Narinder K. Gupta, IndiaEmeritus Professor, Department of Applied Mechanics, Indian Institute of Technology Delhi, New Delhi, India |
Large deformation in thin-walled structures under impact or blast loadingMechanics of large inelastic deformation and failure of thin walled structures and consequent dissipation of kinetic energy has been receiving considerable attention by several investigators, mainly motivated by the considerations of designing for structural crashworthiness and safety in the events of unintended impact or blast loading. Analysis of such phenomenon is made difficult by uncertainties in loading as well as effects of various parameters like strain rate, inertia, history of loading, annealing and thermal processes, and geometry. In this paper, some of the experimental results of large deformation of various thin walled structures of varying geometry and size or plates with various boundary conditions, subjected to impact of drop hammer or projectiles of different features and blast loading are presented. Resulting collapse modes and influence thereon of various parameters are discussed. In particular effect of parameters like annealing and heat treatment, geometry, discontinuities, non uniformity in thickness, and boundary conditions are discussed. Some features of analytical and numerical formulations are presented, and some results discussed. These methods are useful for the analysis under the given conditions and idealizations that are made on the basis of observations made in the experiments. However, further experiments are needed to understand the phenomenon of initiation and propagation of collapse modes, failure criterion and material characteristics in dynamic loading. |
Joseph Loughlan, United KingdomProfessor of Aerospace Structures, Department of Aeronautical and Automotive Engineering, Loughborough University, Loughborough, Leicestershire, UK |
The Failure of Thin-Walled Lipped Channel Compression Members due to Coupled Local-Distortional Interactions and Material YieldingThe compressive failure mechanics of thin-walled sections is complex and there are a great many factors which influence the process of events leading to ultimate conditions. Thin-walled short length sections are likely to fail due to material yielding after an elasto-plastic post local buckling phase of behaviour. Longer length sections become more prone to intermediate or global buckling effects such as distortional buckling or the overall modes of torsional, flexural or torsional-flexural buckling. Clearly, interaction is possible between the different modes of behaviour and coupled instabilities can be encountered in design whereby local-distortional buckling can occur or, indeed, the interaction between local buckling and overall flexural behaviour may be of influence. This paper details appropriate finite element modelling strategies and procedures for the accurate determination of the coupled local-distortional interactive response of thin-walled lipped channel sections. The modelling procedures are able to describe the complete loading history of the compression members from the onset of local buckling through post-local buckling behaviour leading to local-distortional interaction including material yielding and yield propagation to ultimate conditions and then to elasto-plastic unloading. The numerical simulations take due account of the influence of geometrical imperfections on the compressive ultimate failures of the sections and the results from the finite element models are shown to agree favourably with the ultimate loads and failure mechanisms from experimental tests on steel lipped channel sections exhibiting local-distortional interaction. The test programme covers some 20 columns of varying cross section dimensions and column lengths and the columns are loaded in uniform compression in conjunction with the fixed-ended boundary condition. |
Ulrike Kuhlmann, GermanyProfessor, Institute for Design and Construction, University of Stuttgart |
Safety and stability of slender plated elements - New chances and developments of Eurocode 3 Part 1.5In the member states of the European Union the design of slender steel plates is covered by EN 1993-1-5:2006. On one hand this standard gives a unique opportunity to deal with rather complicated plate buckling problems by means of a fairly simple and consistent set of design procedures, suitable for hand calculations. On the other hand this code also opens the gate and gives basic rules for the application of highly sophisticated verification procedures using FE modelling. An overview on the existing code rules and background will be given in the paper. One of the main application fields of EN 1993-1-5 are bridges where the design is dominated by slender plated elements. Highly complex multi-axial stress states maybe involved in typical bridge design situations. However, deficiencies of the existing code rules have become apparent, so that oriented to practical needs such as the launching procedure or the necessity of stiffeners for very large structures have lead to the development of improved rules which should be implemented in a future revised code. Recent developments such as the increased use of high strength steels or the possibility of corrugation have lead to new promising solutions such as hybrid girders or girders with corrugated webs which also need to be covered by the coming Eurocode. Based on recent research results developed also in the frame of the ECCS Working Group TWG8.3 an outlook will be given on the further development giving also an example how in future practitioners and researchers may work together to solve problems and improve the efficiency of steel structures. |
Federico Mazzolani, ItalyProfessor of Structural Engineering, Department of Structural Engineering, University of Naples "Federico II" |
3D aluminium structuresAluminium and its alloys is a new structural material, being available since the end of 19th century only. The first important applications were done for building the skeleton of the dirigibles (Schwarz, Zeppelin), which represented the first 3D metal structure, as ancestor for the development of the modern aeronautic industry. After this challenging start, this new material was used in many structural applications in the field of transportations (on air, ground, water): from aircrafts to ships, from trains to automotives, the aluminium alloys are present under form of 3D structures. Many other applications are developed in the field of structural engineering, where the 3D schemes of stiffened and unstiffened shells are used for storage vessels, silos, tanks, industrial domes,…. The development in the field of the so-called "civil engineering" started after the World war II. Aluminium is selected for structural applications, when it becomes competitive with respect to other structural materials. It happens in all cases, where the designer can exploit the aluminium prerequisites, which are: lightness, corrosion resistance and rational use of extruded shapes. Large span roofing systems represent a very competitive field, under form of space structures for plane and curved shapes. The main aspects of theory, design, codification and application of 3D aluminium structures are examined, by emphasizing the peculiar differences with steel, by referring to real cases. The main applications in the field of geodetic domes represent a challenging example of 3D aluminium structures. The theoretical and experimental results were used for setting-up Part 1.5 "Shell Structures" of Eurocode 9. |
Kim J.R. Rasmussen, AustraliaProfessor and Head of School of Civil Engineering, The University of Sydney, Sydney, Australia |
Recent research on the design and behaviour of drive-in steel storage racking systemsThe paper summarises a recently completed research program carried out at the University of Sydney on drive-in steel storage racks subject to horizontal impact loads. Impact loads develop frequently during the normal operation of drive-in racks when the forklift truck strikes an upright on entering or exiting a bay, and may lead to local or global collapse. The collapse follows the bowing of the upright which may cause a pallet to drop off the supporting beam rails and initiate progressive collapse down through the bay and possibly into adjacent bays as well. The research program comprised full-scale tests on assemblies of a 5-bay wide racking system, tests of components of the system, the development of finite element models capable of accurately predicting the behaviour of the system, parametric studies of the strength and stiffness of steel storage racks, the development of a simple mechanical model for understanding the dynamic behaviour of the system during impact and a reliability analysis for deriving equations for the design impact loads and associated load factors. The purpose of the paper is to give an overview of the methodology adapted for the research program and to present the main findings and final outcomes of the research. |
J. Michael Rotter, United KingdomProfessor of Civil Engineering, Institute for Infrastructure and Environment, School of Engineering, University of Edinburgh, Edinburgh, Scotland, UK |
Challenges in the generalisation of structural buckling assessments to all structures and load casesThe field of buckling strength assessment of structures has always separated each structural form and load case into a separate problem. Examples are the differences between the formulations for lateral buckling of columns, lateral-torsional buckling of beams and buckling of plates. Each situation has been treated as a separate phenomenon, with uncertainties arising only when it was difficult to determine into which category a final structure should be placed. This situation arose because analytical tools could not make the treatments more general. The two complicating factors of plasticity and imperfections were treated as quite distinct for each structure. With the arrival of very powerful computer programs and their widespread adoption, structures of great complexity can be analysed, and the separation of structural forms into different categories is no longer so necessary. Moreover, it is no longer necessary, nor desirable, to break a structure into single elements, each with its own buckling resistance. Although it is now relatively easy to use computational power to determine the buckling strength of a complete structural system, the rules in standards do not accommodate these calculations well, and the complicating factors of plasticity and imperfections continue to draw users back to the traditional formulations. In this paper, the ideas set out in the Eurocode on shell structures EN 1993-1-6 (2007) are used to illustrate how complete structural systems can be treated in a uniform manner irrespective of the their form, boundary conditions and loading. It then identifies some key challenges in making this new vision into a reality for all computational assessments of complete structures. These challenges are discussed and ideas proposed on their possible solution for discussion with the developers of innovative structural assessment rules. |
Luis Simões da Silva, PortugalProfessor, Civil Engineering Department, University of Coimbra, Coimbra, Portugal |
Stability and design of thin-walled steel shellsThin steel shells as a structural solution are applied in many fields of engineering and present a series of advantages due their curvature to support much more efficiently external applied loads than other structures, thus resulting in a much stronger and stiffer load resistant mechanism. The following advantages may be noted: Efficiency of load-carrying performance; High strength vs. weight ratio, i.e. shell structures may be, from this point of view, optimal structures; High stiffness; High value from an architectural point of view. Shells can be easily and harmoniously integrated in both urban or landscape contexts and areas. However, shell-like structures are very slender structures, being prone to stabilities issues that must be taken into account when designing and predicting the overall structural behaviour. For the majority of shells structures the buckling resistance can be significantly lower than the theoretical (classical) buckling load and the post-buckling behaviour is highly unstable, requiring the appropriate consideration of imperfections. This paper presents a review of the stability behaviour of steel shells focusing on the stability phenomena and the influence and treatment of imperfections. The design methodologies are subsequently presented and reviewed. Finally, the issue of curved steel panels for application in bridges is specifically detailed. |
Jin-Guang Teng, Hong Kong, ChinaProfessor of Structural Engineering, Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong, China |
Hybrid FRP-Concrete-Steel Double-Skin Tubular Members: Concept, Behaviour and ApplicationsFibre-reinforced polymer (FRP) composites have been widely used in the strengthening/retrofit of structures. This success has been due to their many advantages, which include their excellent corrosion resistance and high strength-to-weight ratio as well as the possibility to tailor their properties in different directions to achieve the best structural performance. They also have a number of disadvantages including a relatively low modulus-to-weight ratio, a linear-elastic-brittle stress-strain response and poor performance in a fire. This paper presents an innovative hybrid column form which consists of an inner steel tube, an outer FRP tube and an annular concrete infill between them. The two tubes may be concentrically placed to produce a section form more suitable for columns, or eccentrically placed to produce a section form more suitable for beams. The way the FRP composite is used in these hybrid structural members means that the disadvantages of FRP are minimised while its advantages are appropriately exploited. As a result, these hybrid members possess excellent corrosion resistance as well as excellent ductility and seismic resistance. This paper explains the rationale and advantages of this new form of structural members and discusses their potential applications before presenting a summary of the recent and current studies on their structural behaviour and design. These studies form part of a major on-going research programme at The Hong Kong Polytechnic University (PolyU). |
Robert Tremblay, Canada
Professor, Group for Research in Structural Engineering, Department of Civil Geological and Mining Engineering, École Polytechnique Montreal, Canada |
Seismic design of low-rise steel buildings with flexible roof deck diaphragms: a Canadian perspectiveMost single-storey commercial, recreational and light industrial buildings in Canada are designed with steel roof deck diaphragm that resist and transfer lateral loads to the vertical bracing systems. These diaphragms are made from thin corrugated steel deck sheets that are connected to each other and fastened to the supporting structure. The vertical bracing system is commonly built with diagonal steel braces that resist axial lateral loads through axial compression and tension axial loads. According o current seismic design practice, the braces are selected to dissipate seismic input energy through tensile yielding compression inelastic buckling, and roof diaphragms are designed to resist in-plane shear forces that develop when bracing members such that they remain essentially elastic under severe earthquakes. Metal roof deck diaphragms exhibit in-plane flexibility which may affect the fundamental period of buildings used to determine seismic loads. They also dynamically respond to earthquake loading, which may affect the ductility demand imposed on the vertical bracing systems. These aspects are not explicitly addressed in current design codes. Metal roof deck systems also possess some inelastic deformation capacity but such ductility has not been explicitly recognized in design standards. Current Canadian seismic provisions for the design of roof deck diaphragms will be presented. The influence of the flexibility of metal roof diaphragms on building periods and seismic response will be discussed. The potential for ductile inelastic response of steel deck diaphragm under severe seismic ground motions is examined based on the results from large scale dynamic experiments. |