Journal of Composites for Construction

This paper presents the results of an experimental investigation on reinforced concrete (RC) T-beams retrofitted in shear with prefabricated L-shaped carbon fiber–reinforced polymer (CFRP) plates. Shear strengthening of RC beams with L-shaped fiber-reinforced polymer (FRP) plates has proved effective. In this method, grooves are made throughout the beam flange to fully embed the vertical leg of the L-shaped CFRP plate perpendicular to the longitudinal axis of the RC beam and in the RC beam web surface. However, in some cases, drilling grooves in the concrete flange might not be feasible because of the presence of obstacles such as longitudinal steel in the flange of the RC beams. Therefore, the main objective of this investigation was to evaluate the performance of the RC beams strengthened in shear with externally bonded (EB) L-shaped plates as affected by the embedment length of the L-shaped FRP plates. In total, six tests were performed on 2,500-mm long T-beams. Three specimens were strengthened in shear using epoxy-bonded L-shaped CFRP plates with different embedment lengths in the RC beam flange. One specimen was shear-strengthened with fully embedded CFRP plates in the concrete beam flange. The second specimen was strengthened with partial embedment of the L-shaped CFRP plate. This specimen is representative of the case where full penetration of the CFRP plate is not feasible because of an obstacle. In this specimen, the embedment length was set to 25 mm to simulate the minimum concrete cover thickness in RC beams. The third specimen was shear-strengthened with L-shaped CFRP plates with no embedment in the concrete beam flange. In addition, the performance of the beams strengthened with L-shaped CFRP plates was compared with that of a similar specimen strengthened with EB FRP sheets without embedment. Results show that the performance of the specimens strengthened with partially and fully embedded L-shaped CFRP plates in the beam flange was superior to that of the beams strengthened with EB FRP sheets and L-shaped CFRP plates with no embedment.

In the last decade, a new strengthening methodology has been developed for reinforced concrete (RC) frames with hollow clay tile (HCT) infill walls by means of diagonally applied carbon fiber–reinforced polymer (CFRP) fabrics. In the experimental part of a study conducted by the authors, this user-friendly methodology was experimentally investigated considering different aspect (height/width) ratios of the infill walls. In this study, first a numerical model of the FRP strengthened infill walls strengthened with the proposed methodology is developed. Afterwards, the numerical simulation results are validated by use of experimental response curves and finally, a parametric study, which further investigates the effect of aspect ratio of HCT infill walls is presented.

The behavior of concrete members reinforced with fiber-reinforced polymer (FRP) bars has been the focus of many studies in recent years. However, limited research work has been conducted to examine the axial behavior of concrete columns reinforced with FRP bars. In this paper, the behavior and compression strength of 11 full-scale circular concrete columns reinforced with carbon fiber–reinforced polymer (CFRP) bars and spirals were investigated. The test variables included reinforcement type (CFRP versus steel); longitudinal CFRP reinforcement ratio; and the volumetric ratio, size, and spacing of CFRP spirals. The test results indicated that the CFRP and steel reinforced concrete (RC) columns behaved in a similar manner up to their peak loads. The CFRP bars were effective in resisting compression until after crushing of concrete, and contributed on average 12% of column capacity. The design equation is modified to accurately predict the ultimate load capacities of CFRP RC columns. A new factor (${\alpha }_c$) is introduced in the modified equation to account for the FRP bars’ compressive strength properties as a function in their ultimate tensile strength.

An experimental program was conducted at the University of Manitoba to test salvaged timber stringers posttensioned with external carbon fiber–reinforced polymer (CFRP) bars or steel guy cables. A total of 22 creosote-treated Douglas-fir beams with dimensions of $130\times 330\times \mathrm{4,500}\mathrm{mm}$ were tested in three-point bending. Six beams out of the 22 were control beams without any reinforcement. The remaining 16 beams were posttensioned using different reinforcement configurations. Four beams were posttensioned with draped CFRP tendons (Group CD), four beams were posttensioned with straight CFRP tendons (Group C), four beams were posttensioned with draped steel cable (Group SD), and four beams were posttensioned with straight steel cable (Group S). The experimental results found that the strength and the stiffness for Group CD were increased on average by 70% and 10%, respectively, while the strength for Group C was increased on average by 56% and showed no significant increase in stiffness. In contrast, the strength and the stiffness for Group SD were increased on average by 45% and 4%, respectively, while the strength for Group S was increased on average by 49% and showed no significant increase in stiffness.

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) have received significant research attention over the last two decades. However, experimental studies on the behavior of CFFTs filled with high-strength concrete (HSC) remain very limited. This paper presents the results of an experimental study on the axial compressive behavior of 83 monotonically-loaded circular CFFTs. The effects of fiber type, concrete strength, specimen size, and manufacturing method on the compressive behavior of CFFTs were investigated. The CFFTs were manufactured with carbon FRP (CFRP), high-modulus CFRP (HMCFRP), or aramid FRP (AFRP) tubes, and their average unconfined concrete strengths ranged between 34–110 MPa. The diameters of the test specimens ranged from 75–300 mm with all specimens maintaining a $2:1$ height-to-diameter ratio. The effect of the CFFT manufacturing method was investigated through AFRP specimens that were manufactured through either an automated filament winding or manual wet layup technique. The experimentally recorded stress-strain relationships are presented graphically and the ultimate axial stresses and strains and hoop rupture strains are tabulated. The large quantity of the results presented in this paper allows for a number of significant conclusions to be drawn. The results clearly indicate that over a certain confinement threshold, high-strength CFFTs (HSCFFTs) exhibit a highly ductile behavior. However, for the same nominal confinement ratio, compressive behavior of CFFTs degrades as concrete strength increases. The results also indicate that the compressive behavior of CFFTs is significantly influenced by the manufacturing method and fiber type with an improvement in compressive behavior linked to an increase in fiber rupture strain. Finally, the influence of specimen size was found to be negligible for the range of diameters tested in this study. Further experimental observations on these and other key parameters are presented and discussed in the paper.

A new equation to predict the contribution of concrete to the shear strength of fiber-reinforced polymer (FRP) reinforced concrete beams without shear reinforcement is proposed. The new equation considers the elastic modulus ratio of the FRP bars to the steel reinforcement, the shear span to depth ratio, and the flexural reinforcement ratio, and was developed using the results of 60 concrete beam tests. The proposed equation more accurately predicted the results of various experiments available in the literature than the equations of an American Concrete Institute standard, and yielded similar degrees to the equations of a Canadian Standards Association standard, despite making somewhat higher predictions. The applicability of the proposed equation to FRP reinforced lightweight concrete beams was investigated using 24 all-lightweight concrete beam tests. The concrete shear strengths of the FRP reinforced all-lightweight concrete beams were equivalent to 75% of the strengths predicted by the proposed equation for normal concrete. Furthermore, with a reduction factor of 0.85, the proposed equation also showed good results for the concrete shear strength of glass FRP (GFRP) reinforced sand-lightweight concrete panels presented in a recently published paper.

Physical testing is used to characterize the structural properties of beam-to-column joints, comprising pultruded fiber-reinforced polymer (FRP) H-shapes of depth 203 mm, connected by 128 mm-long web cleats and two M16 bolts per leg. Testing is performed on two batches of nominally identical specimens. One batch had web cleats of pultruded FRP and the other had structural steel. The structural behavior of the joints is based on their moment-rotation responses, failure modes, and serviceability vertical deflection limits. Joints with FRP cleats failed by delamination cracking at the top of the cleats, and when the cleats were of steel, the FRP failure occurred inside the column members. Neither failure mode is reported in the design manuals from pultruders. At the onset of the FRP damage, it was found that the steel joints were twice as stiff as the FRP joints. On the basis of a characteristic (damage) rotation, calculated in accordance with Eurocode 0, the serviceability deflection limits are established to be span/300 and span/650 for the joints with FRP and steel cleats, respectively. This finding suggests that appropriate deflection limits, in relation to cleated connections, should be proposed in manufactures’ design manuals and relative design standards and design codes. Failure to address the serviceability, by the engineer of record, could lead to unreliable designs.

Strengthening of steel structures with adhesively bonded carbon fiber–reinforced polymer (CFRP) laminates (or plates) has received extensive research attention over the past few years. Existing studies have revealed that debonding of CFRP plates from a steel substrate is one of the main failure modes in such CFRP-strengthened steel structures. To better understand and model debonding failures, the behavior of CFRP-to-steel bonded joints needs to be well understood. Recent tests conducted by the authors’ have demonstrated that the bond strength of such bonded joints depends significantly on the properties of the adhesive used, and more specifically on the interfacial fracture energy rather than the tensile strength of the adhesive. The study has also showed that the bond-slip curves for nonlinear ductile adhesives have an approximately trapezoidal shape. This paper presents an analytical solution for the full-range behavior of CFRP-to-steel bonded joints with a ductile nonlinear adhesive. Predictions from the analytical solution are presented to explain the different stages of debonding failure and are compared with test data to demonstrate the validity of the analytical solution.

This paper presents results of an experimental study aimed at investigating the effectiveness of different mechanically fastened composite systems for retrofitting relatively large-scale corrosion-damaged reinforced concrete beams. A total of 15 beams, $250\times 275\times \mathrm{3,000}\mathrm{mm}$ each, were constructed and tested. The beams were initially subjected to accelerated corrosion for 60 days that corresponded to an 8% tensile steel mass loss. The beams were then retrofitted with composite plates secured with powder-actuated fasteners (PAF), expansion anchor bolts (EAB), and threaded anchor bolts (TAB). Following the initial corrosion and retrofitting, four retrofitted beams were tested to failure, and four beams were exposed to an additional 40 days of accelerated corrosion until they reached a 15% tensile steel mass loss, then tested to failure. Five beams were not corroded to act as control specimens. Two corroded beams were tested to failure without retrofitting. The undamaged strengthened beams exhibited flexural strength gains in the range of 67–85% with no reduction in the ductility index, except for the beam with the 32-mm-long PAF. Corrosion-related cracks compromised anchorage of the PAF into the concrete; and hence, a significant reduction in the strength gain and ductility index was recorded for the beams with the PAF fastening system. The corroded beams retrofitted with the EAB and TAB fastening systems exhibited insignificant or no reduction in the strength gain and ductility index even at the higher corrosion damage state of 15% tensile steel mass loss. Despite corrosion damage and cracking, the flexural capacity of all retrofitted beams was higher than that of the control beam.

This paper presents a fatigue-life prediction model of reinforced concrete beams strengthened with near-surface mounted (NSM) fiber-reinforced polymer (FRP) composite rods under flexure. This model is based on the fracture-mechanics approach using a cohesive model, and accounts for different bridging properties in steel and FRP reinforcement in strengthened concrete structures. It predicts the number of fatigue cycles to ultimate failure in the strengthened members, in which the failure is defined by unstable propagation of an effective crack in concrete. Several sets of experimental results in the literature are selected to verify the efficiency and precision of this model, in which the writers compare typical stress versus fatigue-life curves. This model is capable of predicting the fatigue life of NSM-strengthened concrete beams to a good precision and relates the fatigue life to the structural stress in an explicit manner.

The concept, design, and experimental validation of the new Avançon Bridge in Bex, Switzerland, are described. The lightweight glass fiber–reinforced polymer (GFRP) sandwich bridge deck adhesively bonded to steel girders, reduced the traffic disruption period by approximately 40 days or 80% compared to a cast-in-place concrete bridge, and also enabled the bridge to be widened to two lanes. The semi-integral bridge concept allows the application of a continuous asphalt layer across the abutments without expansion joints and thus facilitates and reduces maintenance. The GFRP sandwich deck with structural balsa core fulfils all the requirements concerning serviceability, ultimate limit state, and fatigue. The bridge deck dimensions significantly depended on the selected and applied design recommendation. In the case of the Avançon Bridge, the German and British recommendations provided the most conservative sets of material factors, the Dutch recommendation specified the least conservative, with the Eurocomp recommendation lying somewhere in between. In particular, the selected material factor applied to stiffness influenced the deck composition and material consumption.

Experimental results of midrise RC shear walls under quasistatic cyclic loading were used to investigate the interaction of flexural and shear deformations. Four large-scale shear walls—one reinforced with steel bars and three totally reinforced with glass fiber–reinforced polymer (GFRP) bars—were tested to failure where the behavior was dominated by flexure. It was found that relying on the diagonal displacement transducers tended to overestimate shear deformations by 30 to 50%. To correct the shear deformations, the center of rotation of the tested shear walls was evaluated. Based on experimental results, the fundamental equation of flexural deformation obtained values of the center of rotation ($\alpha$). Using the suggested values of $\alpha$ produced consistent results for the flexure and shear deformations. Decoupling the total deformation of the tested shear walls into flexural and shear deformations was discussed. Using elastic materials (GFRP bars) gave uniform distributions of shear strains along the shear region of the GFRP-reinforced shear walls ranging from 15 to 20% of the total deformation, resulting in less shear deformations than those experienced in the steel-reinforced shear wall; for this yielding of the steel bars intensified the shear strains at the yielding location, causing significant degradation in shear deformation ranging from 2 to 20% of total deformation.

Unreinforced masonry (URM) walls have been constructed for the past millennia and are still widely used today. URM walls have proven to have low shear strength and are prone to brittle failure when subjected to in-plane loads caused by earthquake or wind. Retrofitting URM walls is accomplished internally and externally using current techniques, such as placing steel bars in the cavities and grouting, posttensioning with steel tendons, stitching, and adhering fiber-reinforced polymers (FRP) to increase capacity and enhance pseudoductility. In this study, a fabric-reinforced cementitious matrix (FRCM) system is applied to URM walls to determine its feasibility as an alternative external strengthening technology. The experimental program consists of testing a total of nine clay brick walls under diagonal compression. Two FRCM strengthening reinforcement schemes are applied, namely, one and four reinforcement fabrics. An analytical model is used to calculate the shear capacity of strengthened URM walls and compare its results with the experimental database. The effect of limitations in design approach on shear capacity of strengthened walls is discussed.

Sandwich panels composed of glass fiber–reinforced polymer (GFRP) skins and low-density polyurethane core are investigated for potential structural applications such as lightweight insulated roofing or cladding systems. Ten $\mathrm{1,220}\times 318\times 78\text{-}\mathrm{mm}$ panels, including three control specimens, were tested under high-cycle fatigue at maximum load levels of 45–70% of the ultimate static load. Fatigue tests were carried out to failure, thereby enabling the development of the complete fatigue life ($S\text{-}N$) curve and stiffness degradation. Digital imaging correlation was used to map shear deformations and showed that shear contributes about 90% of the deflection. Both static and fatigue failure modes were due to core shear failure. The study showed that fatigue threshold was 37% of the ultimate static capacity, and that to sustain at least 2 million cycles, service load should be limited to 45% of ultimate. The maximum design service live and snow loads, as well as wind load based on the most critical conditions in Canada, were all below the fatigue threshold of the panel. The panels had a strength safety factor of 2.1 relative to the factored maximum design live and snow load, and 6.5 relative to the factored maximum wind load. Deflection limits may govern for some service load conditions, but is not critical when only wind load considered. Stiffness degradation reached a maximum of 15–20%, but residual deflections upon unloading were insignificant.

This article presents the results of an experimental program on two-way flat slabs with central loading. The slabs were designed according to the American Concrete Institute code. One slab without any modification was used as the control and four were strengthened with different carbon fiber–reinforced polymer (CFRP) grid configurations including one with preinstalled and three with postinstalled fiber–reinforced polymer (FRP) strengtheners. For strengthening, 8, 16, and 24 strengtheners were used. A method was developed for predicting maximum loading capacity in slabs strengthened with CFRP grids and epoxy resin used in drilled holes. The results of the experiments show that the proposed strengthening method enhances maximum loading and deformation capacities. Furthermore, the proposed strengthening method prevents brittle failures that may occur under vertical concentrated loadings. The dominant failure mode for flat slabs strengthened with FRP grids is found to be deboning of FRP grids due to the small slab depth. In addition to the increased shear capacity of the slab up to a reasonable value, this method of strengthening is capable of changing slab failure from the shear mode to the flexure mode.

This article investigates the seismic behavior of three full-scale exterior reinforced concrete (RC) beam-column joints rehabilitated and strengthened with externally bonded carbon fiber–reinforced polymers (CFRP). The specimens had inadequate detailing in the core zone and replicated joints of a real substandard building tested as part of the EU-funded project BANDIT. Seven tests were performed in two successive phases. The bare joints were first subjected to reversed cyclic loading tests to assess their basic seismic performance. As these initial tests produced severe damage in the core, the damaged concrete was replaced with new high-strength concrete. The specimens were subsequently strengthened with CFRP sheets and the cyclic tests were repeated. The results indicate that the core replacement with new concrete enhanced the shear strength of the substandard joints by up to 44% over the bare counterparts. ASCE guidelines predict accurately the shear strength of the bare and rehabilitated joints. The CFRP strengthening enhanced further the joint strength by up to 69%, achieving a shear strength comparable to that of joints designed according to modern seismic provisions. Therefore, the rehabilitation/strengthening method is very effective for postearthquake strengthening of typical substandard structures of developing countries.

This paper contributes to the scarce research available regarding the shear behavior of carbon fiber–reinforced polymer (CFRP) prestressed concrete beams. The beams were subjected to four-point bending and tested with different shear span to depth ($a/d$) ratios of 1.5, 2.5, and 3.5, with and without transverse reinforcement. For each group of four beams, two were reinforced with minimum required glass fiber–reinforced polymer (GFRP) stirrups according to the Canadian highway bridge design code. The results showed that the flexural rigidity and the shear capacity of the beams increase significantly as the $a/d$ ratio is reduced to 1.5 from 2.5. The data also showed that the minimum required GFRP stirrups are ineffective in beams with $a/d=1.5$ that are governed by arch action. The experimental results are compared to theoretical estimates from the shear formulas available in design codes and literature.