Lumber Beams Research Articles

Numerical and Theoretical Analyses of Laminated Veneer Lumber Beams Strengthened with Fiber-Reinforced Polymer Sheets

This study outlines a method of utilizing the finite element method and a simple mathematical model to predict the behavior of laminated veneer lumber (LVL) beams strengthened with composite sheets. The numerical models were created using the Abaqus 2017 software. The LVL was considered as a linearly elastic or elastic–plastic material, factoring in Hill’s yield criterion. The composites were simulated as linearly elastic–ideally plastic materials. The mathematical models were predicated on the methodology of transformed cross-section. The theoretical and numerical outcomes were juxtaposed with previous empirical investigations. The comparison encompassed load-bearing capacity, stiffness, and deformation under peak force. Furthermore, presentations of normal stress maps in the LVL and composite have been illustrated. The derived maps were juxtaposed with the delineations of failure modes. An adequate correlation was identified between the theoretical, numerical, and empirical values in the case of beams reinforced with aramid, glass, and carbon sheets. The relative deviation varied from several to multiple percentages. This technique is not applicable for evaluating load-bearing capacity and deformation when only dealing with sheets with low elongation of rupture. This is a consequence of their premature failure. The proposed models may be utilized by researchers and engineers in the design of reinforcements for timber structures.

Numerical Analysis of Laminated Veneer Lumber Beams Strengthened with Various Carbon Composites.

Among the many benefits of implementing numerical analysis on real objects, economic and environmental considerations are likely the most important ones. Nonetheless, it is also crucial to constrain the duration and space necessary for conducting experimental investigations. Although these benefits are clear, the applicability of such models must be appropriately verified. This research subjected validation of numerical models depicting the behavior of unstrengthened and strengthened laminated veneer lumber (LVL) beams. As a reinforcement, a carbon fiber reinforced polymer (CFRP) sheet and laminates were used. Experiments were conducted on full-scale members within the framework of the so-called four-point bending testing method. Numerical simulations were performed using the Abaqus software. Two types of material models were examined for laminated veneer lumber: linearly elastic and linearly elastic-perfectly plastic with Hill's yield criterion. A distinction was made in the material properties of carbon composites based on their location on the height of the cross-section. The outlined numerical models accurately depict the behavior of real structural elements. The precision of predicting load-bearing capacity amounts to a few percent for strengthened beams and a maximum of eleven percent for unstrengthened beams. The relative deviation between numerical and experimental values of bending stiffness was at a maximum of seven percent. Applying the elastic-plastic model enables accurate representation of the load versus deflection relation and the distribution of stress and deformation of strengthened beams. Based on the findings, directives were provided for further optimization of the positioning of composite reinforcement along the span of the beam. Reinforcement design of existing laminated veneer lumber members can be made using presented methodology.

Flexural performance of full-scale two-span Nail-Laminated Timber Concrete composite slabs

This study examines the flexural performance of six 9-m full-scale two-span Nail-Laminated Timber Concrete (NLTC) composite slabs. The slabs were made with lumber beams edge-joined with double nailing, end-joined with butt joints, and the reinforced concrete topping connected with a set of notches, inclined screws, or a combination of both. The multi-span configuration of slabs reduces their deflections simply and effectively. Five-point monotonic bending tests were considered for all slabs. Before full-scale slabs, compressive and tensile pull-out tests of Timber-Concrete Composite (TCC) shear connections were performed, including notches and inclined screws. Tensile pull-out tests of shear connections were also included to emulate the negative bending moments that occur in the middle of the slabs. Failure modes, load–mid-span deflection relation, bending stiffness, and timber-concrete slip were evaluated for all slabs. A detailed 3D micro-Finite Element (FE) model of the shear connections was built in ANSYS software, whereas a macro-FE model of NLTC slabs was made in SAP2000, demonstrating a good fit for the timber-concrete interaction and the load-carrying capacity of the composite slab at the serviceability range. Moreover, an analytical elastic TCC beam with the Girhammar method was assessed and demonstrated as more precise than the traditional γ-method. Finally, an accurate prediction of the numerical and analytical (Girhammar) models for the bending stiffness at service loads up to 30% of capacity is observed, with errors in a range of 2–23% and 9–74%, respectively.

Numerical, Theoretical, and Experimental Analysis of LVL-CFRP Sandwich Structure.

Optimization of structural elements via composition of different components is a significant scientific and practical point-of-view problem aimed at obtaining more economical and environmentally friendly solutions. This paper presents the results of a static work analysis of small-size laminated veneer lumber (LVL) beams reinforced by a Carbon Fiber Reinforced Polymer (CFRP) sheet. The nominal dimensions of LVL beams were 45 × 45 × 850 mm, and 0.333- and 0.666-mm thick reinforcement layers were used. The reinforcement was applied on opposite sides of the cross section obtaining a sandwich-type structure. An epoxy resin was used as a bonding layer. The bending tests were conducted in the so-called four-point bending static scheme in edgewise and flatwise conditions. The results of experimental tests confirmed the validity of this combination of materials. The highest load-bearing capacity was obtained for configuration, where CFRP sheets with a thickness of 0.666 mm were placed on the sides of the core, parallel to the direction of loading and the veneer's grain in the core. The increase in this case was up to a maximum of 57% compared to the core alone. The highest bending stiffness increase, 182% compared to the core alone, involves placing two layers of sheets perpendicular to the direction of loading, i.e., on the upper and lower surfaces. The presented novel sandwich structure can be competitive against traditional steel and reinforced concrete elements in civil engineering and can be utilized as beams or slabs.

Experimental assessment of self-tapping screws for the reinforcement of multiple holes in laminated veneer lumber beams

In recent times, there is increased focus in the built environment on the use of low carbon materials. In tall timber buildings, service ducting needs to be facilitated. Multiple holes in elements may be required in buildings where a high demand of services exist. Limited investigations have been conducted on laminated veneer lumber (LVL) beams in comparison to the literature on timber and glued laminated timber beams and no experimental testing has been conducted where multiple holes in LVL have been reinforced. Such openings are of particular concern when positioned in high shear zones. Therefore, an experimental programme in which seventy-five LVL beams were monotonically tested in three-point bending was conducted. The programme included standard beams, beams with a single round hole, and beams with double round holes for three different hole diameters and two holes spacings. The openings were concentrically positioned and were reinforced using internal screw reinforcement in which three configurations were examined. The programme was designed to evaluate the guidance that is currently available which has been developed based on testing with glued laminated timber. Throughout, it was seen that the self-tapping screws orientated at 60° were the most effective in comparison to when the reinforcement was orientated at 45° or positioned vertically. For LVL beams with single holes and up to hole diameters of 0.45 diameter (d) which far exceeded the current guidance of 0.3d maximum hole size, the reinforcement when positioned at 60°, achieved midspan failures like standard beams. The failure loads of such reinforced beams were in the same range as the standard beams. The screw reinforcement when orientated at 60o, was most effective for the double holed beams when a hole size of 0.35 d for both spacings (0.5 d and 0.75 d) was studied. The load carrying capacity was also in the same range as the standard beams but the failure mode was hole edge failure. Strain profile readings indicated the effectiveness of the reinforcement such that strains at the soffit of the beam where two holes were reinforced with screws exceeded the strains at the soffit of the standard beams.

Application of Transformed Cross-Section Method for Analytical Analysis of Laminated Veneer Lumber Beams Strengthened with Composite Materials

Due to the high cost of laboratory testing, many researchers are considering developing methods to predict the behavior of unreinforced and reinforced wood beams. This work aims to create either numerical or analytical models useful for extrapolating already conducted tests to other schemes/materials used as reinforcement. In the case of timber structures, due to the complexity of timber, this task is difficult. The first part of the article presents an analysis of the suitability of using a simplified mathematical model based on the equivalent cross-section method to describe the behavior of unreinforced and reinforced with carbon-fibre-reinforced polymer (CFRP) composite full-size laminated veneer lumber (LVL) beams. The theoretical results were compared with the results of conducted experimental tests. The scope of the analysis includes the estimation of modulus of rupture, bending stiffness, and determination of the neutral axis position. The equivalent cross-section method showed good agreement in determining the bending stiffness and neutral axis position of the strengthened sections. However, the suitability of using the equivalent cross-section method to estimate the load-carrying capacity of a cross-section reinforced with fiber composites still needs to be confirmed, which, according to the authors, is due to the differences between the assumed (linear) and actual (nonlinear) strain distribution in the compression zone. The second part uses the equivalent cross-section method to estimate the predicted bending stiffness of LVL beams strengthened with aramid-fibre-reinforced polymer (AFRP), glass-fibre-reinforced polymer (GFRP), and ultra-high modulus carbon-fibre-reinforced polymer (CFRP UHM) sheets. The proposed method can be used for preliminary evaluation of strengthening effectiveness of LVL beams.

Application of Digital Image Correlation to Evaluate Strain, Stiffness and Ductility of Full-Scale LVL Beams Strengthened by CFRP.

Due to limitations of traditional measuring methods, a necessity of verification of applicability of optical measuring systems in different fields of science is required. The paper presents the application of a non-contact, non-destructive ARAMIS optical system in the analysis of static work of unstrengthened and strengthened laminated veneer lumber beams (LVL) with composite materials, subjected to a four-point bending test. The beams were strengthened with Carbon Fiber Reinforced Polymer (CFRP) sheets and laminates. The sheets were bonded to the external surfaces in three configurations differing in the number of layers applied and the degree of coverage of the side surface. The CFRP laminates were glued into predrilled grooves and applied to the underside of the beams. An adhesive based on epoxy resin was used. The scope of the work includes analysis of the strain distribution, stiffness and ductility. The analysis was performed on the basis of measurements made with an optical measurement system. The strain analysis indicated a change of the distribution of the strain in the compressive zone from linear for the unstrengthened to bilinear for the strengthened beams. The stiffness increase was equal from 14% up to 45% for the application of the CFRP laminates in the grooves and CFRP sheets bonded externally, respectively. Similar improvement was obtained for the ductility.

Flexural behaviour of wood beams strengthened by flax-glass hybrid FRP subjected to hygrothermal and weathering exposures

This paper addressed the flexural behaviour (i.e., maximum load, ductility index, flexural strength and stiffness) of laminated veneer lumber (LVL) beams strengthened by 2-layer flax-glass hybrid fibre reinforced polymer (HFRP) exposed to hygrothermal (50℃ and 95% RH) and weathering (cyclic water spray-ultraviolet radiation) conditions for one month. Effects of environmental exposure and fabric sequences on flexural behaviour of LVL-HFRP beams were studied. LVL-FG and LVL-GF beams (inner plies bonded to LVL were flax and glass fibres, respectively) were tested under four-point bending. Tensile test on HFRP flat coupons was also conducted to provide the tensile parameters of HFRP in LVL-HFRP beams. This study showed that the hygrothermal and weathering exposures reduced the maximum load (by 11.4–32.2%), flexural strength (by 19.1–40.0%) and increased the ductility index (by 18.3–41.7%) of LVL-HFRP beams. The hygrothermal exposure did not affect flexural stiffness. The fabric sequence affected the flexural behaviour of LVL-HFRP beams. LVL-GF beams showed lower maximum load and flexural strength than those of the LVL-FG beams, which was attributed to the HFRP delamination in the LVL-GF beams. A theoretical prediction model for the ultimate bending moments of LVL-HFRP beams was used, and the calculated values showed a good agreement with the experiments.

SHEAR AND BENDING PERFORMANCE OF HORIZONTAL LAMINATED BAMBOO LUMBER BONDED WITH UREA-FORMALDEHYDE AND PRESERVED WITH DELTAMETHRIN

Deltamethrin has potential to be used for bamboo strip preservation in laminated bamboo lumber (LBL) beam industry. However, there is a lack of information regarding the effect of deltamethrin preservation on the structural performance of the LBL beam. This study was intended to observe shear and bending performance of LBL beam made of Dendrocalamus asper, preserved by deltamethrin, and glued by urea-formaldehyde. The adhesive bonding strength test following ASTM D905 and MD Block method and static bending test based on ASTM D143 were performed toward preserved and unpreserved samples. The performance was observed by calculating adhesive bonding strength, MOE, MOR, ductility index, and investigating failure modes. The results show that the average adhesive bonding strength of the treated sample is 7.28 MPa (ASTM D905) and 7.03 MPa (MD Block), while the average adhesive bonding strength of the untreated sample is 7.67 MPa (ASTM D905) and 7.41 MPa (MD Block). The average MOE (modulus of elasticity) and MOR (modulus of rupture) of the treated specimen is 18,840 MPa and 110 MPa, respectively. The untreated specimen's average MOE and MOR are 18,199 MPa and 109 MPa, respectively. The average ductility index of untreated and treated specimens is 4.8 and 3.9, respectively. The adhesive bonding strength of treated and untreated samples are higher than the bamboo shear strength. The result indicates that deltamethrin has no significant effect on the adhesive bonding strength, MOR, and MOE of the LBL beam. The LBL beams show significant plastic deformation before final beam failure.

Experimental and theoretical investigation of prestressed-steel-reinforced laminated bamboo lumber beams

This paper investigates a technique to strengthen laminated bamboo lumber (LBL) beams by embedding steel bars and prestressed steel bars at the specified locations. The flexural performance of the reinforced beams with different reinforcement ratios and levels of prestressing forces was investigated by studying the failure modes, load–displacement curves, load–strain curves, strain distribution at the critical cross-section and flexural resistance. Obtained experimental results showed that 85% of the beams failed due to the failure of bamboo fibers in the tension zone, and there was no significant failure in the compression zone. After embedding prestressed steel bars, the ultimate tensile and compressive strains of reinforced beam could reach up to 84% and 70% of those from the material test, respectively. The load capacity of both steel-reinforced beams and prestressed-steel-reinforced beams was significantly increased, with a maximum load capacity of 60% higher than the ordinary beams. In addition, both steel-reinforced beams and prestressed-steel-reinforced beams showed significant improvements, 40% and 49% respectively, in flexural resistance when compared to that of the ordinary beams. Theoretical equations for predicting flexural resistance of strengthened LBL beams have been proposed based on the observed strain and stress distributions.

BAMBOO COMPOSITE BEAMS TO SUBSTITUTE LUMBER FRAMING IN RESIDENTIAL CONSTRUCTION

Residential construction plays major role in making people’s dwelling as the basic need. Different cultures perform their construction differently, depending on their available materials and technology. Most typical residential construction use wood or timber as the material because it is easy to work with. However, timber becomes harder to find and get expensive. They also take up to two decades to harvest. Industry is trying to find alternatives to substitute timber uses, such as laminated lumber and all engineered lumbers. These engineered materials do not offer access to everyone. This research explores opportunity for local people to do construction using their available local materials, yet effective. Bamboo is also local and abundant material to most tropical areas. Bamboo is light and strong, yet renewable because it only takes 3 years to produce. The research proposed the composite beams made by bamboo with local lumber. This is to take advantage of the properties of bamboo to increase the structural performance. This research explored five designs of composite beams, using bamboo compositing with lumber and plywood beams. Different bamboo configurations are added to top and bottom of lumber beams. Webs of beam are either dimensional lumber or plywood. Five composite beams were then tested in structural laboratory. It is found that bamboo composite beams significantly made the loading improvement in bending capacity from 1.9 to 3.9 times, comparing to lumber beams alone.

Strengthening of Full-Scale Laminated Veneer Lumber Beams with CFRP Sheets.

This paper presents the results of experimental research on full-size laminated veneer lumber (LVL) beams unreinforced and reinforced with CFRP sheets. The nominal dimensions of the tested beams were 45 mm × 200 mm × 3400 mm. The beams were reinforced using the so-called U-type reinforcement in three configurations, differing from each other in the thickness of the reinforcement and the side surface coverage. An epoxy resin adhesive was used to bond all the components together. A four-point static bending test was performed according to the guidelines in the relevant European standards. The effectiveness of the reinforcement increased with the level of coverage of the side surface and the level of reinforcement. The average increases of bending resistance were 42%, 51% and 58% for configurations B, C and D, respectively. The average value of bending stiffness increased for the beams of series B, C and D by 15%, 31% and 43%, respectively. Their failure mode changed from brittle fracture initiated in the tensile zone for unreinforced beams to more ductile fracture, initiated in the compression zone. The influence of the coverage of the side surface by the CFRP sheet and reinforcement ratio on the mechanism of failure and effectiveness of strengthening was studied in the article.

Experimental Study of Beam Stability Factor of Sawn Lumber Subjected to Concentrated Bending Loads at Several Points

The beam stability factor (CL) is applied in construction practices to adjust the reference bending design value (Fb) of sawn lumber to consider the lateral-torsional buckling. Bending tests were carried out on 272 specimens of four wood species, namely, red meranti (Shorea sp.), mahogany (Swietenia sp.), pine (Pinus sp.), and agathis (Agathis sp.), to analyze a simply supported beam subjected to concentrated loads at several points. The empirical CL value is a ratio of the modulus of rupture (SR) of a specimen to the average SR of the standard-size specimens. The non-linear regression estimated the Euler buckling coefficient for sawn lumber beam (KbE) in this study as 0.413, with 5% lower and 5% upper values of 0.338 and 0.488. Applying the 2.74 factor, which represents an approximately 5% lower exclusion value on the pure bending modulus of elasticity (Emin) and a factor of safety, the adjusted Euler buckling coefficient (KbE′) value for a timber beam was 1.13 (0.92–1.34), which is within the range approved by the NDS (KbE′ = 1.20). This study harmonizes the NDS design practices of CL computation with the empirical results. Because agathis has the lowest ductility (μ), most natural defects (smallest strength ratio, S), and highest E/SR ratio, the agathis beam did not twist during the bending test; instead, it failed before twisting could occur, indicating inelastic material failure. Meanwhile the other specimens (pinus, mahogany, and red meranti), which have smaller E/SR ratio, higher ductility, and less natural defects, tended to fail because of lesser beam stability. This phenomenon resulted in the CL curve of agathis being the highest among the others. The CL value is mathematically related to the beam slenderness ratio (RB) and the E/SR ratio. Because the strength ratio (S) and ductility ratio (μ) have significant inverse correlations with the E/SR ratio, they are correlated with the CL value. Applying the CL value to adjust the characteristic bending strength is safe and reliable, as less than 5% of the specimens’ SR data points lie below the curve of the adjusted characteristics values.

Ductility and Stiffness of Laminated Veneer Lumber Beams Strengthened with Fibrous Composites

The paper presents the results of experimental research on unstrengthened and strengthened laminated veneer beams subjected to 4-point bending. Aramid, glass and carbon sheets with high tensile strength (HS) and ultra-high modulus of elasticity (UHM) glued to external surfaces with an epoxy resin adhesive were used as reinforcement. Two reinforcement layouts were used: (1) sheets glued along the bottom surface and (2) sheets glued to the bottom and side surfaces. Based on the test results, the flexural strength, flexural ductility and stiffness were estimated. Compared to the reference beams, the maximum bending moment was higher by 15%, 20%, 30% and by 16%, 22% and 35% for the Aramid Fiber Reinforced Polymers (AFRP), Glass Fiber Reinforced Polymers (GFRP) and Carbon Fiber Reinforced Polymers (CFRP) HS sheets, respectively. There was no significant increase in the flexural bending capacity for beams reinforced with UHM CFRP sheets. Similar values of bending ductility indices based on deflection and energy absorption were obtained. Higher increases in ductility were observed for AFRP, GFRP and CFRP HS sheets in “U” reinforcement layout. The average increase in bending stiffness coefficient ranged from 8% for AFRP sheets to 33% for UHM CFRP sheets compared to the reference beams.

Evaluasi Perilaku Lentur Balok Tinggi LVL Sengon dengan Pengekang Lateral pada kedua Tumpuan

Slender beams (beams having a large section height to width ratio ( )) are commonly used in a structure that needs a large bending moment capacity. However, the use of slender beams in a structure is susceptible to overturning and torsion occurrence. Therefore, lateral bracing is usually placed in several points of the beam to prevent lateral-torsional buckling. In this study, a three-point bending test was conducted to evaluate the capacity of 250 mm x 50 mm x 2500 mm Laminated Veneer Lumber (LVL) beams made from Sengon. Two lateral supports were placed at both ends to prevent the beam's lateral displacement. The bending test result shows that the ultimate load of the LVL beam reach 27.88 kN before failure. Furthermore, the LVL beams' bending capacity was calculated using the mechanical properties provided by several previous studies. The LVL beam's capacity was predicted using manual calculation (based on SNI 7973: 2013) and numerical analysis. Numerical analysis was performed using ABAQUS software, and the results were evaluated using the Tsai-Hill and maximum strain failure criterion. The results showed that the maximum strain criterion provides a better prediction of the LVL beam's capacity than Tsai-Hill failure criterion.

Load bearing capacity of laminated veneer lumber beams strengthened with CFRP strips

Load bearing capacity of laminated veneer lumber beams strengthened with CFRP strips

Failure Analysis of Glulam Lumber Beam Made from Meranti Lumber Pieces (Shorea SP)

The development of glue-laminated (glulam) lumber beam gives many good results. Meranti (Shorea SP) is one of the construction lumber that can be used as glulam to optimize its use. The limitation of the glulam lumber beam is the limited length of the lumber, so it must be joined to get a certain length. The lumber available in the market on average has a limited size and cross-sectional length. The larger the cross-sectional size and length of the lumber make the higher the price. Used lumber and residual lumber also have many weaknesses, such as the length of suitable lumber is too short, lumber defects, and lumber damages. Further research needs to be done to optimize the use of new, used, and residual meranti lumber through the use of lumber pieces as a glulam lumber beam maker. Standard specimen and test based on ASTM D-198. Glulam lumber beam is made from pieces of meranti lumber planks of certain length which are arranged into lamina beam with the size of 5.5x9.5x150 cm3. Variations in the length of the pieces of meranti lumber planks for making glulam lumber beam, among others, 40 cm, 50 cm, 60 cm, 50 cm with full length lowest layer and 150 cm (full length). The adhesive used is polyurethane glue. The span between supports is 130 cm. The beam is tested for center point loading. The analysis results show that the joints on the outermost layer that receive tensile stress of the glulam lumber beam can cause weakening in the beam because the tensile strength of the adhesive is weaker than the tensile strength of lumber. Failure at the tensile joint of the outer layer of the beam can trigger a shear failure mode. Design of joints should not be placed on layers that are subject to tensile stresses so as not to trigger shear failure modes so that the strength of the glulam lumber beam can be optimal.

Enhancement of bending properties of Douglas-fir and poplar laminate veneer lumber (LVL) beams with carbon and basalt fibers reinforcement

This paper presents the experimental results of the bending mechanical behavior (static and dynamic moduli, and maximum stress) of LVL (Laminated Veneer Lumber) beams reinforced with fiber polymer material (FRP). Different variables were studied: i) Wood species (Douglas fir or poplar); ii) Type of reinforcement (bidirectional carbon, unidirectional carbon or basalt); iii) Veneer quality and iv) Veneers orientation in the beam (flatwise or edgewise). The reinforcement percentages respect to the total cross-section was of 2.17%, 0.89%, and 1.74% for the unidirectional carbon, bidirectional carbon and basalt, respectively. A clear improvement provided by unidirectional carbon has been demonstrated (up to 40% more in the elastic modulus for the flatwise layout and more than 20% of the maximum stress, for both wood species). The influence of the quality of the veneers of the panel was also clearly demonstrated: the weakest wood material obtained the greatest improvements in their mechanical properties when reinforced, allowing to obtain stiff second quality poplar LVL, or strong second quality Douglas fir LVL.

Mechanical performance of laminated veneer lumber and Glulam beams after short-term incident heat exposure

Timber use is becoming more appealing in the recent years especially ‘exposed timber’; however, the information available on the performance of engineered timber after fire is limited. This paper explores the performance of timber elements exposed to well defined thermal boundary conditions and examines the extent of adhesive degradation after heating. Two different types of timber beams are explored; ‘glued laminated timber’ (Glulam) and ‘laminated veneer lumber’ (LVL). A subset of beams was exposed to radiant heat as per a modified ASTM E1321 heating procedure. An additional subset of beams also had an area of their cross-section carved away, equivalent to the char depth of the heated beams. The carved beams allow for the identification of degradation beyond the char layer, as theoretically both the carved and charred beams would have the same effective cross-sectional area. All beams were mechanically loaded to failure using a four-point loading setup. While the current allowance for degradation beyond the char layer is considered to be 7 mm for exposure times of 20 min and greater [1], the results herein indicate that for bending members this layer extends to at least a minimum of 11.7 mm for LVL and 12.3 mm for Glulam. The aim of this paper is to assess the post-fire performance of Glulam and LVL through looking at strength loss due to adhesive degradation, which may contribute towards enabling tall and unencapsulated engineered timber buildings.

Mechanical Properties of Laminated Veneer Lumber Beams Strengthened with CFRP Sheets

AbstractThis paper presents the results of the static work analysis of laminated veneer lumber (LVL) beams strengthened with carbon fabric sheets (CFRP). Tested specimens were 45mm wide, 100 mm high, and 1700 mm long. Two types of strengthening arrangements were assumed as follows: 1. One layer of sheet bonded to the bottom face; 2. U-shape half-wrapped reinforcement; both sides wrapped to half of the height of the cross-section. The reinforcement ratios were 0.22% and 0.72%, respectively. In both cases, the FRP reinforcement was bonded along the entire span of the element by means of epoxy resin. The reinforcement of the elements resulted in an increase in the bending strength by 30% and 35%, respectively, as well as an increase in the global modulus of elasticity in bending greater than 20% for both configurations (in comparison to the reference elements).