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PEOPLE@HES-SO – Directory and Skills inventory

PEOPLE@HES-SO
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Chira Alexandru

Chira Alexandru

Wissenschaftlicher Adjunkt FH

Main skills

FEM Analysis

Textile Reinforced Concrete

Nonlinear Analysis of Structures

Retrofitting of structures

Cold Formed Steel Structures

Nonlinear Dynamic Analysis

Composite structures

  • Contact

  • Research

  • Publications

  • Conferences

Main contract

Wissenschaftlicher Adjunkt FH

Desktop: HEIA_B40.04

Haute école d'ingénierie et d'architecture de Fribourg
Boulevard de Pérolles 80, 1700 Fribourg, CH
HEIA-FR

Complete research profile 

https://www.researchgate.net/profile/Chira-Alexandru

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Completed

Verstärken von Fahrbahnplatten mit Textilbeton
AGP

Role: Collaborator

Financement: OFROU; FR - EIA - Institut iTEC; FR - EIA - Institut iTEC

Description du projet : Das Projekt arbeitet den Kenntnisstand zu Verstärkungen von Betonbauteilen mit Textilbeton gezielt für Kunstbauten auf - gegliedert nach Bauteil und hauptsächlicher Beanspruchungsart - und stellt den Projektverantwortlichen damit Bemessungsgrundlagen zur Verfügung. Die Einpassung dieser relativ neuen Verstärkungsmethode in Schweizer Gepflogenheiten und Regelwerke bei der Tragwerksanalyse und Bemessung werden aufgezeigt. Kenntnislücken für die spezifische Anwendung von Textilbetonverstärkungen auf Betonbauteile von Kunstbauten werden indentifiziert und allenfällige weitere Forschungsbedürfnisse formuliert.

Research team within HES-SO: Maeder Marco , Zwicky Daia , Muresan Alex-Manuel , Chira Alexandru

Durée du projet: 01.01.2017 - 31.08.2021

Montant global du projet: 139'212 CHF

Statut: Completed

Innovative 3D joints for robust and economic hybrid tubular construction

Role: Collaborator

Requérant(e)s: Luis Simoes da Silva, UNIVERSIDADE DE COIMBRA

Financement: Research Fund for Coal and Steel

Description du projet :

(Visiting Researcher)

The main goal of INNO3DJOINTS is to develop innovative plug-and-play joints for hybrid tubular construction, whereby
tubular columns are combined with cold-formed lightweight steel profiles to provide a highly efficient structural system.

Research team within HES-SO: Chira Alexandru

Partenaires académiques: Luis Simoes da Silva, UNIVERSIDADE DE COIMBRA

Durée du projet: 01.02.2018 - 01.04.2018

Statut: Completed

Sustainable structures with textile reinforced concrete

Role: Main Applicant

Financement: Technical University of Cluj-Napoca

Description du projet :

The development of structural elements made of ultra-high-performance-concrete and textile reinforcement. 

Research team within HES-SO: Chira Alexandru

Partenaires académiques: Technical University of Cluj-Napoca

Durée du projet: 22.10.2015 - 30.09.2016

Statut: Completed

Utilisation of ultra high performance silicate composites in facade panels for sustainable buildings

Role: Partner

Requérant(e)s: Petr Hajek, Czech Technical University in Prague

Financement: Czech Technical University in Prague - University Center for Energy Efficient Buildings (UCEEB)

Description du projet :

The aim of this research project was to optimize high-performance silicate composites based on locally available materials and non-conventional reinforcement (textile and fiber reinforcement) for highly efficient applications in integrated façade panels for energy-efficient buildings. The focus was on the utilization of ultra-high-performance concrete (UHPC) in combination with different types of fibers and/or textile 2D or 3D reinforcement. An important part of the research was the fixing system of subtle façade elements to the frame structure. The work focused on experimental and analytical investigation and numerical simulation. The project covered  (i) laboratory work on composite mix and its composition with textile and fiber reinforcement, (ii) verification of mechanical and other physical properties by testing, (iii) development of nonlinear FEM model for parametrical simulation and optimization, (iv) full-scale testing of facade elements.

Research team within HES-SO: Chira Alexandru

Partenaires académiques: Petr Hajek, Czech Technical University in Prague

Durée du projet: 01.11.2013 - 01.10.2015

Statut: Completed

2024

Constitutive modelling of deformation rate dependent response of steel timber shear connections
Scientific paper ArODES

Dan V. Bompa, Alexandru Chira, Daia Zwicky

Journal of Building Engineering,  To be published, 111159

Link to the publication

Summary:

This paper presents experimental and numerical investigations into the deformation rate-dependent constitutive response of steel-timber shear connections with screws. After describing the test specimens and experimental arrangement, a detailed account of the complete deformation response and main mechanical parameters of the tested shear connections under three applied displacement rate levels are given. Specimens with small screw diameters had a relatively brittle response, failing shortly after yielding, whilst those with higher diameters showed ductile failure modes, with plastic hinges forming in the screws and concurrent extensive timber crushing. It was observed that the stiffness increases with the deformation rate due to the viscoelastic response of wood materials, whilst the peak load is largely constant. Nonlinear finite element simulations were carried out to validate the main numerical parameters for steel, timber, and interaction characteristics. After gaining confidence in the ability of the numerical models to predict closely the stiffness and peak load, numerical investigations were carried out to examine the influence of key material and geometric parameters on the stiffness, load resistance and deformation response. The studies showed that higher timber strength increases the initial stiffness and the peak load, while higher screw grades improved both stiffness and strength. Based on the results and observations, code-modified expressions for evaluating the stiffness and load resistance, as a function of the deformation rate, are proposed within the ranges considered, and validated against a collated database. Comparative assessments with existing literature indicate that the proposed equations provide improved estimates. Suggested closed-form relationships enable the characterisation of the full constitutive response of steel-timber shear connections, that can be adopted for discrete nonlinear modelling of connectors.

2023

Load-deformation response of long span prestressed concrete wide beams
Scientific paper ArODES

Alexandru Chira, Attila Puskás, Dan Bompa

Journal of Building Engineering,  65, 105631

Link to the publication

Summary:

This paper examines the full deformational response of prestressed wide beams. The results from full-scale prestressed wide beam tests are used to validate the nonlinear numerical modelling procedures adopted in this paper. Three-dimensional modelling with detailed representation of the prestressing action is used to evaluate the response including strain distributions within the member. Simplified sectional models are also validated against the tests and detailed modelling, and are further used for an extensive parametric investigation. The parameters examined in the study include the section size, amount of non-prestressed and prestressed reinforcement, concrete strengths, and member spans. The numerical results enabled a direct assessment of the full behaviour including the forces and deflections at initial camber, cracking and ultimate state. It is shown that modelling approaches were able to predict well the overall deformation and failure modes, with the three-dimensional approach giving a more detailed insight into the internal strain distributions. Parametric studies showed that the reinforcement ratio has the greatest influence on the overall behaviour, governing the post-cracking response, compared with other parameters varied. Based on the findings, design-oriented expressions are proposed to evaluate the cracked stiffness and ultimate state deflection of prestressed wide beams. These expressions are shown to offer a reliable and practical approach for assessing the full response of such members.

2018

Medical Use of Finite Element Modeling of the Ankle and Foot
Scientific paper

Chira Alexandru, Gozar Horea, Nagy Ors, Derzsi Zoltan

Journal of Interdisciplinary Medicine, 2018 , vol.  3, no  1, pp.  34-38

Link to the publication

Summary:

Finite element modeling is a field of medicine with great potential future in experimental studies and in daily clinical practice as well. Computational modeling is currently used in several medical applications including orthopedics, cardiovascular surgery, and dentistry. In orthopedics, this method allows a proper understanding of joint behavior, as well as of more complex articular biomechanics that are encountered in several conditions such as ankle fractures or congenital clubfoot. Currently, there is little data on the development of a 3D finite elementdefined model for congenital clubfoot. This paper aims to summarize the current status of knowledge and applications of finite element modeling of the foot and ankle.

Finite element based 3D computer modeling for personalized treatment planning in clubfoot deformity: Case report with Technique description
Scientific paper

Chira Alexandru, Gozar Horea, Derzsi Zoltan, Nagy Ors, Benedek Theodora

Medicine (Baltimore), 2018 , vol.  97, no  e11021.

Link to the publication

Summary:

Abstract

Rationale: In clubfoot deformity, planning of corrective treatment requires a complex understanding of the foot anatomy, as well as of the geometry and distribution of altered mechanical forces acting at the level of the deformed foot. At the same time, treatment success depends largely on the selection of the most appropriate shape and angles of the customized orthesis developed for foot correction. Therefore, a complex assessment of the intensity and distribution of the mechanical forces at this site is mandatory prior to initiation of any corrective therapy.

Patient concerns: We present here the case of a 3-year-old male child with clubfoot deformity, weighting 20 kg, with no other congenital malformations, in whom finite element modeling (FEM) technology associated with a newly developed technique of three-dimensional (3D) computational simulation was applied for personalized treatment planning.

Interventions: The FEM-based computational 3D simulation technique allowed selection of the corrective treatment associated with the most physiologic pattern of force distribution at the level of the foot.

Outcomes: The proposed technique led to selection of the most appropriate therapy that successfully corrected the foot deformity. After 3D computer simulations, the elongations recorded were 2.71 cm for Achilles tendon, 1.69 cm for anterior tibialis tendon, 1.35 cm for the long flexor of the toes, and 1.69 cm for the long flexor of the hallux. The Von Mises equivalent stress distribution was σ = 4.26 MPa, not exceeding the elastic capacity of the bones, therefore the residual deformations were minimal. The customized treatment selected in this way was highly appropriate for the child, and led to complete recovery of the deformity in three months.

Lessons: This case is the first one in which FEM-based computational 3D modeling was applied for selection of treatment strategy in a child with clubfoot. The case reported here illustrates the role of advanced medical computer technology, based on complex image processing, FEM and 3D simulations, in providing an effective clinical decision support tool for personalized treatment selection in children with clubfoot deformity.

Nanocoating on alkali-resistant glass fibers by octadecyltrichlorosilane to improve the mechanical strength of fibers and fibers/epoxy composites.
Scientific paper

Chira Alexandru, Kumar Anuj, Vlach Tomas, Laiblova Lenka, Sever Skapin Andrijana, Tywoniak Jan, Hajek Petr

Textile Research Journal, 2018 , vol.  88, no  9

Link to the publication

Summary:

Surface defects cause the measured tensile strength of alkali glass fibers to be significantly lower than their theoretical values. Coatings can be used to “heal” surface flaws and to modify surface properties. In the present work, the nanocoating on alkali-resistant glass (ARG) fiber rovings was carried out by self-assembled monolayers (SAMs) of octadecyltrichlorosilane (OTS). The ARG roving was dipped into OTS nanosol, which deposited the organic–inorganic SAMs of OTS on the ARG surface. The assessment of changes in the fiber surfaces was characterized by scanning electron microscopy (SEM) and fluorescence microscopy, while the chemical changes were characterized by X-ray photoelectron spectroscopy (XPS). Furthermore, the influence of nanocoating on the tensile properties of ARG and OTS-treated ARG with and without an epoxy matrix was also studied. The SEM analysis revealed the formation of nanoscale layers on the ARG surfaces and the XPS confirmed the deposition of organic–inorganic monolayers. The tensile strength of ARG rovings with and without the epoxy matrix was improved significantly. The OTS treatment almost created a superhydrophobic nanocoating on ARG, which was confirmed by the sessile drop water contact angle, and the water absorption by the ARG/epoxy composites reduced.

2016

Property improvements of alkali resistant glass fibres/epoxy composite with nanosilica for textile reinforced concrete applications.
Scientific paper

Chira Alexandru, Kumar Anuj, Vlach Tomas, Laiblova Lenka, Sever Skapin Andrijana, Hajek Petr

Materials & Design, 2016 , vol.  89, no  https://doi.org/10.1016/j.matdes.2015.09.122, pp.  146-155

Link to the publication

Summary:

The aim of this work is to study the tensile, compressive and shear properties of textile rovings and also their matrix. This paper describes the sample preparations to obtain the tensile, compression and shear testing results for alkali resistant glass fibres (ARG)/epoxy composite. Furthermore, the effect of nanosilica particles on the mechanical properties of ARG/epoxy composite was studied. The results obtained for the rovings with nanosilica showed mechanical improvements for all tested properties. A numerical model was developed with the new obtained textile properties for a TRC facade panel to investigate the flexural behaviour.

2015

Numerical Simulation of Cohesion Influence of Textile Reinforcement on bending performance of plates prepared from High Performance Concrete (HPC)
Scientific paper

Chira Alexandru, Vlach Tomas, Laiblova Lenka, Fiala Ctislav, Novotna Magdalena, Hajek Petr

Advanced Materials Research, 2015 , vol.  1106, no  1662-8985, pp.  69-72

Link to the publication

Summary:

Demand for very thin concrete elements, which can’t be reinforced with usually used steel reinforcement, gave rise to a new type of non-traditional reinforcement with technical textiles in matrix of epoxy resin. This type of reinforcement together with concrete is called textile reinforced concrete (TRC). Composite reinforcement is very chemically resistant, so the concrete cover is proposed to regard the durability. It allows a significant saving of concrete and design of thinner elements. For TRC structures is used high performance concrete (HPC) with its fine grained structure and high compressive strength. Textile reinforcement and TRC in general are developed at the Faculty of Civil Engineering and the Klokner Institute, CTU in Prague.

Textile-reinforced concrete facade panels with rigid foam core prisms.
Scientific paper

Chira Alexandru, Kumar Anuj, Vlach Tomas, Laiblova Lenka, Hajek Petr

Journal of Sandwich Structures & Materials, 2015 , vol.  18, no  2

Link to the publication

Summary:

Textile-reinforced concrete (TRC) is a material that is gaining new ground in the field of construction where it not only allows for the manufacture of reduced lightweight structures but also eliminates the problem of corrosion by using alkali-resistant textile reinforcement. The aim of this paper is to investigate the bending behaviour of a newly developed TRC facade panel that incorporates polystyrene foam prisms. Numerical simulations were employed in order to choose the geometry and repartition of prisms inside the facade panel. Experimental results revealed a reduced amount of concrete by 20% via the use of rigid foam prisms with a higher failure load by 16% but a lower elasticity limit by 49% in comparison with the regular facade panels.

2014

Comparison of different methods for determination of modulus of elasticity of composite reinforcement produced from roving
Scientific paper

Chira Alexandru, Vlach Tomas, Laiblova Lenka, Novotna Magdalena, Ctislav Fiala, Zenisek Michal, Hajek Petr

Advanced Materials Research, 2014 , vol.  1054, pp.  104-109

Link to the publication

Summary:

Currently, high performance concrete (HPC) is becoming more and more popular mainly because of its great mechanical parameters. As in the case of ordinary power concrete (OPC) it is necessary to improve the load bearing capacity with using of reinforcement. The present age calls for using of very thin structures for reasons of both environmental parameters and visual quality. Based on this fact, reinforcement start to use durable composite materials, such as technical textiles made of them. Element of HPC with this type of reinforcement is called textile reinforced high performance concrete (TRHPC). It is impossible to use the traditional approach for usually used steel reinforcement if we want to design these extra-thin structures. Modeled structures are very sensitive for input parameters and the development of standards for TRC material lags. The present study is focused on the different method of approach for the determination of tensile modulus of composite reinforcement. Three used methods are compared with each other using numerical analysis of four point bending test of façade element for one type of used reinforcement. Curves from numerical analysis are finally compared with the curve from real experiment and based on this the final evaluation is generated.

Numerical and experimental investigations on the behavior of thermosystem subjected to wind loads
Scientific paper

Chira Alexandru, Bojan Adrian

TRANSILVANIA UNIVERSITY PUBLISHING HOUSE, 2014 , no  2285-7656 -L 2248-7648

Link to the publication

Summary:

The main objective of this paper is to study the behavior of the polystyrene EPS 80 subjected to wind loads in different areas. The properties of the material were determined experimental and an appropriate material law was used in order to model the material. The tested polystyrene samples were cubes having 100x100x100 mm and they have been cut from slabs of 1000x500x100mm. Numerical investigations considering suctionwind load for façade’s thermosystems have been done and conclusions were drawn based on the results. Finite element code Abaqus was used in order to conduct the nonlinear analysis.

2013

Numerical investigations on a wide reinforced concrete beam subjected to fire
Scientific paper

Chira Alexandru, Puskas Attila

Mathematical Models in Engineering & Computer Science, 2013 , pp.  169-174

Link to the publication

Summary:

Use of wide pre-stressed reinforced concrete beams is moderate due to their mechanical disadvantages with respect to the regular ones but also due to the uncertainty in their behavior. Wide beams are still the right solution when complex optimization parameters are imposed. Fire provisions are foreseeing specific concrete cover of reinforcement but excessive deformation of bended concrete elements can lead to crack appearance and excessive exposure of reinforcement to fire. Limited deformation of a concrete beam by pre-stressing could postpone appearance of cracks and as consequence it could increase the fire resistance of the element, but how the large width of the beam is influencing its behavior when subjected to fire? The paper is presenting numerical modeling for three different fire scenarios for the wide pre-stressed reinforced concrete beam.

2012

Finite element analysis of beam to column end plate bolted connection
Scientific paper

Chira Alexandru, Balc Roxana, Chira Nicolae

Acta Technica Napocensis: Civil Engineering & Architecture, 2012 , vol.  55, no  1, pp.  24-29

Link to the publication

Summary:

The improvement of the electronic systems of computation made the use of the finite element method (FEM) possible in the current research and design activity. In the field of the design steel frames, the finite element analysis (FEA) of the joints offers the possibility to simulate their real behavior at low costs and in a relatively short period of time compared with the experimental tests. This paper presents the analysis with finite elements of a steel joint with end plate and prestressed bolts, using the ABAQUS finite element software code. The results obtained after the numerical simulation were compared with the experimental data in order to validate the model.

2024

Evaluation of cyclic response of hybrid steel-timber frame members
Conference ArODES

Dan V. Bompa, Alexandru Chira, Ahmed Y. Elghazouli

Proceedings of the 11th International Conference on Behaviour of Steel Structures in Seismic Areas (STESSA 2024), 8-10 July 2024, Salerno, Italy

Link to the conference

Summary:

This paper describes a nonlinear numerical investigation into the inelastic cyclic response of hybrid steel moment frame members with cross-laminated timber-steel floors. Continuum models of reduced beam section steel moment connections, timber beams and steel-timber interfaces were constructed to validate the numerical procedures. Steel-timber beam and external beam-to-column connection models were then constructed to evaluate the composite action and the influence of the timber slab on the cyclic response, respectively. In the beams, the composite action was modelled using connectors corresponding to screwed steel-timber shear connections, as well as with full interaction. For the beam-to-column connections, screwed shear connections were considered only outside the region where plastic hinging was expected, and the slab was modelled with or without a gap around the steel column. The results from beam modelling show that the degree of shear connection was 74% on average. For the steel-timber connections, there was an average increase in positive moment capacities of 1.5% and 15.2%, for the cases with and without a gap in the slab, respectively, compared to the steel counterpart. Removing the shear connectors from the reduced beam section region and including a gap around the column, enable a cyclic response dominated by the steel beam. The observations from this paper offer insight into the response of hybrid steel-timber floors under lateral loading.

2023

Structural response of hybrid timber - cold formed steel floors
Conference ArODES

Dan V. Bompa, George Dance, Alexandru Chira, Martin G. Walker, Zsolt Nagy

ce/papers ; Proceedings of the 10th Eurosteel conference (Eurosteel 2023), 12-14 September 2023, Amsterdam, The Netherlands

Link to the conference

Summary:

The paper examines the composite performance of hybrid steel-timber lightweight floor assemblies incorporating cold-formed steel (CFS) profiles and plywood (PW) flooring panels with varying degrees of shear connection achieved by means of self-drilling screws. Material, push-out, and three-point short-span floor tests with or without web openings were carried out. The results and observations from the tests provide a detailed insight into the inelastic properties and ultimate response of such floor systems. Push-out tests indicate that denser connector arrangements increase connection stiffness, while push-out and short beam tests suggest an optimum connector spacing equal to the beam depth for a balance between structural performance and constructability. The experimental observations indicate that the ultimate condition of the short composite beams was characterized by CFS web crippling under the load application point, followed by a pull-through of the self-drilling screws. Web openings reduced the strength of the floor elements compared to the members with full webs. Complementary numerical studies are undertaken using nonlinear finite element procedures which were validated against the beam tests, offering a detailed insight into the stress levels in the timber, steel, and connectors. Codified procedures for determining the capacity of composite CFS sections are compared with the test results, and guidance for the practical design and construction of such systems is given.

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