the buckling of cylindrical shells under uniform external lateral pressure loading is presented, based on Flugges stability equations in coupled form; these lead to great accuracy. The numerical process gives the buckling pressure for a selected circumferential buckling mode, material, geometry and boundary conditions. The influence of 17 different homogeneous boundary conditions placed on the displacements u, v and w, and on the slope dw/dx is investigated. A wide range of geometries (0.5 ≤ L/R ≤ 5 and 300 ≤ R/h ≤ 3000) is considered. Comparisons are made with some analyses in the literature. It is also found that, contrary to the widespread understanding that the critical pressure for a free cylinder is the same as for a ring, the present model obtains a slightly lower buckling pressure which depends on the length.

On the buckling analysis and design of silos and tanks

Abstract Buckling considerations arise in the design of steel silos and tanks because the slender shell wall is subjected to compressive stresses, most commonly from the action of wind on the empty structure causing circumferential stresses, and combinations of wall friction forces, roof loads, non-uniform filling and discharge, and non-uniform settlement of the foundation causing meridional stresses. In this paper, recent research work of the author and graduate students relevant to buckling behaviour is briefly reviewed. Problems relevant to buckling behaviour, and which arose in several major tanks and silos with which the author was concerned either at the design stage or arising from operational problems, are discussed. The buckling behaviour and design of slender steel silos and tanks has been reviewed, with particular reference to buckling under wind loading, and under meridional compression. The benefits to be obtained by refined finite element analysis at the design stage have been emphasised, and several examples of buckling phenomena in the design of major structures reviewed. The occurrence of uplift of large emoty tanks under severe wind loadings has been detected. A simplified design method for wind buckling has been given, which includes an approximate consideration of the effects of imperfections, meridional end restraints and form of the wind pressure distributions. Situations under which meridional compression can govern the design have been explored. The beneficial effects of a bulk solid content against buckling have been investigated.

Aspects of corrugated silos

In this paper, the effects of combined lateral pressure and longitudinal compression on vertically corrugated steel silo walls have been investigated and expressions are derived for ultimate capacity. Finite element analysis has shown that if stiffening of the silo is required, then it should extend over the full silo height unless very careful analysis of the local stresses is undertaken. Moreover, a closer bolting reduces stresses and deformations significantly.

Hydrostatic, wind and non-uniform lateral pressure solutions for containment vessels

Abstract The governing Flugge stability equations in coupled form are used for cylinders subjected to external pressure that varies circumferentially. Three cases are considered: fluid (hydrostatic) pressure, wind pressure and partial (patch) circumferential pressure. The wind load follows the Australian Standard AS 1170.2 (1989). Longitudinal variation of the load is not considered. The numerical process gives the stagnation buckling pressure for different shell geometry and simple support conditions at each end. The Galerkin method is employed to orthogonalize the error made with the introduction of the finite series into the governing equations. The solutions are compared with a few published solutions in the literature.

Behaviour of composite steel-concrete beams with longitudinal and transverse partial interaction in fire

The use of composite construction is widely favoured in engineering applications, where the composite action is provided by means of different types of locking devices or mechanical connectors. In the case of composite steel-concrete beams, the kinematical implications of the deformability of the shear connectors become significant and an adequate model needs to account for the displacement discontinuities at the interface between components. Both longitudinal and transverse deformations can occur between the slab and the steel joist connection, and these are usually referred to as longitudinal and transverse partial interaction. This paper presents a novel analytical model which accounts for both longitudinal and transverse partial interaction in the analysis of steel-concrete composite beams subjected to fire loading. In this instance, the thermal distribution in the steel joist and in the concrete slab is likely to be quite different despite the similarities in their thermal expansion coefficients. The proposed model is well suited to depict the complex stress and deformation state of the connectors, as vertical separation between the slab and the steel joist is likely to occur, and significantly affect the structural response. The analytical model is derived using the principle of virtual work and, for completeness, both strong and weak formulations are presented. All materials are assumed to behave linearly while the analysis accounts for the degradation of the elastic moduli. A finite element formulation is then derived to model the composite behaviour.

Dynamic analysis of the Milad Tower

This report involves the modelling of the Milad Tower using the finite element analysis program Strand7. A dynamic analysis was performed on the structure in order to understand the deflections and stresses as a result of earthquake and wind loading. In particular, Linear Static as well as Natural Frequency and Spectral Response solvers were used to determine the behaviour of the structure under loading. The findings of the report highlight that the structure was modelled accurately with the outputs representing realistic values. The report suggests that the design of the beams, columns, slabs and all structural members was sufficient enough to support the tower during maximum loading cases. The governing load case was earthquake loading.

Energy balance in the WTC collapse

The main aim of this report is to provide an analysis of Twin Towers of the New York City’s World Trade Centre collapsed after attacked by two jet aircrafts. The approach mainly focused on the effect of temperature on mechanical properties of the building, by modelling heat energy in the south tower. Energy balance during the collapse between the energy inputs by aircraft petrol and the transient heat to the towers was conducted. Both the overall structure between 80 to 83 stories and individual elements was modelled. The main elements contributed to the heat transition includes external and internal columns. Heat applied in 2D and 3D models for single elements was through convection and conduction. Analysis of transient heat was done using Strand7.

Façade Greening: High-rise apartment building in Milan using pre-stressed concrete slab

In this project, one single level of the Facade Greening was designed and modelled using finite element method in Strand7. A static analysis was performed in order to understand the deflection and the stress due to the extra loads imposed by the soil and plants. The results produced by the linear static solver are compared with the strength of the materials and the European limitations. The maximum tension stress which exceeds the tensile strength in concrete is found in the root of the cantilever balcony. An alternative design of the cantilevered balcony with pre-stressed concrete slab is modelled separately for the balcony. Decrease is found in the tension stress and the significant improvement of deflection of the balcony with pre-stressed concrete slab. The dynamic loads such as wind and earthquake did not suggest significant effect on the pre-stressed concrete slab.

Dynamic analysis of the BMW tower in Munich

In the 1970s, world famous Austrian architect Karl Schwanzer designed an avant-garde suspended skyscraper for the new BMW headquarters. The BMW Tower was envisioned to resemble a four-cylinder motor and become a symbol for the recent flourishing success of BMW. Throughout its four decades, the BMW Tower has become the main architectural feature of modern Munich and a pride for one of the World leading car manufacturers. The structural design of the BMW Tower represented a major challenge to Germany’s finest engineers because the suspended 99.5m-high structure had to whitstand not only static loading but large wind dynamic loading while having deflections within appropriate serviceability limits. Strand7 has been used to determine the stresses and deflections the structure is subjected to in order to analyse its behavior under static and dynamic loadings. Ultimately, this analysis helps to understand the nature of suspended structures in relation to the Eurocode building standards. Finally, thermal resista...

Transient dynamic analysis of the Bao’An Stadium

Bao’An Stadium is a unique structure that utilises 54m span cantilevers with tensioned members to support the roof. This report involves a simplified finite element model of Bao’An stadium using Strand7 to analyse the effects of deflections, buckling and earthquake loading. Modelling the cantilevers of the original structure with a double curvature was problematic due to unrealistic deflections and no total mass participation using the Spectral Response Solver. To rectify this, a simplified symmetrical stadium was created and the cable free length attribute was used to induce tension in the inner ring and bottom chord members to create upwards deflection. Further, in place of the Spectral Response Solver, the Transient Linear Dynamic Solver was inputted with an El-Centro earthquake. The stadium’s response to a 0.20g earthquake and self-weight indicated the deflections satisfied AS1170.0, the loading in the columns was below the critical buckling load, and all structural members satisfied AS4100.