International Concrete Abstracts Portal

This paper presents a closed-form procedure to evaluate the shear strength contribution provided to a Reinforced Concrete (RC) beam by a system of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips. This procedure is based on the evaluation of: a) the constitutive law of the average-available-bond-length NSM FRP strip effectively crossing the shear crack and b) the maximum effective capacity it can attain during the loading process of the strengthened beam. Once the constitutive law of the average-available-bond-length NSM strip is reliably known, its maximum effective capacity can be determined by imposing a coherent kinematic mechanism. The self-contained and ready-to-implement set of analytical equations and logical operations is presented along with the main underlying physical-mechanical principles and assumptions. The formulation proposed is appraised against some of the most recent experimental results and its predictions are also compared with those obtained by a recently developed more sophisticated model.

Retrofitting of existing concrete structures and civil infrastructure has become necessary due to environmental degradation, changes in usage and heavier loading conditions. The use of advanced carbon fiber composite materials (CFRP) as externally bonded reinforcement has found wide application in recent years and has proven to be an effective method of improving the structural performance of existing structures. A good example of this is the West Gate Bridge in Melbourne, Australia for which the following case study is presented. Key innovations in CFRP technology developed specifically for this project have been described in the areas of design and testing of CFRP anchorage technology, involving the utilization of unidirectional and bidirectional fabrics together with mechanical substrate strengthening. These have all resulted in increases in material utilizations and enabled successful transfer of combined shear and torsional forces. Key aspects of the detailing, application, quality control and monitoring program adopted in the project are also presented along with the key aspects which resulted in the successful execution of this world class project.

This paper presents the development of composite beams using hybrid CFRP/GFRP (HFRP) I-beam and Normal Strength Concrete (NSC) slab and precast Ultra-High Performance fiber reinforced Concrete (UHPFRC) slab. UHPFRC has high strength and high ductility allowing for a reduction in the cross-sectional area and self weight of the beam. A number of full-scale flexural beam tests were conducted using different dimensions of slab and with/without epoxy bonding between the slab and HFRP I-beam. The test results suggested that the flexural stiffness of composite beams with bolted and bonded shear connection is higher than that with bolted-only shear connection. Delamination failure was not observed in the compressive flange of the HFRP I-beam and the high tensile strength of CFRP in the bottom flange was effectively utilized with the addition of the UHPFRC slab on the top flange.

FRP Uwraps have been successfully used for shear strengthening of concrete structures; by contrast, few studies have focused on the use of the Uwrap as an anchorage system for FRP flexure strengthening. This study focuses on exploring the limitations and advantages of using non-contact measuring techniques, such as digital image correlation (DIC) and thermography, to characterize the deformation of FRP Uwrap anchors. Digital and thermo images were used to evaluate the slip profiles and debonding propagation of FRP Uwrap anchors on a pull-out test configuration. Results indicated that the geometry of the Uwrap plays an important factor in controlling the delay or arrest of the debonding propagation of the externally bonded FRP sheet. The DIC technique was capable to accurately measure slip along the bonded FRP sheet whereas the thermography technique was successful at capturing the debonding propagation (in two directions), as well as the locations of stress concentrations and fractured areas.

This paper examines the pre-application of a waterproofing slurry overlay on the performance of bonded CFRP strengthening systems. Overall, the waterproofed specimens experienced an undesirable bond failure between the adhesive and waterproofing coating and/or concrete substrate and less flexural capacity compared to the control specimen with only the CFRP composite. The control performed at a higher strength and resulted with concrete substrate failure. Due to the influence of moisture during the waterproofing slurry system application, further experimentation was performed to isolate the effect of moisture in the concrete specimens and its effects on the adhesive component as a performance factor. The moisture tests resulted in bond failures and lower strength capacities. The waterproofing application was altered relative to the manufacturer’s recommendations to accommodate an on-site construction protocol. Future research will vary curing time, active waterproofing compound, and on-site construction prior to applying the CFRP composite system to further improve performance.