Near Surface Mounted Research Articles

Experimental study and numerical analysis of composite strengthened timber columns under lateral cyclic loading

To develop a new composite material column for modern timber buildings and propose a reliable strengthening method for existing timber columns, wrapped carbon fiber reinforced polymer (CFRP) strips and near-surface mounted (NSM) steel bars reinforced timber columns were studied. Five composite strengthened timber columns were designed, fabricated and tested under lateral cyclic loading. The experimental results showed that all specimens exhibited tensile rupture failure of the timber grain. The hysteretic curves showed that the proposed method could enhance the load-bearing capacity and deformation performance of the strengthened timber columns. With an increase in the number of CFRP strips, there was a marked improvement in the hysteretic performance of the specimens. Based on the experimental study, a finite element model of a composite strengthened timber column was developed using the OpenSees software application, the reliability of which was evident from the test results. A parametric study was then conducted to investigate the influence of the axial load, bar diameter, and the number and location of steel bars. This study aimed to provide a reference for seismic design and the practical application of the composite reinforcement method.

Flexural Performance and End Debonding Prediction of NSM Carbon FRP-Strengthened Reinforced Concrete Beams under Different Service Temperatures

This paper aims to evaluate the influence of relatively high service temperatures (near or beyond the glass transition temperature (Tg) of epoxy adhesive) on the flexural performance and end debonding phenomenon in near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP)-strengthened, reinforced concrete (RC) beams. To this end, an experimental program consisting of 24 beams (divided into four groups) was performed, where different parameters was combined (i.e., service temperature, steel reinforcement ratio, CFRP ratio, and concrete compressive strength). In addition, the effect of the testing temperature on the end debonding phenomenon was investigated with an analytical procedure according to fib Bulletin 90, and the predictions were compared to experimental results. Taking specimens tested at 20 °C as a reference, no considerable change was observed in the ultimate load of the specimens tested below 60 °C (being in the range of epoxy Tg), and all specimens failed by FRP rupture. On the other hand, the increase in testing temperature up to 70 and 85 °C was followed by a decrease in the capacity of the strengthened beams and a change in failure mode, moving from FRP rupture to end debonding and concrete crushing. The analytical procedure successfully predicted the occurrence of premature end debonding failure and demonstrated that the effect of temperature on the mechanical properties of materials can be a key factor when predicting the premature end debonding in a NSM joint.

An experimental study on the interfacial bonding performance of horizontally embedded CFRP strips to concrete

The near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strengthening method has a good efficiency in regard to strengthening aging or damaged concrete bridges. To prevent the end debonding failure of NSM CFRP-strengthened beams and simplify the construction, the authors propose a near-end enhanced embedded (NEEE) CFRP strengthening method. In this method, the CFRP strips are horizontally embedded in the grooves that are prefabricated on the surface of concrete structures. To investigate the interfacial bonding performance of the horizontally embedded CFRP strips, a total of 17 single-lap shear test (SST) specimens are fabricated to study the failure mode, ultimate capacity, load–displacement response, and distribution of interfacial shear stress. Moreover, the effects of the groove width, groove depth, embedding depth of horizontal CFRP strips, and concrete strength are analyzed and discussed. Then, a local bond-slip model with characteristic parameters (i.e., the maximum bond stress, critical slip, and residual bond stress) is proposed to describe the interfacial bond behavior. These characteristic parameters are independently determined according to the experimental results of each specimen. Furthermore, a generalized bond-slip model is proposed and validated, which can directly predict the characteristic parameters according to the geometry and material properties of SST specimens.

Experimental study on flexural strengthening of RC beams with NSM technique by different orientation of CFRP laminate

This paper gives the brief description on the use of laminates manufactured using Carbon Fiber Reinforced Polymer (CFRP) as strengthening material for the purpose of assessing the flexural strength in RC beams using Near Surface Mounted (NSM) technique. The main objective of this work was to assess the strengthened RC beam by considering the orientation of laminate as the main priority in NSM strengthening. This study gives the brief description about the utilization of tensile strength of laminate and efficiency of adhesive for different orientation of laminate. The strengthening methodologies adopted in this research work are Near Surface Mounted Laminate with Vertical Orientation (NSMLV), Near Surface Mounted Laminate with Vertical Orientation having Anchorages (NSMLVA) and Near Surface Mounted Laminate with Horizontal Orientation (NSMLH). The dimension of beam used was 200 mm (Breadth) X 200 mm (Depth) X 2300 mm (Length) and the effective span of the beam was considered as 2100 mm. All beams were designed as per Indian design code requirement to operate in under reinforcement criteria. A total of eight beams were casted, out of which two were used as control beams and the remaining were strengthened with different NSM techniques. The groove size used for NSMLV and NSMLH technique were different. The premature debonding takes place in NSMLV technique by not utilizing the tensile strength of laminate to greater extent, to overcome this drawback CFRP fabrics were used as the anchorages in four critical locations where debonding is predominate and this method was expressed as NSMLVA technique. This work was mainly focused on improving the ultimate load carrying capacity by satisfying the serviceability requirement as per codal provisions. The four-point bending test was performed for all the test specimens. In comparison with the control beams, all strengthened beams showed improved ultimate loads by satisfying the serviceability requirement. The ultimate load shows an increase of 21.74 %, 40.22% and 71.74% for NSMLV, NSMLVA and NSMLH technique respectively compared to control beams. The Stiffness of beam was increased by 14% and 30% respectively for NSMLVA and NSMLH technique compared to control beams. NSMLH technique maximizes ultimate load, which is 71.74% higher, and fulfills the serviceability requirements. In comparison with NSMLV and NSMLVA, the NSMLH Technique is the most effective method of strengthening which bears debonding to maximum extent and increases ultimate load by greater margin.

Novel Embedded FRP Anchor for RC Beams Strengthened in Flexure with NSM FRP Bars: Concept and Behavior

The near-surface-mounted (NSM) fiber-reinforced polymer (FRP) strengthening technique for reinforced-concrete (RC) beams has attracted worldwide research attention and application in the past two decades. In spite of improved bond strength between the NSM FRP and concrete, compared with the externally bonded (EB) FRP method, premature debonding failure still occurs, and, hence, the efficiency of the NSM FRP intervention is limited. An intuitive means to enhance efficiency is to apply anchorage devices to the RC beam; however, the availability of viable anchorage is limited for NSM applications. A novel anchorage device is therefore presented in this paper, which is referred to as an embedded FRP anchor (EFA). The concept, manufacture, and installation of the EFAs were initially presented. The effectiveness of EFAs in NSM FRP-strengthened RC beams was then ascertained through full-scale beam tests and comparison with an NSM FRP-strengthened beam anchored with a U-jacket. Moreover, the effects of EFA parameters on the behavior of anchored beam were also investigated. The test results not only prove the high anchoring efficiency of EFA but also reveal the significant effects of EFA parameters on the failure mode, load–deflection response, and NSM FRP strain of the EFA anchored beam.

Bond-slip Behaviour of NSM GFRP Bars in Reinforced Recycled-Aggregate Concrete: Experiments and a Modified Model

Bond-slip behaviour of glass fiber-reinforced polymer (GFRP) bars embedded in conventional concrete has been widely investigated. In contrast, the bond-slip behaviour of near-surface mounted (NSM) GFRP bars bonded in reinforced recycled aggregate concrete (RAC) seems to be less explored, while recycled materials have been increasingly used due to reasons of environmental pollution and resource exhaustion. This study aimed to experimentally and theoretically examine the bond-slip behaviour of NSM GFRP bars in reinforced RAC under monotonic and cyclic loadings. To achieve this aim, twenty-four tests were performed, which were divided into two groups by monotonic and cyclic loadings. In each group, twelve tests were performed on ten reinforced RAC specimens and two reinforced normal aggregate concrete (NAC) specimens. The test results confirmed the brittle shear failure of concrete in the proximity of a resin-concrete surface. Bond-slip behaviour can be characterized by nonlinear and linear branches, in which the linear branch dominates the behaviour. Under monotonic and cyclic loadings, the average slips of GFRP bars in reinforced RAC were 0.238 and 0.284 mm, and their coefficients of variation (COV) were relatively large at 0.142 and 0.130, respectively. In contrast, ultimate loads had a relatively low COV of around 0.038. The effect of cyclic loading significantly increased the ultimate slip by 19.3%, whereas it negligibly reduced the ultimate load; consequently, the stiffness was reduced by 19.4%. A modified smooth model was proposed to predict the bond-slip behaviour of NSM GFRP bars in reinforced RAC under monotonic and cyclic loadings. The simplicity and accuracy of the model can be useful for engineers in structural retrofitting using NSM FRP technique. Doi: 10.28991/CEJ-2023-09-02-01 Full Text: PDF

Evaluation of flexural strengthening methods for beams with simulated deterioration using spike-anchored FRP externally bonded sheets and near-surface-mounted strips

• 20 beams were tested to evaluate FRP flexural strengthening techniques. • Specimens were detailed to mimic the common deterioration of bridge beams. • The effect of FRP spike anchor arrangements were evaluated. • Results show that more FRP spike anchors may not translate to superior performance. • Unsymmetrical steel and NSM reinforcement layouts were considered. In consideration of past research on both externally bonded and near-surface-mounted (NSM) fiber-reinforced polymer (FRP) reinforcement for the strengthening of deteriorated reinforced concrete elements, additional work is needed to investigate the application of FRP for flexural strengthening in specific scenarios and for specific member types. Furthermore, the need exists for guidance regarding reliable anchorage of externally bonded sheets for flexural strengthening. An experimental investigation was conducted on 20 reinforced concrete beam specimens with details and simulated deterioration patterns representative of the beams of in-service adjacent box beam bridges. Special focus was placed on the effective arrangement of FRP spike anchors for externally bonded FRP, unsymmetrical deterioration of steel reinforcement, and the eccentric placement of NSM strips. The results show that spike anchors located only at the ends of the externally bonded FRP sheets provided superior performance compared to anchors placed at multiple locations along the sheets. Moreover, the eccentricity of reinforcement did not play a significant role in the effectiveness of the strengthening systems. The test results also highlight the importance of bond on the performance of members strengthened with NSM reinforcement. Overall, the findings extend beyond adjacent box beam bridges and have a wide applicability to other flexural members.

Experimental and analytical study of RC beams strengthened with prestressed near-surface mounted 7075 aluminum alloy bars

Recently developed high-strength aluminum alloys (AA) have great potentials for strengthening and repairing RC structures because of their merits in high strength-to-weight ratio, high ductility, and inherently corrosion-resistant behaviors. However, few studies have been conducted on taking advantage of AA bars for rehabilitation. This study was therefore carried out to reveal the feasibility of 7075 AA bars on near-surface mounted (NSM) applications for flexural strengthening of reinforced concrete (RC) beams. Experiments of four-point flexural tests were presented to assess the performance of NSM AA bar strengthened beams through eight concrete beams, including a control specimen without strengthening, a specimen strengthened by conventional basalt fiber reinforced polymer (BFRP) bars served as reference, and other six ones using NSM AA strengthening technique with various prestress level and bar arrangement. Results indicate that the application of the strengthening system was able to prevent premature debonding failure and increase the load-bearing capacity by up to 102.1%, but reduced the deformability. In addition, an analytical model for capturing the load–deflection behavior of various strengthening schemes was developed. Good agreements between the results from observations and predictions validated the proposed model, suggesting its potential for guiding the design of the AA strengthening schemes.

Flexural behavior of strengthened concrete beams with multiple retrofitting systems

Due to material deterioration, structure age, changes in building function, fault design, and decreased structural reliability brought on by natural catastrophes, it may require to strengthening the reinforced concrete (RC) beams. The entire carbon footprint is increased by the usage of building materials like cement. Therefore, restoring/improving their overall functionality may be accomplished more sustainably by strengthening and repairing damaged members. In this study, a series of RC beams were tested in three-point bending to determine the ability of various strengthening techniques to improve the beams' flexural capacity. Three strengthening techniques were proposed: External bonding with glass fiber-reinforced polymer (GFRP) laminates, near-surface mounted (NSM), and U-jacket. The experimental study compared the various strengthening methods in terms of ultimate loads, crack loads, maximum deflections, gains in ductility, and energy absorption. The finite element program (ABAQUS) was used for the numerical computations because it is capable of properly simulating experimental research on the flexural behaviour of reinforced concrete beams. Compared to all techniques, the strengthening using GFRP in the different techniques (GFRP laminate, NSM, and U-jacket) propagation of cracks before failure occurred in the RC beam. The sample B3-St. plate-NSM, which used the NSM technique, had the highest peak load of 77.2 MPa compared to all samples and a 36.64% increase over the control sample B0-Control. Moreover, the sample B3-St. Plate-NSM has improved stiffness which contributed to reducing the deflection at peak load by 21.12% than the control sample. The strengthening system using steel plate as NSM showed the lowest cost ($/m`) among the other strengthening systems. The specimen B1-GFRP, which used the GFRP technique, had the highest toughness of 1099.2 kN.mm by an increase of 40.25% over the control sample. Finally, the results obtained by using numerical FE models show good agreement with the experimental results.

Effect of resistive heating on the bond properties between iron-based shape memory bars and cement mortar

Iron-based shape memory alloys (Fe-SMAs) have been widely studied as a new type of prestressing material for near-surface mounted (NSM) or external strengthening, and have been used in numerous strengthening projects in Europe. However, Fe-SMAs have not been widely used in new structures due to their uncertain bond properties after high-temperature activation. Therefore, a new type of application in new structures is proposed, which is composed of Fe-SMA bars, plastic corrugated pipes and high-temperature-resistant cement mortar. The bond properties between Fe-SMA bars and cement mortar after resistive heating were investigated through pull-out tests. The influence of different heating temperatures and heating times on the bond properties was analyzed. It was shown that when the temperature of the inner Fe-SMA bars was 150 °C–350 °C, the surface temperature of the plastic corrugated pipes was only 35 °C–65 °C, which indicated that the activation process would not transfer excessive heat to the concrete outside the plastic corrugated pipes. With the increase of the heating temperature, the ultimate bond strength, bond stiffness, residual bond stress, and energy dissipation all gradually decreased. Compared with the specimens at ambient temperature, the specimens could still maintain a high ultimate bond strength with only approximately 10% loss after being heated to 200 °C and cooled down. When the activation temperature was below 300 °C, the more serious bond degradation could be observed with the longer heating time. However, when the temperature exceeded 300 °C, the influence of heating time was negligible. In addition, prediction models for the ultimate bond strength and the bond-slip curves were proposed, which could provide references for subsequent studies.

In-plane shear strengthening of traditional unreinforced masonry walls with near surface mounted GFRP bars

In this study, the effectiveness of Near Surface Mounted (NSM) method, for in-plane shear strengthening of traditional and historical Unreinforced Masonry (URM) walls, is investigated through a comprehensive experimental study. For this purpose, square solid clay brick masonry wallettes (42 samples) with three different types of traditional mortars including gypsum mortar, lime-cement-sand mortar and lime-sand mortar are prepared and retrofitted with NSM Glass Fiber Reinforced Polymer (GFRP) bars. Then, diagonal shear tests are conducted to evaluate the in-plane shear behavior of the masonry wallettes. The effects of some key variables such as wall thickness, the retrofitted face of the wall, reinforcement ratio, and the type of paste for mounting the reinforcing bars, on the effectiveness of the retrofitting method are investigated. The results of the tests are presented in terms of the failure modes and the lateral shear stress-drift curves of the test specimens. Accordingly, the retrofitting method can enhance the in-plane shear strength, and the ultimate lateral drift capacity of the URM wallettes. According to the test results, the type of filler paste and reinforcement ratio influence the strength enhancement of the test specimens. Furthermore, in specimens retrofitted with the one-side retrofitting scheme, due to the asymmetry of walls under in-plane loads, an unexpected out-of-plane deformation is induced in the walls under in-plane load which adversely affects its global behavior.

Performance of Concentrically Loaded RC Wall-like Columns Upgraded with Innovative Hybrid NSM/CFRP System

In RC (reinforced concrete) frame structures, wall-like columns are laid within the space occupied by masonry walls to maximize usable space and thus minimize the column projections into the usable area. These columns often require strengthening owing to various reasons, including increasing the number of stories, changes in building usage, and others. The use of a hybrid system comprising NSM (near-surface mounted) steel rebars combined with CFRP (carbon-fiber reinforced polymer) laminates may be considered a sound technique for strengthening such wall-like building columns. The prime aim of this study is to devise an efficient scheme using a hybrid NSM/CFRP system to strengthen existing RC wall-like columns. Six half-scale RC wall-like columns were prepared and tested under monotonic concentric axial compression. Two columns were unstrengthened to serve as control specimens (CW1 and CW2), and four specimens were strengthened using four different schemes (SW1, SW2, SW3, and SW4). As favored by architects, all strengthening schemes were designed so that the dimensions of the column cross-section were not increased. The effects of strengthening schemes on the enhancement of axial capacity, energy dissipated, and stiffness were evaluated to find the most efficient scheme. Among the four studied schemes, using vertical continuous NSM rebars in combination with the wrapping of the three CFRP layers onto the exterior column surface (in specimen SW2) was the most efficient as it enhanced the ultimate load capacity by 80%. Three-dimensional FE (finite element) analysis was also conducted to predict the response of test specimens. The test results matched well with the FE outputs, which justified the accuracy of the used constitutive models for concrete, steel rebars, and CFRP sheets.

Flexural behavior of reinforced concrete beams strengthened with hybrid Steel-FRP reinforcements by using near surface mounted technique

This paper investigated the behavior of reinforced concrete (RC) beams of near surface mounted (NSM) strengthening technique with using steel bar and hybrid steel bar. The effects of NSM reinforcement and load patterns on the flexural behavior and ductility of the RC beams have been studied. A four-point bending test was carried out on five reinforced concrete beams divided into two groups. The first group was tested under the effect of static load, whereas the second group was tested under repeated load. The experimental results are reported regarding the failure mode, flexural strength, load-deflection response, cracking behavior, and ductility. These results showed that strengthening of concrete beams with NSM steel bar increased the yielding and ultimate loads by about 28.6% and 28.5% respectively as compared to control beam, whereas the yielding and ultimate load increased to 33% and 35.7% over the control beam when strengthened with hybrid NSM steel bar. The ductility index of the control beam was equal to 2.6, this value increased to about 24.6% and 52.3% of the NSM steel bar and NSM hybrid steel bar strengthened beams respectively. The repeated load decreased the load capacity of the strengthened hybrid beams by about 65%, whereas the mid-span deflection is nearly the same.

Deep embedment and NSM techniques for shear strengthening of reinforced concrete slender beams with cFRP ropes

Shear failure is catastrophic and occurs usually without advance warning, thus it is desirable that the beam fails in flexure rather than in shear. Many existing reinforced concrete beams are found to be deficient in shear strength and need to be strengthened. Reinforced concrete beams can be strengthened against shear failure by using polymer composites reinforced with fibres in many different techniques. This study aims to the most efficient shear strengthening of beams with carbon fibre reinforced polymer (cFRP) between near-surface mounted (NSM) technique and the deep embedment (DE) technique. Reinforced concrete beams with dimensions 15x15x70 cm, with the use of classified C30/37 concrete were constructed, each of which was reinforced with 3Ø10 B500c steel bars, only under bending. The specimens were tested in shear under two-point bending loading conditions, after having been strengthened with NSM or DE technique with cFRP rope by various reinforcing arrangements. As main conclusion, it appears that the NSM strengthening technique gives lower values than DE strengthening technique in correspondingly schemes.

Experimental study of reinforced concrete piles wrapped with fibre reinforced polymer under vertical load

This research mainly focuses on the nature of Fiber-Reinforced Polymers (FRP) wrapped piles for the axial compression load. Normally, the degradation of Reinforced Cement Concrete (RCC) structures occurred due to corrosion, inadequate quality materials, aging, live load increments, fatigue, damages and deterioration, and so forth. RCC pile foundations are commonly affected by the above reasons. So, these structures can be strengthened with suitable methods such as jacketing, stitching, overlaying, sealing, grouting, coating, Near Surface Mounted (NSM) systems, FRP wrapping, repairing, and blanketing. FRP wrapping is well suited for strengthening pile structures because of its easy application, and this method is done without using heavy tools and skilled labor. Due to its being non-metallic, FRP reinforcing has desirable properties such as high resistance to chemicals as well as heat, flexibility, large tensile strength, permeability, and also no oxidation. Thus, FRP wrapping was selected as the chosen approach for this ongoing research. In this study, we apply an axial compression load as well as a skin friction condition to a pile member that has been modified to assess its performance and behavior.

Bond of FRP rods in damaged RC beams strengthened with NSM technique

In strengthening reinforced concrete (RC) elements with composite materials, the role of adherence between concrete and FRP assumes great importance as it guarantees the effectiveness of the consolidation method. In this paper the bond mechanisms between FRP rods and concrete second the Near Surface Mounted (NSM) technique have been analyzed by experimental results of investigation and a theoretical linear model. The experimental investigation consists of direct pull-out tests on RC elements with circular GFRP and CFRP rods inserted into a groove. Through pull-out tests main parameters of bond have been presented. The experimental results are compared with those obtained by the theoretical model.

Predicting the behavior of RC T-beams strengthened with NSMCFRP rods in the negative moment region: a finite element approach for low cyclic loading

In this study, a finite element (FE) model for nonlinear FE analysis was developed to evaluate the performance of reinforced concrete (RC) T-beams, which were strengthened in the negative moment region by near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) rods under low cyclic loading. Furthermore, the rods' depth of embedment was the research variable. Every component of the beam is considered in the model, including the concrete, steel rebars, CFRP rod, CFRP sheet, adhesive, and stirrups. The nonlinear properties of concrete, steel rebars, and adhesive were taken into account, while that of the CFRP was assumed to be linearly elastic till rupture. In addition, the user-programmable capabilities of ABAQUS were used to define the degradation of each material under low cyclic loading. The developed FE model was then compared to some experimental measurements comprising two specimens strengthened with NSM-CFRP rods and one un-strengthened control specimen. Overall, the predicted FE mid-span deflection responses were in line with the corresponding measured experimentally tested data. Finally, the research findings were summarized.

Repair of thermally shocked reinforced concrete beams using near-surface mounted – Carbon fiber reinforced polymers ropes and strips

The use of near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) ropes and strips is a recent and promising repairing/strengthening technique for improving the mechanical properties and structural performance of damaged reinforced concrete (RC) members. This study aimed to evaluate the behavior of RC beams after being damaged by thermal shock and the efficiency of using NSM-CFRP strips and ropes as repairing techniques. Therefore, eleven RC beams with dimensions of (150 mm in width × 200 mm in depth × 1150 mm in length) were cast. Nine of the specimens were heated to a temperature of 600 °C for three hours, cooled rapidly by being immersed in water for 15 min, and repaired with different configurations of NSM-CFRP strips and ropes and CFRP sheets. All specimens were tested under a four-point loading test. Three main parameters were studied, namely: NSM-CFRP type, configuration, and the number of U-wrapping ropes used. Experimental results showed a significant reduction in the concrete’s compressive strength with a percent of about 49% after being damaged by thermal shock. The thermally shocked RC beam exhibited a significant degradation in the mechanical and structural performance represented by a reduction in the ultimate capacity, stiffness, and toughness of the beam with a percentage of about 14.4%, 39%, and 11.8% if compared with the control beam, respectively. Also, using an efficient repairing technique can improve the properties of these damaged beams, especially when using NSM-CFRP ropes with U-wrapping CFRP sheets which contributed to the increase in the ultimate load capacity, stiffness, and toughness by a percent of about 54.7%, 23.8%, and 32.8% if compared with the thermally shocked beam, respectively.

Seismic performance of lap-spliced pre-damaged and intact concrete columns strengthened or retrofitted with UHPC and NSM

Reinforced concrete (RC) columns with deficient lap splice details such as short lap splice length and widely spaced stirrups were vulnerable to earthquakes. In the present study, to evaluate the effectiveness of an innovative retrofitting technique using the combination of ultra-high performance concrete (UHPC) and near surface mounted (NSM) technique on the seismic performance of RC columns with deficient lap splices details, cyclic loading tests were performed on four large-sized RC column specimens. Two RC columns were strengthened with UHPC or the combination of UHPC and NSM, and the other two were retrofitted with the combination of UHPC and NSM after the lateral strength decreased to 85% peak strength during the pre-damage cyclic tests. The load–displacement relationship, stiffness degradation, energy dissipation, and residual displacement of RC columns are evaluated. The test results showed that the peak strength and ductility of RC columns with deficient lap splice are significantly improved after strengthening or retrofitting with the combination of UHPC and NSM. The seismic performance of severely damaged RC columns due to deficient lap splice details can still be effectively restored after retrofitting with the combination of UHPC and NSM. Considering the adverse effect of pre-damage, a design method is proposed to predict the flexural capacity of RC columns retrofitting with UHPC or the combination of UHPC and NSM. The proposed method is also applied to predict the flexural capacity of RC beams strengthened with UHPC. The proposed method predicted well the test results of this study and existing tests.

Performance of composite stone beams with prestressed NSM longitudinal CFRP reinforcement subjected to bending

This paper presents an investigation on the performance of stone beams reinforced with prestressed near-surface mounted (NSM) longitudinal carbon fiber reinforced polymer (CFRP) bars subjected to bending. Seven composite stone beams and four bare ones were tested. The test variables included the reinforcement ratio and prestressing level of CFRP bars, and the shear span to depth ratio of the tested beams. Test results showed that, the composite stone beams with either prestressed or non-prestressed reinforcement exhibited a ductile failure with visible deflection and multiple cracks. As the level of prestressing force increased, the cracking load and the shear capacity of composite stone beams increased but the deformation capacity decreased. The increase in reinforcement ratio could suppress the crack propagation and increase the flexural capacity of composite stone beams. As the shear span to depth ratio decreased, the cracking load, the shear capacity, and the peak load corresponding to flexural capacity of composite stone beams increased accordingly. Theoretical models for predicting the cracking and peak moments of composite stone beams were developed based on sectional mechanical analysis, and a good agreement with the experimental results was obtained.