Model to simulate the behaviour of RC beams shear strengthened with ETS bars

To predict correctly the deformational and the cracking behavior of reinforced concrete elements failing in shear using a smeared crack approach, the strategy adopted to simulate the crack shear stress transfer is crucial. For this purpose, several strategies for modeling the fracture mode II were implemented in a smeared crack model already existing in the FEM-based computer program, FEMIX. Special development was given to a softening shear stress-shear strain diagram adopted for modeling the crack shear stress transfer. The predictive performance of the implemented constitutive model was assessed by simulating up to failure a series of eight beams tested to appraise the effectiveness of a new strengthening technique to increase the shear resistance of reinforced concrete beams. According to this strengthening technique, designated as Embedded Through-Section (ETS), holes are opened through the beam’s section, with the desired inclinations, and bars are introduced into these holes and bonded to the concrete substrate with adhesive materials. The strengthening elements are composed of steel bars bonded to the surrounding concrete with an epoxy adhesive. By using the properties obtained from the experimental programs 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 behavior 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.Fundação para a Ciência e a Tecnologia (FCT

A FEM-based model to predict the behaviour of RC beams shear strengthened according to the NSM technique

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: 90º, 60º and 45º. 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 2 tested beams, as well as the strain fields in the reinforcements. The constitutive model is briefly described, and the simulations are presented and analysed.Fundação para a Ciência e a Tecnologia (FCT

Assessing the applicability of a smeared crack approach for simulating the behaviour of concrete beams flexurally reinforced with GFRP bars and failing in shear

Numerical simulation of beams failing in shear is still a challenge. With the scope of verifying the applicability of smeared crack approaches to simulate the behavior of reinforced concrete (RC) beams failing in shear, a set of concrete beams reinforced with longitudinal glass fiber reinforced polymer (GFRP) bars, experimentally tested up to their failure, and comprehensibly monitored, are numerically simulated. The simulations are carried out with a multi-directional fixed smeared crack model available in the FEMIX computer program that has several options for modeling the crack shear stress transfer, which is a critical aspect when simulating RC elements failing in shear. The predictive performance of the numerical simulations is assessed in term of load vs deflection, crack pattern at failure, concrete strains in critical shear regions, and moment–curvature relationship. The influence on the predictive performance of the following modeling aspects is also investigated: finite element mesh refinement; simulation of the crack shear stress transfer by using the classical shear retention factor and a crack shear-softening diagram; bond conditions between flexural reinforcement and surrounding concrete. The simulations carried out demonstrate that small dependence of the results on the finite element mesh refinement and adequate crack patterns can be obtained with refinement levels suitable for design purposes and taking into account the actual computer performances, as long as a crack shear-softening diagram is used. However, the predictive performance of the simulations depends significantly on the values adopted for the parameters that define this diagram, as demonstrated by the performed parametric studies.The first author aims to acknowledge the support provided by FCT through the research project ICoSyTec -Innovative construction system for a new generation of high performance buildings, with reference: POCI-01-0145-FEDER-027990

Modelling the behavior of I-shape concrete beams reinforced with fibers and prestressed steel and GFRP bars

This paper reports the behavior of I-shaped fiber reinforced concrete (FRC) beams flexurally reinforced with prestressed steel and glass fiber reinforced polymer (GFRP) bars. The use of steel fibers aims to enhance the durability of pre-fabricated concrete structures by partially or completely replacing steel stirrups. In addition, GFRP and steel bars/tendons are combined as flexural reinforcement, creating a hybrid reinforcement system. GFRP bars are immune to corrosion and are positioned with minimum concrete cover, while steel reinforcement has adequate concrete cover thickness to minimize its risk to corrosion and ensure the required flexural capacity in a fire occurrence. Nonlinear finite element analysis (NLFEA) software was utilized for a critical analysis on the use of smeared crack model for predicting the behavior of this type of beams, including deflection, crack pattern, load-carrying capacity, and failure modes.The first author gratefully acknowledges the financial support of “Fundação para a Ciênciae Tecnologia” (FCT-Portugal), through the PhD grant SFRH/BD/09253/2020. The authors acknowledge the support provided by FCT through the project FemWebAI, reference PTDC/ECI-EST/6300/2020, and PID2021-125553NB-I00 (MCI/AEI/FEDER, UE). This work was partly financed by FCT / MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020, and under the Associate Laboratory Advanced Production and Intelligent Systems ARISE under reference LA/P/0112/2020

Shear properties of the strain hardening cementitious composite material

Recently, Strain Hardening Cementitious Composite (SHCC) material has been used for the shear strengthening and the structural rehabilitation of reinforced concrete structures. However, the shear behavior of this material has not been yet fully understood due to lack of an appropriate and accurate direct shear test method. This paper aims to investigate the shear properties of the SHCC material. For this purpose, Iosipescu shear test was selected, where loads are applied in antisymmetric four points bending, assuring a pure shear section at the center of the specimen. A special geometry for the specimen was adopted in order to assure a uniform shear stress distribution in the pure shear section. This experimental test can characterize the shear behavior of SHCC material. The experimental test was simulated by the FEM-based computer program, FEMIX. To predict the average shear stress-sliding response, the shear crack softening diagram, available in the multi-directional fixed smeared crack model, was used. After demonstration the good predictive performance of the numerical model, a parametric study was carried out to evaluate the influence of shear retention factor, fracture energy of mode II, and crack shear strength on the average shear stress-sliding response of the SHCC. The advantage of SHCC instead of conventional mortar was also studied.Fundação para a Ciência e a Tecnologia (FCT) - PTDC/ECM/114511/200

CFRP flexural and shear strengthening technique for RC beams : experimental and numerical research

Near surface mounted (NSM) technique has proved to be a very effective technique for the flexural strengthening of RC beams. Due to the relatively small thickness of the concrete cover that several beams present, cutting the bottom arm of steel stirrups for the installation of NSM laminates might be a possible strategy, whose implications on the beam’s load carrying capacity need to be assessed. When steel stirrups are cut, however, the shear resistance can be a concern. This also happens when a strengthening intervention is carried out to increase the flexural resistance of a beam, since in certain cases it is also necessary to increase the shear resistance in order to avoid the occurrence of brittle shear failure. The present work assesses the effectiveness of a technique that aims to increase both the flexural and shear resistance of RC beams that have the bottom arm of the steel stirrups cut for the application of NSM laminates. This assessment is performed by experimental and numerical research. The main results of the experimental program are presented and analyzed, and the innovative aspects of a constitutive model implemented in a computer program are described, being their virtues and deficiencies discussed.The study reported in this paper forms a part of the research program "CUTINEMO - Carbon fiber laminates applied according to the near surface mounted technique to increase the flexural resistance to negative moments of continuous reinforced concrete structures" supported by FCT, PTDC/ECM/73099/2006. The authors wish to acknowledge the support also provided by the S&P, Casais and Artecanter Companies. The second Author acknowledges the grant under the aforementioned research project. The third author acknowledges the financial support of FCT, PhD Grant number SFRH/BD/23326/2005

Multi-fixed smeared 3d crack model to simulate the behavior of fiber reinforced concrete structures

When a concrete structure is subjected to a multi-stress state, different crack modes can be developed. To simulate with enough accuracy these fracture modes, a three dimensional model must be used. In the present work, a multi fixed smeared 3D crack model is proposed to predict the normal and shear failure modes of concrete structures. Softening stress strain diagrams are proposed to model, after crack initiation, the normal and shear components. The performance of the developed model was appraised by simulating the behavior observed in punching tests with lightweight panels of steel fiber reinforced self compacting concrete (SFRSCC).Fundação para a Ciência e a Tecnologia (FCT) - bolsa de doutoramento SFRH/BD/23326/2005, PABERPRO : Conception and implementation of production system of lightweight steel fibre reinforced self-compacting concrete panels” Program POCI 2010 – IDEIA, nº 13-05-04-FDR-00007, contrato ADI/2007/V4.1/0049

Plastic-damage smeared crack model to simulate the behaviour of structures made by cement based materials

This work proposes a constitutive model to simulate nonlinear behaviour of cement based materials subjected to different loading paths. The model incorporates a multidirectional fixed smeared crack approach to simulate crack initiation and propagation, whereas the inelastic behaviour of material between cracks is treated by a numerical strategy that combines plasticity and damage theories. For capturing more realistically the shear stress transfer between the crack surfaces, a softening diagram is assumed for modelling the crack shear stress versus crack shear strain. The plastic damage model is based on the yield function, flow rule and evolution law for hardening variable, and includes an explicit isotropic damage law to simulate the stiffness degradation and the softening behaviour of cement based materials in compression. This model was implemented into the FEMIX computer program, and experimental tests at material scale were simulated to appraise the predictive performance of this constitutive model. The applicability of the model for simulating the behaviour of reinforced concrete shear wall panels submitted to biaxial loading conditions, and RC beams failing in shear is investigated.The authors wish to acknowledge the FCT financial support provided by the Portuguese Foundation for Science and Technology in the scope of the SlabSys-HFRC research project, with reference PTDC/ECM/120394/2010

A model for the simultaneous prediction of the flexural and shear deflections of statically determinate and indeterminate RC structures

The deformability of the major part of reinforced concrete (RC) structures is the result of the flexural and shear deformations mainly caused by bending and shear diagonal cracking, respectively. However, the evaluation of the shear deformation contribution is relatively difficult due to the complexities involving the shear behavior of cracked RC elements. These complexities are even more complicated when structures are statically indeterminate, since the external and internal forces cannot be determined from direct application of the equilibrium equations. To address these issues, the current study aims to develop a novel simplified analytical model based on the flexibility (force) method to predict the deflections of statically indeterminate RC structures up to their failure, which can be in bending or in shear. This analytical model considers the influence of flexural cracks on the shear stiffness degradation of a RC structure after concrete cracking initiation, and has a format adjusted for design practice. The good predictive performance of the analytical model is demonstrated by simulating experimental tests with RC elements where shear deformation has different level of contribution for the total deflection registered in these tests.Marie Curie Initial Training Networks - "endure" European Network for Durable Reinforcement and Rehabilitation Solutions, project no: 607851.info:eu-repo/semantics/publishedVersio

Shear strengthening of damaged reinforced concrete beams with hybrid composite plates

This paper aims to evaluate experimentally the potentialities of Hybrid Composite Plates (HCPs) technique for the shear strengthening and repairing of reinforced concrete (RC) beams. HCP is a thin plate of Strain Hardening Cementitious Composite (SHCC) reinforced with Carbon Fiber Reinforced Polymer (CFRP) laminates. For this purpose, an experimental program composed of four Rectangular and five T-cross section beams was executed to assess the strengthening efficiency of HCPs technique. There were two control beams without any type of shear reinforcement, and seven beams strengthened with HCPs. The HCPs were applied to the lateral faces of the beams by using a combination of epoxy adhesive and mechanical anchors. The bolts were applied with a certain torque in order to increase the concrete confinement. To have a better understanding of the shear behavior of SHCC material, Iosipescu shear tests were carried out, and the results were used to derive their fracture mode II parameters. To further explore the potentialities of the HCPs technique for the shear strengthening, the experimental tests were simulated numerically by a FEM-based computer program considering the material properties obtained experimentally. After demonstration of the good predictive performance of the numerical model, a parametric study was executed to investigate the influence of some parameters on the load carrying capacity of the strengthened beams, namely: i) Use a mortar instead of the SHCC; ii) application of different applied torque level to the mechanical anchors; iii) different bond condition between HCPs and concrete substrate.Clever Reinforcement Iberica for providing the CFRP laminates and epoxy, Sika for the sand and adhesive, Grace for the superplasticizers, Dow Chemical Co. for viscous modifying agents, ENDESA Compostilla power station for the fly ash, and Casais for assisting in the execution of the beams. FCTinfo:eu-repo/semantics/publishedVersio