جستجوی مقالات مرتبط با کلیدواژه "اثر محصورشدگی" در نشریات گروه "عمران"

Surrounding the central core of a concrete component by means of an internal or external factor such as transverse reinforcements, carbon and polymer fibers and steel sheets causes confinement for the concrete. Confining generally improves the strength and ductility of concrete components. As a result of boosting the local performance of elements, the overall performance of structure is made progress. Recently, tending to build irregular structures has been increasing. The presence of irregularity in the structure has always been one of the challenges faced by engineers.  In this investigation, the influence of confinement phenomenon on the seismic performance (damage level and behavior factor) of the moment resisting reinforced concrete frames with vertical irregularity is assessed. To do so, 31 moment resisting frames with vertical irregularity are categorized in four classes including 3-, 6-, 9- and 12-story and the roof displacement-base shear curves of them are acquired using pushover analysis. The capacity curve of each frame is achieved in two states including neglecting the confinement effect and considering it. The outcomes indicate that not only can confining improve the seismic performance of structures but also it can decrease the imposed damage of structures. In other words, comparing the capacity curves of each frame with/without confining effect shows that taking the confinement effect leads to improving the secant stiffness and strength of the frame. Furthermore, due to confinement effect, lateral load carrying capacities of the frames are boosted and the considered damage levels are achieved in higher base shear and roof displacements in comparison with the state that confinement is not considered. The observed values of damage levels indicate that the influence of confinement for higher frames is more significant and the maximum base shears for the frames with the confining action is around 3-19% higher than those of the frames without confinement effect. For 3-story frames, considering confinement effect leads to improving 3.9, 3.6 and 2.9% in damage levels of DL, SD, and NC. For 6-story frames these values are 6.9, 9.5, and 6.8% respectively. Taking confinement effect results in improving 18.25, 11.8, and 14.6% in damage levels of DL, SD, and NC and 14.3, 14.2, and 13.3% improvement for 12-story frames. Comparing the behavior factors in the two states demonstrates that considering confining effect improves the mean values of behavior factors around 10.4%. In addition, the observed values of behavior factors show that the differences between the amounts of behavior factors (with/without confinement effect) for the frames with more stories are higher. It is manifested that type of irregularity plays significant role on the seismic behavior of the moment-resisting reinforced concrete frames. Comparing the analytical behavior factor obtained in the current study with the prescribed value of behavior factor in Iranian seismic code shows that although the proposed value of Iranian seismic code is conservative for low-rise frames, this value is not met for high-rise frames.

A new kind of double skin CFT has more benefits in construction of bridge and especial buildings due to easily multi beam connections for central columns. In this study 27 double skin specimens filled with concrete, consist of internal circular tube and external hexagonal tubes have been studied using ABAQUSE finite element software. The effects of some parameters on behavior of CFT consists of: height of column, width to thickness ratio of external steel tube, diameter to thickness of internal tube and eccentricity were considered. Loading was applied as an axially compression in a displacement control state. The results show that whenever the eccentricity is matched through gap of two skins, the concrete confinement does not reduce, which is not the same as some codes of practice recommendations. The increase on strength of column depends on height, eccentricity and width to thickness ratio of external tube. The strength reduction of columns is up to 15% when height increases 50%. When the diameter to thickness, eccentricity and height of specimens remain constant, it was considered through the results that, the effects of width to thickness ratio of models is more significant than other parameters. The results also show that, when the height is constant and the width to thickness of external tube increases some outward foldings on columns were existed.