Nueva metodología para el diseño de tubos de hormigón estructural
Authors:   , Fuente Antequera Albert de la 
Published: July 2023

The technical and economic suitability of using fibers has been proved in reinforced concrete pipes.However, the use of fibers in concrete pipe is slow, on the one hand due to the inertia to change in the construction field, and on the other hand due to the lack of a standardized, agile and reliable design method that accounts for the structural contribution of fibers.
In this sense, this Doctoral Thesis aims to cover these aspects with regard to reinforced concrete pipes. For this purpose, a design method allows considering the strength contribution of the fibers in concrete pipes is proposed. Furthermore, in order to favour the spread of the results both to the scientific and the industrial community, the document of the Doctoral Thesis is presented as a compendium of articles accepted and / or in review status in scientific journals. Each of these articles presents the results of each of the lines of work and whose union has helped to achieve the main objective of this Doctoral Thesis.

Firstly, the numerical tool Analysis of Evolutionary Sections (AES) developed to deal with the analysis of the strength response of reinforced concrete sections is presented. The tool is general and can simulate different reinforcement configurations (passive and/or active reinforcement with the possibility of incorporating fibers) and even the evolutionary construction of the section taking into account the rheological behaviour of materials. The model AES was subsequently used as a calculation tool of sections with the aim of addressing parametric studies as well as a subroutine into the other two models developed in the scope of this Doctoral Thesis.

The second line of work focuses on the study of conventional reinforced concrete pipes. To address their optimal design the model Análisis de Tubos de Hormigón (ATH) has been developed. The practical interest of the model lies in the possibility of obtaining the optimal amount of reinforcement which meets the requirements in terms of bearing capacity specified in project. These reinforcements obtained from the models are, in most of the cases, inferior to the amounts in the design tables that are used traditionally.

With the purpose of confirming the suitability of the ATH, an experimental campaign with tubes of 2800 mm of diameter has been carried out. By using the model, reductions up to 30% of the reinforcement have been obtained for pipes with the aforementioned diameter, while the differences in the bearing capacity do not exceed 10% when compared to the results of the three bearing edge test performed in the laboratory.

The third and final line of work deepens into the technical and industrial side of the fiber reinforced concrete pipes. On the one hand, an extensive experimental campaign (some of it developed at the Universidade de São Paulo) is conducted, addressing issues associated with fiber reinforced concrete as well as others regarding the three edges test and the structural response of tubes of different diameters and with different amounts of fibers. On the other hand, the model for the Analysis of Pipes (MAP) was developed simultaneously for simulating the structural response of the fiber reinforced concrete pipes.

The results of the bearing capacity of tubes up to 1000 mm of diameter tested have been compared with simulations performed with the MAP model, obtaining excellent correlations and not exceeding, in any case, the 5.5% relative error between the design loads. In view of the good results, it can be concluded that the design methodology herein presented, based on the use of the MAP model, ensures results that fit real behaviour and that the amounts of reinforcement provided are very close to the optimum necessary to meet the strength requirements established in each case.
El hormigón reforzado con fibras ha demostrado ser una alternativa atractiva frente al hormigón
armado tradicional en numerosas tipologías estructurales. En los últimos diez años, los avances
técnicos llevados a cabo en relación con este material han sido muy importantes, prueba de ello es
que varios códigos normativos nacionales a nivel europeo ya han aceptado las fibras estructurales
como material de refuerzo del hormigón, entre ellos la instrucción española EHE‐08 “Instrucción de
Hormigón Estructural” en su Anejo 14.
A pesar del escenario aparentemente positivo, la consideración de aporte resistente asociado al uso
de las fibras es todavía anecdótica, lo cual no responde en la mayoría de las ocasiones a razones
técnicas, sino a la gran inercia al cambio existente en el sector general de la construcción.
Este es el caso de las tuberías de hormigón armado para redes de saneamiento. Se trata de una
tipología estructural para la cual la idoneidad técnica y económica del uso de fibras ya se ha
demostrado. Asimismo, también ha sido regulado por varias normativas nacionales específicas de
tubos, entre éstas, la UNE‐EN 1916:2008 “Tubos y piezas complementarias de hormigón en masa,
hormigón armado y hormigón con fibra de acero”. Sin embargo, el empleo de forma natural de
fibras en tubos de hormigón está siendo lento, por una parte, debido a la inercia al cambio
anteriormente citada, a lo que debe sumarse el hecho que pocas de las varias experiencias llevadas
a cabo se han plasmado en la literatura técnica, y, por otra, a que no existe un método de diseño
estandarizado, ágil y fiable al alcance de los proyectistas que permita tener en cuenta la
incorporación de las fibras como material resistente.
En esta dirección, la presente Tesis Doctoral tiene como objetivo cubrir estos aspectos asociados
con los tubos de hormigón armado. Para ello, los trabajos llevados a cabo han permitido lograr
distintos avances en relación con los tubos de hormigón armado tradicionales y los tubos de
hormigón armado con fibras. Respecto a estos últimos, se propone el primer método para el diseño
conocido hasta la fecha y que permite considerar la contribución resistente de las fibras. Además,
de cara a maximizar la difusión de los resultados tanto hacia la comunidad científica como hacia la
industrial, el documento de Tesis se plantea como un compendio de artículos aceptados y/o en
estado de revisión en revistas científicas en los que se recogen los resultados específicos de cada
una de las partes, cuya unión, ha permitido alcanzar el objetivo principal de esta Tesis Doctoral.