Experimental methodology on the serviceability behaviour of reinforced ultra-high performance fibre reinforced concrete tensile elements

[EN] Design codes include serviceability limit state (SLS) provisions for stress, crack, and deflection control in concrete structures, which may limit the structural design. When drawing on reinforced ultra-high performance fibre-reinforced concrete (R-UHPFRC), the process of cracking differs significantly from traditional concretes. Thus, it remains unclear whether the traditional provisions are applicable to R-UHPFRC or should be reviewed. Uniaxial tensile tie test is an excellent option to analyse and review these criteria. This work proposes a novel test methodology to study the behaviour of R-UHPFRC under serviceability conditions, which lets the study of the global and local deformation behaviour by using different measurement equipment. Two different types of R-UHPFRC ties with variant fibre content were tested. The global average tensile stressstrain curve, cracking behaviour, number, and width of cracks were obtained. Promising preliminary results admitted that this methodology can be useful to propose design criteria of R-UHPFRC under SLS.State Research Agency of Spain, Grant/Award Number: BIA2016-78460-C3-1-RKhorami, M.; Navarro-Gregori, J.; Serna Ros, P. (2020). Experimental methodology on the serviceability behaviour of reinforced ultra-high performance fibre reinforced concrete tensile elements. STRAIN. 56(5):1-13. https://doi.org/10.1111/str.12361S11356

Tensile behaviour of reinforced UHPFRC elements under serviceability conditions

[EN] Tension stiffening is an essential effect that influences the behaviour of concrete structures under serviceability conditions, mainly regarding crack control and deflection behaviour. Serviceability conditions can be studied experimentally by running the so-called uniaxial tensile test. This paper reports an extensive experimental research conducted to study the tensile behaviour of reinforced Ultra-High Performance Fibre-Reinforced Concrete (R-UHPFRC) under service conditions by uniaxial tensile testing. The parameters studied were the reinforcement ratio and the steel fibre content in a experimental programme including 36 specimens. Special testing equipment and methodology to measure the post-cracking deformation of R-UHPFRC ties were developed, and special attention was paid to the shrinkage effect. The tensile elements' axial stiffness was approximately parallel to the bare bar response after microcracking formation showing a full tension-stiffening response. The average tensile capacity of the reinforced elements (tension stiffening response) was achieved. Concrete's contribution in the R-UHPFRC ties with the tensile properties deriving from four-point bending tests (4PBTs) on non-reinforced UHPFRC specimens was also compared. The experimental results revealed a slight increase in concrete's contribution with the higher reinforcement ratio. Moreover, the concrete's contribution in the tensile elements was higher than the characteristic tensile properties deriving from 4PBTs.This study forms part of Project BIA2016-78460-C3-1-R, supported by the Ministry of Economy and Competitiveness of Spain.Khorami, M.; Navarro-Gregori, J.; Serna Ros, P. (2021). Tensile behaviour of reinforced UHPFRC elements under serviceability conditions. Materials and Structures. 54(1):1-17. https://doi.org/10.1617/s11527-021-01630-zS117541Burns C (2012) Serviceability analysis of reinforced concrete based on the tension chord model, PhD thesis no. 19979, Institute of Structural Engineering, Swiss Federal Institute of Technology, Zurich, SwitzerlandHonfi D (2013) Design for Serviceability-A probabilistic approach. Lund University, SwedenSahamitmongkol R, Kishi T (2011) Tension stiffening effect and bonding characteristics of chemically prestressed concrete under tension. Mater Struct 44(2):455–474Gribniak V et al (2015) Stochastic tension-stiffening approach for the solution of serviceability problems in reinforced concrete: Constitutive modeling. Comput-Aided Civil Infrastruct Eng 30(9):684–702Muhamad R et al (2012) The tension stiffening mechanism in reinforced concrete prisms. Adv Struct Eng 15(12):2053–2069Model Code 2010 (2012), Final Complete Draft, Fib Bull: No.65 and 66, March 2012-ISBN 978-2-88394-105-2 and April 2012-ISBN 978-2-88394-106-9AFGC S (2002) Bétons fibrés à ultra-hautes performances–Recommandations provisoires. AFGC, FranceCommittee JC (2008) Recommendations for design and construction of high performance fiber reinforced cement composites with multiple fine cracks. Japan Society of Civil Engineers, Tokyo, JapanCahier Technique SIA 2052 (2014) Béton fibré ultra-performant (BFUP)-Matériaux, dimensionnement et exécution. ProjetBelarbi A, Hsu TT (1994) Constitutive laws of concrete in tension and reinforcing bars stiffened by concrete. Structural Journal 91(4):465–474Yankelevsky DZ, Jabareen M, Abutbul AD (2008) One-dimensional analysis of tension stiffening in reinforced concrete with discrete cracks. Eng Struct 30(1):206–217Stramandinoli RS, La Rovere HL (2008) An efficient tension-stiffening model for nonlinear analysis of reinforced concrete members. Eng Struct 30(7):2069–2080Collins MP, Mitchell D (1991) Prestressed concrete structures, vol 9. Prentice Hall Englewood Cliffs, NJKaklauskas G (2001) Integral constitutive model for deformational analysis of flexural reinforced concrete members. Statyba 7(1):3–9Hsu TT (2017) Unified theory of reinforced concrete. Routledge, UKFields K, Bischoff PH (2004) Tension stiffening and cracking of high-strength reinforced concrete tension members. Structural Journal 101(4):447–456Patel K, Chaudhary S, Nagpal A (2016) A tension stiffening model for analysis of RC flexural members under service load. Comput Concrete 17(1):29–51Lee SC, Cho JY and Vecchio FJ (2013) Tension-Stiffening Model for Steel Fiber-Reinforced Concrete Containing Conventional Reinforcement. ACI Structural Journal 110(4)Bischoff PH (2003) Tension stiffening and cracking of steel fiber-reinforced concrete. J Mater Civ Eng 15(2):174–182Amin A, Foster SJ, Watts M (2016) Modelling the tension stiffening effect in SFR-RC. Mag Concrete Res 68(7):339–352Deluce JR, Vecchio FJ (2013) Cracking Behavior of Steel Fiber-Reinforced Concrete Members Containing Conventional Reinforcement. ACI Struct J 110(3):481–490Bernardi P et al (2016) Experimental and numerical study on cracking process in RC and R/FRC ties. Mater Struct 49(1–2):261–277Baby F et al (2013) UHPFRC tensile behavior characterization: inverse analysis of four-point bending test results. Mater Struct 46(8):1337–1354Lee S-C, Kim H-B, Joh C (2017) Inverse Analysis of UHPFRC Beams with a Notch to Evaluate Tensile Behavior. Advances in Materials Science and Engineering 2017:1–10Baby F et al (2013) Identification of UHPFRC tensile behaviour: methodology based on bending tests. UHPFRC 2013-International Symposium on Ultra-High Performance Fibre-Reinforced Concrete: 649–658Baby F et al (2012) Proposed flexural test method and associated inverse analysis for ultra-high-performance fiber-reinforced concrete. ACI Mater J 109(5):545López JÁ et al (2015) An inverse analysis method based on deflection to curvature transformation to determine the tensile properties of UHPFRC. Mater Struct 48(11):3703–3718López JÁ (2017) Characterisation of The Tensile Behaviour of UHPFRC by Means of Four-Point Bending Tests. PhD Thesis, Universitat Politècnica de ValènciaKhorami M, Navarro-Gregori J, Serna P (2020) Experimental methodology on the serviceability behaviour of reinforced ultra-high performance fibre reinforced concrete tensile elements. Strain 56(5):e12361Khorami M et al (2019) A testing method for studying the serviceability behavior of reinforced UHPFRC tensile ties. in IOP Conference Series: Materials Science and Engineering. IOP Conference Series 596:12–22Lee N, Chisholm D (2005) Reactive Powder Concrete, Study Report SR 146. Ltd, Judgeford, New ZealandBeigi MH et al (2013) An experimental survey on combined effects of fibers and nanosilica on the mechanical, rheological, and durability properties of self-compacting concrete. Mater Des 50:1019–1029Li VC (2002) Large volume, high-performance applications of fibers in civil engineering. J Appl Polym Sci 83(3):660–686Edgington J (1973) Steel fibre reinforced concrete. University of Surrey, GuildfordLópez J et al (2015) Comparison between inverse analysis procedure results and experimental measurements obtained from UHPFRC Four-Point Bending Tests. in Seventh International RILEM Conference on High Performance Fiber Reinforced Cement Composites (HPFRCC7): 185–192Löfgren I (2005) Fibre-reinforced Concrete for Industrial Construction-a fracture mechanics approach to material testing and structural analysis. Chalmers University of Technology, GothenburgAfroughsabet V, Biolzi L, Ozbakkaloglu T (2016) High-performance fiber-reinforced concrete: a review. J Mater Sci 51(14):6517–6551Buttignol TET, Sousa J, Bittencourt T (2017) Ultra High-Performance Fiber-Reinforced Concrete (UHPFRC): a review of material properties and design procedures. Revista IBRACON de estruturas e materiais 10(4):957–971Fehling E et al (2014) Ultra-high performance concrete UHPC: Fundamentals, design, examples. Wiley, NYMakita T, Brühwiler E (2014) Tensile fatigue behaviour of Ultra-High Performance Fibre Reinforced Concrete combined with steel rebars (R-UHPFRC). Int J Fatigue 59:145–152Rauch M and Sigrist V (2010) Dimensioning of Structures made of UHPFRC. in IABSE Symposium Report. 34th International Association for Bridge and Structural Engineering 97(34):39–46Sigrist V and Rauch M (2008) Deformation behavior of reinforced UHPFRC elements in tension. Anonymous Tailor Made Concrete Structures. CRC Press: 405–410Redaelli D (2006) Testing of reinforced high performance fibre concrete members in tension. in Proceedings of the 6th Int. Ph. D. Symposium in Civil Engineering, Zurich 2006. 2006. Proceedings of the 6th Int. Ph. D. Symposium in Civil Engineering, ZurichInstitution BS (2004) Eurocode 2: Design of concrete structures: Part 1–1: General rules and rules for buildings. British Standards Institution, UKGribniak V, Kaklauskas G and Bačinskas D (2007) State-of-art review of shrinkage effect on cracking and deformations of concrete bridge elements. The Baltic Journal of Road & Bridge Engineering 2(4):183-193Torst H (1967) Auswirkungen des superpositionsprinzips auf kriech-und relaxationsprobleme bei beton und spannbeton. Beton-und stahlbetonbau 10(230–238):261–269Bazant Z (1972) Predictions of concrete effects using age adjusted effective modulus method. J Am Concrete Institute 69:212–217AFGC (2013)  Ultra high performance fibre-reinforced concretes, recommendations. Documents scientifiques et techniques, ParisGowripalan N, Gilbert R (2000) Design guidelines for RPC prestressed concrete beams. School of Civil and Environmental Engineering, University of New South Wales, Sydney, AustraliaOstergaard L, Walter R and Olesen J (2005) Method for determination of tensile properties of engineered cementitious composites (ECC). Proceedings of ConMat'05, Vancouver, CanadaKanakubo T (2006) Tensile characteristics evaluation method for ductile fiber-reinforced cementitious composites. J Adv Concrete Technol 4(1):3–1

An experimental study of steel fiber-reinforced high-strength concrete slender columns under cyclic loading

Structural engineers usually limit the use of HSC columns to seismic active zones because of their britle behavior in comparison with NSC, even though it presents advantages both in terms of mechanics and durability. A possible solution to improve the ductile behavior of HSC columns is the use of transverse reinforcement and steel fibers simultaneously. In addition, the use of HSC makes the design of more slender columns possible, with the consequent increase of second-order effects. However, there are few experimental tests on columns of medium slenderness (between 5 and 10) subjected to cyclic loads including or excluding steel fibers. This article presents experimental research work on the behavior of slender columns subjected to combined constant compression and cyclic lateral loads. Fifteen tests were carried out in order to study the behavior of such elements. The following variables were studied: concrete strength, slenderness, axial load level, transverse reinforcement ratio, and volumetric steel-fiber ratio. The maximum load and deformation capacity of the columns were analyzed. The fact that the inclusion of steel fibers into the concrete mixture increases the deformation capacity was verified. Moreover, a minimum transverse reinforcement is required in order to improve the effectiveness of the steel fibers with no significant decrease in the carrying capacity under cyclic loading. The inclusion of steel fibers in HSC can ensure similar ductility values to those of NSC. It was shown that slenderness influences the deformation capacity.Structural engineers usually limit the use of HSC columns to seismic active zones because of their britle behavior in comparison with NSC, even though it presents advantages both in terms of mechanics and durability. A possible solution to improve the ductile behavior of HSC columns is the use of transverse reinforcement and steel fibers simultaneously. In addition, the use of HSC makes the design of more slender columns possible, with the consequent increase of second-order effects. However, there are few experimental tests on columns of medium slenderness (between 5 and 10) subjected to cyclic loads including or excluding steel fibers. This article presents experimental research work on the behavior of slender columns subjected to combined constant compression and cyclic lateral loads. Fifteen tests were carried out in order to study the behavior of such elements. The following variables were studied: concrete strength, slenderness, axial load level, transverse reinforcement ratio, and volumetric steel-fiber ratio. The maximum load and deformation capacity of the columns were analyzed. The fact that the inclusion of steel fibers into the concrete mixture increases the deformation capacity was verified. Moreover, a minimum transverse reinforcement is required in order to improve the effectiveness of the steel fibers with no significant decrease in the carrying capacity under cyclic loading. The inclusion of steel fibers in HSC can ensure similar ductility values to those of NSC. It was shown that slenderness influences the deformation capacity

Behaviour of steel-fibre-reinforced normal-strength concrete slender columns under cyclic loading

The inclusion of ductility requirements is necessary to guarantee a safety design of concrete structures subjected to unexpected and/or reversal loads. It is important to outline that plastic hinges may develop in columns of reinforced concrete buildings, especially in column-foundation joints. The deformation capacity of the column depends on its slenderness. However, for the case of cyclic loading, few experimental tests of normal and fibre-reinforced concrete columns in the range of medium slenderness (between 5 and 10) have been performed. This paper presents an experimental research work on the behavior of slender columns subjected to combinations of constant axial and lateral cyclic loads. In order to study the behavior of this type of elements fourteen experimental tests are performed. The experimental results make it possible to calibrate numerical models, as well as, to validate simplified methods. The following variables are studied: slenderness, axial load level, volumetric transverse reinforcement ratio, and volumetric steel-fibre ratio. The maximum load and deformation capacity of the columns has been analyzed. It is interesting to note that ductility depends on the four tested variables analyzed. Moreover, the inclusion of steel-fibres into the concrete mixture increases the deformation capacity. In order to improve the steel fibres effectiveness the inclusion of a minimum transverse reinforcement is required. Thus, the column behavior suffers moderate strength losses due to cyclic loads. Finally, slenderness influences the deformation capacity if second-order effects are important, the cross-section has a ductile behavior, and materials capacity is reachedThe inclusion of ductility requirements is necessary to guarantee a safety design of concrete structures subjected to unexpected and/or reversal loads. It is important to outline that plastic hinges may develop in columns of reinforced concrete buildings, especially in column-foundation joints. The deformation capacity of the column depends on its slenderness. However, for the case of cyclic loading, few experimental tests of normal and fibre-reinforced concrete columns in the range of medium slenderness (between 5 and 10) have been performed. This paper presents an experimental research work on the behavior of slender columns subjected to combinations of constant axial and lateral cyclic loads. In order to study the behavior of this type of elements fourteen experimental tests are performed. The experimental results make it possible to calibrate numerical models, as well as, to validate simplified methods. The following variables are studied: slenderness, axial load level, volumetric transverse reinforcement ratio, and volumetric steel-fibre ratio. The maximum load and deformation capacity of the columns has been analyzed. It is interesting to note that ductility depends on the four tested variables analyzed. Moreover, the inclusion of steel-fibres into the concrete mixture increases the deformation capacity. In order to improve the steel fibres effectiveness the inclusion of a minimum transverse reinforcement is required. Thus, the column behavior suffers moderate strength losses due to cyclic loads. Finally, slenderness influences the deformation capacity if second-order effects are important, the cross-section has a ductile behavior, and materials capacity is reache

An inverse analysis method based on deflection to curvature transformation to determine the tensile properties of UHPFRC

“The final publication is available at Springer via http://dx.doi.org/[http://dx.doi.org/10.1617/s11527-014-0434-0”[EN] The determination of the tensile properties of such a deflection hardening response material as UHPFRC is a serious challenge for both researchers and designers. This process involves many factors, such as specimen size, fibre orientation or test typology. The socalled inverse analysis is used to obtain the tensile constitutive properties that are consistent with the specimen response in a bending test. This work focuses on the inverse analysis process. The main aim is to develop a new back-calculation methodology, which is easy to implement, reliable, quick and is consistentwith the measurements taken from a four-point bending test. The new methodology proposed has been validated using an analytical formulation and the experimental results of others authors. This paper also includes an application example of how this methodology works.This work forms part of the ‘‘FIBAC’’ and ‘‘FISNE’’ research projects, with reference BIA2009-12722 and BIA2012-35776, respectively, supported by the Spanish Ministry of Economy and Competiveness and the FEDER fund. Support for this project is gratefully acknowledged. We also wish to thank the Universitat Polite`cnica de Vale`ncia for its Excellence Scholarship (PAID-09-11), the Spanish Ministry of Education, Culture and Sport for its FPU scholarship programme, and also Mr. Toshiyuki Kanakubo for his friendly treatment and help.López Martínez, JÁ.; Serna Ros, P.; Navarro Gregori, J.; Camacho Torregrosa, EE. (2015). An inverse analysis method based on deflection to curvature transformation to determine the tensile properties of UHPFRC. Materials and Structures. 48(11):3703-3718. https://doi.org/10.1617/s11527-0.14-0.434-0S37033718481

Effects of tension stiffening and shrinkage on the flexural behavior of reinforced UHPFRC beams

[EN] This paper presents a study on the flexural behavior of Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) beams, which included conventional reinforcing bars. The study focuses on critical design aspects, such as concrete shrinkage and cracking implications on the tension-stiffening phenomenon. An experimental program with two different sized flexural reinforced UHPFRC beams was run. Beams were cast and tested in a four-point bending test (4PBT) using UHPFRC with different amounts of fibers: 130 and 160 kg/m(3) (1.66% and 2.00% in vol.) to cover a wide range of strain-softening and strain-hardening constitutive UHPFRC behaviors. A nonlinear finite element model (NLFEM) was developed to validate the mechanical tensile characterization of UHPFRC when applied to reinforced elements. Both shrinkage and tension-stiffening effects were considered to improve the model. After the NLFEM simulation, very reliable results were obtained at both the service and ultimate load levels compared to the experimental ones. Finally, some aspects about the design of reinforced UHPFRC cross-sections under bending forces are addressed and satisfactorily compared to the experimental results.This work forms part of Project "BIA2016-78460-C3-1-R" supported by the State Research Agency of Spain and the project "Rethinking coastal defence and Green-energy Service infrastructures through enHancEd-durAbiLity high-performance cement-based materials-ReSHEALience", funded by the European Union Horizon 2020 research and innovation programme under GA No 760824.Mezquida-Alcaraz, EJ.; Navarro-Gregori, J.; Martí Vargas, JR.; Serna Ros, P. (2021). Effects of tension stiffening and shrinkage on the flexural behavior of reinforced UHPFRC beams. Case Studies in Construction Materials. 15:1-28. https://doi.org/10.1016/j.cscm.2021.e007461281

A simplified method to predict the ultimate shear stress of reinforcedconcrete membrane elements

This paper presents a new simplified verification method to predict the ultimate shear stress and the mode of failure of reinforced concrete membrane elements with orthogonal reinforcement under any combination of normal stresses. This method is based on a simplified model designed to take the condition of the concrete at failure into account. The methodology is non-iterative, simple and easy to use for practical purposes. The accuracy of the verification method has been checked using test results from 88 RC membrane elements subjected to a wide range of in-plane normal and shear stresses, concrete strengths, and reinforcement ratios for both x and y directions. Moreover, the proposed method is compared with MCFT using Membrane-2000 software and other simplified methods (SMCS by Rahal 2010, the Marti-Kauffman method 1998 and the Mancini proposal 2001). The proposed method strikes a balance between a general view, accuracy and simplicity, using a wide range of tests that cover different modes of failure.The authors of this work wish to thank the research bureau of the Spanish Ministry of Science and Innovation for the funding of the projects BIA 2009-10207 and BIA 2009-11369, and the Universitat Politecnica de Valencia for the funding through the Programa de Apoyo a la Investigacion y Desarrollo (PAID-06-11).Miguel Sosa, P.; Navarro-Gregori, J.; Fernández Prada, MÁ.; Bonet Senach, JL. (2013). A simplified method to predict the ultimate shear stress of reinforcedconcrete membrane elements. Engineering Structures. 49:329-344. https://doi.org/10.1016/j.engstruct.2012.11.009S3293444

Análisis experimental mediante fotogrametría del comportamiento de fisuras de cortante en vigas esbeltas de hormigón armado reforzado con fibras macro sintéticas

[ES] El presente trabajo estudia mediante técnicas de fotogrametría el comportamiento de fisuras inclinadas de cortante en una series de cuatro vigas de hormigón armado (HA) y hormigón reforzado con fibras de polipropileno (HRFP) con y sin refuerzo transversal. Se presta especial atención a la evaluación de los desplazamientos y deslizamientos de las caras de fisuras. Los resultados obtenidos son comparados con resultados medidos durante el transcurso del ensayo por instrumentos (SDLs). Se observa que con el uso de fibras sintéticas dosificadas en 10 kg/m3 , se reduce significativamente la abertura de la fisura diagonal principal en el orden de un tercio. Adicionalmente se observa una no linealidad de relación abertura – deslizamiento a lo largo de la fisura diagonal principal. Finalmente se proporcionan relaciones de abertura – deslizamientos que pueden ser empleados en ensayos Push – offOrtiz Navas, F.; Navarro Gregori, J.; Serna Ros, P. (2018). Análisis experimental mediante fotogrametría del comportamiento de fisuras de cortante en vigas esbeltas de hormigón armado reforzado con fibras macro sintéticas. En HAC 2018. V Congreso Iberoamericano de hormigón autocompactable y hormigones especiales. Editorial Universitat Politècnica de València. 567-576. https://doi.org/10.4995/HAC2018.2018.6411OCS56757

Estudio teórico de capacidad de deformación de soportes esbeltos de hormigón armado con fibras de acero sometidos a esfuerzos combinados de axil y carga lateral

El estudio de la ductilidad es muy importante en elementos estructurales sometidos a esfuerzos combinados, ya que nos determina la capacidad de resistencia y a la deformación. Actualmente son escasos los ensayos experimentales para el estudio de soportes esbeltos sometidos a carga axial y carga lateral cíclica, donde también hay carencia de estudios con respecto a hormigones de alta resistencia y adicion de fibras metálicas (Caballero-Morrison et al (2011)[5]). Se ha desarrollado un modelo numérico utilizando el software Opensees (http://opensees.berkeley.edu). Opensees es una herramienta de simulación disponibles en la Red para la simulación de Ingeniería Sísmica (Nees). En el análisis numérico se consideran las leyes constitutivas de hormigón reforzado con fibras confinados y no confinados bajo cargas cíclicas, y las leyes constitutivas para las barras de acero bajo cargas cíclicas y sometido a pandeo. Se ha realizado un estudio teórico de comportamiento inelástico de soportes esbeltos de hormigón definiéndose un modelo numérico en Opensees; dicho modelo ha sido calibrado con 25 ensayos experimentales propios. Los parámetros de estudio utilizados son: el nivel de axil, esbeltez a cortante, resistencia del hormigón, la cuantía de la armadura transversal, el tamaño de la sección y la adición de fibras metálicas en la masa del hormigón.El estudio de la ductilidad es muy importante en elementos estructurales sometidos a esfuerzos combinados, ya que nos determina la capacidad de resistencia y a la deformación. Actualmente son escasos los ensayos experimentales para el estudio de soportes esbeltos sometidos a carga axial y carga lateral cíclica, donde también hay carencia de estudios con respecto a hormigones de alta resistencia y adicion de fibras metálicas (Caballero-Morrison et al (2011)[5]). Se ha desarrollado un modelo numérico utilizando el software Opensees (http://opensees.berkeley.edu). Opensees es una herramienta de simulación disponibles en la Red para la simulación de Ingeniería Sísmica (Nees). En el análisis numérico se consideran las leyes constitutivas de hormigón reforzado con fibras confinados y no confinados bajo cargas cíclicas, y las leyes constitutivas para las barras de acero bajo cargas cíclicas y sometido a pandeo. Se ha realizado un estudio teórico de comportamiento inelástico de soportes esbeltos de hormigón definiéndose un modelo numérico en Opensees; dicho modelo ha sido calibrado con 25 ensayos experimentales propios. Los parámetros de estudio utilizados son: el nivel de axil, esbeltez a cortante, resistencia del hormigón, la cuantía de la armadura transversal, el tamaño de la sección y la adición de fibras metálicas en la masa del hormigón

Comportamiento de soportes esbeltos de hormigón armado con fibras de acero sometidos a esfuerzos combinados de axil y carga lateral cíclica

La ductilidad es un indicador de la capacidad de deformación en estructuras sometidas a esfuerzos combinados de axil y carga lateral cíclica. El elemento estructural sometido a estos esfuerzos debe ser capaz de absorber y de disipar la energía sin que se produzca una significativa perdida de capacidad resistente. En la actualidad, las normativas para el diseño sísmico estructural, (EC-8 (2004)[4], ACI-318(11)[1]) especifican la disposición de la cuantía de armadura transversal a disponer en las zonas críticas susceptibles de albergar una rótula plástica. Para niveles altos de axil es necesario disponer una cuantía importante de armadura transversal. Dicha cuantía puede suponer problemas durante la puesta en obra del hormigón. La literatura técnica señala como una posible solución para mejorar la ductilidad de este tipo de soportes utilizar hormigón con fibras en su masa. Por otro lado, los efectos de segundo orden que se producen en los soportes influyen en la capacidad de deformación (Bae y Bayrak (2006)[8]); y en la literatura técnica son escasos los ensayos experimentales de soportes cuya esbeltez sea superior a 6.5. Por tales razones se han realizado 25 ensayos experimentales donde se estudian parámetros como la resistencia del hormigón, la esbeltez geométrica de la pieza, la cuantía de armadura tranversal, el nivel de axil reducido, la sección transversal y la adición de fibras metálicas en la masa del hormigón. Estos ensayos tienen como objetivo conocer la capacidad de deformación y de resistencia sometidos a una carga axial y carga lateral cíclica según los parámetros mencionados anteriormente; y además han de servir para calibrar modelos numéricos y validar métodos simplificados.La ductilidad es un indicador de la capacidad de deformación en estructuras sometidas a esfuerzos combinados de axil y carga lateral cíclica. El elemento estructural sometido a estos esfuerzos debe ser capaz de absorber y de disipar la energía sin que se produzca una significativa perdida de capacidad resistente. En la actualidad, las normativas para el diseño sísmico estructural, (EC-8 (2004)[4], ACI-318(11)[1]) especifican la disposición de la cuantía de armadura transversal a disponer en las zonas críticas susceptibles de albergar una rótula plástica. Para niveles altos de axil es necesario disponer una cuantía importante de armadura transversal. Dicha cuantía puede suponer problemas durante la puesta en obra del hormigón. La literatura técnica señala como una posible solución para mejorar la ductilidad de este tipo de soportes utilizar hormigón con fibras en su masa. Por otro lado, los efectos de segundo orden que se producen en los soportes influyen en la capacidad de deformación (Bae y Bayrak (2006)[8]); y en la literatura técnica son escasos los ensayos experimentales de soportes cuya esbeltez sea superior a 6.5. Por tales razones se han realizado 25 ensayos experimentales donde se estudian parámetros como la resistencia del hormigón, la esbeltez geométrica de la pieza, la cuantía de armadura tranversal, el nivel de axil reducido, la sección transversal y la adición de fibras metálicas en la masa del hormigón. Estos ensayos tienen como objetivo conocer la capacidad de deformación y de resistencia sometidos a una carga axial y carga lateral cíclica según los parámetros mencionados anteriormente; y además han de servir para calibrar modelos numéricos y validar métodos simplificados