Imperial College London

Dr Nicolas Hadjipantelis

Faculty of EngineeringDepartment of Civil and Environmental Engineering

Research Associate
 
 
 
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Contact

 

+44 (0)7842 428 887n.hadjipantelis15

 
 
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Location

 

429Skempton BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

9 results found

Wadee MA, Hadjipantelis N, Bazzano JB, Gardner L, Lozano-Galant JAet al., 2020, Stability of steel struts with externally anchored prestressed cables, Journal of Constructional Steel Research, Vol: 164, ISSN: 0143-974X

Externally anchored prestressed cables can be employed to enhance the stability of steeltruss compression elements significantly. To demonstrate this concept, a system comprisinga tubular strut subjected to an external compressive load and a prestressed cable anchoredindependently of the strut is studied. Energy methods are utilized to define the elasticstability of the perfect and imperfect systems, after which the first yield and rigid–plasticresponses are explored. The influence of the key controlling parameters, including thelength of the strut, the axial stiffness of the cable and the initial prestressing force, on theelastic stability, the inelastic response and the ultimate strength of the system is demon-strated using analytical and finite element (FE) models. To illustrate the application of thestudied structural concept, FE modelling is employed to simulate the structural response ofa prestressed hangar roof truss. A nearly two-fold enhancement in the load-carrying capac-ity of the truss structure is shown to be achieved owing to the addition of the prestressedcable

Journal article

Hadjipantelis N, Gardner L, Wadee MA, 2019, Finite-element modeling of prestressed cold-formed steel beams, Journal of Structural Engineering, Vol: 145, Pages: 04019100-1-04019100-19, ISSN: 0733-9445

The concept and structural benefits of prestressing cold-formed steel beams are explored in the present paper. In the proposed system, prestressing is applied by means of a high-strength steel cable located within the cross section of the beam at an eccentric location with respect to the strong geometric axis. The internal forces generated by the prestressing are opposite in sign to those induced under subsequent vertical loading. Hence, the development of detrimental compressive stresses within the top region of the cold-formed steel beam is delayed and thus the load-carrying capacity of the beam is enhanced. Owing to the precamber that is induced along the member during the prestressing stage, the overall deflections of the beam are also reduced significantly. In the present paper, finite-element (FE) modeling was employed to simulate the mechanical behavior of prestressed cold-formed steel beams during the prestressing and vertical loading stages. Following the validation of the FE modeling approach, a set of parametric studies was conducted, where the influence of the key controlling parameters on the structural benefits obtained from the prestressing process was investigated. The parametric results were utilized to determine how the benefits obtained from the addition of the prestressed cable can be maximized, demonstrating the significant enhancements in the performance of the cold-formed steel beam that can be achieved.

Journal article

Hadjipantelis N, Gardner L, Wadee MA, 2019, Design of prestressed cold-formed steel beams, Thin-Walled Structures, Vol: 140, Pages: 565-578, ISSN: 0263-8231

Structural design rules for prestressed cold-formed steel beams, considering both the prestressing and imposed vertical loading stages, are presented herein. In the proposed approach, the cold-formed steel member is designed as a beam-column using linear interaction equations in conjunction with the Direct Strength Method (DSM), while the prestressed cable is designed by ensuring that its tensile capacity is not violated during the two loading stages. In the present paper, the design approach and the failure criteria, which define the permissible design zone for the prestressed system, are first introduced. The suitability of the design recommendations is then assessed by comparing a set of parametric finite element (FE) results for several combinations of prestress levels, beam geometries and cable sizes, with the corresponding design predictions. Finally, following reliability analysis, the implementation of the design recommendations is illustrated through a practical worked example.

Journal article

Hadjipantelis N, Kyvelou P, Gardner L, Wadee Met al., Numerical modelling of prestressed composite cold-formed steel flooring systems, Seventh International Conference in Structural Engineering, Mechanics and Computation, Publisher: CRC Press

A novel and highly-efficient prestressed composite flooring system comprising cold-formed steel joists and wood-based floorboards is introduced herein. The prestressing is applied by means of a high-strength steel cable housed within the bottom hollow flange of the steel joist, while the composite action is mobilised by making simple alterations to the currently employed fastening arrangements between the joist and the board. Geometrically and materially nonlinear finite element models with initial geometric imperfections have been developed to simulate the behaviour of the proposed system during the prestressing and vertical loading stages. The structural performance of the prestressed system is compared with that of conventional non-prestressed systems, demonstrating that substantial benefits can be achieved both in terms of load-carrying capacity and serviceability performance. Subsequently, a parametric study is conducted to investigate the effect of the steel section thickness on the ultimate moment capacity and bending stiffness of the system.

Conference paper

Hadjipantelis N, 2019, Prestressed cold-formed steel beams

Thesis dissertation

Hadjipantelis N, Gardner L, Wadee MA, 2018, Prestressed cold-formed steel beams – parametric studies and design recommendations, Hong Kong, China, Ninth International Conference on Advances in Steel Structures, Publisher: Hong Kong Institute of Steel Construction Limited

Owing to their enhanced load-carrying and serviceability performances, prestressed coldformed steel beams can potentially open up new applications within the construction industry. In theproposed concept, an eccentric prestressing force is applied to cold-formed steel beams by means of acable that is housed within a bottom hollow flange. During prestressing, tensile stresses are inducedwithin the top region of the beam, thus delaying the occurrence of local instabilities under subsequentvertical loading. Consequently, the moment capacity of the beam is enhanced. Furthermore, owing tothe prestressing, a pre-camber is also induced along the member, thus decreasing the overall verticaldeflections significantly. Following discussion of the mechanical behaviour of the proposed beams,design recommendations are developed by employing interaction equations alongside the DirectStrength Method. Subsequently, finite element (FE) analysis is employed to investigate the effects of theprestress level and the section slenderness of the steel beam on the benefits obtained from theprestressing process. The parametric FE results are then utilised to assess the design recommendations.

Conference paper

Hadjipantelis N, Gardner L, Wadee MA, 2018, Prestressed cold-formed steel beams: concept and mechanical behaviour, Engineering Structures, Vol: 172, Pages: 1057-1072, ISSN: 0141-0296

An innovative concept, whereby the load-carrying capacity and serviceability performance of cold-formed steel beams are enhanced by utilising prestressing techniques, is presented. The prestressing force is applied by means of a high-strength steel cable, which is housed at a location eccentric to the strong geometric axis within the bottom hollow flange of the cold-formed steel beam, inducing initial stresses in the beam that are opposite in sign to those introduced during the subsequent loading stage. As a consequence, the development of local instabilities during loading is delayed and thus the capacity of the beam is enhanced. Furthermore, the pre-camber induced during prestressing, as well as the contribution of the cable to the bending stiffness of the system, decrease the overall vertical deflections of the beam. The conceptual development of prestressed cold-formed steel beams and a study investigating the potential benefits are presented. The mechanical behaviour of the proposed beams in both the prestressing and imposed loading stages is described in terms of analytical expressions, while failure criteria for the design of the cold-formed steel beam and the cable are also developed by employing interaction equations in conjunction with the Direct Strength Method. Geometrically and materially nonlinear finite element analysis with imperfections is employed to simulate the behaviour of the proposed beams. Sample numerical results are presented and compared with the developed analytical expressions and failure criteria, demonstrating the substantial enhancement in moment capacity and serviceability performance offered by these beams.

Journal article

Hadjipantelis N, Gardner L, Wadee MA, 2018, Prestressed cold-formed steel beams - conceptual development, Lisbon, Eight International Conference on Thin-Walled Structures

Conference paper

Hadjipantelis N, Prestressed cold-formed steel beams, Twentieth Young Researchers’ Conference of the Institution of Structural Engineers

Conference paper

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