INESTABILIDAD DE BARRAS COMPRIMIDAS DE ACERO Y DE SMA EN ELEMENTOS DE HORMIGÓN FABRICADOS CON NUEVOS MATERIALES. RECOMENDACIONES DE DISEÑO

The strain capacity of structures depends on the plastic hinge behaviour. There are different proposals in the scientific literature in order to improve this behaviour in reinforced concrete structures such as the following ones: proposals include the use of fiber reinforced concrete, very high performance concrete or replacing in the critical structure zone, the steel reinforcement with shape memory alloy and superelasticity bars (from this point forward SMA), among other solutions. However, the strain capacity of hinges is dependent on the compressed reinforcement buckling, which means a drastic diminishing in the bearing capacity and ductility. This phenomenon happens due to the cover spalling or degradation, or due to an insufficient transverse reinforcement arrangement. The design codes propose requirements related to the diameter of longitudinal bars and to the transverse reinforcement separation to assure the bearing capacity or to assure the hinge rotation without the compressed reinforcements buckle. Nevertheless, the aforementioned requirements are not valid in compressed elements made of new materials (fiber reinforced concrete, very high performance concrete or SMA bars). This doctoral thesis analyzes the compressed steel or NiTi - SMA bars behaviour in elements made of conventional, high strength or very high performance concrete, with or without fibres. Therefore, an experimental research has been carried out to study the local instability of the compressed bars (steel and NITI) in concrete elements. 32 columns subject to a bending-compression load have been analyzed. An analytic model has been proposed to analyze the buckling critical stress and length in the compressed bars in concrete elements. This model has been calibrated based on experimental tests. It has been performed an experimental and numerical research to analyze the behaviour of the NITI bars as isolated bars. It has been proposed an analytic model to calculate the relationship stress-strain of the compressed bars that includes the buckling effect. This model has been verified by both experimental and numerical results. Finally, it has been proposed an expression to calculate the maximum separation of the transverse reinforcement according to the required limited stress, for both steel and SMA bars. In order to define that stress, two criteria have been proposed: one of them is based on stresses and the other one on strains. With respect to the concrete without fibres case, the proposed expression has been compared with the current code.La capacidad de deformación de las estructuras depende del comportamiento de las rótulas plásticas. Para mejorar dicho comportamiento en estructuras de hormigón armado, en la literatura técnica se propone utilizar hormigón con fibras de acero en su masa, hormigón de muy altas prestaciones o sustituir en la zona crítica de la estructura las armaduras de acero por barras de aleación con memoria de forma y superelasticidad (en adelante SMA) entre otras soluciones. Sin embargo, la capacidad de deformación de las rótulas está condicionada por el pandeo de la armadura comprimida, lo que supone una disminución drástica de la capacidad resistente y de la ductilidad. Este fenómeno se produce porque el recubrimiento del hormigón salta o se degrada, o por una insuficiente disposición de armadura transversal. En las normativas de diseño se proponen requisitos acerca del diámetro y de la separación de la armadura transversal para asegurar la capacidad resistente o la deformación de la rótula sin que las armaduras comprimidas pandeen. Sin embargo, dichas expresiones no son válidas en elementos comprimidos fabricados con nuevos materiales (hormigón con fibras en su masa, hormigones de muy altas prestaciones o barras de SMA). En esta tesis doctoral se analiza el comportamiento de barras comprimidas, de acero o de SMA en base NiTi, en elementos fabricados con hormigones convencionales, de alta resistencia o de muy altas prestaciones, con o sin fibras en su masa. A tal efecto, se ha ejecutado un programa experimental para estudiar la inestabilidad local de las barras comprimidas (acero y NiTi) en elementos de hormigón. Se han analizado un total de 32 soportes sometidos a una solicitación de flexo-compresión. Se ha propuesto un modelo analítico para determinar la tensión y la longitud crítica de pandeo de barras comprimidas en elementos de hormigón. Este modelo ha sido calibrado con los ensayos experimentales. Se ha realizado un estudio experimental y numérico para analizar el comportamiento de las barras de NiTi como barras aisladas. Se ha propuesto un modelo analítico para calcular la relación tensión - deformación de barras comprimidas que incluye el efecto del pandeo. Este modelo ha sido verificado tanto con los resultados experimentales como numéricos. Finalmente, se ha propuesto una expresión para el cálculo de la separación máxima de la armadura transversal en función de la tensión límite requerida, tanto para barras de acero como de SMA. Para la definición de dicha tensión se proponen dos criterios: uno basado en tensiones y otro en deformaciones. En el caso de hormigón sin fibras, la expresión propuesta se ha comparado con la normativa actual.La capacitat de deformació de les estructures depén del comportament de les ròtules plàstiques. Per a millorar dit comportament en estructures de formigó armat, en la literatura tècnica es proposa utilitzar formigó amb fibres d'acer en la seua massa, formigó de molt altes prestacions o substituir en la zona crítica de l'estructura les armadures d'acer per barres d'aliatge amb memòria de forma i superelasticitat (d'ara endavant SMA) entre d'altres solucions. No obstant això, la capacitat de deformació de les ròtules està condicionada pel vinclament de l'armadura comprimida, la qual cosa suposa una disminució dràstica de la capacitat resistent i de la ductilitat. Este fenomen es produeix perquè el recobriment del formigó salta o es degrada, o per una insuficient disposició de l'armadura transversal. En les normatives de disseny es proposen requisits quant al diàmetre i a la separació de l'armadura transversal per assegurar la capacitat resistent o la deformació de la ròtula sense que les armadures comprimides vinclen. No obstant això, estes expressions no son vàlides en elements comprimits fabricats amb nous materiales (formigó amb fibres en la seua massa, formigons de molt altes prestacions o barres de SMA). En esta tesis doctoral s'analitza el comportament de barres comprimides, d'acer o de SMA compost per NiTi, en elements fabricats amb formigons convencionals, d'alta resistència o de molt altes prestacions, amb o sense fibres en la seua massa. A tal efecte, s'ha executat un programa experimental per estudiar la inestabilitat local de les barres comprimides (acer i NiTi) en elements de formigó. S'han analitzat un total de 32 soports somesos a una solicitació de flexo-compressió. S'ha proposat un model analític per determinar la tensió i longitud crítica de vinclament de barres comprimides en elements de formigó. Este model ha sigut calibrat amb els assajos experimentals. S'ha realitzat un estudi experimental i numéric per analitzar el comportament de les barres de NiTi com barres aïllades. S'ha proposat un model analític per calcular la relació tensió-deformació de barres comprimides que inclou l'efecte del vinclament. Este model ha sigut verificat tant amb els resultats experimentals com numérics. Finalment, s'ha proposat una expressió per al càlcul de la separació màxima de l'armadura transversal en funció de la tensió límit requerida., tant per a barres d'acer com de SMA. Per a la definició de dita tensió es proposen dos criteris: uno basat en tensions i l'altre en deformacions. En el cas del formigó amb fibres, l'expressió proposada s'ha comparat amb la normativa actual.Pereiro Barceló, J. (2017). INESTABILIDAD DE BARRAS COMPRIMIDAS DE ACERO Y DE SMA EN ELEMENTOS DE HORMIGÓN FABRICADOS CON NUEVOS MATERIALES. RECOMENDACIONES DE DISEÑO [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90650TESI

Mixed model for the analytical determination of critical buckling load of passive reinforcement in compressed RC and FRC elements under monotonic loading

[EN] Compressed reinforcements on reinforced concrete (RC) and steel fibre reinforced concrete (SFRC) columns are generally submitted to cyclic and monotonic loading, which can buckle. This phenomenon can cause the reduction of both ductility and peak loads, which is why design standards propose constructive details to avoid this. Although the bibliography mentions that steel fibres in concrete can delay buckling of reinforcements, design codes do not distinguish between concrete types (with and without fibres) in these constructive details. Analytical models that determine the length and critical buckling stress of reinforcements may consider this effect. Nowadays, analytical models can be classified as discrete and distributed depending on whether they consider transverse reinforcement stiffness and the stiffness of the concrete cover that concentrates on transverse reinforcements, or if they are distributed along the element, respectively. Both discrete and distributed models are valid for small transverse reinforcement separations, while distributed models that only consider the concrete cover effect are valid for large transverse reinforcement separations. This paper proposes a mixed model to determine critical buckling loads of compressed reinforcements subjected to monotonic loading to use the stress-strain relationships of reinforcing bars, including buckling, that are found in the scientific-technical literature. This model considers transverse reinforcements discretely and concrete cover distributedly. The model can be applied to any transverse reinforcement configuration, and to any concrete type (with or without fibres). An analytical equation is also proposed to determine critical compressed reinforcement loads, whose result is presented as abaci. Finally, to calibrate the model in normal-strength concrete columns under eccentric loading, with or without fibres, a programme is presented in which the critical load of longitudinal reinforcements is experimentally determined. The proposed analytical model is calibrated and a procedure to determine critical buckling loads of compressed reinforcements under monotonic loading is proposed.The model presented herein forms part of a research line that is being undertaken at the Concrete Science and Technology Institute (ICITECH) of the Universitat Politècnica de València (UPV). The authors are sincerely grateful to the Spanish Ministry of Economy and Competitiveness for the help it has provided through Project BIA2012-32645 and to the European Union for financial support obtained from FEDER fundsPereiro Barceló, J.; Bonet Senach, JL. (2017). Mixed model for the analytical determination of critical buckling load of passive reinforcement in compressed RC and FRC elements under monotonic loading. Engineering Structures. 150(1):76-90. doi:10.1016/j.engstruct.2017.07.026S7690150

Required tie spacing to prevent inelastic local buckling of longitudinal reinforcements in RC and FRC elements

[EN] Compressed reinforcement buckling in concrete columns can reduce ductility in structural elements. In order to avoid this, design codes propose maximum required tie spacing. Nonetheless, they do not incorporate the positive effect of concrete fibers in their formulation, whose capability of delaying buckling has been proved. For this reason, recommendations for maximum required tie spacing for elements made with concrete, with or without steel fibers, and with normal or high strength, are proposed in this article. In order to achieve this, the mixed model proposed by Pereiro-Barceló and Bonet was extended to consider elements made of HSC with and without steel fibers thanks to the results of an experimental campaign of HSC columns with and without fibers, under monotonic loading. In these tests, the buckling critical load in compressed reinforcement was experimentally determined in all the columns. In addition, a comparison of the proposed transverse concrete separation with respect to the recommendations proposed by the main existing codes was made.The research presented herein forms part of a research undertaken at the Concrete Science and Technology Institute (ICITECH) of the Universitat Politecnica de Valencia (UPV). The authors are sincerely grateful to the Spanish Ministry of Economy and Competitiveness for the help provided through Project BIA2012-32645, and to the European Union for the financial support obtained from FEDER funds. The authors wish to thank the Spanish Ministry of Education, Culture and Sport for Grant FPU12/01451.Pereiro-Barceló, J.; Bonet Senach, JL.; Albiol Ibáñez, JR. (2018). Required tie spacing to prevent inelastic local buckling of longitudinal reinforcements in RC and FRC elements. Engineering Structures. 160:328-341. https://doi.org/10.1016/j.engstruct.2018.01.048S32834116

Safety Issues in Buckling of Steel Structures by Improving Accuracy of Historical Methods

Buckling of structural elements is a phenomenon that has great consequences on the bearing capacity of structures. Historically, there have been serious buckling-related structural accidents that have resulted in loss of human lives and high material costs. In this article, an attempt is made to perform a historical analysis of the diverse models that experts have been using in designing and calculating compression buckling of simple metallic elements in the last 275 years. The analysis covers the lapse from the mid-18th century, in which the pioneers in this classic field of structural design are located, up to the present, highlighting the main standards that have been applied to steel structural analysis in the past and at present all over the world. What the study tries to provide is an overall view and a sense of continuity of the methods used for improving structural safety regarding buckling failures in the last three centuries. Each analyzed buckling model is compared with the results of a numerical finite element model of compressed steel columns. Finally, the conclusion reached is that in the last one hundred years, the convergence of solutions proposed in the field is gradually greater and more accurate

Design Recommendations for Columns Made of Ultra-High-Performance Concrete and NiTi SMA Bars

[EN] The use of new materials in construction endows structures with better mechanical characteristics. The combination of ultra-high-performance concrete (UHPC) and nickel and titanium (NiTi) shape memory alloy (SMA) improves the behavior of building structures by increasing both their ductility and dissipation energy due to the low-damage and self-centering properties of NiTi SMA. Since UHPC and NiTi SMA are expensive materials and still scarce in distribution channels, this article tries to offer design recommendations to reduce the length of the column-beam connection in which these new materials should be introduced, leaving the rest of the column with conventional materials. To achieve this, a nonlinear static pushover analysis of columns using finite element software, SeismoStruct, was performed. This model was calibrated using experimental results. Next, a parametric analysis was carried out to propose the design recommendations. Results indicated that an adequate design for the column-beam connection, considering both economy and performance, should include a main zone with UHPC and SMA reinforcements, a transition zone with UHPC and steel reinforcements, and another zone with conventional reinforced concrete. The transition zone improved the hybrid column's performance without excessively raising the cost. The main zone length, the transition zone length, and the strength of the concrete in the rest of the column must be determined to ensure that the critical section of the column was in the main zone to develop the maximum strength and ductility. The length of the main zone depended on the compressive strength of the conventional concrete, the relative axial load of the column, and the required ductility.This work was supported by the Spanish Ministry of Economy and Competitiveness through Project BIA2012-32645 and by the European Union through European Regional Development Funds (ERDF). The project was executed at the Concrete Science and Technology Institute (ICITECH) of the Universitat Politècnica de València (UPV). The article processing charge was paid by the University of Alicante (UA). The authors wish to thank the Spanish Ministry of Education, Culture and Sport for Grant FPU12/01451.Pereiro-Barceló, J.; Bonet Senach, JL.; Martínez-Jaén, B.; Cabañero-Escudero, B. (2023). Design Recommendations for Columns Made of Ultra-High-Performance Concrete and NiTi SMA Bars. Buildings. 13(4). https://doi.org/10.3390/buildings1304099113

Application of Project-Based Learning in the development of a Bachelor’s Thesis in the Bachelor’s Degree in Civil Engineering

El Aprendizaje Basado en Proyectos (ABP) es un enfoque educativo que consigue motivar al alumnado a través de su implicación activa en el desarrollo de un trabajo que tiene un alto componente práctico. En consecuencia, se genera un aprendizaje profundo de los temas tratados. Con la finalidad de alcanzar estas metas, se aplicó el ABP al Trabajo Final de Grado (TFG) de cuatro alumnos del Grado en Ingeniería Civil de la Universitat Politècnica de València. El trabajo realizado consistió en el diseño, construcción, ensayo y análisis de un modelo reducido de una estructura de hormigón armado. La metodología empleada consistió en la definición de las actividades prácticas y teóricas necesarias para desarrollar el proyecto sobre el elemento estructural y el establecimiento de un sistema de seguimiento por parte del tutor. Los resultados obtenidos demuestran el buen funcionamiento de la innovación, que consiguió motivar a los alumnos, potenciar su aprendizaje y facilitar el alcance de las competencias establecidas en el TFG y otras propias de la titulación, así como despertar el interés de los alumnos por el cálculo de estructuras de hormigón.Project-Based Learning (PBL) is an educational approach that motivates students through their active involvement in the development of a highly practical assignment. As a result, a deep learning process is generated. In order to achieve these goals, PBL was applied to the Bachelor’s Thesis (BT) of four students of the Degree in Civil Engineering of the Universitat Politècnica de València. The work consisted of the design, construction, testing and analysis of a scaled-down model of a reinforced concrete structure. The methodology used consisted of defining the practical and theoretical activities necessary to develop the project on the structural element and the establishment of a monitoring system by the tutor. The results obtained demonstrate the good performance of the innovation, which motivated the students, enhanced their learning and facilitated the achievement of the competences established in the BT and others specific to the degree, as well as awakened the students' interest in the calculation of concrete structures

Ductility of high-performance concrete and very-high-performance concrete elements with Ni-Ti reinforcements

[EN] This article presents an experimental study on the behavior of high performance concrete (HPC) and very high performance concrete (VHPC) concrete columns with Nickel-Titanium (Ni-Ti) shape memory alloy (SMA) reinforcements in critical regions subjected to constant axial and lateral cyclic load combinations. These materials make the cast-in-place of concrete easier by reducing the amount of transverse reinforcement, improving performance, attenuating damage in critical regions, minimizing residual deformations and reducing repair costs in structures located in seismic areas. Seven experimental tests were carried out to analyze the behavior of this element type. A nonlinear static cyclic pushover analysis was performed with finite element software (OpenSees), whose results were compared with the experimental results. This analysis allowed a parametric analysis to be run to extrapolate the experimental results. Strength capacity was approximately 41.8% greater in absolute terms in the specimens manufactured with VHPC and 6.2% greater in a dimensional terms in those manufactured with HPC. Displacement ductility was 34.0% higher in the HPC specimens, and lowered with relative normal force and with transverse reinforcement separation. A residual drift ratio below 0.70% was generally observed when specimens reached 20% strength capacity loss. The residual drift ratio increased as a result of progressive concrete cover degradation, especially in the specimens manufactured with HPC. (C) 2018 Elsevier Ltd. All rights reserved.This article forms part of the research carried out at the Concrete Science and Technology Institute (ICITECH) of the Universitat Politecnica de Valencia (UPV). This work has been supported by the Spanish Ministry of Economy and Competitiveness through Project BIA2012-32645, and by the European Union through ERDF funds. The authors thank the Spanish Ministry of Education, Culture and Sport for Grant FPU12/01451.Pereiro-Barceló, J.; Bonet Senach, JL.; Goméz-Portillo, S.; Castro-Bugallo, MC. (2018). Ductility of high-performance concrete and very-high-performance concrete elements with Ni-Ti reinforcements. Construction and Building Materials. 175:531-551. https://doi.org/10.1016/j.conbuildmat.2018.04.172S53155117

Estudio teórico de las juntas dentadas húmedas pretensadas entre elementos de hormigón. Diseño de un prototipo de ensayo experimental

[ES] Son muchas las construcciones que se ejecutan hoy en día mediante elementos prefabricados de hormigón armado o pretensado como, por ejemplo, los tableros de los puentes. La prefabricación ha llevado consigo muchas mejoras en el mundo de la construcción con respecto a las obras ejecutadas in situ. Estas mejoras esencialmente son el aumento de la calidad y rapidez de elaboración. Sin embargo, abordar la construcción de una obra, o parte de ella, con elementos prefabricados también posee unos inconvenientes inherentes a este sistema, siendo uno de los más limitantes el transporte. Si se piensa en el tablero de un puente, transportar las vigas requiere de un transporte especial, con su problemática asociada, o directamente es imposible realizarlo por las excesivas dimensiones. Partir de varios elementos prefabricados de pequeño tamaño y peso, y poder ser capaz de crear un gran elemento prefabricado perfectamente funcional y seguro a partir de éstos, eliminaría el problema del transporte. El objetivo general de este proyecto es evaluar la capacidad resistente de las juntas que podrían dar lugar a crear un gran elemento prefabricado uniendo otros de menores dimensiones, así como conocer su comportamiento mecánico. Las juntas estudiadas son dentadas, húmedas con mortero y pretensadas. La junta es una parte fundamental del conjunto de la unión entre elementos prefabricados que permitiría transportar una viga de un tablero de puente dividida en varias partes, trasladadas mediante camiones convencionales. Sin embargo no se ha estudiado nada acerca de las juntas húmedas con mortero en la bibliografía existente y no se sabe hasta qué punto sus ventajas son competitivas. Se ha elaborado un completo estado de los conocimientos científico-técnicos acerca de las uniones postesadas existentes, tanto de la formulación existente como de las campañas experimentales realizadas y la forma de llevarlas a cabo. Esto ha creado unas bases sólidas del estudio planteado y ha servido para adquirir ideas para afrontar las etapas posteriores del proyecto, como por ejemplo, diseñar un experimento. Para estudiar la junta, se ha diseñado una completa campaña experimental para llevarla a cabo en los laboratorios de ICITECH. Ésta servirá para cuantificar la resistencia de la junta en función de ciertos parámetros. Además, se ha elaborado un modelo numérico de elementos finitos bidimensional, que recoge todos los parámetros a tener en cuenta para conseguir reproducir el comportamiento real de las juntas húmedas con mortero. Este modelo ofrece campos tensionales, deslizamientos y aperturas en la junta en función de los parámetros insertados y será calibrado y validado con la campaña experimental.[EN] Nowadays, many constructions are built using precast elements of reinforced or prestressed concrete, for example, bridge decks. Prefabrication has involved many improvements in the world of construction with respect in situ constructions. These improvements are essentially increasing the quality and speed of construction process. However, prefabrication has some drawbacks inherent to this system; one of the most limiting disadvantages is the transportation. Transporting bridge beams requires a special transport, with its associated problems, or directly is impossible to do due to the excessive dimensions. Having several small and light precast elements, and being able to create a large prefabricated element perfectly functional and safe from them, eliminate the problem of transportation. The main objective of this project is to evaluate the strength of joints that could create a large prefabricated element joining smaller elements among themselves, and to know their mechanical behavior. Studied joints are toothed, wet with mortar and pretressed. The joint is an essential part of the union set between precast elements. This joint would let to carry a beam of a bridge deck divided into several parts, moved by conventional trucks. But nowadays this kind of joint is not studied in the existing literature and it is unknown how it works and if it is competitive. A complete state of scientific and technical knowledge about the existing post-tensioned connections has been developed. Formulation and experimental campaigns carried out have been searched and, also, how to carry them out. This has created a solid foundation of the actual study and has been useful to have ideas to develop later stages of the project, for example, designing an experiment. A complete experimental program has been designed to carry it out in the ICITECH laboratory to study the wet joint. This will serve to quantify the strength of the joint according to certain parameters. Besides, a numerical model of two-dimensional finite element has been developed, which contains all parameters to reproduce the actual behavior of wet joints with mortar. This model provides tensional distributions, slides and openings across the joint taking into account input parameters. It will be calibrated and validated with the experimental campaign.Pereiro Barceló, J. (2012). Estudio teórico de las juntas dentadas húmedas pretensadas entre elementos de hormigón. Diseño de un prototipo de ensayo experimental. http://hdl.handle.net/10251/27329Archivo delegad

Ni-Ti SMA bars behaviour under compression

[EN] SMA (Shape Memory Alloys) is a type of material suitable for using in civil engineering as concrete reinforcement because of their shape memory effect or superelasticity and their high ductility and damping capacity. However, Ni-Ti alloys Young modulus could be 3 or 4 times lower than steel (200 GPa) depending on the composition and thermal treatment, which can cause the instability of compressed bars. The main objective of this work is to provide a modified constitutive model of SMA bars, particularized for Ni-Ti bars, that considers instability in compression. The inclusion of this effect in the constitutive equation allows for simulating Ni-Ti bars under compression in a simple way as if they were perfectly straight bars. To achieve this, six 12-mm diameter SMA bars made of Ni-Ti were tested under compression. The mechanical slendernesses of the six Ni-Ti samples were: 28.33, 38, 48, 66, 82 and 108.33. Thirty steel specimens were tested beforehand to validate the experimental setup and to calibrate the subsequent Abaqus finite element model. This model aims to conduct a parametric study to validate the proposed constitutive model of Ni-Ti bars, including instability in compression.The model presented here is part of a research strand that is being undertaken within the Concrete Science and Technology Institute (ICITECH) at the Universitat Politècnica de València (UPV). The authors are sincerely grateful to the Spanish Ministry of Economy and Competitiveness for the help it has provided through Project BIA2012-32645 and to the European Union for financial support obtained from FEDER funds. Besides, authors wish to thank Alberto Navarro Gómez and Oscar Sahuquillo Navarro for helping with material characterization.Pereiro Barceló, J.; Bonet Senach, JL. (2017). Ni-Ti SMA bars behaviour under compression. Construction and Building Materials. 155C:348-362. doi:10.1016/j.conbuildmat.2017.08.083S348362155

Buckling of steel and Ni-Ti reinforcements in very high performance concrete (VHPC) elements

[EN] Nowadays, the use of new materials is becoming increasingly common in the construction world due to their improved properties. High or Very High Performance Concrete (HPC or VHPC) and Shape Memory Alloys (SMA), specifically those composed of nickel and titanium (Ni-Ti), are some of these new materials. The low austenitic modulus of Ni-Ti as regards the elasticity modulus of steel (40-65 GPa instead of 200 GPa) can cause local buckling. In order to replace steel bars with Ni-Ti bars in reinforced concrete elements, it is convenient to use concrete with a high steel fibre content to delay local bar buckling. Hence employing either High Performance Concrete or VHPC may be appropriate, due to its composition with a high steel fibre content. For all these reasons, VHPC elements with Ni-Ti reinforcements were studied. The results of an experimental campaign of VHPC columns are shown in this article. The VHPC columns were subjected to monotonic loading where the main goal was to study compressed steel reinforcement buckling. The results of these tests were also used to extend the mixed model proposed by Pereiro-Barceló and Bonet (2017), which determines the buckling critical stress for any transverse reinforcement separation and considers the effect of the concrete cover (with and without steel fibres). This model was recalibrated to consider elements made of VHPC. Besides, specimens made of either High Performance Concrete (HPC) or VHPC, and with Ni-Ti reinforcements, were also tested to study the behaviour of compressed Ni-Ti reinforcements in elements made of high strength fibre-reinforced concrete.The research presented herein forms part of a research undertaken at the Concrete Science and Technology Institute (ICITECH) of the Universitat Politecnica de Valencia (UPV). The authors are sincerely grateful to the Spanish Ministry of Economy and Competitiveness for the help provided through Project BIA2012-32645, and to the European Union for the financial support obtained from FEDER funds. The authors wish to thank the Spanish Ministry of Education, Culture and Sport for Grant FPU12/01451.Pereiro-Barceló, J.; Bonet Senach, JL.; Albiol Ibáñez, JR. (2018). Buckling of steel and Ni-Ti reinforcements in very high performance concrete (VHPC) elements. Construction and Building Materials. 160:551-563. https://doi.org/10.1016/j.conbuildmat.2017.11.113S55156316