Ioannis Vayas - Academia.edu (original) (raw)

Papers by Ioannis Vayas

Design of Steel Structures to Eurocodes, 2018

The chapter presents the structural elements of steel multi storey buildings, such as columns, ma... more The chapter presents the structural elements of steel multi storey buildings, such as columns, main and secondary beams or concrete slabs. For these elements various cross-section types, both pure steel or composite steel-reinforced concrete, are shown and alternative options commented, presenting the advantages and characteristics of each one. Information is included in respect to the serviceability requirements, the behavior under fire conditions and the methods of construction.

Design of Steel Structures to Eurocodes, 2018

This chapter presents the main structural elements of single storey buildings, whether industrial... more This chapter presents the main structural elements of single storey buildings, whether industrial, commercial, serving for sports activities or other use. Several structural solutions are proposed, with their advantages and disadvantages, with emphasis on the most usual ones. Reference is made to both the main and the secondary structural elements. Hot rolled, welded or cold-formed elements are described as well as cladding panels. Several types of bracing systems are also presented, such as vertical bracings, providing lateral stability to the building, wind bracings on roofs or using the panels of the skin as stability elements. Special attention is given to buildings in seismic areas, where enhanced requirements are to be met in respect to strength and ductility.

Proceedings of the 4th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2013), 2014

Journal of Constructional Steel Research, 1995

Reference : FP6 PROHITECH project: Volume 6: Seismic protection of historical buildings: applicat... more Reference : FP6 PROHITECH project: Volume 6: Seismic protection of historical buildings: application... ... Books : Book published as author, translator, etc. ... Jaspart, Jean-Pierre mailto [Université de Liège - ULg > Département Argenco : Secteur MS2F > Adéquat. struct. aux exig. de fonct.& perfor. techn.-écon. >] ... There is no file associated with this reference. ... All documents in ORBi are protected by a user license.

Engineering Structures, Sep 1, 2022

The risk and losses associated with the wind-induced failure of existing steel lattice telecommun... more The risk and losses associated with the wind-induced failure of existing steel lattice telecommunication towers are assessed for a number of upgrade/replace/redesign schemes. Specifically, a performance-based wind engineering framework is employed for assessing a typical tower topology used by EU telecommunication network operators over four different cases: a conventional design, its corroded version after 60 years, a strengthened version of the corroded tower by applying fibre-reinforced polymer plates, and a redesign with high-strength steel. Multiple potential sites of installation were considered throughout coastal and mainland Greece, comprising two different groups of design wind speed. Mischaracterization of the site-specific wind distribution is by far the most important risk factor, with corrosion coming right behind. Still, selecting a rehabilitation approach does not depend only on site and tower characteristics, but also on the projected direct and indirect losses. By considering service to different populations, even after 60 years of corrosion, the "Do Nothing" approach may still be competitive when serving few residents and for short projected lifetime, while an upgrade is considered optimal for larger towns, or wherever higher revenue is on the line.

Polyurethane sandwich panels are factory made, self-supporting structural elements that are used ... more Polyurethane sandwich panels are factory made, self-supporting structural elements that are used for roofs and roof cladding, external walls and wall cladding and walls (including partitions). As new profile-shapes of panels are developed, the determination of their mechanical properties is necessary. A series of experiments was performed in the Laboratory of Steel Structures at NTUA, following the provisions of EN 14509. The test specimens, produced by the company ISOBAU, were of trapezoidal as well as of waved profile. Additionally, evaluation of the experimental results was implemented with the use of a numerical model and design tables were conducted for practical applications.

Modelling, Nov 3, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Bulletin of Earthquake Engineering, Feb 8, 2020

A pre-normative assessment is presented for the q-factor of the FUSEIS pin-link steel lateral loa... more A pre-normative assessment is presented for the q-factor of the FUSEIS pin-link steel lateral load resisting system for use in low/mid-rise buildings, within Eurocode 8. It is achieved by using the INNOSEIS methodology, a performance based methodological procedure to define behaviour factors for innovative systems. Applying this methodology, consistent behaviour factors can be obtained based on the definition of a set of structures to represent each class of buildings, with the use of nonlinear static and dynamic analysis methods and the incorporation of the effect of aleatory and epistemic uncertainty on the actual systems' performance, to reach a uniform level of safety across the entire building population.

In the frame of the INNOSEIS research project, which is funded by RFCS, information documents for... more In the frame of the INNOSEIS research project, which is funded by RFCS, information documents for INERD-pin and FUSEIS-pin links have been produced by NTUA for dissemination to all partners of the construction sector such as architects, structural engineers, construction companies, steel producers and all potential decision makers of the construction sector. For each of the two systems, an approximately 40-page information brochure has been drafted in English. They contain a description of the main features of the system, overall dimensions, preferred structural materials, range of sizes, member shapes, typical cross sections and limitations, possible arrangements for conceptual design, recommended structural details etc. and indicative application examples of selected building structures. In addition, information is given regarding the non-linear force-deformation characteristics and ductility/strength capacities of the systems, the hysteretic behavior of elements under cyclic loading, including rules for stiffness and strength degradation. Finally, pre-normative q-factors are proposed and reference is made to application examples in design practice, previous publications and literature. Case studies on the seismic design of steel buildings incorporating the systems are presented. FUSEIS pin links have been applied on a 2-storey and on a 4-storey office steel building while INERD pin connections have been applied in an existing 6-storey commercial reinforced concrete building. Each case study refers to the conceptual design, loads and load combinations, modelling, analysis, detailed design and structural detailing. Design follows the provisions of the Eurocodes and the pre-normative guidelines that were developed within the project. The existing building was designed according to an outdated national seismic code. It does not comply with the requirements of EN 1998-1, hence the need for upgrading.

The Conventional buckling restrained braces used in concentrically braced frames are expected to ... more The Conventional buckling restrained braces used in concentrically braced frames are expected to yield in both tension and compression without major degradation of capacity under severe seismic ground motions. One of the weakness points of a standard buckling restrained braced frame is the low post-yield stiffness and thus large residual deformation under moderate to severe ground motions. This phenomenon can be related to the low post-yield stiffness of the core segment in comparison to its elastic stiffness. This paper investigates the application of stainless steel as the core material in a hybrid buckling restrained brace. The "hybrid" term arises from the use of more than one core component with different steel materials, including high strength high-performance steel and stainless steel (304L) with high strain hardening in the core of buckling restrained brace. Nonlinear dynamic time history analyses were conducted on a variety of diagonally braced frames with different heights, in order to compare the seismic performance of standard (non-hybrid) and hybrid buckling restrained braced frames. The results showed that the proposed hybrid buckling restrained braces reduce the inter-story and specially the residual drift demands in buckling restrained braced frames.

ce/papers, Sep 1, 2017

Three large scale tests on two-story Moment Resistant Frames (MRF) under cyclic loading were cond... more Three large scale tests on two-story Moment Resistant Frames (MRF) under cyclic loading were conducted in the Laboratory of Steel Structures of NTUA in the frame of the RFCS-supported project MATCH. Selected joints of the frames were formed with Reduced Beam Sections (RBS), in order to achieve plastic hinge formation away from the welded connections and the heat affected zones. In addition, holes were drilled in the flanges in order to study the crack initiation and crack propagation under large plastic deformations. The experimental setup consisted of a rigid test rig frame providing horizontal support to the hydraulic actuator, a base girder on which rested the test frame and a supporting frame, which prevented the out-of-plane movement of the test frames. The base girder was attached to the test rig so that no net horizontal force was transferred to the ground. The experimental setup was anchored to the Laboratory's strong floor. The test frames were simply supported on the base girder. The test frames were designed with weak beams and strong columns. The beam-to-column joints were realized with all-around fillet welds. In the two-bay frames the beams of a selected joint were designed with RBS near the connection regions while the rest of the connection regions were locally reinforced with stiffeners and beam haunches in order to ensure plastic deformation would occur in the selected joint. In the one-bay frame all beams were designed with RBS sections towards the joints. The distance of the RBS sections from the column faces as well as the geometry of the flange reduction was specified in accordance with the provisions of EN 1998-3. The tests were performed under displacement control using a computer controlled hydraulic actuator. A cyclic load of increasing amplitude was applied according to ECCS provisions while the maximum interstory drift reached was approximately 5%. The actuator's force was applied through a vertical spread beam, which ensured that the load was applied in an inverted triangular pattern, in accordance with the anticipated seismic forces. In the present paper, the design of the test specimens and the experimental setup is described in detail, and the preparation and results of the experimental investigations are presented.

ce/papers, Sep 1, 2017

ABSTRACTAngle sections are commonly used in many Civil Engineering applications and especially in... more ABSTRACTAngle sections are commonly used in many Civil Engineering applications and especially in lattice towers for telecommunication purposes. Nevertheless, due to their geometrical characteristics, design expressions, as for example those included in EN1993‐1‐1 or EN 1993‐3‐1, do not apply for cross sections or members composed of angle sections. Although a number of numerical investigations for cross section strength and member stability and proposals for relevant design expressions exist, only limited experimental investigations on members from angle sections, mostly on cold‐formed ones, can be found in literature.In the current paper a test campaign on members from equal leg hot rolled angle sections that has been carried out at the Institute of Steel Structures of the National Technical University of Athens (NTUA) is presented. Tests included eight 3‐point bending tests and thirty‐one buckling tests on columns subjected to concentric and eccentric compression. The aim of the research is to use the experimental data for calibration of numerical models, the investigation of possible inelastic reserves for angles that were detected in analytical models and as reference for the development of new design expressions oriented towards angle sections only.

Design of Steel Structures to Eurocodes, 2018

The chapter presents the structural elements of steel multi storey buildings, such as columns, ma... more The chapter presents the structural elements of steel multi storey buildings, such as columns, main and secondary beams or concrete slabs. For these elements various cross-section types, both pure steel or composite steel-reinforced concrete, are shown and alternative options commented, presenting the advantages and characteristics of each one. Information is included in respect to the serviceability requirements, the behavior under fire conditions and the methods of construction.

Design of Steel Structures to Eurocodes, 2018

This chapter presents the main structural elements of single storey buildings, whether industrial... more This chapter presents the main structural elements of single storey buildings, whether industrial, commercial, serving for sports activities or other use. Several structural solutions are proposed, with their advantages and disadvantages, with emphasis on the most usual ones. Reference is made to both the main and the secondary structural elements. Hot rolled, welded or cold-formed elements are described as well as cladding panels. Several types of bracing systems are also presented, such as vertical bracings, providing lateral stability to the building, wind bracings on roofs or using the panels of the skin as stability elements. Special attention is given to buildings in seismic areas, where enhanced requirements are to be met in respect to strength and ductility.

Proceedings of the 4th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2013), 2014

Journal of Constructional Steel Research, 1995

Reference : FP6 PROHITECH project: Volume 6: Seismic protection of historical buildings: applicat... more Reference : FP6 PROHITECH project: Volume 6: Seismic protection of historical buildings: application... ... Books : Book published as author, translator, etc. ... Jaspart, Jean-Pierre mailto [Université de Liège - ULg > Département Argenco : Secteur MS2F > Adéquat. struct. aux exig. de fonct.& perfor. techn.-écon. >] ... There is no file associated with this reference. ... All documents in ORBi are protected by a user license.

Engineering Structures, Sep 1, 2022

The risk and losses associated with the wind-induced failure of existing steel lattice telecommun... more The risk and losses associated with the wind-induced failure of existing steel lattice telecommunication towers are assessed for a number of upgrade/replace/redesign schemes. Specifically, a performance-based wind engineering framework is employed for assessing a typical tower topology used by EU telecommunication network operators over four different cases: a conventional design, its corroded version after 60 years, a strengthened version of the corroded tower by applying fibre-reinforced polymer plates, and a redesign with high-strength steel. Multiple potential sites of installation were considered throughout coastal and mainland Greece, comprising two different groups of design wind speed. Mischaracterization of the site-specific wind distribution is by far the most important risk factor, with corrosion coming right behind. Still, selecting a rehabilitation approach does not depend only on site and tower characteristics, but also on the projected direct and indirect losses. By considering service to different populations, even after 60 years of corrosion, the "Do Nothing" approach may still be competitive when serving few residents and for short projected lifetime, while an upgrade is considered optimal for larger towns, or wherever higher revenue is on the line.

Polyurethane sandwich panels are factory made, self-supporting structural elements that are used ... more Polyurethane sandwich panels are factory made, self-supporting structural elements that are used for roofs and roof cladding, external walls and wall cladding and walls (including partitions). As new profile-shapes of panels are developed, the determination of their mechanical properties is necessary. A series of experiments was performed in the Laboratory of Steel Structures at NTUA, following the provisions of EN 14509. The test specimens, produced by the company ISOBAU, were of trapezoidal as well as of waved profile. Additionally, evaluation of the experimental results was implemented with the use of a numerical model and design tables were conducted for practical applications.

Modelling, Nov 3, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Bulletin of Earthquake Engineering, Feb 8, 2020

A pre-normative assessment is presented for the q-factor of the FUSEIS pin-link steel lateral loa... more A pre-normative assessment is presented for the q-factor of the FUSEIS pin-link steel lateral load resisting system for use in low/mid-rise buildings, within Eurocode 8. It is achieved by using the INNOSEIS methodology, a performance based methodological procedure to define behaviour factors for innovative systems. Applying this methodology, consistent behaviour factors can be obtained based on the definition of a set of structures to represent each class of buildings, with the use of nonlinear static and dynamic analysis methods and the incorporation of the effect of aleatory and epistemic uncertainty on the actual systems' performance, to reach a uniform level of safety across the entire building population.

In the frame of the INNOSEIS research project, which is funded by RFCS, information documents for... more In the frame of the INNOSEIS research project, which is funded by RFCS, information documents for INERD-pin and FUSEIS-pin links have been produced by NTUA for dissemination to all partners of the construction sector such as architects, structural engineers, construction companies, steel producers and all potential decision makers of the construction sector. For each of the two systems, an approximately 40-page information brochure has been drafted in English. They contain a description of the main features of the system, overall dimensions, preferred structural materials, range of sizes, member shapes, typical cross sections and limitations, possible arrangements for conceptual design, recommended structural details etc. and indicative application examples of selected building structures. In addition, information is given regarding the non-linear force-deformation characteristics and ductility/strength capacities of the systems, the hysteretic behavior of elements under cyclic loading, including rules for stiffness and strength degradation. Finally, pre-normative q-factors are proposed and reference is made to application examples in design practice, previous publications and literature. Case studies on the seismic design of steel buildings incorporating the systems are presented. FUSEIS pin links have been applied on a 2-storey and on a 4-storey office steel building while INERD pin connections have been applied in an existing 6-storey commercial reinforced concrete building. Each case study refers to the conceptual design, loads and load combinations, modelling, analysis, detailed design and structural detailing. Design follows the provisions of the Eurocodes and the pre-normative guidelines that were developed within the project. The existing building was designed according to an outdated national seismic code. It does not comply with the requirements of EN 1998-1, hence the need for upgrading.

The Conventional buckling restrained braces used in concentrically braced frames are expected to ... more The Conventional buckling restrained braces used in concentrically braced frames are expected to yield in both tension and compression without major degradation of capacity under severe seismic ground motions. One of the weakness points of a standard buckling restrained braced frame is the low post-yield stiffness and thus large residual deformation under moderate to severe ground motions. This phenomenon can be related to the low post-yield stiffness of the core segment in comparison to its elastic stiffness. This paper investigates the application of stainless steel as the core material in a hybrid buckling restrained brace. The "hybrid" term arises from the use of more than one core component with different steel materials, including high strength high-performance steel and stainless steel (304L) with high strain hardening in the core of buckling restrained brace. Nonlinear dynamic time history analyses were conducted on a variety of diagonally braced frames with different heights, in order to compare the seismic performance of standard (non-hybrid) and hybrid buckling restrained braced frames. The results showed that the proposed hybrid buckling restrained braces reduce the inter-story and specially the residual drift demands in buckling restrained braced frames.

ce/papers, Sep 1, 2017

Three large scale tests on two-story Moment Resistant Frames (MRF) under cyclic loading were cond... more Three large scale tests on two-story Moment Resistant Frames (MRF) under cyclic loading were conducted in the Laboratory of Steel Structures of NTUA in the frame of the RFCS-supported project MATCH. Selected joints of the frames were formed with Reduced Beam Sections (RBS), in order to achieve plastic hinge formation away from the welded connections and the heat affected zones. In addition, holes were drilled in the flanges in order to study the crack initiation and crack propagation under large plastic deformations. The experimental setup consisted of a rigid test rig frame providing horizontal support to the hydraulic actuator, a base girder on which rested the test frame and a supporting frame, which prevented the out-of-plane movement of the test frames. The base girder was attached to the test rig so that no net horizontal force was transferred to the ground. The experimental setup was anchored to the Laboratory's strong floor. The test frames were simply supported on the base girder. The test frames were designed with weak beams and strong columns. The beam-to-column joints were realized with all-around fillet welds. In the two-bay frames the beams of a selected joint were designed with RBS near the connection regions while the rest of the connection regions were locally reinforced with stiffeners and beam haunches in order to ensure plastic deformation would occur in the selected joint. In the one-bay frame all beams were designed with RBS sections towards the joints. The distance of the RBS sections from the column faces as well as the geometry of the flange reduction was specified in accordance with the provisions of EN 1998-3. The tests were performed under displacement control using a computer controlled hydraulic actuator. A cyclic load of increasing amplitude was applied according to ECCS provisions while the maximum interstory drift reached was approximately 5%. The actuator's force was applied through a vertical spread beam, which ensured that the load was applied in an inverted triangular pattern, in accordance with the anticipated seismic forces. In the present paper, the design of the test specimens and the experimental setup is described in detail, and the preparation and results of the experimental investigations are presented.

ce/papers, Sep 1, 2017

ABSTRACTAngle sections are commonly used in many Civil Engineering applications and especially in... more ABSTRACTAngle sections are commonly used in many Civil Engineering applications and especially in lattice towers for telecommunication purposes. Nevertheless, due to their geometrical characteristics, design expressions, as for example those included in EN1993‐1‐1 or EN 1993‐3‐1, do not apply for cross sections or members composed of angle sections. Although a number of numerical investigations for cross section strength and member stability and proposals for relevant design expressions exist, only limited experimental investigations on members from angle sections, mostly on cold‐formed ones, can be found in literature.In the current paper a test campaign on members from equal leg hot rolled angle sections that has been carried out at the Institute of Steel Structures of the National Technical University of Athens (NTUA) is presented. Tests included eight 3‐point bending tests and thirty‐one buckling tests on columns subjected to concentric and eccentric compression. The aim of the research is to use the experimental data for calibration of numerical models, the investigation of possible inelastic reserves for angles that were detected in analytical models and as reference for the development of new design expressions oriented towards angle sections only.