Plenary lectures

Recent Developments in Design for Structural Stability

Gregory J Hancock, Emeritus Professor and Professorial Research Fellow, University of Sydney, Australia

 

Abstract

 

The potential for structural instability in metal structures has been known since the famous paper of Leonard Euler in 1744 on column buckling.  In recent years, the Structural Stability Research Council (SSRC) of the USA has published its widely used “Guide to Stability Design Criteria for Metal Structures” the most recent edition being the sixth in 2010 edited by Ron Ziemian.  The constant challenge has been the desire to turn the excellent research worldwide in the area into design rules and specifications such as the Eurocodes, American Specifications, Japanese, Chinese and Australian Standards.

New methods of stability analysis and design such as the Direct Strength Method (DSM) in the AISI S100:2016 Specification and Australian/New Zealand Standard AS/NZS 4600 for Cold-Formed Steel Structures have unified stability design across a range of buckling modes such as local, distortional and overall (Euler) buckling.  Further, Advanced Analysis methods (often called GMNIA) which use the Finite Element Method (FEM) are being standardized for routine design of structural systems.  The paper will review these new methods, and their incorporation in design standards and specifications as a continuation of the challenging processes of design for structural stability.

 

 

 

 

From 3-D to 1-D generalised and Cosserat Continua for structural dynamics, fibre reinforced materials and coupled systems

Carlo Sansour, Faculty of Engineering, Civil Engineering department, University of Nottingham, UK; Civil Engineering Department, INSA de Rennes, France.

Abstract

Generalised continua is a phrase used to describe continua with extra degrees of freedom. Cosserat continua would be the simplest case of such continua with rotations being the extra degrees of freedom going beyond that of displacements. In the case of micromorphic continua, the extra degrees of freedom will describe a local distortion which goes beyond a rotation. This kind of continua is strongly related to higher gradient ones, where higher gradients rather than extra degrees of freedom are considered to enhance the kinematics of the otherwise classical continuum. Classical continuum formulations exhibit serious shortcomings. In addition to solution singularities present in the context of unsmooth geometries or loading, classical theories of deformation do not provide internal length scale and so do not exhibit scale effects readily observed in experiments. Not only are scale effects relevant when the specimen or structure’s dimensions themselves are in the micron and submicron scale but also when it comes to high strain concentrations as in the case of localised shear bands or at crack tips etc. In this context so-called generalised continuum formulations have proven to provide remedy as they allow for the incorporation of internal length scale parameters which reflect the micro-structural influence on the macroscopic material response. Indeed, generalised can be understood as a significant step towards multiscale computations expected to reveal information about the micro structure of the material.
On the other hand dimensionally reduced generalised continua such as 2-D and 1-D Cosserat continua provide direct access to shell and rod theories and so to structures in general, where dynamical behaviour is relevant as well. The numerical treatment of extra degrees of freedom such as rotations, especially in a dynamical context, can be demanding as well. Here we will show how a general energy-momentum method can be developed to provide stable time integration schemes capable of capturing the long term dynamics. The numerical treatment of generalised continua in different contexts such as anisotropy, fibre reinforced material and coupled electro-mechanical systems are discussed and many numerical results are presented as well.

Professor Carlo Sansour completed his PhD at the University of Stuttgart and his habilitation in mechanics at the Darmstadt University of Technology before serving as senior lecturer at the Karlsruhe University of Technology. He joined the University of Adelaide, Australia, as Associate Professor before finally taking up a Chair at the University of Nottingham, UK, where he headed the Centre of Structural Engineering. He served as the President of the UK-Association for Computational Mechanics in Engineering and was a member of the Management Board of ECCOMAS (the European Community for Computational Methods in the Applied Sciences) and the Gereal Council of the International Association for Computational Mechanics. He has been on the scientific committees of many international conferences as well as journals in the general areas of theoretical and computational mechanics. For two years he has been a senior Marie Curie Scholar which he spent at INSA Rennes, France. Recently he has moved from the University of Nottingham to which he is still associated to be active at INSA Rennes, France.
His research interests and accomplishments stretch from shell theory and its finite element formulations to computational structural dynamics and energy-momentum methods, from anisotropic inelastic deformations at finite strains to fibre reorientation in biological tissues. Old and recent research area is generalised continua and their numerical implications. Electromechanical coupling is a further area of activity.

 

 

 

 Effective Slab Width for Evaluating Utilimate Seismic Capacities of Reinforced Concrete Buildings

Toshimi Kabeyasawa, University of Tokyo, Japan

Abstract

A series of static and seismic loading tests of reinforced concrete frame assemblies were conducted to identify the effects of slab on the beam strength in 2010, 2012, 2013 and 2014. Three specimens in the first series of 2010 were two-fifth scale three-dimensional reinforced concrete beam-yielding frames with floor slab consisting of four columns and two frames in both directions. The high strength materials were used in the frame specimens representing medium-story of high-rise buildings from lower to higher mid-heights of columns planned and conducted as a part of a research project on the review and development of design method against long-period earthquake motions to identify the hysteretic relations of models for time-history analysis. A special loading set-up was invented and used to simulate the boundary conditions of the medium-story frame so that the axial elongation of the beams would not be constrained by the reaction supports consisting of pin-fixed and pin-roller. One of the two specimens was loaded up to 1/33 which was smaller than the other. The specimen was repaired with epoxy resin into major residual cracks and tested again in 2012 to verify the seismic performance of the repaired members in BRI lab after the recovery from the damage due to the East Japan earthquake. Another series of research projects started from 2013 to 2014 using the same type of frame assemblies and the loading system to identify the effective widths of slab in calculating the ultimate strength of the beams and the ultimate lateral load carrying capacity of frames in the standard seismic design procedure of Japan. Therefore, normal strength materials were used in the similar frame specimens to represent a part of typical medium-rise reinforced concrete frame buildings. The projects were conducted as a part of the research projects on the review of in the technical standard and guidelines for the design practices which was also supported by the Ministry of Construction. Three specimens tested in 2013 and two in 2014. One of the 2013 specimens was a frame without slab so that the effect of slab could be directly compared. The third specimen was a thin depth beam with slab. A thick void slab and the outer end slab was tested in 2014. The damage patterns as well as the lateral resistances of the frames in various inter-story drift ratios were investigated considering the contributions of the slab to the beam resistance. It was generally found from the series of tests that the slab reinforcing bars were increasing almost uniformly through the whole slab width and was fully effective to the flexural strength of the beams at around one percent story drift. The observed and calculated beam strengths with the full width of slab was much higher than those with the effective slab reinforcing bars assumed in the current design practice.