Journal of Composites for Construction

This paper presents the results of a study that was conducted on the sliding behavior of a carbon-fiber-reinforced polymer rod in contact with copper or aluminum sleeves simulating the components of a wedge anchor system. The influence of sandblasting the metal sleeves was related to the displacement and shear stress of the couple for different contact pressures. In general, the interfacial shear stress was found to increase linearly with contact pressure. However, the highest interfacial shear stresses were recorded when sandblasted soft annealed sleeves were used. This effect was the result of a larger contact area which increased the strength of the interface.

This paper presents the flexural behavior of rolled steel beams that were strengthened with partial-length, adhesive-bonded carbon fiber-reinforced polymer (CFRP) plates. The hybrid beams had two types of failure mode, depending on the length of the plate: (1) plate debonding in beams with short plates; and (2) plate rupture at midspan in beams with long plates. The flexural behavior that was investigated includes the development of tensile stresses in the plate, the moment-curvature of the strengthened section, and the load-deflection of the strengthened beam. The analytical methods used include shear lag analysis, section analysis, and application of the virtual work principle. Agreement between the experimental results and the analytical predictions is discussed.

Single-lap and double-lap specimens have been widely used to determine the shear strength of epoxy adhesives for many applications, including mechanical joints and retrofit of wing skins. Although it has been known that the stress state in the adhesive is not uniform in shear, but rather a combined stress state of peeling stress and shear stress, these specimens are useful to determine the bond strength if the application of the adhesive is similar in shape and material properties to the test setup. However, when the application does not have a shape similar to the single-lap or double-lap specimens, the test results of the lap specimens may not be applicable to the practical application. This is often the case for the use of epoxy adhesives in structural engineering applications. In this paper, one example of an application in which a single-lap or double-lap specimen is not appropriate for determination of the bond strength of the epoxy adhesive will be presented. The application of the epoxy adhesive discussed herein involves rehabilitation with bonded carbon fiber-reinforced polymer (CFRP) strips of the tension flanges of fatigued steel I-griders used in bridges. This application provides a cost-effective means of repairing these bridge girders, so long as the effective bond strength of the CFRP and adhesive are sufficient. In this work, the stress distribution in the adhesive layer is analyzed and compared between a prototype repaired bridge girder and various specimen models to determine an appropriate specimen and test setup for assessing the effective bond length of the adhesive. This study points out the strengths and weaknesses of standard single-lap and double-lap specimens and proposes that the new test setup is a suitable alternative for a wide range of applications in which the adherend is subjected to tension plus flexure.

Strengthening concrete girders with fiber-reinforced polymers (FRP) is becoming an increasingly common practice as more research investigations are favorably qualifying the technique. However, important behavioral aspects, such as fatigue in prestressed concrete beams, are yet to be adequately evaluated. An experimental program was conducted to test five pretensioned, prestressed concrete T beams designed for specific prestressing strand stress ranges under live-load conditions. The experimental testing consisted of precracking the beams, strengthening them with carbon FRP, and mechanically loading them to study the effect of increasing the live load on strand fatigue. The beams were either loaded monotonically to ultimate capacity or cyclically fatigued and then loaded monotonically to failure. All the beams were monotonically loaded past their cracking moment at midspan prior to strengthening, to simulate girders in the field. Beam 1 was tested as a control specimen under static loading up to failure. Beams 2 and 3 were strengthened with carbon FRP to have a design stress range of 124 MPa (18 ksi) under service load condition. Beams 4 and 5 were strengthened to have a higher stress range of 248 MPa (36 ksi). For all the strengthened beams, the failure mode observed was FRP rupture. The results favorably qualify the application of FRP strengthening to increase the live load of concrete beams prestressed with straight strands.

Hollow bridge piers are currently being used in high-speed rail and highway projects in Taiwan. The flexural ductility and shear capacity of such piers with the configuration of lateral reinforcement used in Taiwan has recently been studied. This paper reports that circular and rectangular hollow bridge piers retrofitted by carbon fiber-reinforced polymer (CFRP) sheets were tested under a constant axial load and a cyclic reversed horizontal load to investigate their seismic behavior, including flexural ductility, dissipated energy, and shear capacity. An analytical model is also developed to predict the moment-curvature relationship of sections and the lateral load-displacement relationship of piers. Based on the test results, the seismic behavior of such piers is presented. The test results are also compared with the proposed analytical model. It was found that the ductility factors of the tested piers ranged from 3.3 to 5.5 and that the proposed analytical model could predict the lateral load-displacement relationship of such piers with reasonable accuracy. All in all, CFRP sheets can effectively improve both the ductility factor and the shear capacity of hollow bridge piers.

Fiber-reinforced polymer (FRP) composites have largely been used in combination with masonry and concrete structural elements in the last decade. Recent applications showed that new advantages may also be achieved in the field of timber structures, even if currently steel fasteners are used mainly in connecting systems. This study investigated the possibility of using carbon FRP (CFRP) rods as glued-in reinforcement of glulam beams and as glued-in connectors for glulam timber head joints that should transfer flexural moment between two adjacent beams. Half-scale beams were tested both with and without the presence of FRP reinforcement. Flexural behavior of CFRP-reinforced beams was compared with unreinforced beams that were used as control specimens. Two different amounts of CFRP reinforcement were used in the beam section. Experimental results showed a significant influence of the CFRP rods, because the reinforced beams demonstrated an increase in ultimate capacity and stiffness. Experimental results were also compared with numerical analysis, which showed good accordance with regard to the load and deflection values. Full-size head joints were prepared and tested. Flexural behavior of the joints was compared with the mechanical properties of monopiece beams that were used as reference specimens. Three different force transfer lengths were used for the construction of CFRP-timber joints. Experimental results showed that the use of CFRP rods in timber joints was successful, because the capacity of the CFRP-jointed beams was almost the same as that of the monolithic beams for the longest bond length that was adopted. This result is important in order to find an adequate alternative to traditional joints made with steel bolts and plates, which are unable to create rigid connections, increase dramatically the weight of timber structures, and may be subjected to corrosion in an aggressive environment. A numerical modeling based on the virtual work principle was also conducted and theoretical results were found in good accordance with the experimental results for the tested joint.

In this investigation, $90\text{-}\mathrm{cm}$ -long plain concrete beam specimens reinforced with externally bonded wet-laid glass fiber reinforced-polymer sheets are investigated. The specimens are precracked with a three point flexural load, subjected to a constant four point flexural load of about 25% of the initial ultimate moment, and placed into different environmental conditions. The four environmental conditions under investigation are indoor laboratory, outdoor, elevated temperature/dry, and freeze/thaw. By varying the exposure time in different environments and using the photoelastic coating method to evaluate strain distributions, the durability of the externally reinforced concrete beams is evaluated. An innovative approach based on fracture mechanics and local bond shear stress-slip relationships is proposed to explain the degradation mechanism. This approach is capable of qualitatively and quantitatively characterizing the environmental effect in terms of the parameters of the shear stress-slip law. Four one-dimensional shear stress-slip relationships are evaluated in terms of their ability to model the environment-dependent strain distribution and debond data obtained in the present investigation.

This paper describes the behavior of hybrid girders consisting of fiber-reinforced polymer (FRP) bridge decks adhesively connected to steel main girders. Two large-scale girders were experimentally investigated at the serviceability and ultimate limit state as well as at failure. One of the girders was additionally fatigue loaded to 10 million cycles. Compared to the behavior of a reference steel girder, deflections of the two girders at the SLS were decreased by 30% and failure loads increased by 56% due to full composite action in the adhesive layer. A ductile failure mode occurred: Deck compression failure during yielding of the steel girder. The adhesive connections were able to prevent buckling of the yielding top steel flanges. Thus, compared to the reference steel girder, the maximum deflections at failure could be increased up to 130%. No deterioration due to fatigue loading was observed. Based on the experimental results, a conceptual design method for bonded FRP/steel girders was developed. The proposed method is based on the well-established design method for hybrid girders with concrete decks and shear stud connections. The necessary modifications are proposed.

Ballistic impact testing was carried out on panels of both S-2 glass/epoxy system and graphite/epoxy laminates with and without polycarbonate facing. Both the striking velocity and exit velocity were measured using magnetic sensors. The energy absorbed and the ballistic limit for each specimen were calculated using the principal of conservation of momentum. The Florence model was adopted in making theoretical prediction for the absorbed energy and the ballistic limit. The bicomponent composites have demonstrated potential concepts that can provide protection for the shelter against ballistic penetrations.