Internal Reinforcement Research Articles

Bearing capacity of reinforced concrete beams with and without damages of rebar

Abstract The article presents the results of the bearing capacity of reinforced concrete beams with and without damages of internal reinforcement. One of the main elements of the production of the reinforced concrete industry is beams. The analysis of the experimental tests showed that the bearing capacity of reinforced concrete beams with damaged tensile main reinforcement decreases according to control undamaged samples due to the reduction of the reinforcement cross-section. However, the bearing capacity of reinforced concrete beams with tensile main reinforcement Ø20А500C, damaged to the cross-section area equal the rebar Ø16mm is more on 3.7… 24.0% than the bearing capacity of reinforced concrete beams with undamaged Ø16mm rebar. This is due to the non-uniform material properties of used thermally strengthened reinforcement A500C. When during testing the tensile main reinforcement is damaged by drilling a hole, the most damages occur in the core with lower physical and mechanical characteristics. In contrast, the outer thermally strengthened layer with bigger physical and mechanical characteristics is damaged to a lesser extent. The analysis of the obtained results shows that during design of reinforced concrete beams with damaged, it is necessary to consider using thermally strengthened non-uniform steel A500C as tensile main reinforcement.

Evaluation of the fracture behaviour of concrete prisms reinforced with regular and high-strength steel rebars using acoustic emission technique

This study examines the potential of high-strength steel strands of smaller diameter as a substitute for regular steel in normal concrete, aiming to reduce steel consumption and increase sustainability. The fracture behaviour of concrete prisms reinforced with high-strength steel strands is examined using acoustic emission (AE) and digital image correlation (DIC) techniques and compared with those reinforced with thermo-mechanically treated (TMT) bars. The fracture behaviour is examined for the following parameters: the type of reinforcement (TMT and HSS), the number of rebars (1 and 2 rebars), and the percentage of reinforcement (0.22 % of TMT vs. (0.18 % & 0.27%) of HSS, 0.45% of TMT vs. 0.47% of HSS). Test results showed that replacing a similar percentage of TMT rebars with HSS rebars increased load-carrying capacity in serviceability and ultimate load regimes. The enhancement in performance can be attributed to the increased surface area of HSS due to the smaller diameter of bars, which provides better bonding with concrete when compared to TMT rebars. Micro and macro cracking characteristics and damage progression are studied by analysing the peak amplitude from the AE waveform. AE results show that tensile mode cracks dominated initially, and shear mode cracks formed after the specimens reached their first cracking load due to internal reinforcement.

Torsional behavior of FRP-strengthened reinforced concrete members considering various wrapping configurations: Theoretical analysis and modeling

Reinforced concrete (RC) structural members such as spandrel, flanged and curved beams, slab beams, and bridge girders may be subjected to significant torsional loading. Despite extensive research on the strengthening of RC members, very little is known about the torsional behavior of RC members strengthened with fiber-reinforced polymer (FRP) sheets. Therefore, very limited guidelines apply to the design of externally bonded FRP systems for torsional strengthening, and no design provisions exist for the U-wrapped and 2-sided strengthening systems in torsion. This study aims to contribute to this growing area of research by developing a new analytical model to predict the full torsional response of strengthened RC members with many conventional configurations such as spiral, transverse and longitudinal FRP, continuous and intermittent strips along the beam length, side bonded, and full-wrapped systems. Moreover, this study provided an analytical model accurately predicting the contribution, efficiency, and failure mode of side-bonded strengthening systems. Additionally, the influence of various parameters such as FRP stiffness and transverse steel reinforcement ratio is taken into account in the constitutive law of concrete and internal reinforcement for the first time. The good agreement between the test results of 32 collected FRP-strengthened RC beams from the literature and the theoretical ones, which were predicted through programming proves the validity and accuracy of the presented theory.

Internal carbonation reinforcement of cementitious materials: Mechanism and performance

Cement carbonation technologies are garnering increasing interest, but most CO2 curing methods have limited on-site applications. In this study, a CO2 internal curing route was presented and proven to be feasible. Zeolite NaX was selected as a CO2 carrier due to its good adsorption capacity (16.2 g CO2/100 g drying zeolite) and stability (0.16% weight loss) at room temperature for internal carbonation of cement. CO2-saturated zeolite released the adsorbent once it was exchanged by water molecules during the mixing process, and the dissolved CO2 in the paste solution produced carbonation products. It was discovered that, unlike the main products (calcite polymorphs) in CO2 curing conditions, monocarbonate and calcite were the primary carbonation products in CO2 internal curing cement composites. In addition to accelerating the hydration of C3S, zeolite NaX was found to react with cement systems and facilitate the formation of aluminocarbonates. The resulting composites exhibited quicker and higher strength development, increased modulus, reduced porosity, smaller pore intrusion radius, and minimal volume expansion. Moreover, the formation of monocarbonate was found to be correlated with the volume expansion of the composite system, as determined through thermodynamic calculations and autogenous shrinkage experiments. Finally, the composites exhibited a carbon sequestration capacity of 4.86 g CO2/100 g dry solid composites, with 71% of the CO2 being solidified in minerals.

Damage and Defects in Fiber-Reinforced Polymer Reinforced and Strengthened Concrete Elements

Fiber-reinforced polymer (FRP) composites are becoming increasingly popular as an alternative to conventional civil engineering materials in existing structures as externally applied systems for strengthening purposes, and in new structures as internal reinforcements in the form of bars, meshes, and strands. The next phase of development in the application of FRPs in concrete structures could culminate in elements possessing both internal and external FRP systems simultaneously. With these advancements in the application of FRP in civil engineering, it is conceivable that traditional steel reinforcements could become obsolete in certain aggressive and hostile environments, such as coastal areas. Although higher durability and performance are associated with FRP materials in some respects when compared to steel, concerns remain regarding the damage and defects in this material, many of them related to their unique features. Regardless, similarly to other structural materials, it is necessary to understand the damage and defects associated with the use of FRP composites, as well as to identify their sources. This knowledge will support the positive prospects for FRP technology, promoting its application in civil infrastructure. Accordingly, this study investigated the types, characteristics, and identification of the observed or expected damage and defects associated with using FRP in reinforced and strengthened concrete elements. The damage was classified according to location and time of initiation. In addition, the sources of these defects and damage were determined, and a damage etiology was established for preventing the occurrence of such damage in future use. The results of this study are intended to provide the background for the development of a guide and training material for the inspection of structures that use FRP materials. The ability to inspect and properly maintain structures containing FRP will result in the enhanced durability and service life of concrete structures reinforced or strengthened with FRP materials.

Cohort study of short-term outcomes after ACL-reconstruction using autograft with internal brace reinforcement versus isolated autograft demonstrating no significant difference

BackgroundThe gold standard treatment for Anterior Cruciate Ligament injury is reconstruction (ACL-R). Graft failure is the concern and ensuring a durable initial graft with rapid integration is crucial. Graft augmentation with implantable devices (internal brace reinforcement) is a technique purported to reduce the risk of rupture and hasten recovery. Few studies have examined these techniques, in particular when compared to non-augmented grafts. This study assesses the short-term outcome of ACL-R using augmented and non-augmented hamstring tendon autografts. MethodsThis was a retrospective cohort study comparing augmented and non-augmented ACL-R. All procedures were performed in a single centre using the same technique. The Knee injury and Osteoarthritis Outcome Score [KOOS] was used to assess patient-reported outcomes. ResultsThere were 70 patients in the augmented and 111 patients in the control group. Mean graft diameter in the augmented group was 8.82 mm versus 8.44 mm in the non-augmented. Six strand graft was achievable in 73.5% of the augmented group compared to 33% in the non-augmented group. Two graft failures were reported in the non-augmented group and none in the augmented group. Patient satisfaction rates were higher in the augmented group. There was a statistically insignificant improvement in the postoperative KOOS in the augmented group compared to the non-augmented group (p 0.6). Irrespective of augmentation status, no correlation was found between the functional score and age, or femoral tunnel width. ConclusionNo statistically significant difference was demonstrated in the short-term functional outcome of ACL reconstruction using an augmented or non-augmented hamstring graft. Augmented ACL-R may achieve superior graft diameters, failure rates and patient reported outcomes when compared to nonaugmented ACL-R. Prospective trials are needed to examine this further.

Spatio-Temporal Distribution of the Sources of Acoustic Events in Notched Fiber-Reinforced Concrete Beams under Three-Point Bending.

The acoustic activity, generated in notched, beam-shaped concrete specimens, loaded under three-point bending, is studied in terms of the position of the sources of acoustic events, and the frequency of their generation. Both plain specimens (without any internal reinforcement) and specimens reinforced with various types of short fibers were tested. The target of the study is to investigate the existence of indices that could be considered as pre-failure indicators of the upcoming fracture. In addition, an attempt is undertaken to classify the damage mechanisms activated to tensile or shear nature. Considering comparatively the spatio-temporal evolution of the position of the acoustic sources and the respective temporal evolution of the frequency of generation of acoustic events, it was concluded that for relatively low load levels the acoustic sources are rather randomly distributed all over the volume of the specimens. As the load increases toward its maximum value, the acoustic sources tend to accumulate in the immediate vicinity of the crown of the notch and the average distance between them approaches a minimum value. When this minimum value is attained, the load is maximized and the generation frequency of the acoustic events increases rapidly. The simultaneous fulfillment of these three conditions is observed a few seconds before the onset of propagation of the catastrophic macrocrack for all classes of specimens tested, providing a kind of warning signal about the upcoming fracture. Moreover, the classification of the damage mechanisms to tensile and shear ones revealed a crucial difference between the plain and the reinforced specimens after the maximization of the load applied. Indeed, while for the plain specimens, the prevailing damage mechanism is tensile microcracking, for the reinforced specimens a balance between tensile and shear damage mechanisms is observed after the load applied has attained its peak and starts decreasing.

Parametric investigation of continuous beams strengthened with near surface mounted FRP bars

This study evaluates the near surface mounted fiber-reinforced polymer (FRP) reinforcement technique for strengthening continuous reinforced concrete beams. A three-dimensional finite element model was developed and validated with a recent experimental study. The model incorporates robust features, including concrete nonlinear behavior, debonding and slipping of FRP bars, and various failures. It was able to capture the ultimate load (Pu) with maximum deviation of 7%, beam’s load–deflection curves, load–strain responses in rebar and concrete, and various failure modes. A parametric study was conducted and showed that failure mode changes from concrete shear to FRP bar debonding at concrete compressive strength fc’of 20–30 MPa, with a 26–52% increase in Pu relative to the un-strengthened beam. Varying the hogging/sagging FRP reinforcement ratio (ρh/ρs) from zero to 2.0 results in a 39% increase in Pu and a change of failure mode. A value of 1.5 is recommended for ρh/ρs. Also, the synergistic effects of NSM FRP and internal steel reinforcements were studied. An FRP bar length in the hogging and sagging zones of 80% the beam span was found to be sufficient to mitigate debonding and thus is recommended. Pu did not vary significantly with the span ratio for two-span continuous beams. A design expression for the debonding strain in FRP bars based on the American Concrete Institute design guide was assessed and a further refined model is developed.

On the possibility of using waste disposable gloves as recycled fibers in sustainable 3D concrete printing using different additives

Due to the Covid-19 pandemic, using large amounts of personal protective equipment (PPE) throughout the world has extensively increased in recent years. The lack of a practical method to dispose of these recycled materials is one of the main concerns of researchers. Hence, comprehensive experimental tests were conducted in the present study to investigate the feasibility of using disposable gloves in mortars to achieve a sustainable mixture. Accordingly, latex and vinyl gloves as recycled fibers were considered in the experimental program to improve the sustainability of 3D printing concrete. As using these recycled materials causes some deficiencies for printing layers, different mineral and chemical admixtures were used in the present study, including graphene oxide nanomaterials, polyvinyl alcohol, Cloisite 15A nanoclay, and micro silica fume. Also, the hybrid use of latex, vinyl, and polypropylene (PP) fiber was considered to improve the printability of concrete mixtures containing waste fibers. Moreover, the effect of internal reinforcement was also considered by using plain steel wire mesh to increase the composite behavior of printed layers in this simplified experimental program. Results indicate that the synergic influence of recycled fibers and admixtures meaningfully enhanced the 3D printing properties of mortar so that about 20%, 80%, 50%, and more than 100% improvements were obtained for workability, direct tensile strength, flexural strength, and buildability index respectively. However, an average percentage − 28.3% reduction was recorded for the concrete compressive strength. Sustainability analysis also showed that using waste disposable gloves considerably reduced CO2 emissions.

A Review on Fatigue Performance of Concrete Structures Part II, Material Parameters and Environmental Factors

Abstract Fatigue is a critical issue for concrete structures subjected to repetitive and varying loads, particularly in infrastructure and transportation systems. This review paper presents a comprehensive overview of the current state of knowledge on concrete fatigue and identifies areas for further research. Material and size factors that influence fatigue performance and life estimation of concrete such as concrete composition, internal moisture content and reinforcement are explored, along with environmental conditions such as presence of external moisture and seawater exposure. The paper also acknowledges the challenges associated with predicting concrete fatigue life accurately due to the heterogeneous nature of concrete and its complex behavior under cyclic loading.

Experimental investigation on the behavior of fly-ash based geopolymer reinforced concrete beams strengthened with CFRP

Recently, the demand for strengthening and rehabilitation of existing RC structures has increased due to the corrosion of internal steel reinforcement, variations in temperature, and increasing loading. As a result, several experimental studies have been performed to investigate the structural behaviour of strengthening RC beams with CFRP sheets, but few for GPC beams; therefore, this investigation focuses on the behaviour of strengthening GPC beams with CFRP sheets. In this experimental work, a set of ten specimen beams with the same cross section of 100 × 250 mm and 850 mm length with a 750 mm clear span were cast in two groups of five beams each. First group (flexural group) to study the flexural behavior, and the second one for the shear behaviour (shear group). In each group, the first beam was carried out as an RC control beam and the second as a GPC control beam without strengthening, while the other three beams were cast as GPC beams and strengthened with various schemes of CFRP sheets. All specimens were tested up to failure under two-sided static loading (four-point bending). The first cracking, yielding, and ultimate failure loads, the deflection values at midspan, the longitudinal bar strain, and the concrete strain were recorded for all tested specimens. The experimental results indicated that the Flextural Strengthening of GPC with CFRP sheet increased the First Cracking, yield and ultimate load capacity by 25.33%, 15.3% and 15% respectively, as well as, deflection was decreased by 16% on average while ductility and toughness have improved by 10% and 12% on average compared to R.C Beam.On the other side, the Shear Strengthening of GPC with CFRP strips increased the First Cracking, yield and ultimate load by 43%, 70% and 68% respectively, as well as, shear ductility has improved by 8% on average compared to R.C Beam. Overall, the different schemes of externally bound CFRP sheets have improved the flexural and shear behaviour of GPC beams.

Static, dynamic and buckling responses of random functionally graded beams reinforced by graphene platelets

This work proposes a multiscale numerical method that can be used to study the static, dynamic and buckling behavior of functionally graded (FG) beams reinforced with graphene platelets (GPLs), whose random gradation is achieved through tailoring the internal porosity and GPLs reinforcement, either along the transverse or the longitudinal direction. The multiscale numerical method consists of microscale homogenization and structural analysis: micromechanics homogenization methods are introduced to predict the elastic moduli of nanocomposite layers with finite thickness along the transverse direction; Explicitly-expressed composite finite elements are then developed through the proposed variational principle and Hamilton principle. In the meantime, the corresponding governing equations are derived for FG beams with Timoshenko theory. On this basis, the static bending deflection, fundamental frequency and critical buckling load of the FG beams are obtained through the proposed FG finite elements. The effectiveness and accuracy of the proposed method are verified against the numerical results in the existing literature and experimental results in 3D printing with good agreement. Based on the credence of the present method, the effects of boundary conditions, gradient distributions of GPLs and pores, microscopic parameters of GPLs and structural geometric dimension on the static and dynamic performance of the FG beams are systematically analyzed, where the bi-directional gradient distribution pattern corresponding to the GPLs along the thickness direction and the pore along the axial direction demonstrates the best improvement of both bending and dynamic performance.

Impact of Internal CFRP strips on the flexural behavior of heat-damaged reinforced concrete beams

Recent theoretical developments revealed that reinforced concrete (RC) structures are susceptible to deterioration risk upon exposure to high temperatures where the mechanical properties of their constituents are affected and therefore require upgrading their overall performance. However, the overall behavior could be improved by strengthing the RC beams using the well-known carbon fiber-reinforcement polymers (CFRP) materials where its efficiency is highly limited by detachment, and debonding problems appear as a result of the weakness in the bond between the concrete surface and the strengthening material or upon the stress concentration induced by the various anchoring systems. The CFRP sheets have been integrated as internal reinforcement in the maximum bending zone within the thermally damaged beams, a new technology used in this study. The suggested method was the first of its kind and did not need an adhesive to be applied where debonding problem is eliminated. In contrast to conventionally reinforced steel, CFRP composite materials are fully compatible with flexural steel and constrained concrete. A total of 40 RC with (150 × 200) mm2 and an overall length of 1100 mm concrete beams were cast, and the studied parameters were the CFRP length, position, and exposure temperature. The internal strengthening technique has been found to ensure the full utilization of the strengthening material where the externally-strengthened beams fail preceding the CFRP strain reached, and this was confirmed using the linear weighted sum method where the internal strengthening has the highest ranking based on the mechanical characteristics comparisons. Moreover, the internal CFRP reinforcement improves RC beam performance, strength, stiffness, toughness, and serviceability more than exterior CFRP sheets. However, the enhancement percentages are twice as much for internal strengthening as the external one. It has also been found that the reinforcement's location substantially impacted the number and length of flexural cracks and its failure mode. In addition, for every 1% reduction in concrete compressive strength in heat damage, the average ultimate load was reduced by 0.8%. The CFRP profitability indexes decrease as sheet number and temperature increase; the average toughness decrease at 150 °C, 250 °C, and 500 °C is 12%, 21%, and 47%, respectively.

Shear capacity investigation of RC concrete beams using self-prestressing Fe-based shape memory alloys strips

Shear failure is a sudden and brittle failure, which causes human and economic losses. Hence, enhancement of shear capacity is critical for shear-deficient members of existing structures. In this study, the effectiveness of using Shape Memory Alloy ‘SMA’ strips on the shear capacity of reinforced concrete (RC) beams was investigated in a series of experiments. The experimental work included the study of six RC beams with a 200 × 300 mm cross-section considering shear parameters such as transverse shear reinforcement and the effect of prestressing. Beams were strengthened in U configuration using Fe-SMA strips 30 mm wide and anchored by one expansion anchor (M10-Hilti). The testing was performed in a simply supported condition where each beam was tested twice. The purpose of testing specimens twice was to confirm the results. The activation of the strips was achieved by heating the strips using a custom-made heater up to 200°. The method was proven effective, with an increase in shear capacity of up to 32–45% and 24–25% for specimens strengthened with passive strengthening (non-activated strips) and specimens strengthened by activated SMA strips, respectively. However, the active strengthening improved serviceability conditions by delaying the appearance of cracks and reducing the crack width. The occurrence of the main crack was delayed by 12.5–19.2%, the width of the crack was reduced by more than 65% compared to the reference beam, and the angle of the main crack increased compared to the reference beam as a result of activation. Beams containing internal transverse reinforcement performed better than the beams without shear reinforcement.

Study on Cl− Erosion of Concrete under the Combined Effect of Fatigue Load and Wet–Dry Cycles: A Review

The service environment of concrete in the marine environment is harsh, and demands regarding the durability of marine concrete have increased. Marine concrete in harbor and wharf areas suffers from the combined effect of fatigue load, dry–wet cycles, and Cl− erosion, which can result in spalling of the concrete surface, corrosion of the internal reinforcement, and even concrete damage. This paper reviews recent research results on the durability of concrete and reinforced concrete (RC) under the combined effect of fatigue load, dry–wet cycles, and Cl− erosion. We further assess the variation in Cl− transport properties with fatigue load, the causes behind the reduction in the carrying capacity of RC products under fatigue load, the methods of Cl− erosion on concrete under the pressures imposed by dry–wet cycles, and the damage of the protective layer of concrete due to accelerated Cl− erosion caused by the action of dry–wet cycles. Further studies are needed on the durability of concrete under the action of fatigue load, wet and dry cycles, and Cl− erosion, in addition to the testing of the durability of concrete under the combined effects of the afore-mentioned various factors.

Proposals for Flexural Capacity Prediction of Precast Segmental Concrete Beam Prestressed with Internal Un-Bonded CFRP Tendons

The application of CFRP tendons in precast segmental concrete beams (PSCB) as internal un-bonded prestressing reinforcement is a newly developed scheme to improve structural flexural performance. The stress increment of the un-bonded tendon, depending on the whole structural deformation, is a crucial value to be predicted for flexural capacity design. Due to the discontinuity of the opening joints, the deformation modes of segmental beams differ from the monolithic ones. The existing prediction methods built for monolithic beams can not be directly used for segmental beams. In this paper, the new prediction equations of the tendon stress increment and flexural capacity were put forward for PSCB with internal un-bonded CFRP tendons (PSCB-IUCFRP). Firstly, the differences between the deformation modes of monolithic and segmental beams were compared and clarified based on the numerical model analysis. Then, a parametric analysis was conducted on 162 numerical models, and the results were employed to evaluate the applicability of existing methods for PSCB-IUCFRP. The predictions of the ACI 318-14 model and the AASHTO LRFD model were both conservative and scattering compared with numerical results. The ACI 440.4R model underestimated the tendon stress increments of beams under one-point loading but overestimated it for those under two-point loading. According to the failure mode of PSCB-IUCFRP, a simplified curvature distribution mode was assumed, and the relation between tendon elongation and structural deflection was derived. The prediction equations for PSCB-IUCFRP were proposed using the back-calculated plastic hinge length. Compared with existing methods, the proposed equations considered the deformation characteristic of segmental beams and had clear physical significance. The predictions of the proposed method were in good agreement with the numerical and experimental results. Furthermore, a balanced prestressing reinforcement ratio equation is proposed for PSCB-IUCFRP to avoid tendon rupture-controlled failure. The proposed equations provide suggestions for the flexural design of PSCB-IUCFRP and will help to popularize this new structure.

Feasibility of improving shear performance of RC pile caps using various internal reinforcement configurations: Tests and finite element modelling

The loads from columns and bridge piers are transferred to the pile foundation by reinforced concrete (RC) pile caps, which are important structural components whose behavior is significantly affected by the internal reinforcement configuration. Therefore, the current study experimentally investigates the shear response of RC pile caps by testing nine specimens have identical dimensions and various reinforcement configurations. The experimental matrix is designed to study (i) the influence of using a closed transversal reinforcement along with the presence of an upper reinforcement only or an upper and side reinforcement together. (ii) Behavior of RC pile caps internally reinforced with various closed-side bars’ area and (iii) the impact of the interaction between the longitudinal reinforcement of the piles and the column in the presence of upper reinforcement only or side closed bars solely. RC pile cap specimen internally reinforced with closed transversal reinforcement with upper reinforcement and 12 mm-diameter closed side bars can be considered the optimal reinforcement form due to the fact that this specimen achieved the highest ultimate load and toughness of 1286 kN and 1089 kN.mm, respectively. Moreover, the current research involves the development of a three-dimensional (3D) non-linear finite element model to evaluate the response of RC pile caps while taking into account concrete's tensile strength and softening behavior in either tension or compression. Results of the numerical model well agreed with the experimental data. Additionally, a parametric study is conducted using the verified model to examine the impact of utilizing bent bars positioned perpendicular to the shear crack's direction on the ultimate load, failure pattern, and toughness of the RC pile caps.

Experimental and numerical investigation on the flexural performance of RC slabs strengthened with EB/NSM CFRP reinforcement and bonded reinforced HSC layers

In this paper, one-way reinforced concrete (RC) slabs were strengthened using External Bonding (EB) and Near Surface Mounted (NSM) techniques and tested under flexural loading until failure. The area of internal and external reinforcement, shape of strengthening elements (bars, strips, and reinforced high strength concrete (HSC) layers) and strengthening method (EB and NSM) were the experimental tested variables. The experimental results showed significant increases in the load capacities of the upgraded slabs ranging between 133.8% and 264.5% compared to their corresponding un-strengthened slabs. Consequently, the NSM technique showed higher load efficiency than the EB, even though they had nearly the same strengthening properties and area. Compared to the control slab, using NSM strips instead of EB strips or NSM bars amplified the slab load capacity by about 51.7% and 33.2%, respectively, while using NSM HSC layer instead of EB HSC layer increased slab load capacity by 74.7%. Moreover, doubling the area of EB strips improved the load capacity by 10.3%, while increasing the internal steel area by 195% enhanced the slab load capacity by 21% to 48 %, depending on the strengthening method. However, depending on the distance between internal and external strengthening elements the cracks were initiated at the ends of the strengthening element causing the slab shear failure at dissimilar loads. Finally, a verified finite element (FE) model was built to study the effect of bond length, material, and area of the strengthening element on the slab behavior.

RC columns strengthened with engineered cementitious composite (ECC) jacketing

This article aims to study the uniaxial compressive behavior of reinforced concrete (RC) columns strengthened with engineered cementitious composite (ECC) jackets. For this purpose, two advanced ECC mixtures containing polypropylene fibers were designed, and ECC jackets were cast to confine fourteen circular column specimens. Longitudinal and transverse grooving, sandblasting, and abrading were used as surface preparation techniques to achieve better adherence of ECC jackets to eight control (reference) column specimens, while two specimens with no surface preparation but with the same jacketing were used as a reference. The four remaining concrete column specimens lacking either internal reinforcement or an ECC jacket were used as control. All the specimens were subjected to concentric loading to determine the efficiency of ECC jacketing in enhancing load-carrying capacity and ductility. The experimental results revealed that compared to the control column, the reference specimens subjected to longitudinal grooving as surface preparation and ECC jacketing exhibited improvements of up to 1.3 and 2.5 times in their load-bearing capacity and energy absorption, respectively. Besides, ECC jacketing in specimens with the longitudinal grooving method increased the reference columns’ initial and secant stiffness values by up to 3.2 and 1.6 times, respectively. Finally, the models reported in the literature were evaluated in terms of their ability to capture the stress-strain curves of the ECC jacketed RC columns used in the present study.

Flexural performance of concrete beams internally reinforced with steel, geogrid and GFRP meshes

The focus of this study is to evaluate the internal reinforcement effect using different material meshes on the flexural capacity of concrete beams. For this purpose, eleven experimental reinforced concrete beams were tested under four-point bending. The beams were all made of normal concrete with a 150 × 200 mm2 rectangular cross-section and a length of 1200 mm. The conventional flexure and shear steel bar reinforcements were identical for the eleven beams. The reference beam was made without any internal mesh reinforcement, while the rest ten beams were reinforced with three different types of mesh materials, which were incorporated in different numbers of layers and different configurations. The used meshes were steel, geogrid and glass-fiber reinforced polymer (GFRP). One beam with U-shape mesh was made from each material, with the mesh wrapping the stirrups and extending vertically for 50 mm. In the experimental program, failure mode, load-deflection relationship, load capacity and ductility were the main characteristics that have been investigated. The test results showed that the percentage increase in the failure load capacity of the composite beams was approximately 3–25% compared to the reference beam. Furthermore, the beams with U-shape mesh configuration exhibited 17% increase in the load capacity comparing with their straight mesh counterparts. Similarly, the ductility index showed higher percentage improvement approximately 82–136% when layer number increased from 1 to 3 layers.