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Barros J.A.O.,University of Minho | Baghi H.,University of Minho | Dias S.J.E.,University of Minho | Ventura-Gouveia A.,ISISE
Engineering Structures | Year: 2013

Experimental research has demonstrated the excellent performance of the near surface mounted (NSM) technique with carbon fibre reinforced polymer (CFRP) laminates for the shear strengthening of reinforced concrete (RC) beams. This paper presents a finite element analysis to evaluate the behaviour of RC beams shear strengthened with NSM CFRP laminates. To predict correctly the deformational and the cracking behaviour of RC elements failing in shear using a smeared crack approach, the strategy adopted to simulate the crack shear stress transfer is crucial. For this purpose, a strategy for modelling the fracture mode II was implemented in a smeared crack model already existing in the FEM-based computer program, FEMIX. This strategy is mainly based on a softening shear stress-shear strain diagram adopted for modelling the crack shear stress transfer.To assess the predictive performance of the developed model, the experimental tests carried out with a series of T cross section RC beams shear strengthened according to the NSM technique by using CFRP laminates were simulated. In this series of beams, three different percentages of CFRP laminates and, for each CFRP percentage, three inclinations for the laminates were tested: 90°, 60° and 45°. By using the properties obtained from the experimental program for the characterization of the relevant properties of the intervening materials, and deriving from inverse analysis the data for the crack shear softening diagram, the simulations carried out have fitted with high accuracy the deformational and cracking behaviour of the tested beams, as well as the strain fields in the reinforcements. The constitutive model is briefly described, and the simulations are presented and analyzed. © 2013 Elsevier Ltd.

Baghi H.,University of Minho | Barros J.A.O.,University of Minho | Ventura-Gouveia A.,ISISE
Advances in Structural Engineering | Year: 2016

The effectiveness of hybrid composite plates for the shear strengthening of the reinforced concrete beams was assessed by executing an experimental program. Hybrid composite plate is a thin plate of strain hardening cementitious composite reinforced with carbon fiber-reinforced polymer laminates. Due to the excellent bond conditions between strain hardening cementitious composite and carbon fiber-reinforced polymer laminates, these reinforcements provide the necessary tensile strength capacity to the hybrid composite plate. Two hybrid composite plates with different inclination of carbon fiber-reinforced polymer laminates (45° and 90°) were adopted for the shear strengthening of reinforced concrete beams by bonding these hybrid composite plates to the lateral faces of the beams with an epoxy adhesive. The results showed that these hybrid composite plates have assured a significant increase in terms of load carrying capacity, mainly those with inclined laminates. The shear strengthening contribution of the hybrid composite plates was limited by the tensile strength of the concrete of the strengthened beams since their failure mode was governed by the detachment of the hybrid composite plates that included part of the concrete cover. Advanced finite element method-based numerical simulations were performed using a constitutive model, whose predictive performance was demonstrated by simulating the experimental tests carried out. Using this computer program, a parametric study was executed to evaluate the shear strengthening efficiency of the arrangement and percentage of carbon fiber-reinforced polymer laminates in hybrid composite plates, as well as the influence of using mechanical anchors to avoid premature detachment of the hybrid composite plates. © The Author(s) 2016 Reprints and permissions.

Haach V.G.,University of Sao Paulo | Vasconcelos G.,ISISE | Loureno P.B.,ISISE
Construction and Building Materials | Year: 2011

Mortar is the material responsible for the distribution of stresses in masonry structures. The knowledge about the fresh and hardened properties of mortar is fundamental to ensure a good performance of masonry walls. Water/cement ratio and aggregates grading are among several variables that influence physical and mechanical behaviour of mortars. An experimental program is presented in order to evaluate the influence of aggregates grading and water/cement ratio in workability and hardened properties of mortars. Eighteen compositions of mortar are prepared using three relations cement:lime:sand, two types of sand and three water/cement ratios. Specimens are analyzed through flow table test, compressive and flexural strength tests. Results indicate that the increase of water/cement ratio reduces the values of hardened properties and increases the workability. Besides, sands grading has no influence in compressive strength. On the other hand, significant differences in deformation capacity of mortars were verified with the variation of the type of sand. Finally, some correlations are presented among hardened properties and the compressive strength. © 2011 Elsevier Ltd. All rights reserved.

Milani G.,Polytechnic of Milan | Lourenco P.B.,ISISE
Computers and Structures | Year: 2010

A kinematic rigid-plastic homogenization model for the limit analysis of masonry walls arranged in random texture and out-of-plane loaded is proposed. The model is the continuation of a previous work by the authors in which masonry in-plane behavior was investigated. In the model, blocks constituting a masonry wall are supposed infinitely resistant with a Gaussian distribution of height and length, whereas joints are reduced to interfaces with frictional behavior and limited tensile and compressive strength. Block by block, a representative element of volume (REV) is considered, constituted by a central block interconnected with its neighbors by means of rigid-plastic interfaces. Two different classes of problems are investigated, the first consisting of full stochastic REV assemblages without horizontal and vertical alignment of joints, the second assuming the presence of a horizontal alignment along bed joints, i.e. allowing block height variability only row by row. A sub-class of elementary deformation modes is a priori chosen in the REV, mimicking typical failures due to joint cracking and crushing. The model is characterized by a few material parameters and it is therefore particularly suited to perform large scale Monte Carlo simulations. Masonry strength domains are obtained equating the power dissipated in the heterogeneous model with the power dissipated by a fictitious homogeneous macroscopic plate. A stochastic estimation of out-of-plane masonry strength domains (both bending moments and torsion are considered) accounting for the geometrical statistical variability of block dimensions is obtained with the proposed model. The case of deterministic block height (quasi-periodic texture) can be obtained as a sub-class of this latter case. As an important benchmark, the case in which joints obey a Mohr-Coulomb failure criterion is also tested and compared with results obtained assuming a more complex interfacial behavior for mortar. Masonry homogenized failure surfaces are finally implemented in an upper bound Finite Element (FE) limit analysis code. Firstly, to validate the model proposed, two small scale structural examples of practical interest are considered, relying in masonry panels in two-way out-of-plane bending. In both cases, failure load distributions and failure mechanisms provided by the homogenization model are compared with those obtained through a heterogeneous approach. Finally, in order to show the capabilities of the approach proposed when dealing with large scale structures, the ultimate behavior prediction of a Romanesque masonry church façade located in Portugal and arranged in irregular texture is presented. Comparisons with Finite Element heterogeneous approaches and "at hand" calculations show that reliable predictions of the load bearing capacity of real large scale structures may be obtained with a very limited computational effort. © 2010 Elsevier Ltd. All rights reserved.

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