Publications
598 results found
Nethercot D, Kyvelou P, Gardner L, et al., 2018, DESIGNING COLD- FORMED STEELWORK AS STRUCTURAL SYSTEMS, 25th Australasian Conference on Mechanics of Structures and Materials, ACMSM25
Kyprianou C, Kyvelou P, Gardner L, et al., 2018, NUMERICAL STUDY OF SHEATHED COLD-FORMED STEEL COLUMNS, Ninth International Conference on Advances in Steel Structures (ICASS’2018)
Walport F, Gardner L, Real E, et al., 2018, Effects of material nonlinearity on the global analysis and stability of stainless steel frames, Journal of Constructional Steel Research, ISSN: 0143-974X
In structural frames, second order effects refer to the internal forces and moments that arise as a result of deformations under load (i.e. geometrical nonlinearity). EN 1993-1-1 states that global second order effects may be neglected if the critical load factor of the frame αcris greater than or equal to 10 for an elastic analysis, or greater than or equal to 15 when a plastic global analysis is used. No specific guidance is provided in EN 1993-1-4 for the design of stainless steel frames, for which the nonlinear stress-strain behaviour of the material will result in greater deformations as the material loses its stiffness. A study of the effects of material nonlinearity on the stability of stainless steel frames is presented herein. A series of different frame geometries and loading conditions are considered. Based on the findings, proposals for the treatment of the influence of material nonlinearity on the global analysis and design of stainless steel frames are presented.
Kyvelou P, Gardner L, Nethercot D, 2018, Moment redistribution in cold-formed steel two-span overlapped purlin systems, Eighth International Conference on Thin-Walled Structures, ICTWS 2018
Walport F, Gardner L, Nethercot D, 2018, Stability of steel frames in the plastic regime, Eighth International Conference on Thin-Walled Structures, ICTWS 2018
Stylianidis P, Nethercot D, 2018, Considerations for robustness in the design of steel and composite frame structures, Structural Engineering International, Vol: 27, Pages: 263-280, ISSN: 1016-8664
The topic of progressive collapse of structures has increasingly received particular consideration over recent years, with numerous studies of various forms seeking to explore the complex mechanics of the problem and define ways of minimising its effects. Through a continuing research programme at Imperial College London, considerable advance has been made in understanding the physical features of the progressive collapse response of frame structures, identifying the role of the several different controlling parameters and compiling simplified methods for simulating particular effects. Knowledge of the subject has therefore improved to a considerable extent, that it is now possible to make quantitatively justified assessments of structural robustness by specifying the reasons why a structure might be susceptible to progressive collapse as well as to identify potential methods for enhancing performance. The present paper reviews previous developments at Imperial, evaluates information obtained from relevant experimental studies conducted by other research groups and assesses the progress made both in developing a scientific understanding of the subject and establishing improved ways of tackling the problem in practice. Several factors that should be considered in the robustness design of steel and composite frame structures are defined, and needs for further research into specific aspects of the problem are identified.
Kyvelou P, Gardner L, Nethercot D, 2018, Moment Redistribution in Cold-Formed Steel Two-Span Overlapped Purlin Systems, 8th International Conference on Thin-Walled Structures, ICTWS 2018
Kyvelou P, Gardner L, Nethercot DA, 2017, Finite element modelling of composite cold-formed steel flooring systems, Engineering Structures, Vol: 158, Pages: 28-42, ISSN: 0141-0296
The findings from a numerical investigation into the degree of composite action that may be mobilised within floor systems comprising cold-formed steel joists and wood-based particle boards are presented herein. Finite element models have been developed, simulating all the components of the examined systems, as well as the interaction between them. The models include initial geometric imperfections, the load-slip response of the fasteners employed to achieve the shear connection as well as both geometric and material nonlinearities. The developed models were first validated against 12 physical tests reported in the literature, which showed them to be capable of accurately capturing the load-deformation curves and failure modes exhibited by the tested specimens. Parametric studies were then performed to examine the influence of key parameters on the structural behaviour of these systems, including the depth and thickness of the cold-formed steel section, as well as the spacing of the employed fasteners; in total, about 100 systems have been examined. Significant benefits in terms of structural response have been identified from the presented numerical study as a result of the mobilisation of composite action; for the systems investigated, which were of typical, practical proportions, up to 140% increases in moment capacity and 40% increases in stiffness were found. The presented research reveals the substantial gains in structural performance and the influence of the key governing parameters for this novel form of composite construction.
Trahair NS, Bradford MA, Nethercot DA, et al., 2017, The Behaviour and Design of Steel Structures to EC3: Fourth Edition, ISBN: 9780415418652
The fully revised fourth edition of this successful textbook fills a void which will arise when British designers start using the European steel code EC3 instead of the current steel code BS5950. The principal feature of the forth edition is the discussion of the behaviour of steel structures and the criteria used in design according to the British version of EC3. Thus it serves to bridge the gap which too often occurs when attention is concentrated on methods of analysis and the sizing of structural components. Because emphasis is placed on the development of an understanding of behaviour, many analytical details are either omitted in favour of more descriptive explanations, or are relegated to appendices. The many worked examples both illustrate the behaviour of steel structures and exemplify details of the design process. The Behaviour and Design of Steel Structures to EC3 is a key text for senior undergraduate and graduate students, and an essential reference tool for practising structural engineers in the UK and other countries.
Kyvelou P, Gardner L, Nethercot DA, 2017, Testing and analysis of composite cold-formed steel and wood-based flooring systems, Journal of Structural Engineering, Vol: 143, ISSN: 0733-9445
An experimental study was conducted into the degree of composite action that can arise between cold-formed steel joists and wood-based flooring panels. A series of material, push-out and 4-point bending tests were carried out, and alternative means of shear connection, featuring fasteners and adhesives, were investigated. It was found that the spacing of the fasteners and the application of structural adhesive at the beam-board interface had a significant influence on the attained degree of shear connection and, hence, the moment capacity and flexural stiffness of the system. The highest degree of shear connection (up to approximately 60%) was obtained using the structural adhesive, bringing corresponding increases in capacity and stiffness of approximately 100 and 40%, respectively, over the bare steel. Smaller, but still very significant, increases in capacity and stiffness were achieved through the use of screws alone. On the basis of the results of the push-out tests, a load-slip relationship for screw fasteners in wood-based floorboards was proposed; this was designed for use in future analytical and numerical models. The findings of this research demonstrate, for the first time, the benefits that can be derived through the practical exploitation of composite action in cold-formed steel flooring systems in terms of enhanced structural performance and efficiency of material use.
Nethercot DA, 2017, Editorial: Communicating research impact, MAGAZINE OF CONCRETE RESEARCH, Vol: 69, Pages: 973-973, ISSN: 0024-9831
Kyvelou P, Gardner L, Nethercot DA, 2017, Design of composite cold-formed steel flooring systems, Structures, Vol: 12, Pages: 242-252, ISSN: 2352-0124
Recently conducted experimental and numerical investigations have shown that mobilisation of composite action within systems comprising cold-formed steel beams and wood-based floorboards is feasible and can lead to substantial improvements in structural performance. However, no design rules have yet been established for these systems in order to allow the beneficial effect of composite action to be exploited. In this paper, proposals for the design of such systems are devised and their theoretical basis is presented. At the core of the proposals is the calculation of the attained degree of partial shear connection and the shear bond coefficient for the composite members as a function of the geometric and material properties of their components and connectors. The accuracy of the devised design method for the prediction of moment capacity and flexural stiffness is demonstrated through comparisons with the results of 12 physical tests and about 80 numerical simulations reported in the literature. The proposals provide practical design rules for composite cold-formed steel floor beams, which are suitable for incorporation into future revisions of the Eurocodes.
Kyvelou P, Gardner L, Nethercot D, 2017, Design of cold-formed steel composite flooring systems with partial shear connection, 8th European Conference on Steel and Composite Structures (Eurosteel 2017), Pages: 1899-1908
Kyvelou P, Gardner L, Nethercot D, 2017, Utilising Composite Action in Light Steel Framing, 15th East Asia Pacific Conference on Structural Engineering and Construction, EASEC15
Kyvelou P, Gardner L, Nethercot D, 2016, Design of Cold-Formed Steel Composite Flooring Systems with Partial Shear Connection, 8th European Conference on Steel and Composite Structures, Eurosteel 2017
Hui C, Gardner L, Nethercot D, 2016, Moment redistribution and the design of purlin systems subjected to wind uplift loading, 7th International Conference on Coupled Instabilities in Metal Structures. CIMS.
Fisher A, Andreasson A, Chrysos A, et al., 2016, Introduction and background, HEALTH TECHNOLOGY ASSESSMENT, Vol: 20, Pages: 1-+, ISSN: 1366-5278
Stylianidis PM, Nethercot DA, Izzuddin BA, et al., 2016, Robustness assessment of frame structures using simplified beam and grillage models, Engineering Structures, Vol: 115, Pages: 78-95, ISSN: 1873-7323
Simplified analysis methods derived in previous studies are employed for studying the progressive collapse behaviour of steel and composite buildings. A regular frame building is considered and various scenarios of sudden column removal, each affecting different floor areas in terms of geometry and boundary conditions, are applied. Descriptions of the pseudo-static responses of the various constitutive beams are obtained based on both detailed representations of the nonlinear static responses and by applying a new simplified approach proposed in a separate publication. Comparisons between the results of the two methods confirm that the simplified approach is capable of describing behaviour with reasonable accuracy. By employing a simplified multi-level assessment approach that has been previously derived at Imperial College, grillage-type approximations are obtained and used to examine the floor dynamic behaviour for the various column removal cases. It is found that, although the structural response varies depending on the location of the initial damage, substantial connection strength is required in all cases in order to provide resistance to progressive collapse. In addition, for average levels of connection ductility, failure most likely occurs prior to the development of tensile catenary action in the beams, which indicates that the provision of tying resistance may not be effective in enhancing robustness. Therefore, the combined action of flexure and compressive arching in the beams is likely to form the principal collapse resisting mechanism in common practical applications, which confirms similar conclusions made in previous studies at Imperial. The provision of adequate levels of connection moment capacity – in combination with sufficient ductility supply – is, therefore, the most effective way of securing structural robustness.
Stylianidis PM, Nethercot DA, Izzuddin BA, et al., 2016, Study of the mechanics of progressive collapse with simplified beam models, Engineering Structures, Vol: 117, Pages: 287-304, ISSN: 1873-7323
Methods for assessing structural robustness need to move away from the traditional norms of prescriptive rules and become more similar to those used in conventional structural design. They should therefore be based on a sound understanding of the mechanics of the problem and provide quantitative indication of its effects. Several Codes and Design Guides consider the sudden column removal approach as their principal method for progressive collapse assessment. The level of robustness is defined based on the capability of the remaining structure for sustaining the additional loading imposed by the column loss. Most likely, the beams adjacent to the lost column and their supporting connections form the principal load paths. The present paper presents a detailed study of the response of those components under the conditions experienced following column removal. Suitable analysis approaches that have been previously developed at Imperial College London are employed to investigate the basic features of the behaviour, while several simplifications are applied for exploring particular effects. The study concludes with the development of a simplified method for simulating the nonlinear dynamic response of axially restrained and unrestrained beams following column removal. The capability of the new simplified method to accurately describe performance is demonstrated through a set of suitable applications presented in a separate publication.
Kyvelou P, Gardner L, Nethercot DA, 2016, COMPOSITE FLOORING SYSTEMS COMPRISING COLD-FORMED STEEL JOISTS AND WOOD-BASED BOARDS, 8th International Conference on Steel and Aluminium Structures (ICSAS), Publisher: UNIV HONG KONG, DEPT CIVIL ENGINEERING
Hui C, Gardner L, Nethercot DA, 2016, Moment redistribution in cold-formed steel continuous beams, Thin-Walled Structures, Vol: 98, Pages: 465-477, ISSN: 0263-8231
The external envelope of steel framed industrial buildings normally involves the use of purlins and rails spanning between the main hot-rolled frames to support the roofing/cladding. These purlins are typically light-gauge cold-formed steel members of complex shape for which the thin-walled nature of the material means that local instabilities will significantly influence their structural behaviour. Economic design should be based on failure of the system, recognising the opportunity for redistribution of moments. This paper presents the findings from a numerical investigation of the degree of moment redistribution in continuous cold-formed steel beams subjected to a downward (gravity) uniformly distributed load (UDL). Three types of nonlinear finite element analysis were validated against previously reported physical tests: (i) continuous two-span beams subjected to a UDL, (ii) single span beams subjected to a central point load producing a moment gradient and (ii) single span beams subjected to two point loads producing a central region under pure bending. The interior support moments from the continuous beam models were compared against reference moment capacities from the three-point bending models. Based on various different section sizes, covering a range of cross-sectional slenderness, full moment redistribution with no drop-off in moment at the interior support was found to be possible only for stocky sections but not for slender sections. In the case of slender sections, local and distortional buckling caused a reduction in interior support moment prior to failure of the system. Hence a design formula is proposed to estimate the post-peak reduction of interior support moment from its initial peak, and this reduced moment capacity is then used in conjunction with the full span moment to determine the load-carrying capacity of the system. Comparisons show the proposed approach to offer accurate prediction of observed system failure loads.
Stylianidis PM, Nethercot DA, 2015, Modelling of connection behaviour for progressive collapse analysis, JOURNAL OF CONSTRUCTIONAL STEEL RESEARCH, Vol: 113, Pages: 169-184, ISSN: 0143-974X
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Stylianidis PM, Nethercot DA, Izzuddin BA, et al., 2015, Modelling of beam response for progressive collapse analysis, Structures, Vol: 3, Pages: 137-152, ISSN: 2352-0124
A fundamental aspect of the progressive collapse behaviour of building structures is the response of axially restrained beams following partial or total loss of the load bearing capacity of a supporting member. Owing to the various complex effects involved such as material and geometric nonlinearity, advanced numerical approaches tend to be the most effective tools for modelling performance. Such approaches, however, lack the simplicity needed for common use and may provide only limited capability for understanding structural behaviour. For such purposes, more limited analysis approaches that can address adequately the basic features of performance are likely to be more productive. One such method for modelling the response of axially restrained steel and composite beams following column loss is presented in this paper. The method involves explicit modelling of the connection behaviour and employs conventional structural analysis principles to describe beam performance using accessible spreadsheet calculations. Following careful verification against detailed numerical analyses and validation against available experimental results, the proposed method is deemed capable of modelling the various complex features of response with excellent accuracy. Therefore, it may form a promising advance in studying and understanding the basic mechanics of the problem.
Qu X, Chen Z, Nethercot DA, et al., 2015, Push-out tests and bond strength of rectangular CFST columns, Steel and Composite Structures, Vol: 19, Pages: 21-41, ISSN: 1229-9367
Push-out tests have been conducted on 18 rectangular concrete-filled steel tubular (CFST) columns with the aim of studying the bond behaviour between the steel tube and the concrete infill. The obtained load-slip response and the distribution of the interface bond stress along the member length and around the cross-section for various load levels, as derived from measured axial strain gradients in the steel tube, are reported. Concrete compressive strength, interface length, cross-sectional dimensions and different interface conditions were varied to assess their effect on the ultimate bond stress. The test results indicate that lubricating the steel-concrete interface always had a significant adverse effect on the interface bond strength. Among the other variables considered, concrete compressive strength and cross-section size were found to have a pronounced effect on the bond strength of non-lubricated specimens for the range of cross-section geometries considered, which is not reflected in the European structural design code for composite structures, EN 1994-1-1 (2004). Finally, based on nonlinear regression of the test data generated in the present study, supplemented by additional data obtained from the literature, an empirical equation has been proposed for predicting the average ultimate bond strength for SHS and RHS filled with normal strength concrete.
Kyvelou P, Gardner L, Nethercot DA, 2015, Composite Action Between Cold-Formed Steel Beams and Wood-Based Floorboards, International Journal of Structural Stability and Dynamics, Vol: 15, ISSN: 1793-6764
An experimental investigation has been conducted into the degree of shear interaction between cold-formed steel floor joists and wood-based flooring panels and the resulting benefits derived in terms of composite action. A series of four-point bending tests have been carried out to evaluate the overall system behavior, while material tests have been performed to accurately define the material properties of each component of the examined system. Two different shear transfer mechanisms were examined: self-drilling screws with varying spacing and structural adhesive. The bare system was also tested to provide a reference response, against which the stiffness and capacity of the composite system could be bench-marked. The experiments showed that significant benefit could be derived as a result of composite action with as much as a 100% increase in bending capacity and 42% increase in stiffness.
Stylianidis PM, Nethercot DA, Izzuddin BA, et al., 2015, Modelling of beam response for progressive collapse analysis, Structures, Vol: 3, Pages: 137-152, ISSN: 2352-0124
A fundamental aspect of the progressive collapse behaviour of building structures is the response of axially restrained beams following partial or total loss of the load bearing capacity of a supporting member. Owing to the various complex effects involved such as material and geometric nonlinearity, advanced numerical approaches tend to be the most effective tools for modelling performance. Such approaches, however, lack the simplicity needed for common use and may provide only limited capability for understanding structural behaviour. For such purposes, more limited analysis approaches that can address adequately the basic features of performance are likely to be more productive. One such method for modelling the response of axially restrained steel and composite beams following column loss is presented in this paper. The method involves explicit modelling of the connection behaviour and employs conventional structural analysis principles to describe beam performance using accessible spreadsheet calculations. Following careful verification against detailed numerical analyses and validation against available experimental results, the proposed method is deemed capable of modelling the various complex features of response with excellent accuracy. Therefore, it may form a promising advance in studying and understanding the basic mechanics of the problem.
Nethercot D, Kyvelou P, Hui C, et al., 2015, The changing basis for the design of cold-formed steel purlin systems, Eighth International Conference on Advances in Steel Structures (ICASS)
Kyvelou P, Gardner L, Nethercot DA, 2015, Composite action between cold-formed steel beams and wood-based floorboards, Eighth International Conference on Advances in Steel Structures (ICASS)
Nethercot DA, 2014, Developing and adopting the structural Eurocodes, PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-STRUCTURES AND BUILDINGS, Vol: 167, Pages: 265-273, ISSN: 0965-0911
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- Citations: 1
Vidalis CA, Nethercot DA, 2014, Redesigning composite frames for progressive collapse, PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-STRUCTURES AND BUILDINGS, Vol: 167, Pages: 153-177, ISSN: 0965-0911
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- Citations: 5
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