No description available.

Mitigation of the blast risk associated with terrorist attacks and accidental explosions threatening critical infrastructure has become a topic of great interest in the civil engineering community, both in Canada and abroad. One method of mitigating blast risk is to retrofit vulnerable structures to resist the impulsive effects of blast loading. A comprehensive re-search program has been undertaken to develop fibre reinforced polymer (FRP) retrofit methodologies for structural and non-structural elements, specifically reinforced concrete slabs and walls, subjected to blast loading. The results of this investigation are equally valid for flexure dominant reinforced concrete beams subject to blast effects. The objective of the research program was to generate a large volume of research data for the development of blast-resistant design guidelines for externally bonded FRP retrofit systems. A combined experimental and analytical investigation was performed to achieve the objectives of the program. The experimental program involved the construction and simulated blast testing of a total of thirteen reinforced concrete wall and slab specimens divided into five companion sets. These specimens were subjected to a total of sixty simulated explosions generated at the University of Ottawa Shock Tube Testing Facility. Companion sets were designed to study one- and two-way bending, as well as the performance of specimens with simply-supported and fully-fixed boundary conditions. The majority of the specimens were retrofitted with externally bonded carbon fibre reinforced polymer (CFRP) sheets to improve overall load-deformation characteristics. Specimens within each companion set were subjected to progressively increasing pressure-impulse combinations to study component behaviour from elastic response up to inelastic component failure. The blast performance of companion as-built and retrofitted specimens was quantified in terms of measured load-deformation characteristics, and observed member behaviour throughout all stages of response. The results show that externally bonded FRP retrofits are an effective retrofit technique to improve the blast resistance of reinforced concrete structures, provided that debonding of the composite from the concrete substrate is prevented. The test results also indicate that FRP retrofitted reinforced concrete structures may survive initial inbound displacements, only to failure by moment reversals during the negative displacement phase. The experimental test data was used to verify analytical techniques to model the behaviour of reinforced concrete walls and slabs subjected to blast loading. The force-deformation characteristics of one-way wall strips were established using inelastic sectional and member analyses. The force-deformation characteristics of two-way slab plates were established using commonly accepted design approximations. The response of all specimens was computed by explicit solution of the single degree of freedom dynamic equation of motion. An equivalent static force procedure was used to analyze the response of CFRP retrofitted specimens which remained elastic after testing. The predicted maximum displacements and time-to-maximum displacements were compared against experimental results. The analysis indicates that the modelling procedures accurately describe the response characteristics of both retrofitted and unretrofitted specimens observed during the experiment.

Samhället ändras konstant men detta innebär inte bara en förändring för människorna i samhället utan också att nya krav ställs på konstruktionen som brukas av människorna. Många byggnadskonstruktioner kan därmed behöva en förstärkning efter en viss tid. Behovet av en förstärkning kan bero på flera orsaker exempelvis ändrat nyttjande. Det är mer fördelaktigt med en förstärkning av konstruktionen än att den rivs ner och byts ut för att klara av dagens krav. Syftet med detta examensarbete är att undersöka förstärkning av betongkonstruktioner med hjälp av kolfiberkomposit. I rapporten presenteras beräkningar som gjordes för att undersöka tillökningen i böjoch tvärkraftskapacitet efter en utförd förstärkning. Parallellt med beräkningarna kontrollerades och utvecklades befintliga mallar som finns för denna metod. För att kunna uppnå syftet undersöktes två hypotetiska betongkonstruktioner. Ena konstruktionen är en plattramsbro som modellerades i FEM programmet Brigade Standard. Beräkningar på plattramsbron gjordes med avseende på böjande moment. Den andra konstruktionen som undersöktes är en T-balk som är en del utav ett bjälklag. På T-balken granskades tvärkraftskapaciteten innan och efter en utförd förstärkning med kolfiber. I resultatet redovisas mängden kolfiber som erfordras för att uppnå önskad kapacitet hos konstruktionerna. I resultatet redogörs också kapaciteten som uppnås efter kolfiberförstärkningen. / The society changes constantly, but this does not only affect the inhabitants of the society, but also that new demands are made on the construction used by the people. Many constructions may therefore require reinforcement after a certain amount of time. The need for reinforcement may be due many different reasons for example to altered use, corrosion to internal reinforcement or may be due to design errors, accidents or new standards. It is more beneficial to reinforce the structure than to tear it down and replace it to meet current requirements. The purpose of this thesis is to investigate carbon fiber reinforced polymer, CFRP, as a method to strengthen concrete structures. The report presents calculations that were made to investigate the increase in bending and shear capacity after a performed reinforcement. Alongside the calculations, existing templates for this method were checked and developed. In order to achieve the purpose, two hypothetical concrete structures were investigated. One design is a frame bridge modeled in the FEM program Brigade Standard. Calculations on the frame bridge were made with respect to bending. The other construction that was investigated is a T-beam. On the Tbeam, shear capacity was examined before and after reinforced carbon fiber reinforcement. The result present the amount of carbon fiber required to achieve the desired capacity of the structures. The result also describes the capacity achieved after carbon fiber reinforcement.

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.

Das Prinzip eines Schwungmasseenergiespeichers (kurz SMS), d. h. kinetische Energie in rotierenden Massen zu speichern, ist bekannt. In den letzten Jahren haben SMS durch ihre Eigenschaft, große Leistungen bei hohen Zyklenzahlen aufzunehmen/abzugeben, an Attraktivität gewonnen. Durch Neu- und Weiterentwicklungen auf den Gebieten der Leistungselektronik, bei der Herstellung hochfester Werkstoffe wie kohlenstofffaserverstärkte Kunststoffe (kurz CFK, von: carbonfaserverstärkter Kunststoff) für Rotor und Schwungmasse und in der Lagertechnik sind energieeffiziente und sichere SMS bis zu 150 kWh machbar. Mit einem Leistungsband von 0,5-50 MW eignet sich die SMS-Technologie zur Stabilisierung von Verbundnetzen. Dieser Beitrag gibt einen generischen Einblick in die ingenieurwissenschaftlichen Arbeiten an einer Hochgeschwindigkeitsschwungmasse. Dazu wird die strategische Herangehensweise vorgestellt. Die Herausforderungen bei der Gestaltung der hybriden Metall-CFK-Strukturen des Laufzeugs werden vertieft. / The principle of a flywheel storage system (FSS for short), i.e., to store kinetic energy in rotating masses, is well described. In recent years, FSS have become more attractive due to their ability to receive/deliver large power at high cycle rates. Due to new and further developments in the fields of power electronics, in the production of high-strength materials such as carbon fiber reinforced plastics (short CFRP) for rotor and flywheel and in bearing technology, energy-efficient and safe FSS up to 150 kWh are possible. With a power range of 0.5-50 MW, FSS technology is suitable for stabilizing interconnected power grids. This paper gives a generic insight with respect to the engineering work on a high-speed flywheel. The strategic approach is presented. The design challenges regarding the hybrid metal-CFRP structures of the rotating assembly are deepened.

No description available.

yes / This paper reports the testing of 11 reinforced concrete (RC) two-span beams strengthened in flexure with externally bonded carbon fiber-reinforced polymer (CFRP) sheets. The beams were classified into two groups according to the arrangement of the internal steel reinforcement. Each group included one unstrengthened control beam. The main parameters studied were the position, length, and number of CFRP layers. External strengthening using CFRP sheets was found to increase the beam load capacity. All strengthened beams exhibited less ductility compared with the unstrengthened control beams, however, and showed undesirable sudden failure modes. There was an optimum number of CFRP layers beyond which there was no further enhancement in the beam capacity. Extending the CFRP sheet length to cover the entire hogging or sagging zones did not prevent peeling failure of the CFRP sheets, which was the dominant failure mode of beams tested.

The search and research for high performance materials for aerospace applications is a continuous evolving process. Among several fibre reinforced polymers, carbon fibre reinforced polymer (CFRP) is well known for its high specific stiffness and strength. Though high modulus and high strength carbon fibre with structural resin systems have currently been established reasonably well and are catering to a wide variety of aerospace structural applications, these properties are generally directional with very high properties along the fibre direction dominated by fibres and low in other directions depending mainly on the resin properties. Thus, there is a need to enhance the mechanical properties of the resin systems for better load transfer and to improve the resin dominated properties like shear strength and properties in directions other than along the fibre. Use of carbon nanotubes (CNTs) with their extraordinary specific stiffness and strength apparently has great potential as an additional reinforcement in resin for development of CNT-CFRP nanocomposites. However, there are several issues that need to be addressed such as compatibility of a particular resin with CNTs, amount of CNTs that can be added, uniform dispersion of these nanotubes, surface treatment and curing process etc., for optimal enhancement of the required properties. Epoxy and cyanate ester resin systems are finding applications in aerospace structures owing to their desirable set of properties. Of these, bisphenol E cyanate ester (BECy) resin of low viscosity with its low moisture absorption, better dimensional stability, and superior mechanical properties can establish itself as potential structural resin system for these applications. BECy in particular has the advantage of being more suitable for out of autoclave manufacturing process such as Vacuum Assisted Resin Transfer Molding (VARTM). Literature shows that, significant work has been carried out by various researchers reporting improvements using CNTs in epoxy resins along with various associated problems. However, studies on effects of addition of CNTs /fCNTs to BECy-CFRP composite system are not well reported. Thus, objective of this work is to study the effects of adding pristine and functionalized CNTs to low viscosity cyanate ester as well as epoxy resin systems. Further, to study the effects on mechanical properties of nanocomposites with carbon fibre reinforcement in these CNT dispersed resin system through a combination of experimental and computational approaches. Multiwall carbon nanotubes (CNTs) without and with different chemical functionalization are chosen to be added to epoxy and BECy resins. The quantity of these CNTs /fCNTs is varied in steps up to 1% by weight. Different methods of mixing such as shear mixing, ultrasonication and combined mixing cycles are implemented to achieve uniform dispersion of these nanotubes in the resin system. Standard test samples are prepared from these mixtures of nanotubes in resin systems to study the variation in mechanical properties. Further, these nanotubes added resin systems are used in fabricating CFRP laminates by VARTM process. Both uni-directional and bi-directional laminates are made with the above modified resin systems with CNTs/fCNTs. Series of experimental investigations are carried out to study various aspects involved in making of nanocomposites and the effects of the same on different mechanical properties of the nanocomposites. Standard specimens are cut out from these laminates to evaluate them for tension, compression, flexure, shear and interlaminar shear strength. The main parameters investigated are the effects of varied quantity of CNTs and functionalized CNTs in the resin mix and in CFRP nanocomposites, effect of different mixing / curing cycles etc. on the mechanical properties of the nanocomposites. The investigations have yielded very interesting and encouraging results to arrive at optimum quantity of CNTs to be added and also the effects of functionalization to achieve enhanced mechanical properties. In addition, correlation of mechanical property enhancements with failure mechanisms, dispersion behaviour and participation of CNTs / fCNTs in load transfer are explained with the aid of scanning electron microscope images. Computational studies are carried out through atomistic models using computational tools to estimate the mechanical properties, understand and validate the effects of various parameters studied through series of experimental investigations. An atomistic model is built taking into consideration the nanoscale effects of the single wall carbon nanotubes (SWCNTs) and its reinforcement in the BECy resin. Using these atomistic models, mechanical properties of individual SWCNT, BECy polymer resin, polymer with different quantities of added SWCNT, and the CFRP laminates with improved resin are computed. As the interaction of CNT with the polymer is only at the outermost layer and the mechanical properties of either MWCNTs or SWCNTs are too high compared to resin systems, it is not expected to have any difference in the final outcome whether it is MWCNT or SWCNT. Hence, only SWCNTs are considered in computational studies as it helps in reducing the complexity of atomistic models and computational time when coupled with polymer resin. This is valid even for functionalized CNT as functionalization is also a surface phenomenon. To start with, the mechanical behaviour of SWCNT is studied using molecular mechanics approach. Molecular mechanics based finite element analysis is adopted to evaluate the mechanical properties of armchair, zigzag and chiral SWCNT of different diameters. Three different types of atomic bonds, i.e., carbon-carbon covalent bond and two types of carbon-carbon van der Waals bonds are considered in the carbon nanotube system. The stiffness values of these bonds are calculated using the molecular potentials, namely Morse potential function and Lennard-Jones interaction potential function respectively and these stiffness values are assigned to spring elements in the finite element model of the SWCNT. The importance of inclusion of Lennard-Jones interactions is highlighted in this study. Effect of these non-bonded interactions is studied by making the numerical stiffness of these bonds to negligible levels and found that they significantly reduce the mechanical properties. The effect of non-bonded Lennard-Jones atomic interactions (van der Waal interactions) considered here is a novelty in this work which has not been considered in previous research works. The finite element model of the SWCNT is constructed, appropriate boundary conditions are applied and the behaviour of mechanical properties of SWCNT is studied. It is found that the longitudinal tensile strength and maximum tensile strain of armchair SWCNTs is greater than that of zigzag and chiral SWCNTs and its value increases with increasing SWCNT diameter. The estimated values of the mechanical properties obtained agree well with the published literature data determined using other techniques. As the systems become more complicated with the inclusion of polymers, molecular dynamics (MD) method using well established codes is more adoptable to study the effect of SWCNTs on BECy. Hence, it is used to model and solve the nanosystems to generate their stress-strain behavior. Further, MD approach followed here can effectively include interfacial interaction between polymer and the CNTs as well. Mechanical properties of SWCNT functionalized SWCNT (fSWCNT), pure BECy resin and that of the CNT nanocomposite consisting of specific quantity of SWCNT / fSWCNT in BECy are estimated using MD method. Atomistic models of SWCNT, fSWCNT, BECy, BECy with specific quantities of CNT / fSWCNT are constructed. A monomer of BECy is modelled and stabilized before its usage as a building block for modelling of BECy resin and to compute its properties. A cell of specific size containing monomers of BECy and another cell of same size with SWCNT at centre surrounded by BECy monomer molecules are built. The appropriate quantity of SWCNT in resin is modelled. This model captures the required density of the composite resin. The models so constructed are subjected to geometric optimization satisfying the convergence criteria and equilibrated through molecular dynamics to obtain a stable structure. The minimized structure is subjected to small strain in different directions to calculate the Young’s modulus and other moduli of the CNT-BECy resin composite. The process is repeated for different quantities of SWCNT in BECy resin to obtain their moduli. Further, tensile and shear strengths of CNT-BECy are obtained by subjecting the equilibrated structure to a series of applied strains from 0 to 10% in steps of 1%. The stress values corresponding to each strain are obtained and a stress – strain curve is plotted. From the stress- strain curve, the strengths of the CNT -BECy which is the stress corresponding to the modulus after which the material starts to soften are determined. Effects of functionalization on mechanical properties of SWCNT are observed. Further, effects of functionalization of SWCNT are studied with a specific quantity of fSWCNT on different moduli and strengths of BECy are investigated. The properties of enhanced CNT–BECy nanocomposite resin with different quantities of added CNT obtained through MD are used to estimate the mechanical properties of the CNT-BECy-CFRP nanocomposite using micromechanics model. Further, validation with experimental results is attempted comparing the trends in enhancement of properties of the CNT-BECy resin and CNT-BECy-CFRP nanocomposite system. The outcome of this research work has been significantly positive in terms of i) Development of an appropriate process establishing different parameters for dispersing CNTs in the resin system, mixing, curing cycle for making of nanocomposites demonstrating significant and consistent enhancement of mechanical properties of BECy based resin system and CFRP nanocomposites using optimum quantity of CNTs /fCNTs through a series of well planned and executed experimental investigations. Evaluation of mechanical properties for each of the cases has been carried out experimentally. ii) Establishing a computational methodology involving intricate atomistic modelling and molecular dynamics of nanosystems for estimation of mechanical properties of BECy polymer resin and to study the effects by addition of SWCNT / functionalized SWCNT on the properties. Results obtained through series of experimental investigations have been validated through this computational study. This could be an important step towards realising the potential of this resin system for high performance aerospace applications. Thus, in brief, detailed experimental work combined with computational studies performed as presented in this thesis resulted in achieving structurally efficient cyanate ester based nanocomposites which is unique and not reported in open literature.

FRP laminates and fabrics, used as an externally bonded reinforcement (EBR) to strengthen or repair concrete members, have proven to be an economical retrofitting method. However, when used to strengthen long-span members or members with limited access, the labor and equipment demands may negate the benefits of using continuous EBR FRP. Recently, CFRP rod panels (CRPs) have been developed and deployed to overcome the aforementioned limitations. Each CRP is made of several small diameter CFRP rods placed at discrete spacing. To fulfill the strengthening length, CRP’s are spliced together and made continuous by means of overlaps (or finger joints). In this doctoral dissertation, the effectiveness of spliced CRPs as flexural strengthening reinforcement for RC members was investigated by experimental, analytical and numerical methods. The experimental research includes laboratory tests on (1) RC beams under four-point bending and (2) double-lap shear concrete specimens. The first set of tests examines the behavior of concrete members strengthened with spliced CRPs. Several beams were fabricated and tested, including: (a) unstrengthened, (b) strengthened with spliced CRPs, (c) strengthened with full-length CRPs, and (d) strengthened with full-length and spliced CFRP laminates. The double-lap shear tests serve to characterize the development length and bond strength of two commonly used CRPs. Several small-scale CRPs, with variable bond lengths, were tested to arrive to an accurate estimation of development length and bond strength. Several other specimens were additionally tested to preliminarily examine the effects of bond width and rod spacing. A 3D nonlinear finite element simulation was utilized to further study the response of CRP strengthened RC beams, by extracting essential data, that couldn’t be measured in the experimental tests. Additionally, analytical tools were added to investigate the behavior of tested bond and beam specimens. The first tool complements the double-lap shear tests, and provides mathematical terms for important characteristics of the CRP/concrete bond interface. The second tool investigates concrete cover separation failure, which was observed in the beam testing, for RC beams strengthened with full-length and spliced CRPs.

Hydraulic systems are used in many fields of applications for different functions like energy storage in hybrid systems. Generally the mass of hydraulic systems plays a key role especially for mobile hydraulics (construction machines, trucks, cars) and hydraulic aircraft systems. The main product properties like energy efficiency or payload can be improved by reducing the mass. In this connection carbon fiber reinforced plastics (CFRP) with their superior specific strength and stiffness open up new chances to acquire new lightweight potentials compared to metallic components. However, complex quality control and failure identification slow down the substitution of metals by fiber-reinforced plastics (FRP). But the lower manufacturing temperatures of FRP compared to metals allow the integration of sensors within FRP-components. These sensors then can be advantageously used for many functions like quality control during the manufacturing process or structural health monitoring (SHM) for failure detection during their life cycle. Thus, lightweight hydraulic components made of composite materials as well as sensor integration in composite components are a main fields of research and development at the Institute of Lightweight Engineering and Polymer Technology (ILK) of the TU Dresden as well as at the Leichtbau-Zentrum Sachsen GmbH (LZS).