Evangelos Efthymiou

A newly developed life cycle inventory (LCI) database for commonly used structural steel components

The use of steel within the construction sector has enabled the delivery of larger-volume and more complex-shaped structures, while life cycle assessment (LCA) has been introduced as a pro-active design tool to ensure their sustainability. As LCA efficiency greatly depends on the life cycle inventory (LCI) data used, it is the purpose of the current research to present detailed structural steel LCI data and thus increase environmental benefits deriving from the effective use of LCA within construction. Hot-rolled structural steel members were chosen as the research starting point and the necessary information was provided by the leading structural steel manufacturer in Greece. Results include a list of environmental inputs and outputs, which can be used within relevant LCA studies and environmental impact assessment. Critical issues hindering the use of LCA were identified, along with the most environmentally damaging production stages and environmental categories mainly burdened. A new methodology for assessment results comparison was also applied.

Novel Morphologies of Aluminium Cross-Sections through Structural Topology Optimization Techniques

In the last decades, the deployment of aluminium and its alloys in civil engineering fields has been increased significantly, due to the material’s special features accompanied by supportive technological and industrial development. However, the extent of aluminium structural applications in building activities is still rather limited and barriers related to strength and stability issues prevent its wider use. In the context of the extrusion characteristic, appropriate design in aluminium cross-sections can overcome inherent deficiencies, such as the material’s low elastic modulus.This paper investigates a new breed of cross-sectional design for aluminium members employing pioneering structural topology optimisation techniques. Topology optimisation problems utilise the firmest mathematical basis, to account for improved weight-to-stiffness ratio and perceived aesthetic appeal of specific structural forms. The current study investigates the application of structural topology optimisation to the design of aluminium beam and column cross-sections. Through a combination of 2D and 3D approaches, with a focus on post-processing and manufacturability, ten unique cross-sectional profiles are proposed. Additionally, the variation of cross-section along the member is also investigated in order to identify correlation between 2D and 3D topology optimisation results. Conclusions attempt to highlight the advantageous characteristics of aluminium use as well as the potential benefits to the more widespread implementation of topology optimization within the utilization of aluminium in civil/structural engineering.

Novel Optimised Structural Aluminium Cross-Sections Towards 3D Printing

In the last decades, the deployment of aluminium and its alloys in engineering fields has been increased significantly, due to the material’s special features accompanied by supportive technological and industrial development such as the extrusion manufacturing method. However, the extent of aluminium structural applications in building activities is still rather limited, and barriers related to strength and stability issues prevent its wider use. In the context of topology optimisation, appropriate design in aluminium cross-sections can overcome inherent deficiencies, such as the material’s low elastic modulus.

Direct Methods of Plasticity in Aluminium Frames Accounting for Eurocode 9 Failure Criteria

Metal structures, given their broad plastic deformation capacity, have been often at the core of research for the evaluation of the post elastic behavior via the direct methods of plasticity. Limit and shakedown analysis were often exploited to determine the plastic collapse load capacity, as they provide advantages in terms of computational robustness in comparison with incremental non-linear analysis. The aforementioned approach has been widely and effectively applied for steel structures, characterized by rigid-plastic behavior. Υet in the case of aluminium structures, there are special parameters to be considered, as they exhibit a relationship of round-house type, whose trend cannot be interpreted through the classic elastic-perfectly plastic material law idealization.The present paper aims to develop a limit and shakedown analysis formulation suitable for the safety assessment of 3D aluminium frame structures against plastic collapse. Research yielded the proposed two-surface methodology in the framework of stress resultant plasticity, which is capable of estimating the plastic collapse limit state of real-life aluminium frames, incorporating Eurocode 9 codified failure criteria and limited kinematic hardening. A numerical example of a 3D frame is realized utilizing the finite element method and the 3-node Timoshenko column-beam element, in order to showcase the proposed methodology and validate the influence of hardening effect.

Deformation of Perforated Aluminium Plates under In-Plane Compressive Loading

Aluminium plates containing a single hole or multiple holes in a row are recently becoming very popular among architects and consultant engineers in many constructional applications, due to their reduced weight, as well as facilitating ventilation and light penetration of the buildings. However, there are still uncertainties concerning their structural behaviour, preventing them from wider utilization. In the present paper, local buckling phenomenon of perforated aluminium plates has been studied using the finite element method. For the purposes of the research work, plates with simply supported edges in the out-of-plane direction and subjected to uniaxial compression are examined. In view of perforations, circular cut-outs and the total cut-out size has been varied between 5 and 40% of the total plate area. Moreover, different perforation patterns have been investigated, from a single, central cut-out to a more refined pattern consisting of up to 25 holes equally distributed over the plate. Regarding the material characteristics, several aluminium alloys are considered and compared to steel grade A36 on plates of different slenderness. For each case the critical (Euler) buckling load and the ultimate resistance has been determined.A study into the boundary conditions of the plate showed that the restrictions at the edges parallel to the load direction have a large influence on the critical buckling load. Restraining the top or bottom edge does not significantly influence the resistance of the plate.The results showed that the ultimate resistance of aluminium plates containing multiple holes occurs at considerably larger out-of-plane displacement as that of full plates. For very large total cut-out, a plate containing a central hole has a larger resistance than a plate with equal cut-out percentage but with multiple holes. The strength and deformation in the post-critical regime, i.e. the difference between the critical buckling load and the ultimate resistance, differs significantly for different number of holes and cut-out percentage.

On the Separation Zones in Aluminium Base-Plate Connections. Numerical Simulation and Laboratory Testing

The present paper deals with the study of the separation problem under combined loading conditions of aluminium base-plate connections. The classical unilateral contact law of Signorini is applied in order to describe the contact conditions between the contact surfaces and the separation process along the connection. Thus the problem is formulated as a variational inequality that expresses the principle of virtual work of the connection at the state of equilibrium, where the unilateral contact is included in the formulation. The application of an appropriate finite element discretization scheme leads to the formation of a quadratic optimization programming problem which is coupled by inequality constraints with respect to the displacements. The latter problem expresses from the standpoint of mechanics, the principle of minimum potential energy of the connection at the state of equilibrium. The aforementioned problem can be numerically and effectively treated by the application of two easy–to–use solution strategies based on quadratic optimization algorithms. This technique is illustrated by means of a numerical application. Due to the great significance of the problem, laboratory testing has been carried to extensively investigate the phenomenon. The numerical results are compared with respective laboratory testing results.