Increase In Flexural Capacity Research Articles

Strengthening of two-way slabs with fiber-reinforced polymer composites: A new system using grooving technique and fans

The flexural capacity of a reinforced concrete (RC) two-way slab can be efficiently enhanced using fiber-reinforced polymer (FRP) composites if FRP debonding is postponed. On the other hand, with the increase in flexural capacity, the vulnerability of the slab to punching shear failure increases. In this context, the current study examines FRP strengthening of lightly reinforced slabs using the externally bonded reinforcement on grooves (EBROG) technique, which has already been proven successful in postponing FRP debonding. Four slab specimens are tested in two groups under concentric loading. The first group consists of two specimens reinforced with headed shear studs: one reference specimen and one specimen strengthened in flexure with FRP. The second group includes two specimens without internal punching shear reinforcement: one reference specimen and one specimen strengthened with a new simultaneous flexural and punching shear strengthening system, taking advantage of FRP fans. According to the results, flexural strengthening of the slab in Group 1 increased its ultimate load capacity by 77%, and the proposed strengthening system in Group 2 led to a 94% enhancement of the ultimate load capacity. A calculation method based on the yield-line theory is presented to predict the load capacity of the test specimens. According to this method, graphs simplifying the estimation of the flexural capacity of FRP-strengthened slabs are proposed.

Moment curvature response of composite UHPC filled hollow structural steel cross-sections

A mechanics based analytical method for obtaining the complete moment–curvature response of composite hollow structural steel (HSS) and ultra high performance concrete (UHPC) cross-sections is presented. Flexural response at the cross-sectional level is traced past the local buckling of the steel elements and up to the exhaustion of UHPC and steel material capacity. The proposed method is validated using experimental data from seven flexural tests on composite HSS-UHPC beams. Flexural failure mode is classified as either a UHPC compression-controlled failure, UHPC fiber tension-controlled failure, or a balanced failure. Behavioral differences between the cross-sections that fall into these three categories are discussed in terms of flexural capacity, curvature ductility, and relative contributions of HSS and UHPC to flexural capacity. Flexural response of the composite HSS-UHPC cross-section is compared to that of the bare HSS cross-section. The enhancement in flexural capacity and curvature ductility, for UHPC fiber tension-controlled sections compared to the bare HSS cross-section, was 52% and 79%, respectively. For composite cross-sections that feature a balanced failure, the increase in flexural capacity and curvature ductility, compared to the bare HSS cross-section, was 37% and 35%, respectively. Closed form formulations are proposed to identify the flexural failure mode and predict flexural capacity. The influence of various parameters, such as HSS material grade, size of cross-section, and UHPC material characteristics on the complete flexural response of the cross-section is investigated. The average ratio and corresponding coefficient of variation (COV) of tested to computed flexural strength obtained using the proposed procedure was 1.06 and 21.28%, respectively. Similarly, the average ratio and COV of tested to calculated flexural strength obtained using the proposed closed form formulations was 1.07 and 22.18%, respectively.

Impact of Anchored CFRP Composites on the Strengthening of Partially Damaged PC Girders

This manuscript investigated the effect of anchorage CFRP wrapping sheets, bolts, and laminate interlock on increasing the efficiency of flexural strengthening for the post-tension girder using CFRP composites techniques longitudinal laminates at the soffit for partially damaged loss of about 14.3% from its area of prestressed concrete beams, and the impact on restoring the original flexural capacity of PC girder. Mitigating delamination of the soffit of horizontal laminates (CFRP). The texture of the laminate and anchorages influenced the stress of the laminate carbon fiber, the mode of crack propagation and failure, and consequently, the beam's attitude has been investigated in this manuscript. The experimental findings demonstrated that using CFRP laminates significantly affects strand strain, especially when anchorage wrapping is applied. The laminates CFRP-EB enhanced the flexural capacity by around 13% of the original strength, which equates to a 13% increase in strand damage. Despite an increase in flexural capacity of 20%, 22%, and 29% when using anchorage wrapping, mechanical bolts, and laminate interlock, respectively. It has been proposed to use quasi-experimental equations to predicate the actual stress of un-grouted strands, considering the influence of CFRP laminate and wrapping anchorage sheets techniques only. The experiment outcomes demonstrated that using Anchored CFRP significantly affects load-carrying capacity and cracking load by up to 29% and delays the bonding failure.

Flexural behaviour of circular timber columns strengthened by glass fibre reinforced polymer wrapping system

Prefabricated glass fibre reinforced polymer (GFRP) wrapping systems have been established as an attractive retrofitting technique for structural columns in various applications. Further exploration is needed to evaluate their contribution to the flexural performance of timber columns due to their inevitable exposure to bending under different loads, such as wave actions, wind, and earthquake, among the others. This study investigates the contribution of GFRP wrapping systems to the capacity of timber columns tested under three-point bending. Eight unwrapped and GFRP-wrapped circular timber columns with annular space filled by grout or epoxy materials were tested. The inclusion of carbon FRP (CFRP) straps within the epoxy infill was also investigated. The flexural load-midspan deflection, longitudinal strain responses, and failure modes were carefully studied. Finite element modelling (FEM) and theoretical analyses were performed and compared with the experimental results. The results revealed that GFRP-wrapped columns with epoxy infills exhibited a significant increase in flexural capacity by up to 95% compared with unwrapped columns. The results also showed that the provision of epoxy infill along with CFRP straps within the wrapping system can substantially improve the energy absorption of timber columns whilst, those with grout infills revealed a remarkable increase in ductility compared with unwrapped columns. The results predicted by FEM and theoretical analyses were in good agreement with experiments. This study demonstrated that the studied GFRP wrapping system is an adequate strengthening technique that can improve the flexural performance of circular timber columns.

Flexural behavior of all lightweight reinforced concrete beams externally strengthened with CFRP sheets

The usage of structural Lightweight concrete (LWC) has increased over the years and received significant attention owing to its lower density, better economical design, and mechanical properties as compared to conventional normal weight concrete (NWC). However, limited research efforts and codes provisions deal with retrofitting and strengthening of lightweight concrete structures. Therefore, the main objective of this investigation is to evaluate the flexural performance of all lightweight concrete (ALWC) beams externally strengthened using Carbon Fibre Reinforced Polymer (CFRP) sheets. A total of fifteen ALWC beams were divided into three series based on their reinforcement ratio and strengthened with externally bonded CFRP sheets. The test variables studied in the experimental program were the effective reinforcement ratio, number of CFRP layers, and the percentage of pre-loading. All the beams were tested under four-point bending and the experimental results show that the CFRP sheet has significantly increased the ultimate load carrying capacity of pre-loaded and non-preloaded strengthened specimens. The increase in flexural capacity ranged from 28% to 102% over the unstrengthened control specimen. The ultimate load capacity was also predicted using different design standards and compared with the experimental load. The comparison showed that the current design standards have overestimated the flexural capacity of CFRP strengthened ALWC specimens.

Debonding characterization for all-lightweight RC T-Beams strengthened in flexure with FRP

This paper presents an experimental, analytical and numerical comparison of the behavior of lightweight and normal weight concrete beams strengthened with externally bonded high modulus carbon fiber. The main objective of this paper is to study the efficiency of using CFRP with all-lightweight concrete beams in flexural performance and validate the use of the modification factor (λ), proposed by ACI 318-19 for various concrete parameters, in adjusting the ACI 440.2 debonding strain. An experimental program was conducted using six full-scale T-beams made of two different concrete types, normal weight concrete, and all-lightweight concrete. Each series consisted of a control beam, and two beams strengthened using either two or four layers of high modulus CFRP. The results showed that the percent increase in flexural capacity is more evident in the normal weight beams as the number of layers increases. At the same time, this increase in lightweight beams is shown to be about the same beyond the use of two layers. Moreover, the reduction factors were found to be 0.93 and 0.85 leading to accurate recovery of the debonding experimental failure using the ACI 440.2 equation for the two-layered and four-layered beams, respectively. A nonlinear analysis parametric study was conducted to examine the parameter not varied in the experiments. A comparison to the debonding strain specified by other standards and models was also performed.

The axial capacity of a full height rectangular opening castellated steel beam with steel reinforcement stiffeners

The axial capacity of a full height rectangular opening castellated steel beam with steel reinforcement stiffeners is proven to prevent Vierendeel failure mechanism. The effect is an increase in flexural capacity of the structure. Diameter of the steel reinforcement stiffeners is revealed to have an effect on its strength in resisting axial forces occur in the structure. However, size of the diameter is limited to the strength maximum value of the steel flange section in withstanding the moment force. Using optimal design of the castellated steel structure, this research aimed to find out the increase value of the axial capacity. There were two models of steel structures employed in the study, IWF 200x100x5.5x8 and castellated beam 362x100x5.5x8, both were loaded with axial directions. Analyses were conducted using truss and pushover methods. Results of the study showed an increase in both flexural (36.81%) and axial (60.78%) capacities. The increase in the value of structure capacity mainly influenced by the stiffeners shortened the effective length of the structure.

Comparative analysis of the flexural capacity of conventional steel beams with Castellated beams

South Kalimantan, especially Banjarmasin City, has a thick layer of soft soil. Low bearing capacity is a major issue in planning the structure. Castellated beam is an innovation to create high structural capability with low weight. This research aims to gain the effect of the hexagonal opening angle on the bending capacity of the castellated beam. The research was conducted by numerical testing using ANSYS. This research compares the flexural capacity of conventional steel beams to the geometric effect of castellated beam with hexagonal opening angle variations. This research concluded that the geometric effect of a castellated beam can provide an increase in flexural capacity of about 8 to 19% compared to conventional steel beams. The optimum bending capacity is at the hexagonal opening angle of 45° to 50°. At the 60° opening angle, the castellated beam has decreased its flexural capacity.

Flexural strengthening of over-reinforced concrete beams with highly ductile fiber-reinforced concrete layer

This study investigates the effectiveness of highly ductile fiber-reinforced concrete (HDC), which is characterized by its high ultimate compressive strain ability, in improving the failure mode and deformational characteristics of over-reinforced concrete beams. The flexural behavior of over-reinforced concrete beams strengthened with HDC was experimentally investigated. The variables included the tensile longitudinal steel reinforcement ratio, thickness of the layer, strengthening materials, and strengthening methods. The crack pattern, failure mode, load–deflection responses, flexural capacity, ductility, and strain were investigated. The experimental results indicated that applying HDC to strengthen the compression zone of an over-reinforced concrete beam is a highly effective method to change its brittle failure and improve the ductility. HDC-strengthened beams showed an increase in flexural capacity and deformation compared to normal concrete-strengthened beams with equal strengthening thickness. A better deformation capacity can be achieved by using a larger thickness of the strengthening layer, ensuring the coordination between the strengthening layer and the existing beam. The effectiveness of HDC in strengthening over-reinforced concrete beams was improved as the tensile longitudinal steel reinforcement ratio increased. A simplified calculation method for the flexural capacity of HDC-strengthened beams was proposed, which is in good agreement with the experimental results. The compression zone relative depth for the balanced failure could be notably improved by applying a larger thickness to strengthen the compression zone of over-reinforced concrete beams than the critical thickness of the HDC layer, which can be calculated by the proposed approach.

Flexural Capacity of Rattan Cane Reinforced Concrete Beams

To overcome the dependence on the use of reinforcing steel in concrete, alternative materials are used as reinforcement that is easy and cheap to obtain the resistant of corrosion namely rattan rods. With this material the natural resources can be utilized optimally. This research uses rattan as reinforcement for concrete beams. The test is carried out using a two-point loading method, used 4 types of beams, namely 2 rattan reinforcement beam (BR2), 3 rattan reinforcement (BR3), 4 rattan reinforcement (BR4) and 2 steel reinforcement (BS2) as control beams. The test results show that the addition of 2 times the amount of rattan reinforcement resulted in an increase in flexural capacity of 48.51%. The flexural capacity of rattanreinforced beams is lower than the flexural capacity of steel-reinforced beams by 10%, so the use of rattan as reinforcement in non-structural construction.

Experimental Study on Flexural Capacity of Corroded RC Slabs Reinforced with Basalt Fiber Textile

This experimental study investigated the flexural performance of corroded reinforced concrete (RC) slabs strengthened with basalt textile-reinforced mortar (BTRM) and basalt fiber-reinforced polymers (BFRP). Ten RC slabs were designed to achieve the expected corrosion levels (8% mass loss for moderate corrosion and 16% mass loss for severe corrosion) by accelerated corrosion methods. Two slabs served as reference specimens, and eight slabs were strengthened with BFRP or BTRM. The specimens were loaded to failure by the four-point bending method. The corrosion ratio, strengthening materials and the number of layers were tested for comparison. The failure modes, flexural capacities, load–deflection curves and deformation performances of the slabs were obtained from experiments. It was found that the use of BTRM layers was more effective in improving the flexural response than the use of the same amount of BFRP layers externally bonded with the corroded RC slabs under a state of serviceability. The results also showed that the strengthening effects of BFRP and BTRM were affected by the initial corrosion ratio and the number of textile layers. In a moderate state of corrosion, the flexural capacities and deflection capacities of RC slabs strengthened by BFRP and BTRM were increased substantially; the flexural capacities were increased by 27.81%~61.85%. In a severe corrosion state, the increase in flexural capacity of strengthened slabs is marginal but the increase in ductility indexes was 18% to 35% compared with the corresponding control slabs. By increasing the number of textile layers from three to five, the increments of the flexural capacity of strengthened slabs are almost doubled. Finally, the calculated results of the flexural capacity of the corroded RC slabs strengthened with BFRP and BTRM were found to be in good agreement with the experimental results.

PERILAKU LENTUR BALOK BETON BERTULANG HIGH VOL-UME FLY ASH (HVFA) DENGAN VARIASI UKURAN BUTIR MAKSIMUM AGREGAT

Global warming is a serious environmental issue. Production process of Portland Cement (SP) contribute 5% of all carbon dioxide emissions, the main cause of global warming and making cement means making pollution. High Volume Fly ash (HVFA) concrete technology is one solution that can be offered to overcome this problem. HVFA concrete is a type of concrete made using high enough fly ash, which is more or equal to 50% by weight of cement. In this study, the use of fly ash (FA) as a cement replacement material is about 50%. One disadvantage of HVFA concrete is the low early strength or slower, so in this study HVFA concrete was made with coarse aggregate size to smaller. This study compared HVFA concrete beams with size of aggregates are 20 mm and 4.75 mm, the planed compressive strength (f’c) is 25 MPa. Fly ash will substituted by 50% of the weight of the cement and the addition of superplasticizer about 0.4% by weight of cement. The size of specimens for flexural capacity of reinforced concrete beams about 140 x 240 mm with a span of 2000 mm. The flexural strength test arrangement with two-point loading. And the results of the study showed an increase in flexural capacity of 13.38%.

The Effect of Hole Width on Full Height Rectangular Opening Castellated Steel Beam with Diagonal Stiffener Concerning Its Flexural Capacity

The use of a diagonal stiffener in a full height rectangular opening castellated steel beam can prevent the failure mechanism of vierendeel. This results in the flexural capacity of the castellated beam higher than the original IWF profile. The flexural capacity of a castellated steel beam can be optimized by designing the hole width on the web section. This research aims to find out the effect of several values of castellated steel beam hole width on the flexural capacity. In this research, there are 4 castellated steel beam models whose flexural capacity values are calculated using the truss analysis and pushover analysis methods. Based on the calculation results, it can be concluded that the smaller the value of the hole width, the greater the flexural capacity of the castellated steel beam will be. The largest increase in flexural capacity from the original IWF to the castellated beam is 140.93%.

FRP-FLEXURAL STRENGTHENING OF STEEL BEAMS: A FINITE ELEMENT ANALYSIS STUDY

Fiber reinforced polymer (FRP) strengthening has been widely used for concrete structures. However, limited studies have been conducted on its application to steel structures. The use of FRP materials to retrofit steel members is an effective replacement for welded or bolted steel plates and offer high strength-to-weight ratio, resilience to environmental degradation, and a robust fatigue performance. Past studies have shown that the application of FRP to steel is a promising technical solution to help against corrosion and also to increase the load carrying capacity of steel members. In the present study, finite element analysis (FEA) model of a steel beam strengthened with carbon fiber reinforced polymer (CFRP) laminates was developed using ANSYS Mechanical finite element software program. The model was validated by comparing the FEA and experimental results of an existing study in the literature and they were in good agreement. A parametric study was conducted on the validated steel beam model with the aim to investigate the effects of basalt fiber reinforced polymer (BFRP) and two types of adhesives on its performance under static loading. The FRP laminates provided an increase in flexural capacity and pseudo ductility of the beams. The optimum bond length was found to be 2/5 of the span length for the beam in this study.

Behavior of RC beams strengthened with NSM CFRP strips under flexural repeated loading

Strengthening with near surface mounted carbon fibre reinforced polymers (NSM-CFRP) is a strengthening technique that have been used for several decades to increase the load carrying capacity of reinforced concrete members. In Iraq, many concrete buildings and bridges were subjected to a wide range of damage as a result of the last war and many other events. Accordingly, there is a progressive increase in the strengthening of concrete structures, bridges in particular, by using CFRP strengthening techniques. Near-surface mounted carbon fibre polymer has been recently proved as a powerful strengthening technique in which the CFRP strips are sufficiently protected against external environmental conditions especially the high-temperature rates in Iraq. However, this technique has not been examined yet under repeated loading conditions such as traffic loads on bridge girders. The main objective of this research was to investigate the effectiveness of NSM-CFRP strips in reinforced concrete beams under repeated loads. Different parameters such as the number of strips, groove size, and two types of bonding materials (epoxy resin and cement-based adhesive) were considered. Fifteen NSM-CFRP strengthened beams were tested under concentrated monotonic and repeated loadings. Three beams were non-strengthened as reference specimens while the remaining were strengthened with NSM-CFRP strips and divided into three groups. Each group comprises two beams tested under monotonic loads and used as control for those tested under repeated loads in the same group. The experimental results are discussed in terms of load-deflection behavior up to failure, ductility factor, cumulative energy absorption, number of cycles to failure, and the mode of failure. The test results proved that strengthening with NSM-CFRP strips increased both the flexural strength and stiffness of the tested beams. An increase in load carrying capacity was obtained in a range of (1.47 to 4.49) times that for the non-strengthened specimens. Also, the increase in total area of CFRPs showed a slight increase in flexural capacity of (1.02) times the value of the control strengthened one tested under repeated loading. Increasing the total area of CFRP strips resulted in a reduction in ductility factor reached to (0.71) while the cumulative energy absorption increased by (1.22) times the values of the strengthened reference specimens tested under repeated loading. Moreover, the replacement of epoxy resin with cement-based adhesive as a bonding material exhibited higher ductility than specimen with epoxy resin tested under monotonic and repeated loading.

Effectiveness of Surface Preparation on the Capacity of Plated Reinforced Concrete Beams

One of the most important methods for strengthening and repairing reinforced concrete beams is to use external bonded steel plates, however, the success of this technique depends on the effectiveness of the surface preparation of the steel and concrete beams. The International Concrete Repair Institute (ICRI) recognises ten standard concrete surface profiles (CSP), according to the level of roughness, which ranges from CSP 1 (nearly smooth) to CSP 10 (very rough). Each level of roughness is associated with particular bond strength. The purpose of this investigation is to study the effectiveness of four different levels surface preparation, namely; no surface preparation (NSP), wire brushing (WB), scabbling (SC) and hand chipping (HC), on the capacity of plated reinforced concrete beams.The quality of the surface preparation established was measured based on the flexural performance of the externally strengthened steel-concrete beams. A total of 9, 250 × 450 × 3600 mm reinforced concrete beams were prepared, strengthened with glued steel plates on their soffits, and tested under two-point static loading until failure. The results showed that beams with rougher surface preparation have a high bond strength as compared to smoother surface preparations. The increase in flexural capacity of the roughened beams in Group A ranges from 18% to 32% as compared to the control beam, whilst the increase in flexural capacity of the roughened beams in Group B ranges from 20% to 42%.

STRENGTHENING OF PRESTRESSED HOLLOW CORE SLABS WITH OPENINGS USING NSM-CFRP STRIPS

Precast, prestressed, hollow-core (HC) slabs are extensively used in many structures such as parking garages, commercial and industrial buildings. It is common for such structures to undergo changes while still in service, which may result in a reduction of their strength. One of these changes is to add in-situ openings at different locations along the slab to accommodate services such as intake/exhaust ducts or utility conduits. Near surface mounted (NSM) strengthening technique has proved to be an adequate technique that can be employed to restore or enhance the performance of the original structure. In this paper, the effect of openings and the efficiency of using NSM carbon fiber reinforced polymer (CFRP) strips as strengthening technique are investigated. A total of three full-scale prestressed HC slabs were tested; one without opening, one with an opening in the pure flexural zone and one with strengthened opening. Test results showed the presence of opening along the flexure span had a significant adverse effect on the post-cracking flexural stiffness, cracking load and the ultimate capacity of the slab. However, strengthening the opening with two strips of NSM-CFRP effectively enhanced the post-cracking stiffness, increased the ductility of the member and restored the flexural strength deficit incurred as a result of cutting the opening, and provided a net increase in flexural capacity.

Different NSM FRP technique for strengthening of RC two-way slabs with low clear cover thickness

An experimental program was carried out to investigate the effectiveness of a novel near surface mounted (NSM) technique using innovative manually made CFRP rods (MMRs) and manually made CFRP strips (MMSs) for flexural strengthening of reinforced concrete (RC) two-wayslabs with low clear cover thickness. Four full-scale RC slabs (1500×1500×120 mm) were tested under monotonic four-point bending. One slab was kept un-strengthened as the control specimen, one slab was strengthened using NSM GFRP rods, and the other two slabs were strengthened using NSM CFRP MMRs and NSM CFRP MMSs. The load-deflection responses, strain measurements, and failure modes of the tested slabs were studied and discussed. The behavior of slabs strengthened with this technique was compared to the behavior of the slab strengthened with GFRP rods. The test results confirmed the feasibility and efficacy of this technique in improving the flexural behavior of RC two-way slabs. Strengthened slabs showed an increase in flexural capacity between 279 and 394% over the control specimen. A 3D nonlinear numerical model was developed using the finite element (FE) method to predict the flexural behavior of the tested slabs. A good agreement between experimental and numerical results was observed.

Strengthening of Existing RC Two-Way Slabs using New Combined FRP fabric/rod Technique

This study presents the results of an experimental program to investigate the effectiveness of an innovative combined FRP technique using combination of externally bonded (EB) FRP fabrics and near surface mounted (NSM) FRP rods for flexural strengthening of existing reinforced concrete (RC) two-wayslabs with low clear cover thickness. Three full-scale RC slabs (1500×1500×120 mm) were tested under monotonic four-point bending. One slab was kept un-strengthened as the control specimen, one slab was strengthened using NSM GFRP rods, and the other one slab was strengthened using combination of EB CFRP fabrics and NSM GFRP rods. The load-deflection responses, strain measurements, and failure modes of the tested slabs were studied and discussed. The behavior of the slab strengthened with this technique was compared to the behavior of the slab strengthened with GFRP rods. The test results confirmed the feasibility and efficacy of this technique in improving the flexural behavior of RC two-way slabs. Strengthened slabs showed an increase in flexural capacity between 250 and 394% over the control specimen. The slab strengthened using this technique showed higher ductility compared to the slab strengthened using GFRP rods. A 3D nonlinear numerical model was also developed using the finite element (FE) method to predict the flexural behavior of the tested slabs. A good agreement between experimental and numerical results was observed.

Flexural Response of Corroded Reinforced Concrete Beams Strengthened with Powder-Actuated Fastened Composites

This paper examines the effect of corrosion exposure on the flexural response of reinforced concrete (RC) beams strengthened with a powder-actuated fastened (PAF) composite system. Twenty-one RC beams were constructed and tested to failure under four-point bending. The corroded beams were subjected to 30, 60, and 100 days of accelerated corrosion that corresponded to measured tensile steel mass losses of 6, 11, and 18%, respectively. Other test parameters included width of the fiber-reinforced polymer (FRP) composite strip, fastener length, and number of fastener rows. For the undamaged beams, the PAF-FRP system resulted in up to 24% increase in flexural capacity and 20% average reduction in beam ductility. The strengthening effectiveness reduced with increased level of corrosion damage. Nevertheless, the flexural strength of the strengthened specimens at all levels of corrosion was either higher or almost same as that of the control specimen. Increasing the fastener length increased the gain in flexural capacity of the undamaged beams but had no noticeable effect on the flexural strength gain of the corroded beams. Doubling the width of the FRP strip or number of fastener rows had insignificant effect on the flexural strength gain. An analytical model that can predict the flexural capacity of corroded RC beams strengthened with a PAF-FRP system has been introduced. The model accounts for the nonlinear behavior of materials and strain incompatibility between the PAF-FRP strip and concrete. The validity of the model has been demonstrated by comparing its predictions with the experimental results.