Towards a unified mechanical model for design and assessment of structural concrete members under shear, flexure and punching

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.A mechanical shear model for structural concrete members with and without stirrups is presented, which incorporates the most relevant shear transfer mechanisms. The model is based on the principles of structural mechanics, on a number of assumptions supported by the observed experimental behaviour and by the results of refined numerical models. Simple, direct and robust expressions are derived for shear strength verification and for design of the transverse reinforcement. The general theory behind the model enables it for steel or FRP simply supported or continuous, reinforced or prestressed concrete members, with any cross section, subjected to distributed and point loads or to axial forces. Excellent agreement between the results of a large number of shear tests and the model predictions has been obtained. The model is currently being extended to punching of slabs, for which the critical perimeter is obtained as a result of the model formulatio

Modelo mecánico para la resistencia a cortante de vigas de hormigón armado reforzado con fibras, sin armadura de cortante

Despite the numerous studies made showing that the addition of steel fibres to concrete enhances the shear strength of RC beams, current design formulations are still empirical and present large scatter in front of the test results. In this paper, the previously developed Multi-Action Shear Model is extended to SFRC beams without stirrups, adopting an analytical formulation to evaluate the residual tensile stress of SFRC and incorporating the effects of the crack bridging capacity of SFRC in the shear resisted trough the different shear-transfer mechanisms. The proposed model predicts the tests results included in a recently published database with 448 shear tests with less scatter than any of the existing models.The financial support provided by the University of Messina (Italy), through the scholarship granted for a two-months research and teaching stage of the first author, is acknowledged. This work is part of the Research Projects BIA2015-64672-C4-1-R, funded by the Spanish Ministry of Economy and competitiveness, and RTI2018-097314-B-C21, funded by the Spanish Ministry of Science and Innovation.Postprint (published version

Optimization of existing equations using a new genetic programming algorithm: application to the shear strength of reinforced concrete beams

[Abstract] A method based on Genetic Programming (GP) to improve previously known empirical equations is presented. From a set of experimental data, the GP may improve the adjustment of such formulas through the symbolic regression technique. Through a set of restrictions, and the indication of the terms of the expression to be improved, GP creates new individuals. The methodology allows us to study the need of including new variables in the expression. The proposed method is applied to the shear strength of concrete beams. The results show a marked improvement using this methodology in relation to the classic GP and international code procedures.Ministerio de Ciencia e Innovación; BIA2007-60197Ministerio de Ciencia e Innovación; BIA2010-21551Xunta de Galicia; 08TMT005CTXunta de Galicia; 10TMT034

The compression chord capacity model for the shear design and assessment of reinforced and prestressed concrete beams

This is the accepted version of the following article: [Cladera, A., Marí, A., Bairán, J. M., Ribas, C., Oller, E. and Duarte, N. (2016), The compression chord capacity model for the shear design and assessment of reinforced and prestressed concrete beams. Structural Concrete, 17: 1017–1032. doi:10.1002/suco.201500214], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/suco.201500214/fullA simplified mechanical model is presented for the shear strength prediction of reinforced and prestressed concrete members with and without transverse reinforcement, with I, T or rectangular cross-section. The model, derived with further simplifications from a previous one developed by the authors, incorporates the contributions of the concrete compression chord, the cracked web, the dowel action and the shear reinforcement in a compact formulation. The mechanical character of the model provides valuable information about the physics of the problem and incorporates the most relevant parameters governing the shear strength of structural concrete members. The predictions of the model fit very well the experimental results collected in the ACI-DAfStb databases of shear tests on slender reinforced and prestressed concrete beams with and without stirrups. Due to this fact and the simplicity of the derived equations it may become a very useful tool for structural design and assessment in engineering practice.Peer ReviewedPostprint (author's final draft

Efecte de la incorporació d’àrid mixt reciclat a les propietats de formigons no estructurals

[cat] Els àrids mixts reciclats són els que, provinents del tractament dels residus de construcció i demolició, inclouen com a principals components residus de formigó, àrids no lligats i productes ceràmics. A l’article es presenten els resultats obtinguts a una campanya experimental sobre la influència de la substitució d’àrid convencional per àrid mixt reciclat en dosificacions de formigons no estructurals. Es contempla la utilització de dos tipus de ciment, un ciment Portland mixt i un ciment compost resistent a sulfats. S’observa un comportament diferent del formigó, segons el tipus de ciment utilitzat, a mesura que s’augmenta el percentatge de substitució de l’àrid convencional per àrid mixt reciclat. L’estudi conclou que, a falta d’un estudi del comportament a llarg termini i de dosificacions específiques per a cada ús, l’àrid mixt reciclat pot ser vàlid per la fabricació de formigó no estructural

Shear design of reinforced concrete beams with FRP longitudinal and transverse reinforcement

The shear resisting mechanisms of reinforced concrete (RC) beams with longitudinal and transverse FRP reinforcement can be affected by the mechanical properties of the FRP rebars. This paper presents a mechanical model for the prediction of the shear strength of FRP RC beams that takes into account its particularities. The model assumes that the shear force is taken by the un-cracked concrete chord, by the residual tensile stresses along the crack length and by the FRP stirrups. Failure is considered to occur when the principal tensile stress at the concrete chord reaches the concrete tensile strength, assuming that the contribution of the FRP stirrups is limited by a possible brittle failure in the bent zone. The accuracy of the proposed method has been verified by comparing the model predictions with the results of 112 tests. The application of the model provides better statistical results (mean value V-test/V-pred equal to 1.08 and COV of 19.5%) than those obtained using the design equations of other current models or guidelines. Due to the simplicity, accuracy and mechanical derivation of the model it results suitable for design and verification in engineering practice. (C) 2015 Elsevier Ltd. All rights reserved.Peer ReviewedPostprint (published version

Un modelo unificado de resistencia a flexión y cortante de vigas esbeltas de hormigón armado bajo caras puntuales y repartidas

Se presenta un modelo mecánico para la predicción de la resistencia a cortante-flexión de vigas esbeltas de hormigón armado sometidas a cargas puntuales y/o repartidas. El modelo incorpora las contribuciones a la resistencia a cortante de la cabeza comprimida, del alma fisurada y de las armaduras longitudinales y transversales. Se considera que la rotura tiene lugar en la cabeza comprimida no fisurada de hormigón, sometida a un estado biaxial de tensiones, cuando se alcanza la envolvente de Kupfer, habiendo plastificado las armaduras transversales. Basándose en consideraciones de equilibrio y en una distribución de tensiones en ELU para la cabeza comprimida, se proponen ecuaciones sencillas y directas para dimensionamiento y comprobación. Las predicciones del modelo se han comparado con más de 1300 ensayos a cortante de vigas, obteniéndose muy buenos resultados. El modelo proporciona una explicación física del comportamiento a cortante, lo que junto a su sencillez y precisión, le convierte en una herramienta muy útil para el proyecto basado en prestaciones.Peer ReviewedPostprint (author's final draft

Joint strengthening by external bars on RC beam-column joints

[EN] Column strengthening is a very common practice for improving the seismic performance of reinforced concrete frame structures or repairing damage after a seismic event. Several methods are employed for column strengthening, which can improve column strength by preventing its shear, bending or compression failure. However, not all methods allow column strengthening connections between adjacent floors, thus the beam-column joint strength could be limited by the column-joint interface capacity. This work aimed to analyse two joint strengthening designs, for which an experimental campaign of eight full-scale beam-column joints strengthened with steel caging, and subjected to cyclic and gravity loads, was carried out. As access to joint panels is very complex in existing structures, joint strengthening consists of external solutions: vertical or diagonal bars and capitals connecting columns. The results showed that these techniques significantly increased beam-column joint strength and highlighted that failure can be undesirably transferred to the joint. Vertical bars prevented the bending failure of the column-joint interface, but failure occurred at the joint in this study. Diagonal bars can also prevent joint failure.The authors wish to thank the financial support provided by the Spanish Ministry of Science and Innovation and the Spanish Ministry of Economy and Competitiveness with Research Projects BIA 2008-06268 and RTI2018-099091-B-C22.Ruiz Pinilla, JG.; Cladera, A.; Pallarés Rubio, FJ.; Calderón García, PA.; Adam, JM. (2022). Joint strengthening by external bars on RC beam-column joints. Journal of Building Engineering. 45:1-14. https://doi.org/10.1016/j.jobe.2021.1034451144