Emergency repair of severely damaged reinforced concrete columns using active confinement with shape memory alloys

2011 ◽  
Vol 20 (6) ◽  
pp. 065018 ◽  
Author(s):  
Moochul Shin ◽  
Bassem Andrawes
Author(s):  
Eunsoo Choi ◽  
Tae-hyun Nam ◽  
Man-Cheol Kim ◽  
Jong Wan Hu ◽  
Bak-Soon Cho ◽  
...  

Two kinds of shape memory alloy wires, NiTiNb and NiTi, are manufactured and pre-elongated during the manufacturing process. After fixing the pre-elongated wires, heating on the wires induces recovery stress on them. Several tests to measure the recovery stress are conducted with varying initial strains. Stress-reduction of the recovery stress is observed after the temperature of the wires is cold down; the remaining stress is called residual stress that is also measured. Also, this study measures the stress-strain curves of the SMA wires under the state that the residual stress is working. The tension behavior of the wires under residual stress is very unique. The NiTi is martensitic state at room temperature, thus a residual deformation remains after applying a large strain. However, under residual stress, the tensile behavior of the wire does not remain residual deformation and return to the original position by unloading; this looks like viscoelastic behavior. The residual stress of the SMA wires can be used as active confinement for civil structures and the behavior under residual stress can be used as like an elastic spring with hysteretic damping. This study confines concrete cylinders and reinforced concrete columns using the pre-elongated SMA wires to introduce an active confinement on them. The SMA wire jackets on concrete cylinders increase the peak strength and the ductility so much comparing to the plain concrete cylinders. Also, the wires on reinforced concrete columns increase the ductility so much without the reduction of flexural strength.


Author(s):  
Л. Р. Маилян ◽  
С. А. Стельмах ◽  
Е. М. Щербань ◽  
М. П. Нажуев

Состояние проблемы. Железобетонные элементы изготавливаются, как правило, по трем основным технологиям - вибрированием, центрифугированием и виброцентрифугированием. Однако все основные расчетные зависимости для определения их несущей способности выведены, исходя из основного постулата - постоянства и равенства характеристик бетона по сечению, что реализуется лишь в вибрированных колоннах. Результаты. В рамках диаграммного подхода предложены итерационный, приближенный и упрощенный способы расчета несущей способности железобетонных вибрированных, центрифугированных и виброцентрифугированных колонн. Выводы. Расчет по диаграммному подходу показал существенно более подходящую сходимость с опытными данными, чем расчет по методике норм, а также дал лучшие результаты при использовании дифференциальных характеристик бетона, чем при использовании интегральных и, тем более, нормативных характеристик бетона. Statement of the problem. Reinforced concrete elements are typically manufactured according to three basic technologies - vibration, centrifugation and vibrocentrifugation. However, all the basic calculated dependencies for determining their bearing capacity were derived using the main postulate, i.e., the constancy and equality of the characteristics of concrete over the cross section, which is implemented only in vibrated columns. Results. Within the framework of the diagrammatic approach, iterative, approximate and simplified methods of calculating the bearing capacity of reinforced concrete vibrated, centrifuged and vibrocentrifuged columns are proposed. Conclusions. The calculation according to the diagrammatic approach showed a significantly better convergence with the experimental data than that using the method of norms, and also performs better when using differential characteristics of concrete than when employing integral and particularly standard characteristics of concrete.


2018 ◽  
Vol 12 (1) ◽  
pp. 47-61
Author(s):  
Wenjuan Lv ◽  
Baodong Liu ◽  
Ming Li ◽  
Lin Li ◽  
Pengyuan Zhang

Background: For reinforced concrete structures under different humid conditions, the mechanical properties of concrete are significantly affected by the moisture content, which may result in a great change of the functional performance and bearing capacity. Objective: This paper presents an experiment to investigate the influence of the moisture content on the dynamic characteristics and hysteretic behavior of reinforced concrete column. Results: The results show that the natural frequency of reinforced concrete columns increases quickly at an early stage of immersion, but there is little change when the columns are close to saturation; the difference between the natural frequencies before and after cyclic test grows as the moisture content rises. The damping ratio slightly decreases first and then increases with the increase of moisture content; the damping ratio after the cyclic test is larger than before the test due to the development of the micro-cracks. Conclusion: The trend of energy dissipation is on the rise with increasing moisture content, although at an early stage, it decreases slightly. According to the experimental result, a formula for the moisture content on the average energy dissipation of reinforced concrete columns is proposed.


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