Abstract: The strengthened effectiveness and the performance capacity of repaired Reinforced Concrete (RC) structures with Carbon Fibre Reinforced Polymer (CFRP) sheets is dependent on the properties of the adhesive interface layer. Adhesive material requires a specific setting time to achieve the maximum design capacity. Adhesive producer provides technical data which demonstrates the increase with time of the capacity, up to the maximum. The aim of this study is to investigate the effect of the adhesive setting time on the modal parameters as an indication of the effectiveness of CFRP on repaired RC beams. Firstly, datum modal parameters were determined on the undamaged beam and subsequently the parameters were obtained when damaged was induced on the RC beam by application of load until the appearance of the first crack. Finally, the RC beam is repaired with externally bonded CFRP sheets, and modal parameters are once again applied after 0.5, 1, 2, 3, 5, 8, 11, 15 and 18 days. The comparison is made with the data based on half day results in order to monitor the change in the modal parameters corresponding to the adhesive setting time. The modal parameters where used as indicators for the effectiveness of CFRP are affected by the adhesive time as shown in this study. Results are compared with the adhesive technical data provided by the adhesive producer.
Abstract: This paper presents a study to determine the effectiveness of Carbon Fiber Reinforced Polymer (CFRP) sheets as a flexural repair system for Reinforced Concrete (RC) beams. The effectiveness of these sheets is ascertained by monitoring the flexural stiffness recovery. Experimental work is conducted on scaled beams where four beams are used as the datum. The first beam is without CFRP sheets, the second is a repaired beam after pre-damaged under design load limit, whilst the third is a repaired beam after pre-damaged under steel yield load limit, and the fourth is a repaired beam after pre-damaged under ultimate load. Comparisons are made based on the flexural stiffness recovery, crack patterns, load capacity, and failure modes of the beams. The study validates the ability of the flexural stiffness change in order to monitor the effect of the damage as well as the effectiveness of the repair on stiffness recovery. The results prove the effectiveness of the CFRP sheets as a repair technique which increases the flexural stiffness and the ultimate load capacity whatever the pre-repair damage levels. In addition, this study indicates the ability of re-repairing the beams in the case of CFRP debonding. The failure modes are controlled by the pre-repair damage flexural crack wherein it causes the CFRP debonding.
Abstract: This article presents a statistical analysis of the design methods for calculating the load-carrying capacity of reinforced concrete elements in flexure strengthened with external FRP reinforcement. To perform calculations a database of experimental research has been created. Calculations of the load-carrying capacity were performed following the ACI440.2R-08, fib bulletin 14, TR55 recommendations. Distribution of experimental and theoretical results was determined on the basis of Wilk–Shapiro test. The evaluation of design methods was done by testing the statistical hypotheses on the difference of the means of the ratio between the experimental and theoretical results. Confidence intervals of the ratios of the experimental and calculated load carrying capacity were also calculated. In order to assess the accuracy of the design methods it is suggested to calculate the coefficient of confidence.
Abstract: This paper presents an experimental assessment of the repair effectiveness of Carbon Fibre Reinforced Polymer (CFRP) laminate for damaged Reinforced Concrete (RC) beams with a circular web opening at the shear zones. The study highlights the effect of the opening diameter on CFRP repair effectiveness by examining the effect on the ultimate load capacity, deflection, steel strain, CFRP laminate strain and failure modes. In the experimental programme, a total of four beams were used inclusive of one solid beam used as a control beam. The other three beams were designed with different opening diameters and were exposed to damage at the pre-repair stage, up to their ultimate capacity. Damaged beams were repaired using externally bonded CFRP laminate around the openings. The results concluded that the CFRP laminate repair system was effective regardless of the web opening diameter. It was found that the increase in the opening diameter resulted in a higher deflection as well as higher strain values for the mid-span reinforcement and shear stirrups. The CFRP repaired beams behaviour transformed from brittle at the pre-repair stage to ductile at the post-repair stage. The failure mode of the CFRP repaired beams with a smaller opening diameter changed from shear failure to flexural failure, while the larger opening diameter beams failure mode was governed by CFRP deboning at the shear zone.
Abstract: The paper deals with results of experimental research on cement glue mortars containing non-milled fly ash and organic–mineral modifiers are given. The organic–mineral modifiers (OMM) include finely dispersed additives like microsilica or milled fly ash and organic substances (naphthalene formaldehyde superplasticizers and redispersed polymers). Glue cement mortars, modified by OMM additives allow reducing Portland cement consumption, stabilizing and improving the mortars’ properties, especially their adhesive and cohesive strength. The influence of the modifier compositions on the strength parameters of mortars for masonry stone walls, facing by ceramic tiles or gluing heat isolation materials was studied. The experimental results show that as the silica additives dispersion is higher the positive effect on adhesive and cohesive strength increases. Optimal content of modifiers in mortars is obtained.
Abstract: Both modal analysis procedure and the results obtained on a three-component 3D-printed carbon-fiber reinforced composite (CFRC) are presented. Experimental modal analysis of on the composite has been carried out to obtain the dynamic behavior characteristics. As revealed, the different eigen-oscillations waveforms possess different sensitivity of its amplitude frequency response to structural defects of the composite. For the similar waveforms we observed the differences in eigen-oscuillation frequencies, vibration velocities and damping factors which can be caused by the presence of numerous defects homogeneously distributed in one of the samples.
Cites background from "Assessment of adhesive setting time..."
...Even more difficulties arise in manufacturing the structural units from fiber reinforced composites [1-3], in particular, there is a risk of forming defects such as delamination, disbanding and the lack of resin in the fiber cross zones....
Abstract: *Co-chairs of the subcommittee that prepared this document. Note: The committee acknowledges the contribution of associate member Paul Kelley. ACI encourages the development and appropriate use of new and emerging technologies through the publication of the Emerging Technology Series. This series presents information and recommendations based on available test data, technical reports, limited experience with field applications, and the opinions of committee members. The presented information and recommendations, and their basis, may be less fully developed and tested than those for more mature technologies. This report identifies areas in which information is believed to be less fully developed, and describes research needs. The professional using this document should understand the limitations of this document and exercise judgment as to the appropriate application of this emerging technology.
Abstract: The present paper illustrates the results of an experimental program on Reinforced Concrete (RC) beams externally strengthened with carbon Fibre Reinforced Plastic (FRP) laminates and Near Surface Mounted (NSM) bars under monotonic and cyclic loads, the latter ones characterized by a low number of cycles in the elastic and post-elastic range. Comparisons between experimental and theoretical failure loads are discussed in detail.
Abstract: Beams and slabs externally reinforced with FRP are often in contact with moisture and temperature cycles that reduce the expected durability of the system. Bond degradation is a frequent cause of premature failure of structural elements and environmental conditions are known to relate to such failures. The study shows the effects of cycles of salt fog, temperature and moisture as well as immersion in salt water on the bending response of beams externally reinforced with GFRP or CFRP, especially on bond between FRP reinforcement and concrete. Temperature cycles (−10 °C; 10 °C) and moisture cycles were associated with failure in the concrete substrate, while salt fog cycles originated failure at the interface concrete–adhesive. Immersion in salt water and salt fog caused considerable degradation of bond between the GFRP strips and concrete. However, immersion did not lower the load carrying capacity of beams, unlike temperature cycles (−10 °C; 10 °C) that caused considerable loss. No significant differences were detected on the behavior of the systems strengthened with GFRP and CFRP, perhaps because the design of the tests impeded failure of the fibres.
Abstract: An experimental assessment of several vibration based statistical time series methods for Structural Health Monitoring (SHM) is presented via their application to a lightweight aluminum truss structure. A concise overview of the main non‐parametric and parametric methods is provided, including response‐only and excitation‐response schemes. Damage detection and identification is based on univariate (scalar) versions of the methods, while results for three distinct vibration mea surement positions on the structure are presented. The methods’ effectiveness is assessed via multiple experi ments under various damage scenarios. The results of the study confirm the high potential and effectiveness of s tatistical time series methods for SHM.
Abstract: Fire related structural degradation is a challenge to the safe design of structural members. Carbon fibre reinforced polymer (CFRP) strengthened concrete members show degradation of bond properties with temperature. Therefore, a detailed investigation of heat effects on composites is required before further application of this system can be effective. This paper focuses on a 3D model developed to predict the behaviour of CFRP–concrete composites under fire. Heat transfer analysis was employed to predict the temperature within the adhesive layer of epoxy, which is the most critical part of the member at high temperature. The model showed that the epoxy reached the failure point within a short time under standard fire. The model was also used to predict the required insulation thickness requirement for two-hour and three-hour fire resistance levels. The effects of rate of temperature increase on bond strength of composite structures are demonstrated through numerical analysis. The model results were validated with experimental data.