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[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 ...

[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.2018.01.048 ; S ; 328 ; 341 ; 160

551 563 160 ; S ; [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 ...