Fabricreinforced cementitious matrix (FRCM) composites are materials that are usually applied to strengthen existing structures. In this study, a hemp mesh coated with epoxy was manufactured and combined with a cementitious matrix to strengthen a concrete beam. This beam was subjected to bending cyclic loading tests and a nondestructive modal analysis test. The modal analysis was performed to determine the dynamic elastic properties of the beam under precracking, postcracking, and strengthened conditions. The beam stiffness increased following strengthening with hempFRCM. The results of the experimental cyclic loading test showed that the hempFRCM system improved the loadbearing capacity of the beam at the service limit state by 42%. Analytical and numerical models were adjusted and validated using the experimental results, and both proved to be effective calculation tools. The models accurately reproduced the behaviour of the FRCMstrengthened concrete beam if the strengthening connection could prevent sliding and mortar debonding failures.
Los compuestos de matriz cementicia reforzada con tejidos (FRCM) son materiales que generalmente se aplican para el refuerzo de las estructuras existentes. En este estudio, se fabricó una malla de cáñamo recubierta con epoxi y se combinó con una matriz cementicia para reforzar una viga de hormigón. Esta viga se sometió a ensayos de carga cíclica de flexión y un ensayo no destructivo de análisis modal. El análisis modal se realizó para determinar las propiedades dinámicas elásticas de la viga en condiciones de prefisuración, postfisuración y reforzado. La rigidez de la viga aumentó después del reforzar con FRCM de cáñamo. Los resultados del ensayo de carga cíclica experimental mostraron que el sistema de FRCM de cáñamo mejoró la capacidad de carga de la viga en el estado límite de servicio en un 42%. Los modelos analíticos y numéricos se ajustaron y validaron utilizando los resultados experimentales, y ambos demostraron ser herramientas de cálculo efectivas. Los modelos reproducen con precisión el comportamiento de la viga de hormigón reforzado con FRCM cuando la conexión de refuerzo podía evitar fallas por deslizamiento y desprendimiento del mortero.
In recent decades, the damage recorded as a result of dynamic actions (such as that caused by heavy road and rail traffic as well as heavy machinery) has led to research being conducted on structural strengthening and rehabilitation. Therefore, there is an evident need to develop strengthening techniques that allow the structures to be maintained for a longer period of time at a competitive global cost (considering environmental factors) rather than demolish and build again.
Consequently, over the years, there has been a development of increasingly efficient and sustainable structural reinforcement techniques that respond to the accumulated damage over time, such as the fabricreinforced cementitious matrix (FRCM).
FRCM is a composite material formed by a mesh embedded in an inorganic matrix that has emerged as an alternative to the organic matrix of fibrereinforced polymers (FRPs) (
In the case of reinforced concrete (RC) beams, several studies have been conducted to study the contribution of FRCM strengthening systems to the behaviour of beams subjected to bending (
However, FRCM compounds have two technical drawbacks that need to be overcome: (i) their high stiffness makes it difficult to dissipate energy against dynamic stresses, resulting in stress concentration on the existing structure (
Therefore, the use of natural resources and sustainable materials is a topic that is receiving increasing attention from the scientific community. The use of vegetable fibres as reinforcements of polymers and mortars is an example of this. Because of the demonstrated mechanical properties of fibres such as flax, hemp, sisal, jute, and banana, along with their low cost, low density, recyclability, and biodegradability, vegetal fibres have become an effective alternative to synthetic fibres (
Despite the numerous advantages that vegetal fibres have over synthetic fibres in terms of strength capacity, their use is limited by their average mechanical performance. However, in a study published by Wambua et al. (
In the field of engineering, numerous studies have focused on the development of composites by incorporating vegetal fibres as structural reinforcements. An example of this is the study by Huang et al. (
Numerous articles have addressed the behaviour of vegetal fibres in FRCMs (
The organic origin of vegetal fibres favours their degradation in the environment of cementitious matrix composites (
Coating with resin affects the sustainability of vegetal fibres, as it increases their cost and generates toxicity. However, coating the meshes used in FRCM composites is a widely used technique. In some cases, this coating prevents fibre degradation within the cementitious matrix (
Regarding the experimental study of RC beams subjected to cyclic loads, the study published by Shao and Billington (
The authors have not found publications that report comprehensive experimental tests aimed at demonstrating the behaviour of RC beams strengthened with FRCM of vegetal fibres and subjected to cyclic loading. Therefore, this study aimed to analyse the behaviour of a beam subjected to cyclic loads and reinforced with hempFRCM. Nondestructive characterisation tests (modal analysis) were carried out on the control, cracked, and strengthened beams to evaluate the evolution of the dynamic modulus of elasticity. Based on the results of the cyclic flexural test and modal analysis of the beam, it was possible to develop an analytical and numerical model capable of reproducing the experimental behaviour of the beam strengthened with hempFRCM.
The results of this study demonstrate the ability of hempFRCMs to improve the structural response of an RC beam subjected to cyclic loads. Numerical and analytical procedures that could effectively reproduce experimental behaviour have also been presented.
Two RC beam specimens were manufactured and tested. One of them was statically loaded under a threepoint bending configuration until failure. The other was loaded in the same configuration until it cracked. After that, it was strengthened with hempFRCM and finally subjected to a bending cyclic loading test.
To prepare the strengthened beam, a singlecomponent thixotropic mortar composed of cement, synthetic resins, and silica fume and reinforced with polyamide fibres was used. This mortar complies with the type R3 requirements as defined in UNEEN 15043 (
The control mortar specimens were tested in flexion, and the resulting halves were then tested under compression. These tests were performed according to EN 101511: 2000 (
Chemical composition (1)  Prepared cement mortar improved with synthetic resins and silica fume and reinforced with polyamide fibres 

Density of fresh mortar (1):  2.1 g/cm^{3} 
Compressive strength (2):  39.25 MPa 
Flexural strength (2):  6.56 MPa 
(1) Supplied by manufacturer; (2) results of tests (EN 101511: 2000)
To obtain a mesh of hemp fibres with a load capacity comparable to that of synthetic fibre meshes, a hemp mesh was designed (see
A wooden rectangular support was assembled as a handloom to manufacture the meshes. The support size was 200 × 4500 mm and had nails at its external boundaries (
Once the mesh was weaved, it was coated with an epoxy resin using a brush. The epoxy employed to coat the yarns was a lowviscosity and highadhesion resin. The mechanical properties of the resin are presented in
Properties  Epoxy 

Density (g/cm^{3}):  1.05 
Tensile strength (MPa):  22.9 ± 4 
Elongation (%):  18.2 ± 7 
Flexural strength (MPa):  No break 
Flexural modulus (MPa):  233.1 
The mechanical properties of the yarn are listed in
Properties  Hemp  

Without epoxy  With epoxy  
Yarn diameter (mm)  0.5  
Yarn linear density (g/m)  0.40  0.89 
Yarn volumetric density (g/cm^{3})  2.04  4.54 
Epoxy/yarn length (g/m)    0.5 
Tensile strength (MPa)  295.54  520.76 
Strain (%)  1.03  1.30 
Young’s Modulus (GPa)  26.33  38.74 
Before applying the FRCM strengthening layer to the beam, the face to be strengthened was moistened. Subsequently, the first layer of mortar was applied, and the mesh was placed such that it adhered to the mortar. Finally, the strengthened beam was finished by covering the mesh with another layer of mortar, leaving the mesh completely embedded (thickness of the FRCM = 10 mm).
The experimental modal analysis fits into the category of nondestructive tests with inputoutput experimental modal identification, in which different points are excited and the vibration response (in terms of acceleration) is measured at a fixed point. In particular, the proposed experimental campaign aimed to capture the vibration modes (shape, frequency, and damping) and analyse how cracking and strengthening patterns affected them. The procedure described in (
Three modal analyses were undertaken for the same beam: one before strengthening (precracking), one postcracking, and the other after curing the strengthening system. To carry out the experimental modal analysis, 36 points were defined on half of the strengthened face of the beam, forming a grid of 12 rows and 3 columns.
A unidirectional accelerometer (Brüel & Kjær piezoelectric charge accelerometer type 4370 with charge converter type 2646, sensitivity of 10.11 pC/ms^{−2}, and measuring range of up to 4.8 kHz) was placed asymmetrically to capture as many vibration modes as possible. This sensor was oriented along the vertical direction and was attached to a transmission plate, which was bonded to the beam using cyanoacrylate, as previously described (
The beam was physically supported by a bridge crane during modal testing, with no additional constraints. The modal analysis was repeated in all the beam states (precracking, postcracking, and strengthened) with exactly the same configuration and laboratory conditions to obtain comparable results. The grid used to define the impact points was maintained.
A numerical modal analysis of the beam was implemented using Abaqus^{TM} 6.144 (
Only the second bending vibration mode was observed for all the modal analysis tests. The third bending vibration mode was clearly observed in the precracking state. The values of the corresponding frequencies (ω) and damping ratios (ζ) are summarised in




Vibration modes  2^{nd} bending mode  3^{rd} bending mode  
Modal analysis  beam state  ω (Hz)  ξ (%)  ω_{u} (Hz)  ξ_{u} (%) 
Experimental  Precracking  202  0.74  379  0.572 
Postcracking  135  1.45      
Strengthened  179  1.6      
Numerical  Precracking  201.77    372.64   
Postcracking  135.68        
Strengthened  178.75       
The elastic modulus used in the simulation was adjusted to fit the simulated vibration frequencies to the experimental values. This comparison was performed for each state (precracking, postcracking, and strengthened), resulting in a particular dynamic elastic modulus (E_{d}) for each case
Beam state  Dynamic modulus  Static modulus E (GPa)  Flexural stiffness EI (kNm^{2})  Variation EI (%)  

E_{d} (GPa)  
Precracking  28.58  8.57  9145.60  
Postcracking  11.67  3.50  3734.40  59  vs Precracking 
Strengthened  22.13  6.64  13831.25  270  vs Postcracking 
The figures in
The control beam was subjected to a static load test (contrast element), and the beam strengthened with the hempFRCM was subjected to cyclic load tests to study its effectiveness.
For both cases, the beams were subjected to threepoint bending at a displacement rate of 1 mm/s, which was imposed by a 250 kN range oleohydraulic actuator. Measurements of deflection were monitored during the experiment using two external potentiometer sensors (see
Although the fourpoint bending test configuration is commonly preferred to study flexural response, real structures are subjected to bending and shear efforts simultaneously. Thus, a threepoint bending test was selected to better represent the real concomitance of the flexural and bending efforts in this research.
The cyclic loading protocol was adopted based on FEMA 461 (
(a) cyclic loading test, (b) static test
Beam  HempFRCM  Control  Δ (%) 

F_{max} (kN)  45.51  41.16  10.56 
M_{max} (kNm)  47.79  43.22  10.56 
y_{max} (mm)  24.87  73.89  −66.34 
EI_{max} (KNm^{2})  2820  860  227.91 
M_{u} (kNm)  44.09  38.12  15.66 
y_{u} (mm)  113.88  112.71  1.04 
EI_{u} (KNm^{2})  570  500  14.00 
y_{service} (mm)  14.00  14.00   
M_{service} (kNm)  39.70  27.92  42.19 
EI_{max} (KNm^{2})  4170  3080  35.39 
where F is the total applied load, is the vertical displacement at the midspan section, and L is the free span between the supports (4200 mm).
The values obtained for the flexural stiffness are useful for examining the general behaviour trends of the applied composite reinforcements with respect to the flexural stiffness of the entire structure. The changes caused by the FRCM in the flexural stiffness of the RC beams are presented in
According to the results presented in
Beam state  Model  F (kN)  M_{max} (kNm)  ε_{c} (/)  ε_{s} (/)  ε_{s2} (/)  ε_{f,u} (/)  f_{ck} (MPa)  f_{ys} (MPa)  A_{FRCM} (mm^{2})  f_{FRCM} (MPa) 



42.40  44.52  0.00110  0.01074  0.00031  0.013  30  500  23.55  520.00 

45.80  48.09  0.00123  0.01211  0.00034  0.013  30  500  1953.45  11.08  

45.51  47.79        0.013  30  500      

−6.84  

0.64  


38.78  40.72  0.00350  0.05055  0.0001    30  500     

41.16  43.22          30  500      

−5.78 
M_{1}= Analytical model 1, M_{2}: Analytical model 2, Exp: Experimental results, Δ_{1}: Variation of model 1 with experimental results,
Δ_{2}: Variation of model 2 with experimental results
The maximum increase in flexural stiffness during the service stage suggests that the FRCM reinforcement is activated at low loading stages. In contrast, the hempFRCM did not provide a significant increase in the flexural stiffness with respect to a control beam after reaching the maximum moment. This is in accordance with the evidence found in the flexural capacity analysis, in which FRCM strengthening systems showed less bending improvement capacity as the cracks of the specimens damaged the FRCM.
In addition, comparing the initial flexural stiffness obtained from the experimental bending test with the flexural stiffness obtained from the modal analysis (precracking and strengthened beam), the variation in the initial flexural stiffness was 15% (10741 kNm^{2}) for the control beam (precracking value) and 3% (14279 kNm^{2}) for the strengthened beam. This highlights the importance of modal analysis results.
According to
The analytical method to determine the ultimate flexural capacity of the strengthened beams is based on the following assumptions: (1) failure of the strengthening composite while the concrete substrate and FRCMconcrete bonding maintain their capacities, (2) strain compatibility during the loading process, and (3) equilibrium of forces at the crosssection.
The constitutive behaviour of concrete, steel, and fibres is shown in
a) concrete and b) steel and fibres
To calculate the maximum bending moment (M_{max,an}), the concrete and tensile steel could reach their ultimate capacities in compression and tension, respectively, according to the considered failure domain. The ultimate strain of the reinforcement steel (ε_{s,u}) is considered to be 12%, and the ultimate strain of the concrete in compression is considered to be 0.35%, as suggested by EHE (
a) geometry, b) strain distribution, and c) force equilibrium
According to
For beams without FRCM:
For beams strengthened with FRCM:
where M_{c}, M_{s}, M_{s,2}, and M_{fib} are the ultimate flexural contributions of the concrete, tensile steel reinforcement, compressive steel reinforcement, and fibres of the strengthening system. The contributions of each withstanding material and neutral axis depth (x) can be determined using the following equations [
Ultimate flexural contributions of the concrete
The values of the concrete breakage deformation (ε_{c0}) and ultimate deformation (ε_{cu}) in compression were set to 0.002 and 0.0035, respectively. n = 2. These values are valid for concrete with a characteristic compressive strength f_{ck} ≤
The moment produced by the compression block will be as follows
where (
Tensile steel reinforcement
where ε_{s,y} is the elastic limit deformation, and
Compressive steel reinforcement
In this case, the same criteria as in
Fibres of the strengthening system
where A_{f} is the area of fibres, f_{fib,u} is the tensile strength of the fibre, and d_{f} is the distance from the FRCM reinforcement fibres to the most compressed fibre of the concrete.
In addition, this study also raises the possibility of using a formulation to introduce the contribution of the tensile strength of the cementitious matrix. This approach is based on the law of mixtures, where
In the case of the FRCMreinforced beam, it is known that the hemp mesh breaks before other materials. In this case, the mesh ultimate deformation (ε_{f,u}) is used to determine the point where the maximum load is reached.
For the control beam, it is considered that the crushing failure of concrete occurs before the breakage of steel. The compressive ultimate deformation of concrete is taken (ε_{c,u}═ 0.0035) to set the point at which the maximum tension is reached in this case. Once the ultimate deformations of the materials are known, the following conditions must be satisfied:
ε_{c} ≤ 0.0035 (Code (
ε_{s} ≤ 0.12 (Code (
ε_{f} ≤ 0.013(Experimental (
Hence, this analytical model considers material failure but does not consider other failures, such as debonding of the FRCM strengthening system. Note that this case represents a desirable situation for practitioners, in which the FRCM may develop its maximum tensile capacity as a flexural strengthening material.
The results obtained from the analytical model are presented in
The first aspect to highlight in the data of
In the case of the beam with FRCM, both models 1 and 2 properly approximated the experimental results. The best fit was for model 2 (0.64% variation). This demonstrates that considering the matrix contribution yields more accurate results for the bending capacity of the strengthened beams.
In general, the results presented in
The commercial mechanical simulation software Abaqus^{TM} 6.144 (
One of the most used approaches for the simulation of FRCMs and RC is based on the assumption of a concrete plastic damage model (
In addition, this model assumes that the stressstrain response for the uniaxial compression of concrete is characterised by damaged plasticity, as shown in
(a) tension, (b) compression
The cracking stress corresponds to the appearance of microcracks in the material. From this point, the tensile tension that transmits the material does not disappear, but it gradually decreases as the deformation increases. This behaviour simulates the interaction between reinforcement and concrete or fabric and mortar (FRCM), and provides numerical stability to improve convergence. The damage variable d_{t}, whose minimum value is 0 (undamaged material) and maximum value is 1 (totally damaged material), defines the slope of the discharge branch. Therefore, if E_{0} is the modulus of elasticity of the elastic material, the module of the discharge branch becomes (1−d_{t}) E_{0}.
Under uniaxial compression, the response is linear up to the initial yield σ_{c0}. In the plastic zone, the response is typically characterised by stress hardening, followed by stress weakening beyond the final stress σ_{u}. This representation, although somewhat simplified, captures the main characteristics of the concrete response and is also valid for mortar. As in the case of tension, there is a damage parameter d_{t} that varies between 0 and 1, which reduces the stiffness of the discharge branch.
Regarding the plastic zone of the cementitious matrix under tension, it was necessary to define the following parameters:
Dilatation angle: It controls the amount of plastic volumetric deformation developed during the plastic shear and is assumed to be constant during the plastic flexibilisation. The first value used for this parameter was 13. It was chosen on the basis of existing literature (
Eccentricity: This parameter defines the speed at which the function approaches the maximum stress asymptote. The predetermined eccentricity suggested by Abaqus is 0.1, which implies that the material has almost the same angle of expansion in a significant range of confining pressure values.
Form parameter of the plasticising surface K: This is the ratio of the second invariant tension in the meridian to that of the compression meridian in the initial yield for any given value of the invariant pressure. The default value was 2/3.
Relationship between maximum uniaxial and biaxial compression stresses at the beginning of the loading process. The default value was 1.16.
Viscoplastic regularisation: models of materials that exhibit a smoothing behaviour and degradation of rigidity often lead to serious convergence difficulties in implicit analysis programs. A common technique for overcoming some of these convergence difficulties is the use of a viscoplastic regularisation of the constitutive equations, which causes the constant tangent stiffness of the softening material to become positive during sufficiently small increments of time. Values of 0.00001, 0.0001, 0.001, 0.002, and 0.003 were tested for an objective choice, proving that 0.00001 (for the beam) and 0.003 (for the FRCM) were the only values that allowed model convergence.
Once these material properties were defined, the matrix stressstrain curves and the corresponding damage variables were calculated. To calculate these damage variables, the procedure indicated by (
To define the mechanical properties of the FRCM to be used to model the strengthening of the concrete beam, it was necessary to first implement and validate a numerical model of previous FRCM experimental tensile tests (
To simulate the hemp fabric, truss elements were chosen, as in other studies (
In the FRCM model, four “truss” elements were used. These simulated four longitudinal hemp fabric tows were embedded in the FRCM specimens. The tows in the weft direction were not simulated because the adhesion contribution of the tows placed in the weft direction was neglected when only tensile axial loads were applied.
Two types of materials were defined: one corresponding to the deformable solid that represented the cementitious matrix, and the other corresponding to the truss element that represented the tufts in the warp direction of the vegetal fabric.
The aforementioned plastic damage model was chosen to define the material of the cementitious matrix. The tensile elastic behaviour of the cementitious matrix was experimentally determined by compression and tensile tests of mortar specimens (see Table 1 in (
Regarding the boundary conditions, one of the transverse faces of the mortar model (deformable solid) was fixed (restriction of displacement in all directions), and a displacement equivalent to the integration of a constant strain equal to the ultimate fabric strain was imposed on the opposite face.
Two meshes with characteristic size of 2 and 5 mm were tested for the convergence analysis, and no significant difference was observed in the results (3% variation in the failure strain). Hence, the size of the elements used was set to 5 mm for all the parts to reduce the calculation cost. The resulting mesh had 800 solid elements and 160 truss elements (
(a) deformable solid, (b) truss type element
The results of the numerical simulation of the tensile specimens of hempFRCMs are presented in
Fibres  σ_{mc} (MPa)  σ_{cu} (MPa)  E_{I} (GPa)  E_{III} (GPa) 


4.97  7.36  9.25  0.45 

−9.71  3.81  −56.99  −23.14 

3.03  10.50  −0.77  14.31 
The elastic moduli of zones 1 (E_{I}) and 3 (E_{III}) obtained from the first slope (before the tensile cracking stress) and the second ascending slope (linear part in the slope after tensile cracking) in the stressstrain diagrams (see
numerical vs analytical vs experimental results
The difference between the cracking and ultimate tension calculated by the numerical model to the experimental results ranges from 3% to 10%; therefore, this model is an effective calculation tool for the analysis of FRCMs with hemp fibres if there is sufficient interaction between the mesh and matrix. This allowed us to define the mechanical properties of the hempFRCM used to simulate the strengthened concrete beam in Section 4.3.2.
For simulation of the FRCM, Abaqus^{TM} 6.144 (
For this analysis, a deformable solid was used to simulate the concrete part defined by a length of 4.5 m, width of 200 mm, and height of 400 mm (
(a) deformable solidbeam, (b) truss elementsreinforcement steel, (c) Shell elementFRCM
Truss elements were used to simulate the steel reinforcement (longitudinal steel bars and stirrups). The steel elasticplastic model suggested by the code (
A concrete damage plastic model (previously used for mortar in the FRCM simulation) was used to define the concrete response. The corresponding material properties were obtained as follows. The concrete tensile strength (corresponding to the cracking state) was calculated using
where
The static elastic modulus of concrete determined in the modal analysis (Section 2.2.1) was used to define its elastic properties.
Two mesh sizes for concrete discretisation were tested for the convergence analysis: 0.05 and 0.025 m. The 0.05 m sized mesh was chosen because no significant difference between the 0.05 and 0.025 m meshes was observed (4.7% variation of the maximum reaction force), and the calculation time was 30 times less using the 0.05 m mesh.
The boundary conditions were set according to the static loading setup adopted in Section 2.4 (
A steel solid (length of 0.2 m, wide of 0.1 mm and height of 0.1 mm) was modelled to simulate the loading tool. The load was indirectly applied by imposing a vertical displacement that caused the failure of the experimental specimen (Section 2.5).
Finally, to identify and verify the breaking condition, the concrete compressive ultimate strain (0.0035) was considered as the governing criterion.
In the case of the beam strengthened with hempFRCM, the same unstrengthened beam model was used, with the difference that shell elements were added to simulate the FRCM (see
Shell elements are intended to model structures with one dimension significantly smaller than the other two dimensions. The stresses in the thickness direction must be negligible to properly use the shells. An elasticplastic model was used on the shell elements to represent the FRCM. The numerical stressstrain diagram presented in
For the interaction between shell elements (FRCMs) and deformable solids (concrete beams), tie connections were used. This approach has been considered in other studies (
The same boundary condition as that for the unreinforced beam was imposed. The input displacements were set according to the adopted cyclic loading setup (
The results obtained from the numerical model are presented in
Beam  Model  F_{max} (kN)  M_{max} (kNm)  M_{service} (kNm)  y_{max} (mm)  ε_{s} (/)  ε_{f,u} (/) 



46.03  48.33  35.76  39.41  0.01  0.012 

1.14  −9.93  58.45      

0.50      −6.86  −7.69  


42.60  44.73  32.35  78.35  0.039   

3.50  15.88  6.04      

5.62      −22   
Δ_{E}: variation with respect to experimental test, Δ_{A}: variation with respect to the analytical results
The fitting capabilities of the numerical model are analysed for both beams as follows:
Control beam: the maximum and service moment and the deflection at maximum moment properly fit the experimental and analytical results, with differences ranging between 3.5% and 16%. However, the numerically predicted maximum strain of the steel was much lower than that of the analytical model (22%).
Beam strengthened with hempFRCM: the model for the strengthened beam was able to obtain values of maximum moment, service moment, and strain in the reinforcement steel (ε_{s}) and FRCM (ε_{f,u}) close to the experimental and analytical results, with differences ranging from 0.5% to 10%. However, in the case of the deflection at the maximum moment, the numerical model yielded a far lower value than the experimental tests (58%).
(a) static load (control beam), (b) cyclic load (strengthened beam)
(a) stiffness degradation and (b) damping factor
To evaluate the energy dissipation capacity of the strengthened beam, the viscous damping factor was determined for each loading cycle (ξi). This parameter is defined as the capacity of a structure to dissipate the input energy (Epi). The damping factor for each cycle can be determined using the following equation:
where
The results presented in this section demonstrate that the proposed numerical models can accurately reproduce the experimental response. These results depend, for the hempFRCM strengthened beam, on the fulfilling of the hypothesis that the connections meshmortar and mortarconcrete are sufficiently good to avoid sliding and debonding failures.
In general, this study shows how by using a novel vegetable fabric (hemp) it was possible to increase the stiffness of a previously cracked beam by more than 200% and increase its service load by 42% (results confirmed by analytical and numerical models). Therefore, this fabric is a competitive reinforcement material to strengthen RC beams subjected to dynamic loads. In addition to the efficiency demonstrated in this article by the hempFRCM, its use would entail a significant reduction in cost and density as well as a greater environmental sustainability (compared with the synthetic fibre FRCM (
An experimental, analytical, and numerical study of a beam strengthened with hempFRCM and subjected to cyclic loading was conducted. It was complemented with a control case. The following conclusions were drawn from this research:
The modal analysis of the beam strengthened with hempFRCM showed an increase of 270% in the flexural stiffness of the beam after cracking, demonstrating the effective contribution of the hempFRCM to the stiffness of the beam. These results were corroborated by experimental bending tests.
The experimental results showed that the greatest contribution of the hempFRCM system was the significant increase in the ultimate service limit state of the beam, by over 42 %.
The analytical models confirm that in the case of the beam strengthened with hempFRCM, the hemp mesh broke before the crushing failure of concrete or tensile breaking of steel.
The adjusted analytical model yielded better results (variation of 0.64% from the experimental results) than the traditional model when calculating the maximum bending moment. This demonstrates the efficiency of introducing the FRCM contribution when calculating the structural response of the hempFRCMstrengthened beam.
The numerical FRCM model developed in this study was useful for defining the mechanical properties of the FRCM used to simulate the hempFRCMstrengthened concrete beam.
The numerical model for the hempFRCMstrengthened beam was effective at predicting the maximum bending moment and displacement. However, it presented an inability to reproduce the reversible crack openings observed in the experimental tests.
The numerical and analytical procedures used to model the FRCMstrengthened beam presented in this study provide a useful calculation tool to reproduce the behaviour of this type of structure when the mechanical bonding in FRCMconcrete and fabricmatrix interfaces is assured.
The authors gratefully acknowledge partial financial support from the Ministerio de Economía y Competitividad of the Spanish Government through the SEVERUS project (ref. num. RTI2018099589BI00). The authors gratefully acknowledge partial financial support from AZVI, S.A. company through REDUVE contract. Third author is a Serra Húnter fellow.
Conceptualization: L. Mercedes. Data curation: L. Mercedes. Formal analysis: L. Mercedes, E. BernatMaso, L. Gil. Investigation: L. Mercedes. Methodology: L. Mercedes, E. BernatMaso. Project administration: L. Mercedes. Resources: L. Mercedes, V. Mendizával. Software: L. Mercedes. Supervision: L. Mercedes. Validation: L. Mercedes. Visualization: L. Mercedes. Writing, original draft: L. Mercedes, V. Mendizával. Writing, review & editing: L. Mercedes, E. BernatMaso, L. Gil.