Comportamiento adherente del hormigón autocompactante en transmisión y anclaje

Self-compacting concretes (SCC) provide solutions to the problems facing precast concrete construction, enhancing competitiveness, reducing turnaround times and improving final product quality. SCC is fast becoming a key product for the future development of the precast pre-stressed concrete industry.The present paper compares the bond performance of SCC and traditional concrete (TC). The bond performance results confirm the viability of SCC in precast pre-stressed concrete manufacture, despite a slightly higher loss of pre-stressing force and slightly greater anchorage lengths in SCC with a low water/cement ratio. No differences in transfer or anchorage length were detected,however, when high strength TC and SCC were compared. The ECADA test method proved to be well suited to detecting the differences between the concretes analyzed.El desarrollo de los hormigones autocompactantes (SCC)ofrece muchas posibilidades a las construcciones con hormigón prefabricado, aumentando su competitividad, reduciéndolos plazos de fabricación y ofreciendo mejoras en la calidad del producto final. El SCC se está convirtiendo en un producto clave para el futuro desarrollo de la industria de prefabricados de hormigón pretensado.En este estudio se compara el comportamiento adherente de los SCC con el de los hormigones tradicionales (TC) actuales. Los resultados obtenidos confirman la viabilidad del uso de los SCC para la fabricación de elementos prefabricados con hormigón pretensado, en lo relativo a su comportamiento adherente, aunque con la necesidad de considerar unas pérdidas de pretensado ligeramente mayores. Asimismo,debe esperarse un ligero aumento de las longitudes de anclaje cuando se trabaje con SCC de baja relación agua/cemento. Sin embargo, no se han detectado diferencias de comportamiento entre ambos tipos de hormigón cuando la resistencia a compresión es alta en lo relativo a las longitudes de transmisión y anclaje. El método de ensayo ECADA muestra una buena adecuación para detectar las diferencias de comportamiento entre los hormigones analizado

Multi-performance experimental assessment of autogenous and crystalline admixture-stimulated self-healing in UHPFRCCs : validation and reliability analysis through an inter-laboratory study

The huge benefits brought by the use of Ultra High-Performance Fibre-Reinforced Cementitious Composites (UHPFRCCs) include their high “intrinsic” durability, which is guaranteed by (1) the compact microstructure and (2) the positive interaction between stable multiple-cracking response and autogenous self-healing capability. Hence, self-healing capability must be properly characterized addressing different performances, thus providing all the tools for completely exploiting such large potential. Within this context, the need is clear for a well-established protocol for self-healing characterization. To this end, in the framework of the Cost Action CA15202 SARCOS, six Round Robin Tests involving 30 partners all around Europe were launched addressing different materials, spanning from ordinary concrete to UHPFRCC, and employing different self-healing technologies. In this paper, the tailored experimental methodology is presented and discussed for the specific case of autogenous and crystalline-admixture stimulated healing of UHPFRCC, starting from the comparison of the results from seven different laboratories. The methodology is based on chloride penetration and water permeability tests in cracked disks together with flexural tests on small beams. The latter ones are specifically aimed at assessing the flexural performance recovery of UHPFRCCs, which stands as their signature design “parameter” according to the most recent internationally recognized design approaches. This multi-fold test approach allows to address both inherent durability properties, such as through-crack chloride penetration and apparent water permeability, and more structural/mechanical aspects, such as flexural strength and stiffness.peer-reviewe

Ductility of wide-beam RC frames as lateral resisting system

[EN] Some Mediterranean seismic codes consider wide-beam reinforced concrete moment resisting frames (WBF) as horizontal load carrying systems that cannot guarantee high ductility performances. Conversely, Eurocode 8 allows High Ductility Class (DCH) design for such structural systems. Code prescriptions related to WBF are systematically investigated. In particular, lesson learnt for previous earthquakes, historical reasons, and experimental and numerical studies underpinning specific prescriptions on wide beams in worldwide seismic codes are discussed. Local and global ductility of WBF are then analytically investigated through (1) a parametric study on chord rotations of wide beams with respect to that of deep beams, and (2) a spectral-based comparison of WBF with conventional reinforced concrete moment resisting frames (i.e. with deep beams). Results show that the set of prescriptions given by modern seismic codes provides sufficient ductility to WBF designed in DCH. In fact, global capacity of WBF relies more on the lateral stiffness of the frames and on the overstrength of columns rather than on the local ductility of wide beams, which is systematically lower with respect to that of deep beams.Gómez-Martínez, F.; Alonso Durá, A.; De Luca, F.; Verderame, GM. (2016). Ductility of wide-beam RC frames as lateral resisting system. Bulletin of Earthquake Engineering. 14(6):1545-1569. doi:10.1007/s10518-016-9891-xS15451569146ACI (1989) Building code requirements for reinforced concrete (ACI 318-89). ACI Committee 318, American Concrete Institute, Farmington Hills, Michigan, USAACI (2008) Building code requirements for structural concrete (ACI 318-08) and commentary (318-08). ACI Committee 318, American Concrete Institute, Farmington Hills, Michigan, USAACI-ASCE (1991) Recommendations for design of beam-column connections in monolithic reinforced concrete structures (ACI 352R-91). 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J Earthquake Eng 11:493–511Benavent-Climent A, Zahran R (2010) An energy-based procedure for the assessment of seismic capacity of existing frames: application to RC wide beam systems in Spain. Soil Dyn Earthq Eng 30:354–367Benavent-Climent A, Cahís X, Zahran R (2009) Exterior wide beam-column connections in existing RC frames subjected to lateral earthquake loads. Eng Struct 31:1414–1424Benavent-Climent A, Cahís X, Vico JM (2010) Interior wide beam-column connections in existing RC frames subjected to lateral earthquake loading. Bull Earthq Eng 8:401–420BHRC (2004) Iranian Code of Practice for Seismic Resistant Design of Buildings. Standard Nº 2800, 3rd edn. Building and Housing Research Center, TehranBorzi B, Elnashai AS (2000) Refined force reduction factors for seismic design. Eng Struct 22:1244–1260Borzi B, Pinho R, Crowley H (2008) Simplified pushover-based vulnerability analysis for large-scale assessment of RC buildings. 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Earthquake Eng Struct Dynam 42(4):523–543De Luca F, Verderame GM, Gómez-Martínez F, Pérez-García A (2014) The structural role played by masonry infills on RC building performances after the 2011 Lorca, Spain, earthquake. Bull Earthq Eng 12(5):1999–2026Decanini LD, Mollaioli F (2000) Analisi di vulnerabilità sismica di edifici in cemento armato pre-normativa. In: Cosenza E (ed) Comportamento sismico di edifici in cemento armato progettati per carichi verticali. CNR—Gruppo Nazionale per la Difesa dei Terremoti, Rome (in Italian)Dolšek M, Fajfar P (2004) IN2—a simple alternative for IDA. In: Proceedings of the 13th World conference on Earthquake Engineering. August 1–6, Vancouver, Canada. Paper 3353Domínguez D, López-Almansa F, Benavent-Climent A (2014) Comportamiento para el terremoto de Lorca de 11-05-2011, de edificios de vigas planas proyectados sin tener en cuenta la acción sísmica. Informes de la Construcción 66(533):e008 (in Spanish)Domínguez D, López-Almansa F, Benavent-Climent A (2016) Would RC wide-beam buildings in Spain have survived Lorca earthquake (11-05-2011)? Eng Struct 108:134–154Dönmez C (2013) Seismic Performance of Wide-Beam Infill-Joist Block RC Frames in Turkey. J Perform Constr Facil 29(1):04014026Fadwa I, Ali TA, Nazih E, Sara M (2014) Reinforced concrete wide and conventional beam-column connections subjected to lateral load. Eng Struct 76:34–48Fardis MN (2009) Seismic design, assessment and retrofitting of concrete, Buildings edn. Springer, LondonGentry TR, Wight JK (1992) Reinforced concrete wide beam-column connections under earthquake-type loading. Report no. UMCEE 92-12. Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan, USAGómez-Martínez F (2015) FAST simplified vulnerability approach for seismic assessment of infilled RC MRF buildings and its application to the 2011 Lorca (Spain) earthquake. Ph.D. Thesis, Polytechnic University of Valencia, SpainGómez-Martínez F, Pérez García A, De Luca F, Verderame GM (2015a) Comportamiento de los edificios de HA con tabiquería durante el sismo de Lorca de 2011: aplicación del método FAST. Informes de la Construcción 67(537):e065 (in Spanish)Gómez-Martínez F, Pérez-García A, Alonso Durá A, Martínez Boquera A, Verderame GM (2015b) Eficacia de la norma NCSE-02 a la luz de los daños e intervenciones tras el sismo de Lorca de 2011. In: Proceedings of Congreso Internacional sobre Intervención en Obras Arquitectónicas tras Sismo: L’Aquila (2009), Lorca (2011) y Emilia Romagna (2012), May 13–14, Murcia, Spain (in Spanish)Gómez-Martínez F, Verderame GM, De Luca F, Pérez-García A, Alonso-Durá, A (2015c). High ductility seismic performances of wide-beam RC frames. In; XVI Convegno ANIDIS. September 13–17, L'Aquila, ItalyHawkins NM, Mitchell D (1979) Progressive collapse of flat plate structures. 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Statistical Approach to Effect of Factors Involved in Bond Performance of Steel Fiber-Reinforced Concrete

It has been shown that the role fibers play in the bond of reinforcing bars in concrete is of the same importance as that of concrete cover or reinforcing bar diameter. It is especially remarkable that the mere fact of adding fibers—regardless of the amount—considerably ..

A Comprehensive Study on the Effect of Fibers and Loading on Flexural Creep of SFRC

This paper reports the results of a research whose aim was to study how the following variables affect the way SFRC behaves in the postcrack region when under sustained flexural loads: fibers length and slenderness, fibers content, maximum aggregate size, and the load applied. A new methodology based on a test setup developed by the authors has been followed in this research, where notched prismatic 150x150x600 mm specimens are subject to a flexural creep test which follows the four-point bending scheme. Several parameters have been measured: initial crack width, crack width at 90 days, and crack opening rates and creep coefficients at 14, 30, and 90 days. The effect of the variation of the variables considered on these parameters has been evaluated by means of statistical inference based on multiple linear regression models. Results clearly show that varying fiber slenderness leads to important differences regarding concrete’s flexural creep behaviour. The mere fact of adding fibers is good from the point of view of controlling creep strain, though variation in fiber content between 40 kg/m3 and 70 kg/m3 has turned out to be not so important when compared to the effect that varying the load applied has on many of the parameters analysed

New Views on the Study of Variables Affecting Bond of Reinforcing Bars to Steel Fiber Reinforced Concrete

Fibers have a positive effect on bond of rebars to concrete since they clearly improve bond capacity in terms of ductility although their influence on bond strength, i.e. peak bond stress, is of relatively little importance. This paper reports the results of two series of pullout tests carried out on prismatic specimens made with two different SFRCs (required compressive strengths of 25 MPa and 45 MPa respectively) and comprehensively analyses the effect of four factors (fiber geometry and content, concrete cover, and rebar diameter) upon bond performance. In order to come to conclusions that can be considered as statistically reliable, all results have been analyzed by means of statistical inference based on multiple linear regression models. Furthermore, having some specimens where concrete splitted before the rebar was pulled out, the effect of the aforementioned factors on the probability of splitting has been analyzed by means of logistic regression. It has been shown that the role fibers play in bond of rebars to concrete is of the same importance as that of concrete cover. It is especially remarkable that the mere fact of adding fibers, no matter the amount, decreases the probability of splitting and increases the ductility of bond failure considerably, this underlining the role of fibers in bond performance as passive confinement

APULOT test: a tool for concrete's quality control based on bond performance

The APULOT test, or bottle test, is a cheap and simple alternative to cylindrical specimens that can be applied in those regions where conventional quality control is difficult to introduce due to the lack of apropriate means. Specimens for this test are produced by casting concrete into an empty plastic bottle (the mould) with a reinforcing bar longitudinally centered, so that the result is a bottle-shaped concrete specimen with an embedded rebar. At the desired age, the rebar is simply pulled out of the concrete specimen, and the maximum pulling force achieved is the parameter used for quality control. A considerable number of bottle specimens and cylindrical specimens have been produced and tested according to a statistically designed experiment. It has been investigated how different parameters affect the bottle test results and their relation to compressive strength of concrete in order to compare the reliability of the bottle test with the conventional assessment of compressive strength by means of cylindrical specimens for quality control. All results have been analyzed by means of analysis of variance, multiple linear regression and logistic regression. These analyses have made possible: the identification of the best configuration of the parameters considered to be taken into account for an eventual standardization of the test, and finding expressions showing how the test results are to be translated in terms of concrete compressive strength

Autogeneous self healing of High Performance Fibre Reinforced Cementitious Composites

In this paper the results are shown of a thorough characterization of the self-healing capacity of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs). In detail, the capacity of the material to completely or partially re-seal cracks will be investigated, as a function of its composition, maximum crack opening and exposure conditions. The topic has been investigated including the effect of different flow-induced alignment of fibres, which can result into an either a strain hardening or softening behaviour, whether the material is stressed parallel or perpendicularly to the fibres. Specimens were initially pre-cracked in 4-point bending and up to different values of crack openings, and submitted to different exposure conditions, including water immersion, exposure to humid or dry air, and wet-and-dry cycles. After scheduled exposure times, from one to six months, specimens were tested up to failure according to the same test set-up and outcomes of the self-healing, if any, were quantified in terms of recovery of stiffness, strength and ductility. In a durability-based design framework, self-healing indices to quantify the recovery of mechanical proper-ties were also defined and their significance checked