Hybrid FRP jacketing for enhanced confinement of circular concrete columns in compression

Abstract

The main goal of the study herein described was to evaluate the performance of an innovative confining unidirectional hybrid FRP solution for circular concrete columns, exploiting the hybrid effect and pseudo-ductility of FRP jackets made of different fibres. First, an experimental study on the compressive stress-strain curves of small-scale plain circular concrete columns confined with hybrid FRP was conducted. Jackets were produced with dry unidirectional fabrics of high-modulus carbon, standard-modulus carbon, E-glass, and basalt. Different combinations were tested, varying the number of layers of each material. Next, two new simple design-oriented models were developed in order to predict the compressive peak stress of compressed concrete columns confined with hybrid FRP jacketing. Predictions were in close agreement with test results. Finally, an existing analysisoriented model developed for non-hybrid FRP-confined concrete was adapted to also predict dilation and the compressive stress-strain curve of hybrid FRP-confined concrete. Likewise, predictions were in close agreement with test results. It was concluded that hybridisation can effectively contribute to maximize the lateral strain efficiency of FRP jacketing and its behaviour can be predicted with the developed analytical models.

3D finite element model for hybrid FRP-confined concrete in compression using modified CDPM

“…The performance of the proposed CDPM is validated with the experimental results described in Section 3.1. In the work of Ribeiro et al [3], it has already been proven that the analytical model here presented allows to accurately simulate both the dilation behaviour and the compressive stress-strain behaviour of all confined concrete specimens analysed. Since the material parameters for the modified CDPM were obtained from the referred to analytical model, predictions obtained with both models (analytical and numerical) are expected to have similar accuracy.…”

“…The analytical model was developed based on large database of unconfined and actively confined concrete results, please see the details in [32]. It was also proved that the model is able to predict the dilation behaviour of hybrid FRP confined concrete, please see details in [3]. are not in agreement with analytical ones.…”

“…The model of Lim and Ozbakkaloglu [33] was used to define the compressive stress-strain curve of plain concrete, i.e., the material input data of the numerical model that gave rise to the results of proposed FE model against experimental results published in a previous work by the authors [3]. In the mentioned work, it is possible to observe that the ultimate confining pressure in tested specimens varied between 6 and 26…”

“…A ready-mix concrete was used in the experimental campaign [3]. In ABAQUS software [40], two parameters are needed to describe the elastic behaviour of concrete: (i) the elastic modulus, and (ii) the Poisson's ratio.…”

“…Although pseudo-ductile tensile response has occurred as well in 1C/1CHM/1C combination [63], this behaviour did not have a significant influence in the compressive results. This is due to the fact that (i) pseudo-ductile strain (defined as the extra strain between the final failure strain and the strain on the extrapolated initial slope line at the failure stress of the stress-strain diagram, as it is shown in Figure 9) of this combination is very low, and (ii) the hybrid FRP failure of the jacket occured sooner that it was expected [3]. In this way, the application in practice of this combination in confinement would lead to fragile failures.…”