Sagging and hogging strengthening of continuous reinforced concrete beams using CFRP sheets.

yesThis 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

Extrapancreatic actions of incretin-based therapies on bone in diabetes mellitus

Diabetes mellitus is correlated with modifications in bone microarchitectural and mechanical strength, leading to increased bone fragility. The incretin hormones, with a classical effect to increase insulin secretion following food ingestion, are now postulated to have important direct effects on bone. As such, glucose-dependent insulinotropic polypeptide (GIP) has dual actions on bone cells; enhancing bone�forming activity of osteoblasts and suppressing bone resorption by osteoclasts. The sister incretin of GIP, glucagon-like peptide-1 (GLP-1), is also suspected to directly influence bone health in a beneficial manner, although mechanism are less clear at present. The physiological actions of incretins are attenuated by dipeptidyl peptidase (DPP-4) activity and it is speculated that introduction of DPP-4 inhibitor may also positively affect quality of the skeleton. As such, this thesis evaluates the potential beneficial effects of a DPP-4 resistant GIP analogue, namely [D-Ala2 ]GIP, on osteoblastic-derived, SaOS-2 cells, and also preliminary in vivo studies on the impact of genetic deficiencies of GIPRs and GLP-1Rs on bone mineral density and content. Further studies characterised the beneficial effects of incretin-based therapies on metabolic control, bone microstructure and bone mechanical integrity in animal models of pharmacologically-, genetically- and environmentally-induced diabetes. GIP and related stable analogue increased bone-forming biomarkers in SaOS-2 cells and importantly, [D-Ala2 ]GIP was shown to be more potent than native GIP. Knockout mouse studies revealed that both GIPR and GLP-1R signaling are important for optimum bone mass. All diabetic mouse models displayed reduced bone mass, altered bone micromorphology and impairment of bone mechanical strength, similar to the human situation, confirming their appropriateness. The incretin-based therapeutics, [D-Ala2 ]GIP and Liraglutide, in streptozotocin-diabetic significantly increased bone matrix properties, indicating recovery of bone strength at the tissue level. The beneficial effects of administration of [D-Ala2 ]GIP�oxyntomodulin on bone health in db/db mice were more prominent as the Oxm analogue did not only improve bone strength at tissue level, but also at whole-bone level. These modifications were independent of metabolic status. Twice-daily Exendin-4 therapy improved glycaemic control and increased work required to resist bone fracture in high-fat fed mice. It was also established that Sitagliptin had neutral effects on bone microstructure and mechanical strength in high-fat mice. In summary, these data demonstrate the negative impact of diabetes mellitus on normal skeleton development and bone quality. Moreover, this thesis highlights the growing potential of incretin-based therapies for ameliorating bone defects and improving the increased fragility fracture risk associated with diabete

Autonomous robotic system for thermographic detection of defects in upper layers of carbon fiber reinforced polymers

Carbon Fiber Reinforced Polymers (CFRPs) are composites whose interesting properties, like high strength-to-weight ratio and rigidity, are of interest in many industrial fields. Many defects affecting their production process are due to the wrong distribution of the thermosetting polymer in the upper layers. In this work, they are effectively and efficiently detected by automatically analyzing the thermographic images obtained by Pulsed Phase Thermography (PPT) and comparing them with a defect-free reference. The flash lamp and infrared camera needed by PPT are mounted on an industrial robot so that surfaces of CFRP automotive components, car side blades in our case, can be inspected in a series of static tests. The thermographic image analysis is based on local contrast adjustment via UnSharp Masking (USM) and takes also advantage of the high level of knowledge of the entire system provided by the calibration procedures. This system could replace manual inspection leading to a substantial increase in efficiency

CFRP shear strengthening of reinforced-concrete T-beams with corroded shear links

This paper investigates the structural behavior of uncorroded as well as corroded RC T-beams strengthened in shear with either externally bonded (EB) carbon fiber–reinforced polymer (CFRP) sheets or embedded CFRP rods. Nine tests were carried out on RC T-beams having an effective depth of 295 mm and a shear span to effective depth ratio of 3.05. The investigated parameters are the shear link corrosion level (uncorroded, 7% corroded, or 12% corroded) and type of CFRP strengthening system (EB CFRP sheets or embedded CFRP rods). The unstrengthened beams with shear link corrosion levels of 7 and 12% had shear strengths that were 11 and 14%, respectively, less than the shear strength of the uncorroded unstrengthened beam. Both the embedded CFRP rods and EB CFRP sheets were effective in enhancing the shear strength of tested beams but the effectiveness of both strengthening systems decreased with increasing shear link corrosion level. The shear strength enhancement provided by the embedded CFRP rods and EB CFRP sheets decreased from 19 and 15%, respectively, to 12 and 11%, respectively, with an increase in shear link corrosion level from 7 to 12%. Corrosion of the shear links did not have a significant effect on the beam stiffness. Premature debonding limited the effectiveness of the EB CFRP sheets whereas the embedded CFRP rods did not exhibit signs of debonding and therefore showed higher effectiveness.The authors would like to thank Fyfe Europe for supplying the CFRP sheets and epoxy laminating resin used in this study. The first author acknowledges the financial support of the UK Engineering and Physical Sciences Research Council.This is the author accepted manuscript. The final version is available from American Society of Civil Engineers via http://dx.doi.org/10.1061/(ASCE)CC.1943-5614.000054

Lightweight Carbon Fiber Mirrors for Solar Concentrator Applications

Lightweight parabolic mirrors for solar concentrators have been fabricated using carbon fiber reinforced polymer (CFRP) and a nanometer scale optical surface smoothing technique. The smoothing technique improved the surface roughness of the CFRP surface from ~3 {\mu}m root mean square (RMS) for as-cast to ~5 nm RMS after smoothing. The surfaces were then coated with metal, which retained the sub-wavelength surface roughness, to produce a high-quality specular reflector. The mirrors were tested in an 11x geometrical concentrator configuration and achieved an optical efficiency of 78% under an AM0 solar simulator. With further development, lightweight CFRP mirrors will enable dramatic improvements in the specific power, power per unit mass, achievable for concentrated photovoltaics in space.Comment: IEEE Photovoltaic Specialist Conference (PVSC), DC, USA, 201

Passiv damping on spacecraft sandwich panels

For reusable and expendable launch vehicles as well as for other spacecraft structural vibration loads are safety critical design drivers impacting mass and lifetime. Here, the improvement of reliability and safety, the reduction of mass, the extension of service life, as well as the reduction of cost for manufacturing are desired. Spacecraft structural design in general is a compromise between lightweight design and robustness with regard to dynamic loads. The structural stresses and strains due to displacements caused by dynamic loads can be reduced by mechanical damping based on passive or active measures. Passive damping systems can be relatively simple and yet are capable of suppressing a wide range of mechanical vibrations. Concepts are low priced in development, manufacturing and application as well as maintenancefree. Compared to active damping measures passive elements do not require electronics, control algorithms, power, actuators, sensors as well as complex maintenance. Moreover, a reliable application of active dampers for higher temperatures and short response times (e. g. re-entry environment) is questionable. The physical effect of passive dampers is based on the dissipation of load induced energy. Recent activities performed by OHB have shown the function of a passive friction-damping device for a vertical tail model of the German X-vehicle PHÖNIX but also for general sandwich structures. The present paper shows brand new results from a corresponding ESA-funded activity where passive damping elements are placed between the face sheets of large spacecraft relevant composite sandwich panels to demonstrate dynamic load reduction in vibration experiments on a shaker. Several passive damping measures are investigated and compared

Impact of Embedded Carbon Fiber Heating Panel on the Structural/Mechanical Performance of Roadway Pavement

INE/AUTC 12.3

Analysis of FRP shear strengthening solutions for reinforced concrete beams considering debonding failure

In this paper, a fiber beam model previously developed by the authors for the nonlinear analysis of strengthened elements, including the effects of shear, is used to predict the response of reinforced concrete (RC) beams strengthened in shear with fiber reinforced polymers (FRP) sheets. In the previous version of the model, debonding failure of FRP was not included; hence, its application was limited to the simulation of wrapped configurations. The model is now extended to account for debonding failure in order to allow for its application to beams strengthened with U-shaped and side-bonded configurations. Existing experimental tests on RC beams strengthened in shear by FRP sheets in both wrapped and U-shaped configurations were numerically simulated. The model reproduces, with reasonable accuracy, the experimental failure loads, the load-deflection behavior, and the strains in FRP and stirrups with increasing load. The advantages of this proposal are related with the simplicity and straightforwardness of the beam models to be applied in practical engineering problems.Peer ReviewedPostprint (author's final draft

X-ray CT analysis after blast of composite sandwich panels

Four composite sandwich panels with either single density or graded density foam cores and different face-sheet materials were subjected to full-scale underwater blast testing. The panels were subjected to 1kg PE4 charge at a stand-off distance of 1 m. The panel with graded density core and carbon fiber face-sheets had the lowest deflection. Post-blast damage assessment was carried out using X-ray CT scanning. The damage assessment revealed that there is a trade-off between reduced panel deflection and panel damage. This research has been performed as part of a program sponsored by the Office of Naval Research (ONR)

The influence of service temperature on bond between FRP reinforcement and concrete

The interest in fibre reinforced polymer (FRP) reinforcement in construction has considerably increased and especially the application of FRP as externally bonded reinforcement (FRP EBR) has become more and more established. The use of FRP EBR has been adopted world-wide as a very attractive technique for structural strengthening and rehabilitation. At Ghent university, the fire behaviour of slabs and beams strengthened with advanced composites, including the use of fire protection systems, has been investigated. In addition, the behaviour of the FRP-concrete interface at increased temperatures has been considered, as elevated temperatures may occur during service conditions, especially for outdoor applications. According to fib Bulletin 14, the glass transition temperature of the adhesive used to bond the FRP should equal 20°C in excess of the maximum ambient temperature at normal service conditions, and should be at least 45°C. When reaching the glass transition temperature, the properties of the adhesive decrease to a large extend and bond interaction between the concrete and the external FRP reinforcement may be completely lost. To study the bond behaviour at elevated temperatures, a joint test program between the Universities of Ghent and Lecce has been executed, comprising a series of 20 bond tests performed at the Magnel Laboratory for Concrete Research. The present paper will discuss the experimental work and the main test results obtained