Journal of Composites for Construction

This study introduces an innovative scheme of bridge superstructure for expedited construction, improved serviceability, and extended life span. The new bridge superstructure is assembled from precast prestressed decked bulb $T$-beams reinforced and prestressed with corrosion-free fiber-reinforced polymer (FRP) materials. An experimental investigation accompanied by analytical and numerical simulations was developed to evaluate the performance of the newly developed beams. Through the experimental investigation, three single decked bulb $T$-beams were constructed and tested to failure. The first beam, served as a control beam, and was prestressed and reinforced with conventional steel strands and reinforcing bars. The second and third beams were prestressed and reinforced with carbon-fiber composite cable (CFCC) strands and carbon-fiber-reinforced polymer (CFRP) tendons, respectively. The investigation revealed that the performance of beams reinforced with CFRP tendons or CFCC strands was comparable with the performance of the control beam at both service and ultimate limit states. All three beams exhibited high load-carrying capacity with large corresponding deflection and fair amount of absorbed energy before failure. The study showed that the corrosion-free FRP-reinforced decked bulb $T$-beams can be safely deployed in construction to enhance the performance and extend the life span of bridge superstructures.

Fiber-reinforced polymer (FRP) plate strengthening relies critically upon the adhesive that is used to bond it to the existing structure. A typical two-part ambient-cure epoxy adhesive for structural strengthening has a glass transition temperature of approximately 40°C–70°C, but the stiffness and strength of the adhesive typically decrease at temperatures somewhat below this characteristic temperature. This paper investigates the implications of the changes in adhesive properties at warm temperatures ($<100°\mathrm{C}$) for FRP-strengthened beams, through short-term experimental and analytical work. Tests were conducted on FRP-strengthened steel beams subjected to sustained load and increasing temperature; the results, however, are also relevant to strengthened concrete beams. Digital image correlation was used to measure the slip between the strengthening plate and beam, and hence to observe the behavior of the adhesive joint. A bond analysis was also developed to predict the slip across the adhesive joint at an elevated temperature, based upon the glass transition characteristics of the adhesive measured using dynamic mechanical analysis. The analysis allows the response of the strengthened beams to warm temperatures to be examined in further detail. Both the experimental and analytical results show that substantial slip can occur between the plate and beam at temperatures over 40°C. As the temperature increases and the adhesive softens, a greater length of adhesive joint is required to transfer load from the plate to the beam, resulting in an increase in slip that eventually causes debonding of the plate from the beam.

An experimental program was conducted at the University of Manitoba to test salvaged timber stringers strengthened with glass fiber-reinforced polymer (GFRP) laminates. A total of 20 creosote-treated Douglas Fir beams with dimensions of $130\times 330\times 4,500\mathrm{mm}$ were tested in three-point bending. Two groups were studied to examine the effect of GFRP reinforcement on the stiffness increase of the beams. The first group of 10 samples were reinforced with GFRP laminates on the tension side only (Group T), whereas the other group of 10 samples was reinforced with GFRP laminates alongside both tension and compression zones (Group TC). This study found that the strengthening with GFRP laminates, on average, increased the strength and the stiffness of the beams, respectively, by 36 and 3% for Group T and by 31 and 3.5% for Group TC. An analysis of a database of fiber-reinforced polymer (FRP)–strengthened timber beams tested by other researchers facilitated further study on the effect of FRP on the behavior of timber. The comprehensive analysis revealed a minimal stiffness increase in timber beams strengthened with FRP. Some evidence exists, however, that the beam span-to-depth ratio is an important factor to consider when strengthening timber beams. Beams with smaller span-to-depth ratios showed some increase in stiffness with increasing the reinforcement ratio; however, beams with larger span-to-depth ratios showed no real enhancement of beam stiffness, unless the reinforcement ratio was around 7 times the minimum code-recommended value. This result supports the current CSA provisions that do not advocate for stiffness increase when this strengthening method is used. The analysis shows that stiffness increase in GFRP-strengthened timber beams, based on results of small-scale samples, is minimal.

This paper presents the residual behavior of unreinforced concrete beams repaired with carbon fiber-reinforced polymer (CFRP) sheets in shear subjected to elevated temperatures up to 200°C. An experimental program is conducted to examine the effects of high-temperature exposure on the response of constitutive materials, adhesive–concrete interface, and shear repaired beams. All test beams are notched to represent various levels of shear deficiency. A predictive modeling approach is proposed based on classical laminate theory. Elevated temperatures influence the capacity and interfacial characteristics of the repaired beams. Temperature effects, however, are not significantly correlated with the formation of diagonal tension cracks (shear crack) and their propagation rate. Shear resistance of the CFRP is found to be independent of high-temperature exposure because of the load-resisting mechanism associated with crack-plane strains and shear-failure angle.

There are many existing deteriorated steel bridges that need to be retrofitted. This paper investigates the effectiveness of using carbon fiber-reinforced (CFRP) composite systems in retrofitting deteriorated steel beams. A total of 13 medium-scale steel I-beams with a span of 1.6 m was tested in a four-point bending setup. The tested beams were divided into four groups according to their studied parameter. Group 1 consists of four unretrofitted beams with different percentages of artificial deterioration to simulate corrosion in the bottom flange with the aim to investigate their behavior and to determine the residual flexural capacity. The other three groups have deteriorated steel beams that were retrofitted with different CFRP systems with the aim to evaluate the effectiveness of the proposed retrofit schemes. Four deteriorated beams were retrofitted with CFRP sheets bonded to the tension flange and were tested in Group 2. Group 3 consists of two deteriorated steel beams that were retrofitted with CFRP plates externally bonded to the bottom flange of the tested beams. Group 4 consists of three beams retrofitted using an unbonded CFRP sheet attached to two ductile anchorage systems at the beams’ ends. The study shows that steel beams retrofitted with external bonded CFRP systems experienced limited ductility upon the failure of the CFRP either by debonding or rupture at higher load capacities than that of the unretrofitted beams. The proposed anchorage system could increase the strength of the deteriorated beam, behave in a ductile manner, and eliminate the early peel off of the CFRP sheet.

Fiber reinforced polymers (FRP) are increasingly used for repairing corrosion-damaged concrete structures. The performance of the repairs is critically dependent on the oxygen permeability of the FRP-concrete system. This paper presents the results of an experimental study in which the oxygen permeation of concrete and FRP-concrete systems were determined. In the study, concrete specimens with three different water-cementitious ratios were initially tested. Subsequently, uni directional one and two-layer carbon and fiberglass material were bonded to the concrete surface, and the oxygen permeation of the FRP-concrete systems were determined. The results showed a significant reduction in the oxygen permeation of concrete after FRP had been bonded. The best performance was obtained for FRP bonded to concrete with the highest water-cementitious ratio. An expression for the equivalent thickness of FRP-concrete systems was derived by using Fick’s law. This facilitates the evaluation of the effectiveness of alternate FRP-concrete corrosion repair schemes.

Many existing reinforced concrete (RC) substandard structures in seismically active regions, designed and/or constructed improperly or constructed before up-to-date seismic design codes, are in urgent need of seismic retrofitting. Beside financial issues, disturbance to the occupants and functions of the structures are among obstacles for seismic retrofitting. Utilization of fiber reinforced polymer (FRP) composites can reduce disturbance to the occupants and hindrance of the functions of the structures remarkably. In this study, the applicability of flexural seismic retrofitting using carbon FRP precured laminates and rods is investigated experimentally. In seismic retrofitting, the key issue is the effect of reversed cyclic actions, which impose cycles of compression and tension stresses on the FRP reinforcement. Two major issues examined in the study are (1) the anchorage of FRP precured laminates/rods used for cyclic flexural strengthening to the low-strength concrete support (foundation) and (2) the efficiency of the presented flexural seismic retrofit technique for the case of low-strength concrete members subjected to reversed cyclic loading conditions. Furthermore, the flexural strengths of the reference and retrofitted specimens are predicted analitically. The accuracy of the predictions varied depending on the assumed and actual failure modes of the specimens.

The fatigue performance of Reinforced Concrete (RC) beams strengthened using prestressed Near Surface Mounted (NSM) Carbon Fiber Reinforced Polymer (CFRP) strips was evaluated in this paper. Five full-scale RC beams were tested under fatigue loading simulating in-service loading conditions: one control unstrengthened beam and four beams strengthened using NSM-CFRP strips prestressed to 0, 20, 40, and 60% of the CFRP ultimate tensile strength. All beams were subjected to fatigue loading for 3 million cycles at a frequency of 2.0 Hz such that the stress range induced in the tension steel, during the initial cycle, is 125 MPa as specified by the Canadian Highway Bridge Design Code. Experimental test results show that the percentage deflection increase at the end of fatigue loading was almost the same for all beams, which implies that damage accumulation is independent from the prestress level. CFRP strain variation at midspan indicated the occurrence of deboning during the initial cycling of beams prestressed to 0 and 20%, whereas no signs of bond degradation were observed in the other beams. Therefore, prestressing the CFRP strips was shown to enhance the bonding properties and results in an overall CFRP strain increase at the completion of the fatigue loading. For all beams, steel and concrete strains and crack widths at midspan increased rapidly in the initial 500 cycles, followed by stabilized linear increase trends for the rest of the fatigue loading.

In this paper, a detailed procedure for nonlinear finite-element analysis of fiber reinforced polymer (FRP) and textile reinforced mortar (TRM) upgraded reinforced concrete (RC) beam-column exterior joints is presented for predicting their seismic performance under simulated earthquake loading. The finite-element (FE) model was developed using a smeared cracking approach for concrete and three-dimensional layered elements for the FRP and TRM-composites. The results obtained from FE analysis were compared with the test results. The tests were conducted on four as-built exterior beam-column joint specimens under simulated seismic loads. Out of these four specimens, one specimen was tested as a control specimen and the other three were tested after strengthening with TRM, carbon FRP, and glass FRP sheets, respectively. The FE results were compared with the test results through load-displacement behavior, ultimate loads, and crack pattern. Comparison of FE results with the experimentally observed response indicated that the proposed nonlinear FE model can accurately predict the behavior and response of tested RC beam-column joints.

This paper presents the results of an experimental investigation on the performance of full-scale reinforced concrete (RC) T-girders strengthened in shear using externally bonded (EB) fiber-reinforced polymer (FRP) U-jackets end-anchored with different systems. Debonding of FRP, particularly in shear, is a major failure mode when using FRP sheets to strengthen concrete structures. Design code provisions and guidelines related to shear-strengthening of RC beams using externally bonded FRP (EB FRP) suggest the use of end-anchorage systems to prevent FRP debonding. However, no guidelines are available for the design and effectiveness of end-anchorage systems. The main objective of this study is to evaluate the effectiveness of different end-anchorage systems for RC beams strengthened using EB FRP methods. To this end, nine tests were performed on 4520-mm-long RC T-beams. Four specimens were strengthened in shear using EB FRP methods with various end-anchorage systems, and their performance was compared with similar specimens strengthened with: (1) EB FRP with no anchorage; (2) near-surface-mounted (NSM) FRP rods; and (3) embedded through-section (ETS) FRP rods. The results of this study reveal that specimens retrofitted with EB FRP methods and properly designed end-anchorage systems can achieve a superior contribution to shear resistance compared with specimens strengthened using EB FRP with no anchorage, NSM, or ETS methods.

The reversed cyclic loading behavior of full-scale shear wall specimens was investigated before and after retrofit. The wall specimens were designed and detailed to simulate nonductile reinforced concrete construction of the 1960s, having lap splices of the longitudinal reinforcement in the potential plastic hinge region, and having inadequate confinement of the boundary regions. The lap splices in these walls failed in a brittle manner before yielding occurred in the main flexural reinforcement. The use and effectiveness of carbon fiber-reinforced polymer (CFRP) wrap for improving the lap splice behavior and the shear strength of the walls were investigated. The walls were tested under reversed cyclic loading with loading applied near the tip of the walls. The retrofit technique improved the displacement ductility, energy dissipation, and prevented premature failure of the lap splices. The target ductility level of 2.0 was achieved with this CFRP retrofit.

This paper presents test results to show the effect of hot-wet conditioning on the pin-bearing strength of a pultruded fiber-reinforced polymer material. Knowledge of this strength property, taking account of any reduction over the service lives of structures, is required to reliably calculate bearing strength when designing bolted connections. Pin-bearing strength is determined using an in-house test method with batches of nominally identical specimens, cut from the web of a $203\times 203\times 9.53\mathrm{mm}$ wide flange shape. This shape is from the 1525 series of Creative Pultrusions and had a polyester-based matrix. Specimens were immersed before strength testing under water for 3,000 h at the constant temperature of 40° C. This paper presents the accelerated aging protocol and its relation to service life, and an explanation is given as to why the material was aged for an unknown number of service years. Variables in the test matrix are the direction of the bearing force (0, 45, and 90° to the direction of pultrusion) and plain pin diameter (four sizes from 9.7–25.4 mm). Comparing aged pin-bearing strengths with equivalent strengths for nonaged material found that the average reduction in characteristic strength (calculated in accordance with Eurocode 0) of the 12 batches is in the range of 18–31%. The extent of strength reduction is found to be independent of pin size, except when the diameter is 25.4 mm. For the 0° situation, a comparison is made between the characteristic strengths for the four pin diameters determined using BS EN 1990:2002 and ASTM D7290 to show that the latter Weibull distribution values are less by 4–18%.