Yes / Tests results of three flanged and two rectangular cross-section concrete beams reinforced with carbon fibre reinforced polymer (CFRP) bars are reported. In addition, a companion concrete flanged beam reinforced with steel bars is tested for comparison purposes. The amount of CFRP reinforcement used and flange thickness were the main parameters investigated in the test specimens. One CFRP reinforced concrete rectangular beam exhibited concrete crushing failure mode, whereas the other four CFRP reinforced concrete beams failed due to tensile rupture of CFRP bars. The ACI 440 design guide for FRP reinforced concrete members underestimated the moment capacity of beams failed due to CFRP tensile rupture and reasonably predicted deflections of the beams tested. A simplified theoretical analysis for estimating the moment capacity of concrete flanged beams reinforced with FRP bars was developed. The experimental moment capacity of the CFRP reinforced concrete beams tested compared favourably with that predicted by the theoretical analysis developed.

Excellent properties of Carbon Fiber Reinforced Polymer (CFRP) composites are usually obtained in the direction at which carbon fibers are embedded in the polymeric matrix material. The outstanding properties of this material such as high strength to weight ratio, high stiffness and high resistance to corrosion can be tailored to meet specific design applications. Despite their excellent mechanical properties, application of CFRPs has been limited to more lucrative sectors such as aerospace and automotive industries. This is mainly due to the high costs involved in manufacturing of this material. Machining, milling and drilling, is a critical part of finishing stage of manufacturing process. Milling and drilling of CFRP is complicated due to the inhomogeneous nature of the material and extreme abrasiveness of carbon fibers. This is why CFRP parts are usually made near net shape. However, no matter how close they are produced to the final shape, there still is an inevitable need for some post machining to obtain dimensional accuracies and tolerances. Problems such as fiber-matrix debonding, subsurface damage, rapid tool wear, matrix cracking, fiber pull-out, and delamination are usually expected to occur in machining CFRPs. These problems can affect the dimensional accuracy and performance of the CFRP part in its future application. To improve the efficiency of the machining processes, i.e. to reduce the costs and increase the surface quality, researchers began studying machining Fiber Reinforced Polymer (FRP) composites. Studies into FRPs can be divided in three realms; analytical, experimental and numerical. Analytical models are only good for a limited range [0° – 75°] of Fiber Orientations , to be found from now on as “FO” in this thesis. Experimental studies are expensive and time consuming. Also, a wide variety of controlling parameters exist in an experimental machining study; including cutting parameters such as depth of cut, cutting speed, FO, spindle speed, feed rate as well as tool geometry parameters such as rake angle, clearance angle, and tool edge/nose radius. Furthermore, the powdery dust created during machining is known to cause serious health hazards for the operator. Numerical models, on the other hand, offer the unique capability of studying the complex interaction between the tool and workpiece as well as chip formation mechanisms during the cut. Large number of contributing parameters can be included in the numerical model without wasting material. Three main objectives of numerical models are to predict principal cutting force, thrust force and post-machining subsurface damage. Knowing these, one can work on optimization of machining process by tool geometry and path design. Previous numerical studies mainly focus on the orthogonal cutting of FRP composites. Thus, the existing models in the literature are two-dimensional (2D) for the most part. The 2D finite element models assume plain stress or strain condition. Accordingly, the reported results cannot be reliable and extendable to real cutting situations such as drilling and milling, where oblique cutting of the material occurs. Most of the numerical studies to date claim to predict the principle cutting forces fairly acceptable, yet not for the whole range of fiber orientations. Predicted thrust forces, on the other hand, are generally not in good agreement with experimental results at all. Subsurface damage is reported by some experimental studies and again only for a limited FO range. To address the lack of reliable force and subsurface damage prediction model for the whole FO range, this thesis aims to develop a 3D finite element model, in hope of capturing out-of-plane displacements during stress formation in different material phases (Fiber, Matrix and the Interface bonding). ABAQUS software was chosen as the most commonly used finite element simulation tool in the literature. In present work a user-defined material subroutine (VUMAT) is developed to simulate behavior of carbon fibers during the cut. Carbon fibers are assumed to behave transversely isotropic with brittle (perfectly elastic) fracture. Epoxy matrix is simulated with elasto-plastic behavior. Ductile and shear damage models are also incorporated for the matrix. Surface-based cohesive zone technique in ABAQUS is used to simulate the behavior of the zero-thickness bonding layer. The tool is modeled as a rigid body. Mechanical properties were extracted from the literature. The obtained numerical results are compared to the experimental and numerical data in literature. The model is capable of capturing principal forces very well. Cutting force increases with FO from zero to 45° and then decreases up to 135°. The simulated thrust forces are still underestimated mainly due to the fiber elastic recovery effect. Also, the developed 3D model is shown to capture the subsurface damage generally by means of a predefined dimensionless state variable called, Contact Damage (CSDMG). This variable varies between zero to one. It is stored at each time step and can be called out at the end of the analysis. It was shown that depth of fiber-matrix debonding increases with increase in FO. / Graduate

yes / This paper presents test results of six concrete beams reinforced with longitudinal carbon fiber reinforced polymer (CFRP) bars and without vertical shear reinforcement. All beams were tested under a two-point loading system to investigate shear behavior of CFRP reinforced concrete beams. Beam depth and amount of CFRP reinforcement were the main parameters investigated. All beams failed due to a sudden diagonal shear crack at almost 45°. A simplified, empirical expression for the shear capacity of FRP reinforced concrete members accounting for most influential parameters is developed based on the design-by-testing approach using a large database of 134 specimens collected from the literature including the beams tested in this study. The equations of six existing design standards for shear capacity of FRP reinforced concrete beams have also been evaluated using the large database collected. The existing shear design methods for FRP reinforced concrete beams give either conservative or unsafe predictions for many specimens in the database and their accuracy are mostly dependent on the effective depth and type of FRP reinforcement. On the other hand, the proposed equation provides reasonably accurate shear capacity predictions for a wide range of FRP reinforced concrete beams.

Yes / This paper reports the testing of five reinforced concrete continuous beams strengthened in flexure with externally bonded carbon-fibre-reinforced polymer (CFRP) laminates. All beams had the same geometrical dimensions and internal steel reinforcement. The main parameters studied were the position and form of the CFRP laminates. Three of the beams were strengthened using different arrangements of CFRP plate reinforcement, and one was strengthened using CFRP sheets. The performance of the CFRP-strengthened beams was compared with that of an unstrengthened control beam. Peeling failure was the dominant mode of failure for all the strengthened beams tested. The beam strengthened with both top and bottom CFRP plates produced the highest load capacity. It was found that the longitudinal elastic shear stresses at the adhesive/concrete interface calculated at beam failure were close to the limiting value recommended in Concrete Society Technical Report 55.

No / Although several research studies have been conducted on simply supported concrete elements reinforced with fibre reinforced polymer (FRP) bars, there is little reported work on the behaviour of continuous elements. This paper reports the testing of four continuously supported concrete slabs reinforced with carbon fibre reinforced polymer (CFRP) bars. Different arrangements of CFRP reinforcement at mid-span and over the middle support were considered. Two simply supported concrete slabs reinforced with under and over CFRP reinforcement and a continuous concrete slab reinforced with steel bars were also tested for comparison purposes. All continuous CFRP reinforced concrete slabs exhibited a combined shear–flexure failure mode. It was also shown that increasing the bottom mid-span CFRP reinforcement of continuous slabs is more effective than the top over middle support CFRP reinforcement in improving the load capacity and reducing mid-span deflections. The ACI 440.1R–06 formulas overestimated the experimental moment at failure but better predicted the load capacity of continuous CFRP reinforced concrete slabs tested. The ACI 440.1R–06, ISIS–M03–07 and CSA S806-06 design code equations reasonably predicted the deflections of the CFRP continuously supported slabs having under reinforcement at the bottom layer but underestimated deflections of continuous slabs with over-reinforcement at the bottom layer.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This study set out to determine the debonding of externally applied Carbon Fibre Reinforced Polymer (CFRP) plates from RC structures under cyclic loading. Triplet shear tests and finite element (FE) analyses were done on the epoxy to determine the bond stress between the CFRP plate and a reinforced concrete specimen. From these tests and analyses the average shear strength of the bond between the epoxy and concrete substrate was determined and the shear strength of the epoxy specified by the supplier could be confirmed. A case study of a statically loaded beam was performed to verify the bond strength. Finally a reinforced concrete (RC) T-section was designed and pre-cracked to simulate a damaged beam in practice. These sections were then externally reinforced by bonding CFRP plates onto the face of the web. The sections were subjected to static and cyclic loading at different force amplitudes. Along with the experimental tests, FE models were developed and analysed which had the same geometrical and material properties as the experimental specimens. Due to time constraint a FE mesh objectivity study was not done, but the chosen element size is believed to be sufficiently small to replicate the experimental tests objectively. The FE analyses and the experimental tests yielded results that were close to each other on both the global scale and in terms of localised behaviour, thus it was decided that the computational approach could be used for the final design of a model of the debonding of CFRP plates bonded onto RC beams under cyclic loading because the data can be analysed more easily and a large variation of tests can be done. For the T-section 3 tests were conducted; a pull-off (static) test where the bonded CFRP plate was pulled from a specimen to get the ultimate failure envelope of the test specimens. The static test was followed by cyclic tests with force amplitude of 85% and 65% of the ultimate pull-off strength. Different measurements were taken to get the global and local displacement behaviour of the section. The global displacement was measured by means of a linear variable displacement transducer (LVDT, displacement meter) clamped onto the CFRP plate that pushed on the top of the concrete and the local displacement was measured with the help of the Aramis system. The displacement was then compared to the same displacements of nodes and elements in the FE models. The result was a confirmation that the results from the FE models were sufficient to design a model for cyclic debonding of CFRP plates from RC structures. From the FE models the relative displacement between the CFRP plate and concrete was obtained in the vicinity of a crack. This relative displacement was then normalised by the respective stress range of the different tests, from which the normalised relative displacement was plotted against the number of cycles to get an equation limiting the number of cycles for a specific stress range. From the results, it appears that for cyclic load levels up to 65% of the peak static resistance, a threshold number of load cycles are required for delamination initiation. Subsequently, a near constant delamination rate is reached. The delamination rate is significantly lower for lower cyclic load levels. Finally, an unstable delamination stage is reached at a level of about 65 μm for all the analyses, after which CFRP pull-off is imminent. Service life design of CFRP reinforcement of RC beams should take into consideration the delamination initiation threshold, the subsequent delamination rate and finally the initiation of unstable delamination. / AFRIKAANSE OPSOMMING: Die projek is uitgevoer om die delaminasie van ekstern aangewende Koolstof Vesel Versterkte Polimeer (KVVP) stroke op gewapende beton strukture te bepaal onder sikliese belasting. Triplet skuif toetse is gedoen op die gebruikte epoksie om die verband-sterkte te bepaaltussen die KVVP stroke en die beton proefstuk. Die skuif toetse is ook met behulp van die eindige element (EE) metode geanaliseer. Die resultaat van die toetse en analises het gewys dat die verband sterkte tussen die KVVP stroke en beton gelyk is aan die skuif sterkte van die epoksie wat verskaf is. `n Gevalle studie van `n monotonies belaste balk is gedoen om die verband-sterkte te verifieër. `n Gewapende beton T-snit is ontwerp en voor-af gekraak om `n beskadigde balk in die praktyk voor te stel. Die beskadigde proefstukke is vervolgens ekstern versterk met KVVP stroke wat aan die web van die T-snit vas geplak is. Die versterkte T-snitte is getoets onder statiese en sikliese belasting. Die sikliese toetse is ook onder verskillende spanningsamplitudes getoets. Om die eksperimentele toetse te verifieër is EE modelle gebou en geanaliseer wat dieselfde geometriese en materiaal eienskappe as die eksperimentele proefstukke gehad het, maar as gevolg van `n tydsbeperking is `n sensitiwiteit studie oor die element grootte nie gedoen nie. Die element grootte is klein genoeg gekies en word beskou as voldoende om die gedrag objektief te simuleer. Die EE analises en eksperimentele resultate was na genoeg aan mekaar op beide globale en lokale vlak. Dus is `n analitiese benadering tot die toetse vervolgens gebruik vir die ontwerp van `n model vir delaminasie van KVVP stroke van gewapende beton strukture onder sikliese belasting. Die EE metode stel die analis in staat om `n verskeidenheid van toetse relatief vinnig uit te voer en om die data van die toetse vinniger te interpreteer as deur fisiese eksperimentele toetse. Drie eksperimente is uitgevoer op die T-snitte, `n aftrek-toets (staties) waar die KVVP strook van `n proefstuk afgetrek is om die falingsomhullende diagram te kry en dan ook twee sikliese toetse teen 85% en 65% van die krag amplitude van die falingskrag. Verplasingsmeters is gebruik om die globale verplasing te kry, deur dit vas te klamp op die KVVP strook en dan die verplasing te meet relatief tot die bokant van die beton. Die lokale veplasing is met behulp van die Aramis sisteem verkry. Die eksperimentele verplasings is dan vergelyk met verplasings van die ooreenstemmende nodes en elemente in die EE modelle. Deur die vergelyking van die resultate is dit bevestig dat die eindige element modelle voldoende is om die model vir sikliese delaminasie van KVVP stroke van gewapende beton strukture te gebruik vir die ontwerp. Uit die EE modelle is die relatiewe verplasing tussen die KVVP strook en die beton gekry in die omgewing van `n kraak. Die relatiewe verplasing is genormaliseer deur elkeen se spanningsamplitude. Die genormaliseerde relatiewe verplasing is dan teenoor die aantal siklusse geteken waarvan `n vergelyking vir die maksimum verplasing afgelei is om die aantal siklusse vir `n gegewe spanning amplitude te beperk. Uit die resultate blyk dit dat vir sikliese laste tot en met 65% van die piek statiese weerstand `n aantal siklusse moontlik is voordat delaminasie begin waarna `n konstante delaminasie tempo bereik word. Die delaminasie tempo is stadiger vir sikliese laste teen `n laer belastings amplitude. Laastens word `n onstabiele delaminasie fase bereik by `n vlak van ongeveer 65 μm, na die oorgang delamineer die KVVP strook binne enkele siklusse. Die beginpunt van delaminasie, die delaminasie tempo en laastens die begin van onstabiele delaminasie moet in gedagte gehou word by die ontwerp diens leeftyd van KVVP versterkte gewapende beton balke.

An investigation on the application of basalt fibre reinforced polymer (BFRP) and carbon fibre reinforced polymer (CFRP) bars as longitudinal reinforcement for simple and continuous concrete slabs is presented. Eight continuously and four simply concrete slabs were constructed and tested to failure. Two continuously supported steel reinforced concrete slabs were also tested for comparison purposes. The slabs were classified into two groups according to the type of FRP bars. All slabs tested were 500 mm in width and 150 mm in depth. The simply supported slabs had a span of 2000 mm, whereas the continuous slabs had two equal spans, each of 2000 mm. Different combinations of under and over FRP (BFRP/CFRP) reinforcement at the top and bottom layers of slabs were investigated. The continuously supported BFRP and CFRP reinforced concrete slabs exhibited larger deflections and wider cracks than the counterpart reinforced with steel. The experimental results showed that increasing the bottom mid-span FRP reinforcement of continuous slabs is more effective than the top over middle support FRP reinforcement in improving the load capacity and reducing mid-span deflections. Design guidelines have been validated against experimental results of FRP reinforced concrete slabs tested. ISIS-M03-07 and CSA S806-06 equations reasonably predicted the deflections of the slabs tested. However, ACI 440-1R-06 underestimated the deflections, overestimated the moment capacities at mid-span and over support sections, and reasonably predicted the load capacity of the continuous slabs tested. On the analytical side, a numerical technique consisting of sectional and longitudinal analyses has been developed to predict the moment-curvature relationship, moment capacity and load-deflection of FRP reinforced concrete members. The numerical technique has been validated against the experimental test results obtained from the current research and those reported in the literature. A parametric study using the numerical technique developed has also been conducted to examine the influence of FRP reinforcement ratio, concrete compressive strength and type of reinforcement on the performance of continuous FRP reinforced concrete slabs. Increasing the concrete compressive strength decreased the curvature of the reinforced section with FRP bars. Moreover, in the simple and continuous FRP reinforced concrete slabs, increasing the FRP reinforcement at the bottom layer fairly reduced and controlled deflections.

The performance of reinforced concrete (RC) columns during recent earthquakes has clearly demonstrated the possible failures associated with inadequate confining reinforcement. The confinement reinforcement requirements of older codes were less stringent than present standards. Many studies were conducted by applying different retrofitting techniques for RC columns that have inadequate confinement reinforcement. A new retrofitting technique by means of Carbon Fiber Reinforced Polymer (CFRP) was developed and tested in many countries in the last decade. This technique is performed by CFRP wrapping the critical region of columns. The effectiveness of CFRP retrofitting technique was shown in many studies conducted worldwide. In Turkey, the frame members are considerably deficient from the seismic detailing point of view. Therefore, in order to use the CFRP retrofitting technique effectively in Turkey, experimental evidence is needed. This study investigates the performance of CFRP retrofitted RC columns with deficient confining steel and low concrete strength. It was concluded by experimental and analytical results that the CFRP retrofitting method can be implemented to seismically deficient columns. Moreover, two design approaches were proposed for CFRP retrofit design of columns considering safe design regulations.

Due to inadequate lateral stiffness, many reinforced concrete buildings are highly damaged or collapsed in Turkey after the major earthquake. To improve the behavior of such buildings and to prevent them from collapse, repair and/or strengthening of some reinforced concrete elements is required. One of the strengthening techniques is the use of CFRP sheets on the existing hollow brick masonry infill. While using the CFRP sheets their attachment to both structural and non-structural members are provided by CFRP anchor dowels. In this study, by means of the prepared test setup, the pull-out strength capacities of CFRP anchor dowels are measured. The effects of concrete compressive strength, anchorage depth, anchorage diameter, and number of fibers on the tensile strength capacity of CFRP anchor dowel are studied.

An investigation on the application of basalt fibre reinforced polymer (BFRP) and carbon fibre reinforced polymer (CFRP) bars as longitudinal reinforcement for simple and continuous concrete slabs is presented. Eight continuously and four simply concrete slabs were constructed and tested to failure. Two continuously supported steel reinforced concrete slabs were also tested for comparison purposes. The slabs were classified into two groups according to the type of FRP bars. All slabs tested were 500 mm in width and 150 mm in depth. The simply supported slabs had a span of 2000 mm, whereas the continuous slabs had two equal spans, each of 2000 mm. Different combinations of under and over FRP (BFRP/CFRP) reinforcement at the top and bottom layers of slabs were investigated. The continuously supported BFRP and CFRP reinforced concrete slabs exhibited larger deflections and wider cracks than the counterpart reinforced with steel. The experimental results showed that increasing the bottom mid-span FRP reinforcement of continuous slabs is more effective than the top over middle support FRP reinforcement in improving the load capacity and reducing mid-span deflections. Design guidelines have been validated against experimental results of FRP reinforced concrete slabs tested. ISIS¿M03¿07 and CSA S806-06 equations reasonably predicted the deflections of the slabs tested. However, ACI 440¿1R-06 underestimated the deflections, overestimated the moment capacities at mid-span and over support sections, and reasonably predicted the load capacity of the continuous slabs tested. On the analytical side, a numerical technique consisting of sectional and longitudinal analyses has been developed to predict the moment¿curvature relationship, moment capacity and load-deflection of FRP reinforced concrete members. The numerical technique has been validated against the experimental test results obtained from the current research and those reported in the literature. A parametric study using the numerical technique developed has also been conducted to examine the influence of FRP reinforcement ratio, concrete compressive strength and type of reinforcement on the performance of continuous FRP reinforced concrete slabs. Increasing the concrete compressive strength decreased the curvature of the reinforced section with FRP bars. Moreover, in the simple and continuous FRP reinforced concrete slabs, increasing the FRP reinforcement at the bottom layer fairly reduced and controlled deflections.