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The purpose of this research is to investigate the relative importance of Avicennia marina organic matter in the feeding of Ilisha melastoma fish in the Mangrove Biosphere Reserve; It was stable isotope approach. Three primary food sources including mangrove tree leaves, microphytobenthos and suspended organic particles were analyzed isotopically. The samples of primary food sources and fish are converted into pure and simple gases such as CO, CO2 and N2 after minimizing the size and turning into powder. Then the identified isotope ratios are compared with a measured standard and the exact amount of isotope formed in the sample is obtained. In this research, sampling was done seasonally in August in the summer season and February in the winter season of 2019 in the mangrove ecosystems of Bandar Khmer, Hormozgan province.In the summer season, the average stable carbon isotope of primary food sources fluctuated from -28.07 units per thousand for mangrove leaves to -13.58 units per thousand for microphytobenthos.This average in the winter season was obtained from -28.05 units per thousand for mangrove leaves to -13.54 units per thousand for microphytobenthos.The average stable nitrogen isotope of primary food sources in the summer season fluctuated from 1.44 units per thousand for microphytobenthos to 10.72 units per thousand for suspended organic particles.The results of this research showed that in the summer season, suspended organic particles with 63% and in the winter season, microphytobenthos with 45% play the most important role in providing the food needed by the small shemsk fish.
 

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One of the most concerns about design and maintenance of structures in civil engineering is the safety of structures in the events of natural disasters, including earthquakes, which requires adequate resistance and providing expected performance of structures. Different factors can have an impact on the occurrence of damage and the damage content in structures and, consequently, the loss of economic assets as well as human health and life safety during earthquakes. Normally, high alkaline property of concrete, PH about 13, forms a protective oxide layer on the reinforcement steel surface. The Carbon dioxide in the atmosphere or the chloride ion in the concrete environment especially in the coastal zone, along with the moisture and the oxygen can penetrate through the concrete pores and micro-cracks and can reach the rebar surface. Then, they cause rebar corrosion inside the concrete by destroying the protective oxide layer on the steel surface. Chloride ions reach the passive layer according to the explained pattern and they begin to react in the passive layer when the amount of chloride ions exceed the critical value and cause the perforation corrosion. Therefore, the performance of deteriorating structures can be different from the desirable performance of pristine structures. Corrosion of steel reinforcement in reinforced concrete (RC) structures is one of the main factors in increasing the vulnerability of RC structures. Due to corrosion, mechanical properties of steel involving yield and ultimate stresses, their corresponding strains, and the elasticity modulus of steel will change. Also the cross-sectional area of steel reinforcement decreases. Furthermore, after cracking, the mechanical properties of concrete will change. In this study, in order to investigate the seismic fragility and vulnerability of RC structures due to steel reinforcement corrosion, two buildings involving a 3-storey and a 7-storey RC moment frames are modeled based on the lumped plasticity model for considering nonlinearity. Two corrosion scenarios of 10 and 20 percent reduction of steel reinforcement cross section and their effects applied to the structural members of these RC frames. Then, seismic performance and the fragility of these two RC frames are investigated using nonlinear static analysis (pushover analysis) and incremental dynamic analysis. Fragility analysis results show that the probability of failure and seismic fragility of RC structures increased due to reinforcement corrosion. Therefore, fragility curves shifted to the left due to corrosion, illustrating the increase in the probability of damage at different spectral accelerations. The safety margin of the collapse of the 3 and 7-storey structures also decreased due to corrosion. For example, as a result of 20 percent corrosion scenario, safety margin of three-storey structure decreased by 16.5 percent and the safety margin of seven-story structure decreased by 28 percent. Results also illustrate that the collapse margin ratios of both structures (CMR) are reduced for 10 percent corrosion scenario. Although the probability of failure increased for 3-storey RC frame, it remains below 10 percent. However, for 7-storey RC frame, the probability of failure exceeds 10% (allowable failure probability adopted by the code) and the frame needs to be rehabilitated.

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As service years increase, the corrosion of steel rebar stands out as a major problem for existing reinforced concrete (RC) structures in corrosion-inducing environment. The mechanism of steel corrosion in concrete is an electro chemical process, which is often accelerated by the ingress of aggressive chemicals, for example chloride ion. The accumulation of corrosion products on steel rebar is able to generate circular stress which could result in cover cracking. Corrosion of steel rebar will degrade the physical appearance and reduce its original cross section. Corrosion often appears to be non-uniform and localized. Corrosion damaged RC elements displayed smaller yield strength, ductility, energy dissipation capacity, etc. Corrosion level of stirrup tends to be higher than longitudinal rebar due to smaller diameter and less cover protection. Stirrup corrosion decreased confinement behaviour on concrete, thus exacerbating the degeneration of the deformation capacity and the ductility of the RC structures. The corrosion of reinforcement steel bars (rebar) is a natural electrochemical reaction RC structures have to face with. It is exacerbated by exposure to corrosion-inducing environment factors, including de-icing salt, marine salty water, carbon dioxide, sulfur dioxide, etc. The chloride from salt (NaCl) could make hazardously chemical attack on steel bar by acting as an efficient catalyst in the corrosion process. The corrosion of steel bar in the existing reinforced concrete structure has raised great concern over its safety and seismic performance among practising engineers, researchers and residents, etc., because steel bar is the most essential element in RC. Corrosion reduces the effective cross-section area of longitudinal and transverse rebars.
Due to a small concrete cover of transverse rebars compared with longitudinal rebars, the corrosion of them becomes earlier and more severe, leading to cracks in concrete, a decrease of confinement, an intensification of reduction in deformation capacity and ductility of reinforced concrete structures. For this purpose, an experimental investigation is carried out on reinforced concrete specimens include spiral and stirrup and the variables include the corrosion percentage, rebar diameter, transverse rebar pitch, and confined core diameter. Results demonstrate that the high degree corrosion has a fewer significant effect on the reduction in confinement strength, and smaller-sized transverse reinforcements are less sensitive to corrosion.