Current Issue : January - March Volume : 2019 Issue Number : 1 Articles : 5 Articles
Contemporary structures can resist earthquakes as they deform and dissipate energy.\nHowever, during strong ground motions, these structures can sustain significant concrete damage\nand overall permanent deformations. Therefore, it is of great benefit if earthquake-resisting structures\ncan deform and dissipate energy, and yet sustain mitigated damage. This paper illustrates the\nfindings of an experimental study focused on the mitigation of damage and reduction of residual\ndisplacements in reinforced concrete (RC) shear walls. In this study, the cyclic properties of\ntwo innovative shear wallsâ??a slender and a squat wallâ??which were cast with fiber-reinforced\ncementitious composites and reinforced with steel and glass fiber reinforced polymer bars are\ninvestigated. Then, the improvements of the innovative specimens with respect to two conventional\nRC shear walls are discussed in terms of damage propagation, self-centering, stiffness retention\nand energy dissipation. As the experiments showed, the innovative walls sustained mitigated\nconcrete damage and less residual drift ratios while illustrating significant stiffness and energy\ndissipation capacities....
The long-term existence of dam structures significantly modified the river\nchannel. In accordance with a drastic increase of low-head dams under consideration\nfor removal in recent years, it is important to predict the effects of\nlow-head dam removal from the modified river channel by the low-head dam\nconstruction. This study intends to investigate the long-term channel evolution\nprocess following low-head construction and removal and to find out the\ninfluential parameters (sediment diameter, river bed slope, dam height) for\nthose channel evolution by two-dimensional numerical simulation model.\nFollowing the low-head dam construction, sediment deposition rates in upstream\nof the low-head dam are varied with the influential parameters. The\nsediment deposition rates and sandbar formation with riparian vegetation\nsettlement on sandbars have significantly affected for channel evolution following\nlow-head dam removal. Especially the knickpoint formation and the\ntypes of vegetation (grass type and tree type) on the sandbars are critical factors\nfor channel evolution following low-head dam removal. Through the\nnumerical simulation results of low-head dam construction (50 years) and\nlow-head dam removal (50 years), it is identified that the modified river\nchannel by low-head dam may not be easily restored to pre-dam conditions\nfollowing its removal especially in river geomorphology and riparian vegetation.\nConsequently, this study found that the reversibility following low-head\ndam construction and removal depends on the sediment deposition rates in\nupstream of the low-head dam....
The aim of this project is to investigate the behaviour of several special types plasters\nspecifically designed to degrade the most common pollutants which are present in the atmosphere.\nIn particular, specific additives have been added to these plasters, in order to obtain a broad spectrum\nof active and synergic response, each of which have peculiar functions: - microporous materials,\nsuch as clinoptilolite, a natural zeolite, that promotes the adsorption of air pollutants thanks to\nits porous nature; - nano-fillers, such as carbon nanotubes, that behave both as reinforcing agents\nas well as adsorbent materials; - photochemical agents, such as titanium oxide, that degrade air\npollutants, previously adsorbed on carbon nanotubes and zeolites, thanks to the action of light that\nactivates photodegradation reactions. All the samples were also characterized in terms of mechanical\nproperties, adhesion to supports and water absorption. Furthermore, photodegradation tests were\ncarried out by exposing plaster surfaces, wetted with a Rodamine solution, to Ultraviolet rays (UV)\nfor different times. Plasters photodegradative capacity was evaluated and the results highlighted the\nfact that the designed admixtures showed an important photodegradative action, strictly dependent\non the types and specific ratios of the selected additives....
Glass fiber-reinforced polymers (GFRPs) have received increasing attention in recent years\ndue to their overall performance of light weight, low cost and corrosion resistance, and they are\nincreasingly used as reinforcement in concrete structures. However, GFRP material has low elastic\nmodulus and linear elastic properties compared with steel bars, which introduces different bonding\ncharacteristics between bars and concrete. Therefore, a reliable monitoring method is urgently needed\nto detect the bond slip in GFRP-reinforced concrete structures. In this paper, a piezoceramic-based\nactive sensing approach is proposed and developed to find the debonding between a GFRP bar\nand the concrete structure. In the proposed method, we utilize PZT (lead zirconate titanate) as\ntwo transducers. One acts as an actuator which is buried in the concrete structure, and the other\nacts as a sensor which is attached to the GFRP bar by taking advantage of machinability of the\nGRRP material. Both transducers are strategically placed to face each other across from the interface\nbetween the GFRP bar and the concrete. The actuator provokes a stress wave that travels through\nthe interface. Meanwhile, the PZT patch that is attached to the GFRP bar is used to detect the\npropagating stress wave. The bonding condition determines how difficult it is for the stress wave\ntraveling through the interface. The occurrence of a bond slip leads to cracks between the bar and\nthe concrete, which dramatically reduces the energy carried by the stress wave through the interface.\nIn this research, two specimens equipped with the PZT transducers are fabricated, and pull-out tests\nare conducted. To analyze the active sensing data, we use wavelet packet analysis to compute the\nenergy transferred to the sensing PZT patch throughout the process of debonding. Experimental\nresults illustrate that the proposed method can accurately capture the bond slip between the GFRP\nbar and the concrete....
Local buckling in steel tubes was observed to be capable of reducing the ultimate loads\nof thin-walled concrete-filled steel-tube (CFST) columns under axial compression. To strengthen\nthe steel tubes, steel bars were proposed in this paper to be used as stiffeners fixed onto the tubes.\nStatic-loading tests were conducted to study the compression behavior of square thin-walled CFST\ncolumns with steel bar stiffeners placed inside or outside the tube. The effect and feasibility of steel\nbar stiffeners were studied through the analysis of failure mode, loadâ??displacement relationship,\nultimate load, ductility, and local buckling. Different setting methods of steel bars were compared as\nwell. The results showed that steel-bar stiffeners proposed in this paper can be effective in delaying\nlocal buckling as well as increasing the bearing capacity of the columns, but will decrease the ductility\nof the columns. In order to obtain a higher bearing capacity of columns, steel bars with low stiffness\nshould be placed inside and steel bars with high stiffness should be placed outside of the steel\ntubes. The study is helpful in providing reference to the popularization and application of this new\nstructural measure to avoid or delay the local buckling of thin-walled CFST columns....
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