Neikō Ingeniería takes part on gCons challenge
Last Wednesday 29th of January, the shear resistance test of the biggest shear reinforced concrete beam tested on an European laboratory, within the HORVITAL project, was held by Construction Group (gCons) of the University of A Coruña (UDC) on the facilities of the Centre for Technological Innovation on Building and Civil Engineering (CITEEC), whose cutting-edge facilities made possible to achieve this milestone. Tested beam dimensions, with 12 m long, 2 m height and 24 cm width made the test a difficult challenge. With its 14 tons the lifting, moving, and test preparation had to be held under the most rigorous and carefully planned processes.
The aim of the test was to search empirical evidence of the so called “size effect” on tall beams. It is well known, endorsed by practice, that common standards suppose a shear capacity for tall beams above their real value. Due to the fact that this will imply an unsafe design, usual practice tends to increase the amount of steel and concrete used on beam manufacturing, which is an impractical solution from environmental point of view.
After the test carried out on the 29th by the gCons, size effect remains empirically well proved, due to the fact that breaking load on the tested beam was 973 kN, about a 70% of the theoretical capacity obtained from the standards. This fact, along with the rest of the tests and studies carried out by gCons and all the other groups and universities involved on the project will result on a future improvement of the actual standards, adapting them to the real behaviour of the materials and contributing to a better management of natural resources. This is the main objective of the HORVITAL project, which this series of test are part of.
Parallel to the test planning, gCons itself launched an international contest challenging everyone interested to predict the load that will cause breakage of the tested beam. From Neikō Ingeniería we accepted the challenge. We proposed a finite element model (FEM) that will simulate the concrete plastic behaviour, along with the reinforcement steel. For that, we relied in various academic documents (such as papers, thesis, etc.) on which plastic behaviour on concrete is studied and models for simulation of it on calculation software are proposed. After obtaining the stress-strain curves and the plastic damage parameters for the concrete used on the beam manufacturing, this data was set into the FEM model. Once beam was discretized on its corresponding calculation elements, a displacement-controlled test was held on the calculation software. Descending of the bearing plate was forced downwards, loading this way the beam on the contact between both. Crack location was evidenced by the appearance of plastic damage on the FEM model.
During the loading sequence, first flexural cracks appeared approximately on the vertical of the loading point. When process advanced, first diagonal cracks appeared left from the loading point, which was the expected behaviour do the fact that we were looking for shear breakage. On the following steps we could observe how cracks spread through the beam, finally composing a continuous crack from the loading point to the left support, which suggest the theoretical position of the critical crack on the breaking point of the beam.
Once the test on the CITEEC laboratories was held, the results given from our FEM model seem to be quite accurate, at least regarding to the beam capacity (the only test result published on the moment of this publication). Load transmitted from the bearing plate to the beam at breakage of our FEM model was of 960 kN, while real test reached 973 kN.
From Neikō Ingeniería we wanted to send our thanks and congratulations for the opportunity offered, as well as for their hard work and involvement at all levels to the gCons of the UDC and to all of the groups and universities involved on the HORVITAL project (Universitat Politècnica de Catalunya, Universitat dels Illes Balears, Universidad Politécnica de Valencia and Universidade da Coruña).