J.C. Gálvez

Mixed Mode Fracture of Concrete under Proportional and Nonproportional Loading

A novel testing procedure for mixed mode crack propagation in concrete is presented: four point bend of notched beams under the action of two independent force actuators. In contrast to classical procedures, this method allows nonproportional loading and crack trajectory modifications by changing the action of one actuator. Different experimental crack trajectories, under mixed mode and nonproportional loading, are presented together with the corresponding curves of load-CMOD and load-displacement. The tests were performed for three homotetic specimen sizes and two mixed mode loading conditions. The results are useful for checking the accuracy of mixed mode fracture analytical and numerical models. The models should predict the crack trajectory and a complete group of experimental records of load and displacements on several control points in the specimen.

Modelling the fracture of concrete under mixed loading

A simple and efficient numerical procedure for mixed mode fracture of quasibrittle materials is shown: This technique predicts crack trajectories as well as load-displacement or load-CMOD responses. The model is based on the cohesive crack concept and uses the local mode I approach. Numerical results agree quite well with three experimental sets of mixed mode fracture of concrete beams; one from Arrea and Ingraffea, another from García, Gettu and Carol and from a nonproportional loading by the authors. In constrast to more sophisticated models, this method offers two major advantages: it requires only material properties measured by standardized methods and it can easily be implemented with general multipurpose finite element codes.

A discrete crack approach to normal/shear cracking of concrete

This paper presents a numerical procedure for mixed mode fracture of quasi-brittle materials. The numerical procedure is based on the cohesive crack approach and extends it to mixed mode fracture. The crack path is obtained, and the mixed mode fracture model is incorporated into the crack path. The crack model is based on the formulation of the classical plasticity. The model is incorporated into a commercial finite element code by an user subroutine and is contrasted with experimental results. The numerical results agree quite well with two experimental sets of mixed mode fracture of concrete beams; one from Arrea and Ingraffea, the other from a nonproportional loading by the authors. Two other sets of experimental fracture results were modeled based on double-edge notched testing. The numerical procedure, mainly based on standard properties of the material measured by standard methods, predicts the experimental records of the load versus displacement at several control points of the specimens for three homothetic sizes of specimen.

Influence of shear parameters on mixed-mode fracture of concrete

The influence of the mode II fracture parameters on the mixed mode fracture experimental tests of quasibrittle materials is studied. The study is based on experimental results and numerical analyses. For the numerical study, a procedure for mixed mode fracture of quasibrittle materials is presented. The numerical procedure is based on the cohesive crack approach, and extends it to mixed mode fracture. Four experimental sets of mixed mode fracture were modelled, one from Arrea and Ingraffea and another from a nonproportional loading by the authors, both with bending concrete beams. Two other sets of experimental fracture were modelled, based on double-edge notched testing; in these tests an important mode II is beforehand expected. The numerical results agree quite well with experimental records. The influence of the main parameters for mode II fracture on the mixed mode fracture is studied for the four experimental set of tests and compared with these results. In all them, large changes in the mode II fracture energy hardly modify the numerical results. The tangential and normal stresses along the crack path during the loading proccess are obtained, also with different values of the mode II fracture energy. For the studied experimental tests it is concluded that the crack is initiated under mixed mode but propagated under predominant mode I. This allows a development of mixed mode fracture models, mainly based on standard properties of the material measured by standard methods, avoiding the problems associated with the measurement of mode II fracture parameters, such as mode II fracture energy and cohesion.

Crack trajectories under mixed mode and non-proportional loading

A novel testing procedure for mixed mode crack propagation is presented; it offers the possibility of non-proportional loading and of changing the crack trajectory during testing, features which allow non-traditional mixed mode tests which, in turn, may help in discriminating mixed mode fracture criteria. Detailed experimental stable crack trajectories and corresponding load-CMOD (or load-displacement) curves from these non-traditional tests are proposed as benchmarks for numerical programs of mixed mode crack propagation.

Experiencias Docentes en Innovación Educativa como Mejora de una Enseñanza Tradicional de los Materiales de Construcción

This paper presents the results of a teaching experience in the subject Construction and Building Materials after incorporating active methodologies as suggested by the European Higher Education Area (EHEA). From the academic year 2006-07 traditional teaching methods were improved, based on the use of cooperative learning, continuous assessment and new technologies. In the last three courses there has been a marked increase in the number of students passing the course, 32% increase over students enrolled in the subject, in comparison with previous academic years. Based on these results it can be concluded that the use of active teaching techniques to complement traditional teaching improves learning of students and enhance student’s motivation. However, the use of these techniques requires greater dedication of teachers and greater involvement of students in their learning process.

Introduction of Innovations into the Traditional Teaching of Construction and Building Materials

The traditional teaching methods used for training civil engineers are currently being called into question as a result of the new knowledge and skills now required by the labor market. In addition, the European Higher Education Area is requesting that students be given a greater say in their learning. In the subject called Construction and Building Materials at the Civil Engineering School of the Universidad Politecnica de Madrid, a path was set three academic years ago to lead to an improvement in traditional teaching by introducing active methodologies. The innovations are based on cooperative learning, new technologies, and continuous assessment. The writers proposal is to offer their experience as a contribution to the debate on how students can be encouraged to acquire the skills currently demanded from a civil engineer, though not overlooking solid, top-quality training. From the outcomes obtained, it can be concluded that using new teaching techniques to supplement a traditional approach provides more opportunities for students to learn while boosting their motivation. In our case, the introduction of these changes has resulted in an increased pass rate of 29% on average, when such a figure is considered in the light of the mean value of passes during the last decade.

Study of the brickwork masonry cracking with a cohesive fracture model

Este articulo presenta un modelo de calculo que permitensimular el comportamiento en rotura de la fabrica denladrillo bajo solicitaciones de traccion y cortante. Elnmodelo extiende el modelo cohesivo formulado por losnautores para hormigon, considerando la anisotropia delnmaterial. El procedimiento de calculo consta de dosnfases: 1) obtencion de la trayectoria de grieta mediantenun calculo elastico lineal; 2) incorporacion del modeloncohesivo en la misma mediante elementos de intercara.nEl modelo se ha implementado en un programa de elementosnfinitos comercial con una subrutina de usuario ynse ha contrastado con los resultados experimentales denlos ensayos a escala. Las propiedades mecanicas de lanfabrica, en especial las de fractura, se miden con ensayosnde caracterizacion en dos direcciones. Estas se incorporannal modelo de calculo para simular los ensayos denfractura en modo mixto, prediciendo los resultados adecuadamentenpara distintas orientaciones de los tendeles

Structural Cast-in-Place Application of Polyolefin Fiber–Reinforced Concrete in a Water Pipeline Supporting Elements

AbstractResearch has shown that polyolefin-based macrofibers can meet the requirements of the standards to consider their postcracking contribution in the structural design of fiber-reinforced conc...

Modeling Quasibrittle Material Cracking with Cohesive Cracks: Experimental and Computational Advances

Fracture processes in concrete and other quasibrittle materials can be realistically described by means of the cohesive crack model which, as introduced by Hillerborg in his celebrated fictitious crack model, can be viewed as a constitutive assumption for the fracturing behavior of the material [1].