Academic literature on the topic 'External anchorage system'

The cables of high-strength carbon fiber reinforced polymer (CFRP) plates are starting to be applied to large spatial structures. However, their main anchorage systems rely on the adhesive force, which entails risks to their integrity resulting from aging of the binding agent. In this study, a friction-based wedge anchorage system was designed for CFRP plates. The working mechanism of the proposed anchorage system was explored both theoretically and experimentally. The anti-slip mechanism and condition of CFRP plates were formulated so that the equivalent frictional angle of the contact surface between a CFRP plate and wedges must not be smaller than the sum of the dip angle of the wedge external conical surface and the frictional angle between the wedges and barrel. An analysis of the stress distribution in the anchorage zone of the CFRP plate was conducted using the Tsai-Wu failure criterion, which concluded that the compressive stresses should be reduced on the section closer to the load-bearing end of the anchorage system. Furthermore, the anchorage efficiency coefficient was proposed, which depends on stress concentration coefficients, plate thickness, length of anchorage zone, dip angle of wedge external conical surface, and its frictional angle. Then, it was determined that the minimum length of an anchorage zone for the CFRP plates with various specifications should be at least 49 times larger than the CFRP thickness. A finite element analysis and static tensile tests on six specimens were carried out. The experimental results revealed that the anchorage efficiency coefficient of the optimized anchor reached 97.9%.

Objective Documentation of the application of maxillary distraction osteogenesis using rigid external distraction (RED) with skeletal anchorage combined with predistraction alveolar bone grafting (ABG) in cleft maxilla. Design Case report. Patient A patient with numerous congenital missing teeth and severe maxillary deficiency related to complete bilateral cleft lip and palate with large alveolar bone defect. Intervention The patient received preoperative orthodontic treatment, predistraction ABG, and maxillary distraction osteogenesis using RED with skeletal anchorage. Results Predistraction ABG completely united the cleft maxilla. The united maxilla was successfully advanced by the RED system with skeletal anchorage, despite unsound dentition with numerous congenital missing teeth. Conclusion The present study demonstrates that the combination of predistraction ABG and RED system with skeletal anchorage is effective for the treatment of severe maxillary deficiency related to complete bilateral cleft lip and palate with large bone defect and numerous congenital missing teeth.

A Nonlinear finite element based ABAQUS modeling studies were conducted to evaluate the performance of exterior Beam Column Joint (BCJ) under quasi-static test loads. Six integrated BCJ models representing different configurations of beam reinforcement anchored in joint are verified by using a novel retrofitting technique called "Post Installation of Supplementary Anchorage" (PISA) by using headed bar as supplementary steel. The configuration of beam reinforcement anchored in column are described by straight bar,90 degree bend ,180 degree hook (confirming to design code IS456:2000) and single head, double head bars (confirming to ACI 318-19, ACI 352R-02 ) and 90 degree long bend of ductile detailing (as per IS 13920-2016). Two series (A&B) of integrated joint specimens representing conventional (series-A) and retrofitted anchorage (series-B) systems are modeled and tested by using ABAQUS software. The test parameters considered are configuration of anchorage system and presence of supplementary anchorage. The test variables representing nonlinear performance of retrofitted joint system are Von Mises stress conditions, Principal tensile stress, Moment-Rotation, Degraded stiffness, Crack mechanics and Damage index. The results shows good improvement of post failure conditions of exterior beam-column joint such as relocation of plastic hinge mechanism and failure mechanics of retrofitted joint system. Also the results validated with experimental program on typical specimens casted and tested. This study imparts useful information on implicit retrofitting methods applied by external means in exterior beam-column joint. It also promotes performance based design principles with viable construction practice.

The aim of this paper is to clarify the structural performance of reinforced concrete (RC) beams with weak or without any internal shear reinforcement and externally strengthened in flexure with carbon fibre reinforced polymer (CFRP) laminates, when subjected to a shear-dominant-loading regime. Seven RC beams were specifically designed, without and with an external anchorage system, which was carefully detailed to enhance the benefits of the strengthening laminate and counteract the destructive effects of shear forces. All the beams were identical in terms of their geometry, longitudinal internal reinforcement, and concrete strength but varied, to highlight the role of shear behavior, in terms of their internal and external shear reinforcement as well as in their loading test regime. The beams were tested under four-point bending and extensively instrumented to monitor strains, deflection, cracking, load carrying capacity, and failure modes. The structural response of the tested beams has, then, been critically analyzed in terms of deformability, strength, and failure processes that occur under a shear-dominant loading regime. It is shown that with a carefully designed anchorage system, a brittle behavior without yielding of tension steel reinforcement of a flexural strengthened beam can be transformed to a less brittle behavior with yielding of tension steel reinforcement and a well-defined enhancement of structural performance in terms of both deformation and strength. The results presented in this paper should enable engineers to counteract shear failure of externally strengthened beams with little or even no internal shear reinforcement.Key words: carbon fibre reinforced polymer, shear behavior, external flexural strengthening, structural performance.

Abstract The external bonding of carbon fiber-reinforced polymer (CFRP) strips by two-component epoxy adhesive on the concrete surfaces of buildings and bridges is a retrofitting method accepted worldwide. The gradient anchorage (GA) is an anchoring method especially developed to anchor prestressed CFRP strips to concrete elements without a need for mechanical clamping after the installation phase. This method takes advantage of the adhesives property to undergo accelerated curing when heated. The results of more than fifteen years of research on the development of the gradient anchorage at the Swiss Federal Laboratories for Materials Science and Technology (Empa) are presented in this paper. The basic principles and application steps are explained, and the main results starting from the development of the technique up to the testing of real scale girders are described, and the new challenges posed by this innovative system are highlighted. The gradient anchorage is a valid alternative to a mechanically anchored system for prestressed FRP (P-FRP).

In this study, a post-tensioning method using externally unbonded steel rods was applied to pre-damaged reinforced concrete beams for flexural strengthening. Nine simply-supported beams, three reference beams and six post-tensioned beams, were subjected to three-point bending. The design parameters observed in this study were the amount of tension reinforcements (3-D19, 4-D19, and 2-D22 + 2-D25; “D” indicates the nominal diameter of the rebar) and the diameters of the external rod (φ22 mm and φ28 mm). A V-shaped profile with a deviator at the bottom of the mid-span was applied to the pre-damaged beams, and a post-tensioning force was added to overcome the low load resistance and deflection already incurred in the pre-loading state. The post-tensioning force caused by tightening the nuts at the anchorage corresponded to a strain of 2000 με in the external rods; this value was approximately equal to the strain caused by torque that two adults can apply conveniently. The post-tensioning system increased the load-carrying capacity and flexural stiffness by approximately 40–112% and 28–73%, respectively, when compared with the control beams. However, the external rods did not yield in the post-tensioned beam with larger steel reinforcements and external steel rods. The external rod with the larger diameter increased the flexural strength more effectively.

Integrated construction technology is in developing quickly in Chinas civil engineering community. With its space saving and heat insulation properties, people both in cold and hot region both need the thin wall settled structure to avoid burning hot or extremely cold. This article proposed an innovative integrating construction technology that has gained more and more popularity in construction project by adoption of thin wall thermal insulation board. The detail of the anchorage of the structure surface and the board, bond together with a special nail, and the whole system was controlled by the fastening system. It is one type vertical integration strategy and will gain more competition advantages for the construction enterprises.

Four medium -scale reinforced concrete beams were constructed and tested to investigate the effectiveness of external poststrengthening with prestressed carbon fiber reinforced polymer (CFRP) plates. The various variables included the strengthening method and the amount of prestressing. The experiments consisted of one control beam, one nonprestressed CFRP-bonded beam, and two prestressed CFRP-bonded beams, all the beams were subjected to four-point bending tests. In comparison to the control beam and the nonprestressed CFRP-bonded beam, the cracking load, yield load, ultimate load and stiffness of the beams with bonded prestressed CFRP plates were increased. The failure mode of the prestressed CFRP-plated beams was not debonding, but concrete crushing. After the debonding of the CFRP plates, the behaviour of the bonded CFRP-plated beams changed to that of unbonded CFRP-plated beams due to the effect of the anchorage system. The ductility of the beams strengthened with CFRP plates having the anchorage system was considered high if the ductility index was above 3.

Versatility and high performance in terms of specific stiffness and strength, as well as non-corrosive sensitivity, make FRP (Fiber-Reinforced Polymer) cables a viable alternative to steel ones in the development of prestressing systems. On the other hand, the orthotropic and brittle nature of FRPs could trigger a premature failure of the cable in the anchorage system, for which several solutions have been proposed so far in civil structural applications. In this context, after a preliminary state of the art, the work introduces a split wedge anchorage for FRP (ϕ = 12 mm) cables proposing two different solutions for steel wedges having the external surface: either (1) a constant (3 degrees) slope or (2) a double slope obtained by shaping it with an angle of 3.0 degrees before and then of 3.1 degrees along the most tapered part. The goal was to exploit the nominal cable capacity (257 kN), avoiding stress peaks that cause its premature failure. The proposed solutions have been experimentally tested and, as far as the double angle solution is concerned, the failure loads were equal to 222 and 257 kN, denoting that the proposed solution can reach the cable capacity. Clearly, further investigations are needed to check the variability of the results and eventually improve the system.

The introduction of Fibre Reinforced Polymers (FRP) to the civil engineering market in the late 1980s resulted in the emergence of a range of new tools for rehabilitating and strengthening concrete structures. Strengthening using FRPs is typically accomplished using non-prestressed externally bonded FRPs. The technical and economic benefits of such strengthening could be further increased by prestressing the FRPs, especially when dealing with concrete structures. Prestressing concrete structures suppresses the appearance and growth of cracks in the serviceability limit state. This in turn increases the structure’s stiffness and resistance to degradation. Prestressing also increases the structure’s yield load but does not change its failure load relative to that of an analogous non-prestressed structure, provided that all other parameters are kept constant. In 2004, a pilot study was carried out at the Luleå University of Technology (LTU) to investigate the scope for using unbonded Carbon Fibre Reinforced Polymer (CFRP) strengthening systems, particularly those involving prestressing. In the early stages of this project, a number of difficulties were encountered in anchoring the CFRP rods to concrete structures: the conical wedge anchorages that were used tended to either cause premature failure of the rods or allowed the rod to slip out of the anchorage. It was therefore decided to study the mechanisms at work within these anchorages in more detail. The goal of the project was to develop a small, practical, reliable, and userfriendly anchorage for use in unbonded external CFRP strengthening systems. On the basis of a thorough literature review, which is described in Paper 1, it was concluded that despite the difficulties encountered, the conical wedge anchorages used with steel reinforcing rods were the most promising starting point for the design of a new anchorage for use with CFRPs. Importantly, the conical wedge anchorage can be made small in size and easy to mount while retaining a high degree of versatility; this is not true of bonded, sleeve, and clamping anchorages. Analytical and numerical models were used to investigate the distribution of radial stress within these highly pressurized anchorages. Paper 2 describes an evaluation of the capability of three types of models - an analytical axisymmetric model based on the thick-walled-cylinder-theory and two Finite Element (FE) models, one axisymmetric and one three-dimensional - to predict the behaviour of a conical wedge anchorage. It was concluded that the axisymmetric models were incapable of modelling the stress distribution within the anchorage with sufficient accuracy, and so 3D FE models were used exclusively in subsequent studies. Paper 3 describes the development of a new anchorage for CFRP rods. The design process involved conducting pull-out studies on a series of prototypes, in conjunction with computational studies using a basic FE model, to identify and understand the prototypes’ failure modes. Between the computational data and experimental results, a good understanding of the factors affecting the interaction between the CFRP rod and the anchorage was obtained. The new anchorage design employs a one-piece wedge which effectively incorporates the three wedges and the inner sleeve from more conventional wedge anchorages into a single unit. This increases the reliability and user-friendliness of the anchorage because it eliminates the need to check the alignment of individual wedges. The new design has been patented; the published Swedish patent is included in the thesis as Paper 6. The newly-developed anchorage was then incorporated into a prestressing system and its performance was evaluated using a series of test beams. In parallel with the planning of these tests, a series of pull-out tests was conducted using the new anchorage. The strain measurements obtained in these experiments were compared to predictions made using a new, more advanced FE model, and used to refine the design of the new anchorage. Paper 4 describes this new FE model, the most important parameters affecting anchorage behaviour, and the final anchorage design. Paper 5 focuses on the possibilities provided by the new anchorage. Tests were performed using seven three meter long concrete beams prestressed with external unbonded CFRP tendons. One beam was unstrengthened; the other six were strengthened in different ways, with different prestressing forces, initial tendon depths, and with or without the use of a midspan deviator for the tendons. The results of these tests were compared to those obtained using otherwise identical beams prestressed with steel tendons and to the predictions of an analytical beam model developed for use with steel tendons. These tests showed that the prestressing works as intended and that the behaviour of beams prestressed with external unbonded CFRP tendons is fully comparable to that of beams prestressed with steel tendons. It was also found that the predictions of the analytical model were in good agreement with experimental observations, although there were some differences between the measured and predicted tendon stresses. The development of a functional anchorage represents a fulfilment of the objectives laid out at the start of this project, and represents an important step towards the practical use of prestressed unbonded external CFRP tendons in strengthening concrete structures. However, a number of outstanding questions remain to be addressed. Little is known about the safety of this kind of system, and the benefits of using CFRP tendons should be quantified. Furthermore, there are a number of potential technical issues that must be addressed. These include the risk of creep-rupture in the CFRP, the effects of thermal contraction and expansion on the anchorage, and the scalability of the anchorage as the tendon diameter is increased. Finally, the long-term behaviour of the anchorage and prestressing system should be investigated.
I och med introduktionen av fiberkompositer i byggbranschen under slutet av 80-talet har en rad nya verktyg för förstärkning och underhåll av betongkonstruktioner utvecklats. Förstärkning har oftast utförts med pålimmade kompositer utan förspänning. För att ytterligare öka verkningsgraden, både den tekniska och ekonomiska, kan förspänning vara en möjlighet. Särskilt för betongkonstruktioner. Förspänning av en betongkonstruktion medför att man i bruksgränstillståndet begränsar uppkomsten av sprickor och deras storlek. Det ger i sin tur en ökad styvhet hos konstruktionen. Därutöver höjs lasten för när det slakarmerade stålet flyter. I jämförelse med ospända konstruktioner är dock brottlasten densamma, så länge övriga parametrar behålls. Under 2004 genomfördes en pilotstudie vid Luleå tekniska universitet (LTU) för att undersöka framtida möjligheter och utmaningar med förspända, icke vidhäftande kolfiberkompositkablar. I det läget upptäcktes svårigheter att förankra kompositkabeln mot betongen. De koniska killås som användes orsakade antingen brott på kabeln redan vid låga belastningar eller glidning hos kabeln, som omöjliggjorde fullgod kraftöverföring. Ett beslut togs då att tills vidare fokusera på förankringen och genomföra en mer ingående studie kring denna. Som mål sattes upp att arbetet skulle resultera i en liten, tillförlitlig och användarvänlig förankring. Den skulle sen i en förlängning kunna användas för att slutföra pilotstudien och därefter i större tillämpningar. Trots de förhållandevis nedslående resultaten från pilotförsöken visade den grundliga litteraturstudien som presenteras i Artikel 1 att koniska killås trots allt verkar vara den mest lovande typen av förankring för kolfiberkablar. Den bör därför användas som utgångspunkt för fortsatt utveckling. I motsats till vidhäftande, hyls och klämmande förankringar kan killåset göras litet, lätt att montera och också användas i många praktiska tillämpningar. För att undersöka hur de höga radiella tryckspänningarna i ett sådant killås fördelas är olika former av beräkningsmodeller nödvändiga verktyg. I Artikel 2 jämförs tre olika modeller med avseende på hur väl de kan beskriva komplexiteten hos ett koniskt killås. Det är dels en analytisk axisymmetrisk modell, som också härleds i artikeln, dels en axisymmetrisk Finita Element (FE) modell och dels en 3D FE modell. Undersökningen visade att ingen av de axisymmetriska modellerna har kapacitet nog att tillförlitligt modellera killåset. I fortsatta undersökningar har därför endast 3D FE använts. Resultaten från en enkel FE modell ligger också, tillsammans med tidiga laboratorieförsök, som grund för Artikel 3. Däri beskrivs hur ett nytt killås via prototyper och nya lösningar utvecklats, och hur arbetet för att få fram det nya låset också gett en bättre förståelse för interaktionen mellan kolfiberkompositkabel och lås. Som avslutning presenteras en innovativ design där de tre kilarna och den inre hylsan sammanfogats till en enhet. Med den nyutvecklade designen blir förankringen såväl mer tillförlitlig som användarvänlig. Alla kilar har då redan från början rätt position i förhållande till varandra. Den utvecklade förankringslösningen har också lett fram till ett beviljat svenskt patent, bifogat i avhandlingen som Artikel 6. Efter utvecklingen av den nya förankringen var nästa steg i de uppsatta målen implementering av densamma i ett förspänningssystem och nya balkförsök i konstruktionslabbet. Parallellt med planeringen för balkförsöken pågick ett arbete med att ytterligare förbättra låsdesignen. Bland annat användes en mer detaljerad FE modell som sedan jämfördes med mätningar från en ny serie med dragprov. Den nya FE modellen tillsammans med en utvärdering av viktiga parametrar och den slutliga förankringsdesignen presenteras i Artikel 4. Artikel 5 sammanfattar och avslutar forskningsstudien med en testserie om sju stycken, tre meter långa, betongbalkar förspända med utanpåliggande kolfiberkompositstavar. En av balkarna provades utan förstärkning. Förstärkningen hos de övriga varierades med avseende på förspänningsgrad, förspänningens effektiva höjd och användandet av deviator vid balkmitt. Resultaten har jämförts mellan de provade balkarna, med identiska balkar förspända med stålkablar samt med en analytisk modell utvecklad för förspänning med stålkablar. Från resultaten kan utläsas att förspänningen fungerar bra och att beteendet hos balkarna förspända med utanpåliggande kolfiberkablar är fullt jämförbart med det hos balkarna förspända med stålkablar. Likaså visar jämförelsen med de modellerade beteendena på god överensstämmelse, även om vissa skillnader finns mellan uppmätta och modellerade spänningar i kolfiberkabeln. Med målen för forskningen uppfyllda och en ny fungerande förankring framtagen så har vägen till praktiska tillämpningar kortats betydligt, ändå finns några frågetecken kvar att räta ut. Ett är säkerheten hos den här typen av system och nyttan av att använda kolfiberkomposit istället för stål. Innan systemet används i praktiken bör därför följande frågeställningar belysas: Risk för krypbrott i kolfiberarmeringen, inverkan av temperaturförändringar (och temperaturrörelser) i förankringen samt eventuella storlekseffekter vid förankring av kablar med större diametrar. De här frågorna tillsammans med långtidsförsök på förankringen och förspänningssystemet bör ses som viktiga framtida forskningsfrågor.
Godkänd; 2011; 20110128 (ysko); DISPUTATION Ämnesområde: Konstruktionsteknik/Structural Engineering Opponent: PhD Chris Burgoyne, Dep of Engineering, University of Cambridge, UK Ordförande: Professor Björn Täljsten, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Fredag den 18 februari 2011, kl 10.00 Plats: F1031, Luleå tekniska universitet

Monolateral external fixation is a system for the stabilization, reduction, and manipulation of bone segments by means of bone anchorage consisting of pins fastened to an external frame. Monolateral external fixators in their various forms have the advantage that they allow the use of half-pins (bicortical pins that do not penetrate both sides of the soft tissue envelope), thereby avoiding major damage to the neurovascular structures contralateral to the insertion point. The simple structure of monolateral systems permits rapid application and simplified preoperative planning, both of which are features particularly appreciated in traumatology.

<p>The design and application of strengthening measures aiming to effectively counter possible weaknesses related to the extensive architectural modification of a characteristic reinforced concrete building is discussed in this chapter. Several balconies were removed as part of the architectural interventions. Externally bonded reinforcement consisting of steel and fibre reinforced polymer laminates was applied as an “answer” to possible changes in flexural stress of selected structural elements in the immediate area of the demolitions. A unique anchorage system was also designed and applied as an answer to the loss of development length of the main reinforcement bars of selected beams due to the removal of their cantilever parts.</p>

<p>The present study investigates the force transfer mechanisms for external bonded (EB) FRP layers/strips attached on Reinforced Concrete (R/C) members with or without anchorage systems. The EB-FRP open hoop strips are utilized to upgrade either the shear or the flexural capacity of R/C structural elements. This type of retrofitting is necessary for R/C structures designed with less stringent seismic loading conditions than those currently required. The combination of anchoring systems together with EB-FRP strips is mandatory in those cases that the debonding mode of failure has to be avoided. This research is proposing a loading arrangement, utilizing specimens with realistic geometry, for the evaluation of the efficiency of the strengthening scheme, a combination of EB-FRP strips with or without the use of an anchoring system. In all codes and norms, the use of anchoring system is proposed and allowed for driving the mode of failure to the fracture of the FRP strip. Despite this fact the code provisions are not proposing a specific anchoring system, they are not proposing a methodology to prove that the anchoring system is efficient and transfers safely the loads form the FRP to the R/C element. The proposed, novel loading arrangement is allowing the application of the demanded, imposed by the design, forces onto the prototype R/C prismatic specimen, where the desired instrumentation can be placed for capturing in detail the overall behaviour of the strengthening scheme (FRP strips combined with anchorage) up to failure. Finally, typical applications are also presented.</p>

<p>The objective of this paper is to summarize current theory, design, and construction methods of concrete segmental girder bridges and to propose future research needs. First, the analytical theory will be overviewed, including concrete creep and shrinkage, bending strength with external tendons and unbounded tendons, web crack control, anchorage, etc. Then, the paper covers design methods regarding corrosion, including the use of Electrically Isolated Tendons (EIT) system, Fiber Reinforced Polymer (FRP) tendons and other corrosion protection techniques. In addition, internal redundance; the use of ultra-high-performance concrete (UHPC); and standardization for expediting the concrete segmental bridge design will be presented. The paper concludes with a discussion of research needs for future development of concrete segmental bridges.</p>

<p>The externally bonded reinforcement (EBR) technique is one of the most widely used strategies for the flexural strengthening of reinforced concrete (RC) with fibre reinforced polymer (FRP) materials. The EBR technique offers several structural advantages when the FRP material is prestressed. The development of high shear stresses at the ends of the prestressed FRP material can cause premature FRP peeling-off failure. This premature failure can be delayed or even avoided with the use of special end-anchorage systems, like the mechanical anchorage (MA) system and the gradient anchorage (GA) system. This paper presents an experimental and a numerical study on RC slabs strengthened in flexure with prestressed carbon FRP (CFRP) laminate strips, namely: (i) one reference slab; (ii) one slab strengthened with non- prestressed externally bonded CFRP (EB-CFRP) laminate; (iii, iv) and two slabs strengthened with prestressed EB-CFRP laminates using the MA and GA systems. The performance of these simulations was compared with results of the slabs experimentally tested up to failure. Subsequently, these models were used on a parametric study that intended to investigate the influence of different parameters affecting the behaviour of the slabs strengthened with prestressed EB-CFRP laminates.</p>

<p>Based on the design and construction of the second Yangtze river bridge in Wuhu (hereinafter referred to as Wuhu Second Bridge), this article introduces the structure system of the full-floating cable-stayed bridge with four cable planes, single-column tower and separated steel box girders. A series of innovative structural measures have been taken to improve the safety and economy of the bridge, such as the looping stayed cable anchorage system, the diagonal damping constraint system, and the externally prestressed segmental assembled box girder used in the approach bridge. In addition, the finite element analysis software was used to study and analyse the mechanical characteristics of the bridge. The reliability of the structural anchorage system and damping constraint system was verified either.</p>

<p>The strengthening of reinforced concrete (RC) structures using fiber reinforced polymer (FRP) composites is a viable reality, consolidated by many studies and practical applications. One of the most common methods used to apply the FRP is the externally bonded reinforcement (EBR) technique. The development of stresses at the anchorage zones of the EBR-FRP composite might cause premature debonding. Two main situations required the use of mechanical systems to delay (or avoid) premature failure: (i) when the EBR-FRP systems are prestressed and (ii) when higher effective strain in passive EBR-FRP is required.</p><p>This works aims to assess the performance of a metallic anchorage plate commercially supplied by S&amp;P Clever Reinforcement Company by means of an experimental program composed of fourteen pull-out specimens (concrete/CFRP/anchorage).</p><p>Each metallic plate is fixed to the concrete element through six prestressed bolts, creating confinement in the anchorage region. All specimens are tested up to failure under two types of pull- out configurations: (i) the steady-state temperature, where the laminate is pulled from the block with increasing force under constant temperature (of 20C, 60C and 80C); and, (ii) the transient temperature, where the laminate is pulled with constant force (0.5% and 0.6% of CFRP strain) and the temperature is gradually increased. Besides temperature and test configuration, the influence of the laminate width (50 mm and 100 mm) and level of transverse compression in the metallic plate (torque level of 30 N∙m, 100 N∙m, and 150 N∙m is applied in the anchorage bolts) were also studied.</p>

The paper shows the results of a theoretical and experimental research activity oriented to the design and the realization of a of a low cost pneumatronic prototype, proposed for tasks of pipes and ducts inspection. Geometries and sizes of ducts are significantly different and for their inspection very flexible units are needed. Different researchers propose several solutions: the present proposal is specifically oriented to an automated pneumatic low cost unit. The prototype is conceived to emulate the grub’s motion: variable geometry components are deformed under the action of pneumatic power supply, following a programmable logic actuation. A fluidic muscle is used to generate the motion and two deformable air chambers are arranged at the ends of the muscle in order to assure the anchorage to the internal pipe wall. The automatic phases of the motion are managed by an external micro-PLC, allowing flexible and bi-directional motions. The unit is equipped with a micro-camera and can be also equipped with micro grippers and micro mechanical tools. The design and the optimization of the prototype’s mechanical structure is discussed and related to the mechatronic approach applied to perform the cyclical movement.

The subject of this work is to examine the hypothesis that some sublytic levels of mechanical perturbation of cells can stimulate cell metabolism. As a marker metabolite, we have chosen arachidonic acid. Principal metabolites for platelets include the cyclooxygenase product thromboxane A2(TXA2) and the lipoxygenase product 12-hydroperoxy-eicosatetraenoic acid (12-HPETE). Polymorphonuclear leukocytes (PMNLs) initally produce principally 5-HPETE, somtimes leading to the formation leukotrienes, though many other metabolites of arachidonic acid have been isolated from activated neutrophils. Human umbilical vein endothelial cells utilize arachidonic acid to produce mainly prostaglandin I2(PGI2). All of these metabolites are biologically active and modulate cell function - sometimes in quite contrasting ways. We will show that levels of sublytic mechanical stress exposure can stimulate arachidonic acid metabolism in all three of the cell types mentioned above. The biological implications of this stress/metabolism coupling may be quite far reaching.Human platelets, leukocytes and endothelial cells all appear to be sensitive to mechanical stress induced activation of arachidonic acid metabolism. Sheared PRP exhibited greatly increased synthesis of 12-HETE and surprisingly little thromboxane B2 production. This indicates that shear stress stimulation of platelets may produce quite different arachidonic acid metabolism than that seen with many direct chemical stimuli, such as thrombin or collagen.Our data demonstrate that a substance derived from shear induced platelet activation may activate the C-5 lipoxygenase of human PMNL under stress, leading to the production of LTB4. We hypothesize that this substance maybe 12-HPETE. LTB4 is known to be a very potent chemotactic factor and to induce PMNL aggregation and degranulation. Our studies provide further evidence that lipoxygenase products of one cell type can modulate production of lipoxygenase products in a second cell type, and that shear stress can initiate cell activation. This kind of coupling could have far reaching implications in terms of our understanding of cell/cell interaction in flowing systems, such as acute inflammation, artificial organ implantation and tumor metastasis.The data on PGI2 production by endothelial cells demonstrate that physiological levels of shear stress can dramatically increase arachidonic acid metabolism. Step increases in shear stress lead to a burst in production of PGI2 which decayed to a steady state value in several minutes. This longer term stimulation of prostacyclin production rate increased linearly with shear stress over the range of 0-24 dynes/cm2. In addition, pulsatile flow of physiological frequency and amplitude caused approximately 2.4 times the PGI2 production rate as steady flow with the same mean stress. Although only PGI2 was measured, it is likely that other arachidonic acid metabolites of endothelial cells are also affected by shear stress.The ability of cells to respond to external stimuli involves the transduction of a signal across the plasma membrane. One such external stimulus appears to be fluid shear stress. Steady shear flow induces cell rotation in suspended cells, leading to a periodic membrane loading, with the peak stress proportional to the bulk shear stress. On anchorage-dependent cells, such as endothelial cells, steady shear stress may act by amplifying the natural thermal or Brownian fluttering or rippling of the membrane. There are several possible mechanisms by which shear stress induced membrane perturbation could mimic a hormone/receptor interaction, leading to increased intracellular metabolism. Shear stress may induce increased phospholipase C activity, caused by translocation of the enzyme, increased substrate (arachidonic acid) pool availability to phospholipase C (particularly from that stored in phosphoinositols) due to shear-induced membrane movements or changes in membrane fluidity, direct activation of calcium - activated phospholipase A2 by increased membrane calcium ion permeability, or most probably by a combination of these mechanisms.