Shear Strengthening of R/C Beams with FRP Strips and Novel Anchoring

Abstract The shear strengthening behaviour of R/ C beams, when applying FRP strips externally with or without anchoring, is studied. This is done by subjecting six specimens of prototype dimensions with or without such strengthening to four-point bending. Specimens strengthened with either carbon or steel FRP strips without the use of anchors exhibited a modest increase in shear capacity, when co mpared to the non-strengthened control specimen, due to the debonding mode of failure of these FRP strips. The patented anchoring device was utilized together with either carbon or steel FRP strips for shear strengthening. In this case, the FRP strips debonding failure was prevented and the increase of the shear capacity was much larger than in identical specimens without anchors. An expert system developed for this purpose is quite efficient in producing successful shear capacity predictions based on the provisions of various codes. The Greek Code for ret rofitting existing R/ C structures yields shear capacity predictions in good agreement with measured values

Investigation of cell-level potential-induced degradation mechanisms on perovskite, dye-sensitized and organic photovoltaics

The study focuses on the effect of bias voltage degradation or Potential Induced Degradation (PID) on the efficiency of perovskite (PSCs), dye-sensitized (DSSCs) and organic (OPVs) solar cells. For the PID study, voltage-depended and time-depended degradation tests have been carried out at solar cell level; the cells were fabricated and tested in the same conditions. Furthermore, the solar cells were exposed to both, annealing and cooling tests in order tp highlight the various PID characteristics. Thus, the mechanisms induced during the PID degradation were thoroughly investigated. Results revealed that DSSCs are far more vulnerable to voltage degradation than other solar cell technologies. The current work illustrates that OPV solar cells can be considered as voltage durable compared to PSCs and DSSCs ones. OPV solar cells lost 23% of their initial efficiency whereas PSC and DSSC cells were entirely degraded after the application of 5.5 V and 2.5 V voltage respectively. Furthermore, in contrast to OPV, DSSCs and PSCs did not exhibit charging effect when a 5 V voltage was applied. © 2019 International Solar Energy Societ

Effect of water storage on hardness and interfacial strength of resin composite luting agents bonded to surface-treated monolithic zirconia

Background: Durable bonding between resin composite luting agents (CLA) and zirconia is still a matter of controversy. The purpose of this study was to evaluate the effect of water storage on hardness and interfacial strength of three CLA, a non-adhesive (Multilink Automix/ML), an adhesive (Panavia F 2.0/PF) and a self-adhesive (PermaCem 2.0/PC), bonded to polished (CL) and grit-blasted (AL: 50 µm alumina, SJ: Sil-Jet + Monobond Plus silane) monolithic zirconia surfaces. Methods: CLA specimens (n = 5/cement, condition) were prepared, stored under dry conditions or immersed in water, and Vickers hardness (VH) measurements were obtained at 1 h, 24 h, 1 week and 3 weeks intervals. Optical profilometry was used to determine the roughness parameters (Sa, Sz, Sdr, Sci) of zirconia surfaces (n = 5/treatment). A shear strength test (SBS, n = 10 × 2/cement) was performed to assess the strength and fractography of the cements bonded to zirconia after isothermal water storage and thermal-cycling (TC). Results: PF demonstrated significantly lower VHN after water storage at all time intervals, PC at 1 w, 3 w and ML at 3 w. SJ and AL showed significantly higher values from CL in all roughness parameters. Weibull analysis revealed the following significance in σo ranking within the same material: AL, SJ, ALTC > SJTC, CL > CLTC (PF); SJ, SJTC, AL, ALTC > CL, CLTC (PC) and SJ, SJTC > AL > ALTC > CL, CLTC (ML). Within the same surface treatment subgroups, the significance in σo ranking was PC, ML > PF (before/after TC) for SJ; PC > PF > ML (before TC), PC, PF > ML (after TC) for AL, and PC > PF > ML (before/after TC) for CL. For the m ranking, the only significant difference within each material group was found in PC (AL > ALTC) and for the same surface treatment in AL (PC > ML). Conclusion: There are significant differences in the water plasticization susceptibility of the CLA tested; the materials with adhesive monomers were the most affected. Tribo-chemical silica coating combined with a silane coupling agent was the most efficient bonding treatment for the non-adhesive and the self-adhesive materials. The adhesive CLA performed better on alumina-blasted than on tribo-chemically coated surfaces. © 2021 by the authors. Licensee MDPI, Basel, Switzerland