Reinforced concrete cantilever slabs are among structures that are most likely to develop structural integrity problems, as they are statically determinate and often exposed to the outdoor environment. This article presents an experimental study on the strengthening of reinforced concrete cantilever slabs where the anchorage of the top steel reinforcing bars into the adjacent wall was insufficient. The experimental study involved the use of a fibre-reinforced polymer strengthening system and fibre Bragg grating sensors for strain monitoring. The fibre-reinforced polymer strengthening system consisted of glass fibre–reinforced polymer sheets and glass fibre–reinforced polymer spike anchors which connected the glass fibre–reinforced polymer sheets to the adjacent concrete wall. The test results showed that the fibre-reinforced polymer strengthening system was effective in improving the load-carrying capacity of reinforced concrete cantilever slabs and the fibre Bragg grating sensors worked efficiently and reliably for strain monitoring. The debonding in glass fibre–reinforced polymer sheet/glass fibre–reinforced polymer anchor-to-concrete bonded joints was found to be a progressive process associated with an increasing load. The fibre-reinforced polymer strengthening system examined in this study is thus a potential ductile solution for deficient cantilever slabs.
Reactor Pit Flooding System (RPF) is adopted under the severe accidents situation in CPR1000+ units. It can move the heat generated from the reactor core via external reactor vessel cooling (ERVC) to keep the integrity of RPV and achieve the in-vessel corium retention (IVR). But if IVR function of RPF is failed, there is Ex-Vessel Steam Explosion (EX-SE) risk. The Ex-Vessel Steam Explosion is analyzed by MC3D software which is for fuel and cooling interaction (FCI). The physical model of CPR1000+ for Steam Explosion is built firstly and then the phenomenon of Ex-Vessel Steam Explosion under typical severe accident is analyzed. The conclusion of this study is that the impulse load of pressure on the cavity wall induced by steam explosion is about 310KPas ∼ 440KPas. Referencing the structure capacity of AP600 containment, if the structural capacity of CPR1000+ containment is equal to AP600, the impulse load of pressure is lower than it. So it could be preliminarily estimated that steam explosion will not threaten the integrality of CPR1000+ containment.
Pure pyrite was combusted in a laboratory drop tube furnace(DTF) in O2/N2 and O2/CO2,a Dekati low pressure impactor(DLPI) was used to collect submicron particles(PM1) from pyrite combustion and obtain their mass fraction size distributions.Particle samples collected were subjected to physical and chemical analysis using an X-ray fluorescence(XRF) analyzer and a scanning electron microscope equipped with energy dispersive X-ray spectrometer(SEM-EDS).The mass size distribution,concentration,elemental composition and morphology of the PM1 were investigated.The results show that pyrite combustion has an important contribution to the PM1 formation.Under the same O2 concentration,the PM1 production and its peak size for the O2/CO2 condition are smaller than those for the O2/N2 condition.In the O2/N2 or O2/CO2 condition,the PM1 production and its peak size increase with the O2 concentration.The PM1 consists mainly of sulfur(S).The O2 concentration has an important influence on the partitioning of different S-containing compounds under the O2/N2 condition.With a low O2 concentration,the S in the PM1 mainly exists in the form of the element sulfur,with a higher O2 concentration,the S mainly exists in the form of sulfuric acid and sulfate.
This study was conducted for the Morgantown Energy Technology Center (METC) to analyze and correlate its data on flash carbonization of coal. Mathematical models were formulated to simulate the downflow co-current flash carbonizer. Various rate expressions on the pyrolysis of coal were tested and compared with the experimental data. Although the rate expression on coal carbonization, based on Wen et al., seemed to fit the data better than that based on Badzioch and Hawksley, neither of them could predict the effect of pressure. In addition, two rate expressions were formulated to account for the pressure effect and were tested against the data rom METC as well as against two other sets of published data. The result indicated that these expressions could predict the trends of the data, but there were still considerable discrepancies from the experimental data. One of the reasons was due to the inconsistency and inaccuracy of the experimental data. Additional work to obtain more reliable data is indicated for improvement of rate expressions in flash coal carbonization.
Fiber-reinforced polymer (FRP) bar has attracted extensive attention as an alternative to steel bar to eliminate the issue of steel corrosion over the past decade. However, FRP bar reinforced concrete (FRP-RC) structures may exhibit lower ductility and stiffness compared to steel reinforced concrete (steel-RC) structures due to the lower elastic modulus and linear tensile behavior of FRP bars. Furthermore, FRP bars have a much less favorable performance in compression because of the micro-buckling damage of fibers, which makes them rarely used as longitudinal reinforcement in compression. To tackle these challenges, a novel FRP-steel-ultra-high performance concrete (UHPC) hybrid bar was proposed. This novel hybrid bar consists of an outer FRP layer (with or without ribs), an inner steel tube and in-filled UHPC. In this paper, an experimental program was conducted to investigate the compressive behavior of the proposed novel hybrid bars, focusing on variables such as the thickness of FRP layer, the type of FRP layer, the thickness of steel tube and the steel fiber content in UHPC. The test results demonstrated that FRP-steel-UHPC hybrid bars generally exhibited a bilinear stress-strain behavior with good ductility and high strength under concentric compression.
This paper proposes a novel method to quantitatively monitor pitting corrosion level of steel bars through a combined use of distributed optical fiber sensing (DOFS) technique and mechanical analysis using finite element modeling (FEM). Tensile tests on steel bars with notches simulating corrosion pits were conducted, and strain distributions measured from fiber sensors attached on tensile bars were analyzed. Further, three-dimensional FEM demonstrated that the monitored strain distribution along a line on the bar surface was greatly dependent on its position relative to the pit mouth. Finally, the procedure to determine the corrosion level from DOFS data and FEM results was presented by mathematically comparing the similarity of strain curves given by the fiber sensor on a corroded bar and FEM of steel bars with different corrosion levels. This study revealed the importance of considering the relative location of fiber sensors when explaining the data of DOFS, and also provided a promising way to quantitively monitor the pitting corrosion level based on the strain distribution of steel bars.
The objectives of the project were to investigate coal-char gasification reactions with CO/sub 2/, H/sub 2/O and other gases, to examine fluid dynamics of char present in a fluidized bed, and to develop a computer model of the fluid-bed gasification which can incorporate such information. To these ends a unique high pressure/temperature thermogravimetric analysis instrument, a pressurized 30 cm-dia. fluid bed, and a high-temperature 13 cm fluid bed were constructed. Coal pyrolysis and char reactions were examined at temperatures to 1600/sup 0/C and pressure to 28 atm. Extent of pyrolysis was shown to depend on particle size and pressure, and in three stages on temperature. Char properties were determined, including diffusion coefficients of CO/sub 2/ in char and surface areas. Char reactivity does not strongly depend on pressure in the range 1 to 28 atm. Diffusion limits are strongly present above 1000/sup 0/C. Inhibition by CO and H/sub 2/ increase rapidly with pressure. Elutriation of particles in a hot bed can be determined from low-temperature results if compared at the same value of excess fluid velocity above minimum fluidization. Bubble size and numbers change slightly with pressure. Fluid bed gasificaton can be modeled successfully, and a basic model is presentedmore » here.« less
The flexural strength of reinforced concrete (RC) beams can be effectively increased using either externally bonded (EB) or near-surface mounted (NSM) fibre-reinforced polymer (FRP) reinforcement. A likely failure mode of such FRP-strengthened RC beams is the plate-end cover separation failure mode which involves debonding of the bonded FRP reinforcement and the cover concrete along the level of the steel tension reinforcement. Despite many existing studies on this failure mode, the accurate prediction of this failure mode using the finite element (FE) method has remained a great challenge. This paper presents a novel FE smeared-crack approach for accurate prediction of plate-end cover separation in which the radial stresses generated by the steel tension reinforcement are taken into account for the first time. The capability and validity of the proposed FE model are verified using existing experimental results.
