Flexural Retrofitting Research Articles

Shear strengthening and damage control effects of CFRP and self-prestressing iron-based SMA for concrete columns

Although prestressed shape memory alloy (SMA) has shown a great performance in flexural retrofitting of slender RC columns, its shear strengthening effect for squat RC columns has been barely studied. This study explores the shear strengthening and damage control effects of iron-based SMA (Fe SMA) for squat RC columns. The heat-activated prestressing of Fe SMA was evaluated first at material level, then applied to component level structural testing of RC columns. The four circular RC columns with different retrofitting schemes were tested under quasi-static lateral cyclic loading. The specimens strengthened with carbon fiber-reinforced polymer (CFRP) sheet and Fe SMA strip exhibited satisfactory global responses without showing significant shear failure. From the visual inspection and non-destructive damage assessment, the prestressed Fe SMA was found to be superior in delaying damage accumulation in concrete compared to CFRP.

Near-surface mounted-FRP flexural retrofitting of concrete members using nanomaterial-modified epoxy adhesives

This study, serving as the first of its kind in this scope, investigates the effectiveness of nanomaterial-modified epoxy adhesives (NMEAs) for Near-Surface Mounted (NSM)-FRP flexural retrofitting of concrete. A total of 48 concrete prisms were retrofitted using three different types of FRP reinforcement bars (CFRP, GFRP and BFRP) inserted in grooves sized 8 × 8, 10 × 10 or 12 × 12 mm and bonded to the concrete substrate using either neat epoxy (NE) or NMEAs. NMEAs were developed by incorporating either carbon-based (i.e. CNF, cellulose and graphite) or silicon-based (i.e. silica and MMT clay) nanoparticles into epoxy at 0.1 wt. %, whereas the graphite NMEAs were prepared with more wt.% (i.e. 0.2 and 0.3). SEM and XRD techniques were used to assess the dispersion quality of nanoparticles within the matrix along with the porosity and crystallinity percentages of the NMEAs. Results showed that using silica, clay and graphite NMEAs rather than NE enhanced the retrofitted concrete capacities, whereas a decrease in strength was observed when using CNF- and cellulose-modified epoxies. Moreover, it was found that the specimens bonded with silicon-based NMEAs had, on average, higher capacities than those bonded with carbon-based NMEAs, which, on the other hand, showed more ductile behaviour. Results also suggested that the specimens’ capacities decreased as the wt. % concentration of the nanoparticles (i.e. graphite) increased. Increasing the groove size from 8 × 8 mm to 10 × 10 mm decreased the capacities but enhanced the ductility, whereas increases in both the capacities and ductility were achieved when moving from 8 × 8 mm to 12 × 12 mm.

Comparative Study on the Behavior of Reinforced Concrete Beam Retrofitted with CFRP Strengthening Techniques.

Lateral reinforcement has a significant impact on the strength and ductility of concrete. Extra confinement is provided in this project by carbon fiber reinforced polymer (CFRP) sheets wrapped around the outside of reinforced concrete (RC) beams. To determine the failure criteria and maximum load-carrying capacity of beams, numerous specimens were cast and tested in a flexural testing machine. This paper presents the results of an experimental investigation of functionally damaged reinforced concrete beams repaired in flexure with CFRP sheets. The most essential variable in this study is the CFRP sheet scheme, and seven different strengthening schemes (B1 to B7) were explored in the experimental program. In conclusion, the findings of the study showed that flexural retrofitting of reinforced concrete beams with CFRP sheets is functionally effective, with restored strength and stiffness values roughly equivalent to or greater than those of the control beam (CB1). The efficiency of the flexural retrofitting mechanism appears to vary depending on the layout of the CFRP sheet. Steel rupture and concrete crushing were shown to be the most common failure modes in the investigation, causing CFRP sheets to break in retrofitted beams.

REINFORCED CONCRETE FLAT SLABS WITH COMMON ARRANGEMENTS OF FIBRE REINFORCED POLYMER SHEETS

Retrofitting of reinforced concrete (RC) flat slabs using fibre reinforced polymer (FRP) composites has become common in recent years. Flexural retrofitting of one-way and two-way RC flat slabs using five common arrays of carbon FRP (CFRP) strips has been investigated in this paper. A comparison of the obtained results provided optimum scheme. Finite element method has been used to conduct the study using a commercial computer program. Results from the numerical analyses suggest that the use of CFRP sheets leads to improved load bearing capacities of slabs, which depends on both the type of array and the widths of FRP strips. The most optimal array of the retrofitting material (considering the effects on both strength and deflection) is the cross-like condition, which increases the capacities for one- and two-way slabs, respectively, by thirty-four percent and thirty percent while decreasing their maximum deflection by ten percent and four percent, respectively.

Textile-Reinforced Mortar (TRM) Strengthened One-Way Reinforced Concrete Slabs

The issue of upgrading and strengthening the reinforced concrete (RC) infrastructure has become of great importance. Recently, textile-reinforced mortar (TRM) was used in the field of structural strengthening. In the current study, using of TRM for flexural retrofitting of one-way reinforced concrete (RC) slabs was experimentally and theoretically investigated. The parameters examined included; the number of TRM layers (1, 3, 5 layers) and the strengthening configuration fully and partially). For this purpose, eight specimens were prepared and tested under three points- loading up to failure. The result showed that the TRM increases substantially the flexural capacity of RC slabs. The highest flexural capacity increase recorded was 103 %. It was also noted that increasing the number of retrofitting layers resulted in different increases in the flexural capacity. It was also shown that the strengthening configuration plays an important role in the effectiveness of the technique. The fully covered approach showed higher loading capacity than the partial cover technique provided that the same TRM layer is applied. Finally, the ultimate moment of the strengthened specimens was calculated theoretically and compared with that obtained experimentally. The results of calculations showed a good agreement between the theoretical and experimental results.

Performance of reinforced concrete beams strengthened with NSM CFRP composites for flexure using cement-based adhesives

Numerous studies have been conducted on flexural strengthening using epoxy adhesive for both externally-bonded and Near-Surface Mounted carbon fibre reinforced polymer (NSM CFRP) composites. Substitution of epoxy with cementitious bonding material for flexural retrofitting of concrete structures has great potential to overcome the drawbacks and disadvantages associated with the use of epoxy adhesive. However, limited studies have been conducted for the use of cementitious adhesives for near-surface mounted strengthening system due to the special physical properties required for this technique. A modified cement-based adhesive has been developed for this purpose and comparable bond properties have been achieved. In this paper, an experimental program has been conducted to investigate the flexural behaviour of reinforced concrete beams retrofitted with NSM CFRP textile and laminate using modified cement-based adhesive. Numerical analysis using finite element has been used to evaluate the experimental results and parametric study for future design requirements. The findings showed significant and excellent increase in flexural strength, achieving almost same that results gained from epoxy adhesives and comparable finite element results.

Experimental and Analytical Investigation on Flexural Retrofitting of RC T-Section Beams Using CFRP Sheets

The large portfolio of aging highway bridges worldwide includes many reinforced concrete T-section beams with various levels of damage and degradation. However, there is currently dearth of research on the anchoring behavior of CFRP sheets used for strengthening such RC T-section beams. Moreover, there is a need for rational and accurate analytical models to predict the strengthening effect of CFRP sheets for RC T-section beams. In this study, eight RC T-section beam specimens strengthened with externally bonded CFRP sheets were tested under quasi-static loading. The failure mode, cracking resistance, yielding and ultimate capacity were examined. The effects of U-wrap spacing, flexural reinforcing ratio, and concrete compressive strength on the flexural behavior of the CFRP strengthened RC T-section beams were analyzed and discussed. New analytical models were developed to predict the cracking, yielding and ultimate load resistance of the RC T-section beams strengthened with CFRP sheets. The analytical models were validated through comparing its predictions with experimental results, and they demonstrated adequate accuracy. The findings could be deployed for the retrofitting of a large portfolio of aging highway bridges with deteriorated reinforced concrete T-section beams.

Flexural Retrofitting of the Damaged Reinforced Concrete Beams by Using HPFRCC

Damaged structures are not usually reliable to tolerate designed loads and therefor, need to retrofit in structural parts. The main purpose of this paper is to utilize HPFRCC as a high-performance material to recover the damaged beams and improve their ductility and moment capacity with experimental approaches. In addition to, a retrofitting method is presented using high-performance fibre reinforced cement-based composite (HPFRCC). The experimental study is performed on three simply supported beams with the same dimension, materials, and reinforcement configuration. The first beam, which is known as the reference beam (RC), is subjected to pure bending condition till its failure and the others are prone to a certain amount of load according to the final capacity of the first beam. Thereafter, two damaged beams are retrofitted using HPFRCC in the created grooves on tensile surface of the beam and finally these retrofitted beams are loaded to determine the bending behaviour. Experimental Results demonstrate that retrofitting can improve the first crack strength, load at yield condition, and maximum load capacity. Also, the proposed method increases the ductility and energy absorption of retrofitted beams.

Experimental and analytical investigations of a novel end anchorage for CFRP flexural retrofits

Flexural strengthening of reinforced concrete (RC) structures using fiber-reinforced polymer (FRP) composites has gained ground as a technique preferred over its rival ones. However, premature failure of FRP retrofitting systems in the form of debonding or delamination still remains to be an element of concern when using this technique. Despite many studies devoted to this phenomenon, no consensus has as of yet been gained on a universal anchorage system that is capable of preventing different premature debonding failures. In an attempt to address this issue, a novel end anchorage method is developed in this study and its efficiency evaluated through experimental tests. The proposed method involves squeezing carbon FRP (CFRP) sheets at their ends into a groove and stitching them with CFRP anchors. To evaluate their combined action in precluding different types of debonding, the end anchors are combined with different types of middle ones. The experimental program was comprised of uses six large scale RC beams, five of which are retrofitted with CFRP composite sheets. All the beams are then tested monotonically under a four-point bending setup. The results are reported in terms of loading capacity, ultimate displacement, flexural stiffness, ductility factor, and failure modes. The proposed anchorage technique is found capable of preventing different debonding scenarios that might occur in flexural retrofitting with CFRP composites. Finally, an analytical procedure is implemented to predict the experimental load-displacement curves of the retrofitted specimens.

Effects of CFRP/GFRP flexural retrofitting on reducing seismic damage of reinforced concrete frames: a comparative study

Flexural retrofitting of structures using glass/carbon fibre reinforced polymer (GFRP/CFRP) has been widely investigated. However, comparison on the effects of GFRP/CFRP flexural retrofitting at plastic hinges on reducing the potential seismic damage of reinforced concrete (RC) structures is hardly found in the literature and is thus aimed by this study. Toward this aim, two-, four- and eight-storey RC frames were chosen to represent different building structures. These frames were then retrofitted by CFRP/GFRP bonded sheets to increase flexural capacities of beams and columns at plastic hinge regions. The original, CFRP and GFRP retrofitted frames were modelled using nonlinear hysteresis elements. After verification, nonlinear time-history analyses of those frames under various seismic intensities were carried out, followed by cumulative damage analyses. Damage states of original, CFRP and GFRP retrofitted frames were compared with one another. The obtained comparison results reaffirmed the effectiveness of CFRP and GFRP flexural retrofitting. More importantly, obtained results indicated that CFRP is more effective than GFRP on reducing seismic damage of RC structures when they are employed for flexural retrofitting. These outcomes can help in deciding on the FRP type to be used for flexural retrofitting of RC structures.

Numerical Representation of Multiple Premature Failures in Steel-Plated RC Beams

Realizing the importance of widely used technique of plating for flexural retrofitting of reinforced concrete (RC) beams and its drawbacks due to premature failure(s), present work concentrates in developing a finite element tool model capable of successfully capturing multiple premature failure modes and their corresponding behaviors. The model is simple but focused; the capability and accuracy of the results have been validated through test literature, particularly focusing on the load capacities of beams at progressive stages of failure modes; which is from crack initiation through to complete failure, such as the load of crack initiation, first crack and complete failure. Acceptable accuracy is shown in terms of crack type(s), crack patterns, sequence, location and direction of propagation through the innovative use of cohesive zone model (CZM). The model clearly explains that debonding and peeling, although originating from a same location for most cases, are extensions of different types of cracks.

Capturing failures in steel-plated RC beams through a combination of discrete and continuum models

In recent decades, a significant research has been conducted towards understanding the behaviour of plated beam. Initially designed to achieve a desired capacity, the plated beams prematurely fail in undesirable modes of failure, such as debonding and peeling. The uncertainty related with such modes of failure poses a real challenge towards quantifying them. This field is far from being clearly understood. Realising the importance of widely used technique for flexural retrofitting of reinforced concrete (RC) beams and its drawbacks due to premature failure(s), present work concentrates in developing a finite element tool model capable of successfully capturing multiple premature failure modes and their corresponding behaviours related to RC beam retrofitted with steel plates at their soffits. The capability and accuracy of the results has been validated through test literature in terms of load capacities of beams at progressive stages of failure type(s) through crack patterns, location, and direction of propagation. Numerical beams are showing expected load/displacement behaviour with the ability to predict further direction of propagation of cracks especially at concrete-plate interface with the use of Cohesive Zone Model (CZM).

Retrofitting of RC Beams using Glass Fiber Reinforced Polymer Sheets: An Experimental Study

Objective: An experimental investigation to check flexure and shear behavior of Reinforced concrete (RC) beams retrofitted with glass fiber reinforced polymer composites. Methods/Analysis: Two point symmetric loading. In this study two set of beams were cast out of those first set was weak in flexure (A) and second was weak in shear (B). In all beams same grade of concrete was used but with different structural detailing. In set a three beams (weak in flexure) were cast out of which one was control beam and other two were retrofitted using Glass Fiber Reinforced Polymer Sheets (GFRP) sheets in soffit of beam and till neutral axis including soffit. In set B three beams (weak in shear) were cast out of which one was control beam and other two were retrofitted by using GFRP sheets on sides and U-jacking at corners respectively. Hand wet lay-up method was used for application of GFRP sheets on beam. The retrofitting of beams was done with different amount and configuration of GRFP sheets. Retrofitted RC beams with epoxy-bonded glass fiber reinforced sheets were tested till failure using a symmetric two point loading system. Load, deflection, failure modes and crack pattern of each beam was recorded for a particular GFRP orientation. Experimental investigation concluded that there was increase in load at initial crack and also at ultimate failure for retrofitted beams as compare to control beams. Failure in case of set a retrofitted beams was flexural shear failure. It was also recommended that flexural retrofitting should be performed along with shear retrofitting. In case of set B beams failure was shifted to flexural failure which was initially shear failure. So retrofitting in shear zones was observed most effective. Finding: Retrofitting in shear zones was observed most effective in case of ultimate, flexural failure and shear failure.

Experimental and Numerical Investigation on Shear Retrofitting of RC Beams by Prefabricated UHPFRC Sheets

Different methods are used for retrofitting RC members. One of the new methods in this field is using externally bonded fiber-reinforced Concrete (FRC) sheets in order to increase RC member’s shear and flexural strength. In this study, applicability of ultra-high performance fiber-reinforced concrete sheets in shear and flexural retrofitting of RC beams was investigated. In total, eight RC beams (dimensions 10×20×150 cm) with two different bending capacity and lack of shear strength were used and were tested in 3-points bending test. Of these, four were control beams and four were retrofitted with laterally bonded UHPFRC sheets. Dimensions of the sheets used for retrofitting were (3×15×126 cm). Also FEM analysis was used to model the effect of The method. the results show that this method can be well used for retrofitting RC beams. In this method the way of connecting sheets to beam’s surfaces has a fundamental role in behavior of retrofitted beams.

Flexural Retrofitting of RC Beams Using Extra Rebars and U-Wraps

Flexural Retrofitting of RC Beams Using Extra Rebars and U-Wraps

Flexural Retrofitting of R.C Beam Using Hybrid Laminates

Flexural Retrofitting of R.C Beam Using Hybrid Laminates

RC beams retrofitted using external bars with additional anchorages-a finite element study

Study on flexural retrofitting of RC beams using external bars with additional intermediate anchorages at soffit is reported in this paper. Effects of varying number of anchorages in the external bars at soffit were studied by finite element analysis using ANSYS 12.0 software. The results were also compared with available experimental results for beam with only two end anchorages. Two sets of reference and retrofitted beam specimens with two, three, four and five anchorages were analysed and the results are reported. FE modeling and non-linear analysis was carried out by discrete reinforcement modeling using Solid65, Solid45 and Link8 elements. Combin39 spring elements were used for modeling the frictional contact between the soffit and the external bars. The beam specimens were subjected to four-point bending and incremental loading was applied till failure. The entire process of modeling, application of incremental loading and generation of output in text and graphical format were carried out using ANSYS Parametric Design Language.

Unified Design Method for Flexure and Debonding in FRP Retrofitted RC Beams

Flexural retrofitting of reinforced concrete (RC) beams using fiber-reinforced polymer (FRP) plate is a common way to increase the flexural capacity. There is a lack of rational design method to determine where the strengthening plate can safely be curtailed. As a result, retrofitted beams commonly fail by debonding of the FRP plate, which occurs well before the target flexural capacity. Debonding is brittle failure; thus, ductility of the retrofitted beam needs to be ensured by debonding prevention. With sufficient ductility the ultimate strength can continuously increase beyond steel yields with the elastic behavior of the FRP strengthening plate. Debonding prevention has been accounted for empirically in most design approaches so far. The global energy balance approach (GEBA) using fracture mechanics has been proposed to determine the debonding load of an FRP-RC beam that is affected by the plate curtailment location. The GEBA results for various FRP-RC beams can be summarized using debonding contours on plots of moment capacity against the safe plate curtailment locations. The debonding contours constructed in this way for the beams with the same ratio of depth to fracture energy are virtually the same. This paper shows how GEBA can be incorporated into the design process to prevent premature debonding of the FRP plate. The method makes use of the debonding contours and derives from these simplified design charts that could be made available to designers. The retrofitting design consideration and the theoretical background of this unified design method are first explained, followed by the derivation of the conceptual design charts. Numerically correct design charts are then constructed for a wide range of design cases. Finally, a worked example is used to explain the way to apply the unified design method using design charts.

Flexural retrofitting of RC buildings using GFRP/CFRP – A comparative study

The effectiveness of fibre reinforced polymers (FRPs) in retrofitting/repairing of the reinforced concrete (RC) components has been studied in the past to great detail. However, the seismic performance of RC structures retrofitted using FRP composites is yet to be scrutinised in terms of lateral resistance, ductility, and failure mechanism. This is of high importance if the retrofitted structures are to withstand higher seismic ground motions than they were designed for and/or pulse-type ground motions. In a comparative study, this paper reports on the results of an investigation into the flexural strengthening of RC buildings using glass/carbon fibre reinforced polymers (GFRP/CFRP). An 8-storey code-compliant RC building was considered as the case study to represent the medium-rise structures. With a slight intervention in the lateral displacement ductility and provision of the weak-beam strong-column design philosophy, the strengthening design strategy is aimed at increasing the lateral resistance. For this purpose, composite sheets are designed to be applied at the two end regions of all beams and columns on a practical flange-bonded scheme. The nonlinear pushover analysis with lumped plasticity approach was implemented in order to compare the seismic response of the original structure with the GFRP/CFRP retrofitted structures. Following validation of the adopted models, the force–deformation curves of the nonlinear plastic hinges are determined in a rigorous approach considering the material inelastic behaviour, reinforcement details, and dimensions of the members. While the nonlinear results confirm a significant increase in the lateral load carrying capacity using both composite materials, the CFRP improvement was as much as twice of the GFRP. However, the latter provides higher ductility.

Flexural retrofitting of RC beams using external bars at soffit level – An experimental study

Throughout the globe, huge stock of buildings become vulnerable to damage due to aging, rebar corrosion, and natural hazards, particularly earthquake. Section enlargement, bonded steel plating, external post-tensioning and FRP composites wrapping are some of the techniques being widely followed to retrofit various structural elements. Each technique has at least one or more number of limitations. High cost, difficulty in execution, reduction in headroom, loss of aesthetic value, increase in self-weight, careful surface preparation, de-bonding failure are some of the innate limitations of these techniques. A maiden attempt has been made by the authors to devise a new technique to retrofit RC beams with external reinforcement. The proposed method overcomes most of the drawbacks of the above said existing methods. Some work has already been reported on external reinforcement by keeping the reinforcement at the sides of the beam using deflectors, mechanical anchoring devices and strengthening end anchorage zones. The reported technique in the present work overcomes all the drawbacks of the above method. The authors propose the external bars to be kept at the soffit level of the beam section, thus eliminating the use of deflectors, mechanical anchoring devices and making it amenable, simple and effective. Additional advantages of the present technique are the enhanced moment carrying capacity, reduced deflection and crack width and improved ductility.