Journal of Composites for Construction

This paper presents an investigation into the effectiveness of using fiber-reinforced composite overlays to strengthen existing unreinforced masonry walls to resist out-of-plane static loads. A total of fifteen wall panels [1,200 × 1,800 × 200 mm (4 ft × 6 ft × 8 in.)] were tested. Twelve panels were assembled with fiber-reinforcing systems attached to the tension side, and the remaining three control walls were left without any external reinforcement. Two configurations of external reinforcement were evaluated. The first reinforcement configuration consisted of two layers of fiber-reinforced plastic webbing and the second consisted of vertical and horizontal bands of undirectional fiber composites. The three wall specimens without external reinforcement were tested to evaluate the change in the system strength and behavior with application of the external reinforcing systems. In addition to the two fiber configurations, the testing program also evaluated two methods of surface preparation of the walls, sand blasting, and wire brush. All specimens were thoroughly washed by water jet, 48 hours prior to application of the fiber-reinforcing systems. Three specimens were tested for each variable. A uniformly distributed lateral load was applied to each panel using the procedures described in the ASTM Standard E-72 Test Method (airbag). Failure loads, strains in the external reinforcement (FRP), out-of-plane deformations, and failure modes were recorded. Recommendations on the usefulness of the proposed technique as a means of strengthening masonry walls for out-of-plane loads are presented. In general, flexural strength of masonry walls can be increased if the shear failure is controlled.

This paper describes a study on the behavior of fiber-reinforced polymer (FRP) jacketed square concrete columns subjected to eccentric loading. The effect of strain gradient on the behavior of concrete columns confined by the FRP jacket was investigated through experimental and numerical analysis methods. Nine (108 × 108 × 305 mm) square concrete column stubs with zero, one, and two plies of unidirectional carbon FRP fabric were tested under axial compressive loading. In addition to the FRP jacket thickness, the effects of various eccentricities were examined. The nonlinear finite-element analysis results were compared and validated against the experimental test results. The results show that the FRP jacket can greatly enhance the strength and ductility of concrete columns under eccentric loading and that the strain gradient reduces the retrofit efficiency of the FRP jacket for concrete columns. Therefore, a smaller enhancement factor should be used in designing FRP-jacketed columns under eccentric loading. Furthermore, the nonlinear finite-element models established in this study can be used as templates for future research work on FRP-confined concrete columns.

Results are presented of an experimental program undertaken to investigate the effects of strain rate on the behavior of reinforced concrete (RC) beams strengthened with carbon fiber-reinforced polymer (CFRP) laminates. Nine 3-m RC concrete beams, one unstrengthened, four strengthened with S-type CFRP laminates, and four strengthened with R-type laminates, were loaded under four different loading schedules. The stroke rates ranged from 0.0167 mm/s (slow rate of loading) to 36 mm/s (fast rate of loading). This induced a strain rate in the CFRP of 2.96 με/s (slow rate) to 6,930 με/s (fast rate). Some beams were subjected to either 1 or 12 cycles of loading prior to a fast rate of loading to failure. The rapidly loaded beams showed an increase of approximately 5% in capacity, stiffness, and energy absorption. Ductility and the mode of failure were not directly affected by the change in loading rate. Precycled beams performed similarly to the beams loaded monotonically to failure but showed a 10% increase in service stiffness and a 10% loss in energy absorption. A finite-element, layered analysis is presented to predict the moment-curvature response of CFRP strengthened RC beams. The model includes the effects of strain rate and correlates well with the experimental data.

The results of experimental research on brick masonry vaults strengthened at their extrados or at their intrados by fiber-reinforced polymer (FRP) strips is presented here. The presence of the fibers prevents the typical brittle collapse that occurs in a plain arch because of the formation of four hinges; therefore, depending on the position and amount of the reinforcement in the strengthened vaults, three mechanisms are possible: (1) masonry crushing, (2) detachment of the fibers; and (3) sliding along a mortar joint due to the shear stresses. Some first theoretical approaches describing some of these mechanisms are discussed, and the formulation of further models based on the local interaction among the constituent materials is proposed. Six masonry vaults strengthened by glass FRPs or carbon FRPs have been tested. The results have pointed out the enhancement in strength and ductility of the strengthened vaults and the influence in the ultimate strength of the width of the strips and of the bond between the laminate and the masonry.

Fiber-reinforced polymers (FRP) can provide a strengthening alternative for unreinforced and underreinforced masonry. The ease with which FRP can be installed on the exterior of a masonry wall makes this form of strengthening attractive to the owner, considering both reduced installation cost and down time of the occupied structure. Six unreinforced concrete masonry walls (four at 1.8 m tall and two at 4.7 m tall) were tested in out-of-plane flexure up to capacity. The walls were strengthened with glass FRP composite composed of unidirectional E-glass fabric with an epoxy matrix. The composite was adhered to the surface of the masonry using the same epoxy with the fibers oriented perpendicular to the bed joints. General flexural strength design equations are presented and compared with the results of the testing. It was found that the equations overpredicted the actual capacity of the test specimens by no more than 20%.

Fiber-reinforced polymer composites represent an alternative construction material without many of the performance disadvantages of traditional materials. The use of fiber-reinforced polymer as a pile material can eliminate deterioration problems of conventional piling materials in waterfront environments and aggressive soils. This paper presents the preliminary results of an experimental study conducted to assess the durability of piling made of recycled plastics in aggressive soils for long-term usage in civil infrastructure applications. An accelerated testing protocol permitting prediction of the behavior of plastic piles was developed. Specimens were exposed to solutions with fixed acidic, basic, and neutral pH at elevated temperatures. Compressive strength was used as an index to quantify the degradation of the specimens. An Arrhenius model was used to predict the service life of the product.

The results of an analytical and experimental study on the behavior of reinforced concrete T-beams retrofitted with carbon-fiber-reinforced polymer (CFRP) plates are discussed in this paper. CFRP plates were bonded to the underside of the beams with the main objective of increasing the service life load capacity. A test series comprising a prototype beam and six 5-m-long simply supported beams were tested under repeated cyclic and monotonic load conditions to failure. Particular emphasis was given to the development of the CFRP plates and to the behavior of the service and ultimate load ranges. This paper examines variables that have not previously been considered such as the use of staggered plates and the use of plates on beam with curtailed longitudinal steel reinforcement. The effect of diagonal tension cracking is also considered in this study by adapting a simple version of the modified compression field theory into the discrete element method. An important conclusion in this paper is that staggered CFRP plates can be used in lieu of full-length plates when considering flexural strengthening of beams.

The demand for the use of carbon-fiber-reinforced plastics (CFRP) in rehabilitation of deteriorating infrastructure is increasing worldwide. The design characteristics of reinforced concrete or steel members can be enhanced significantly by epoxy bonding CFRP laminates to the critically stressed tension areas. There is, however, a concern regarding possible galvanic corrosion when carbon and steel are bonded together. This paper presents the result of a study on the galvanic corrosion between CFRP laminates and steel. A total of 38 specimens made of steel and carbon fibers were prepared and tested. Two simulated aggressive environments and three different amounts of epoxy coating were used in addition to samples with no coating at all. Furthermore, the effect of the sizing agent on the galvanic corrosion rate was investigated, and three different solvents were used to remove the sizing agents from the surface of the carbon fibers. Potentiodynamic polarization and galvanic corrosion tests were conducted. The results of the experiments showed the existence of galvanic corrosion; however, the rate of such corrosion could be decreased significantly by epoxy coating.