Study On Seismic Performance Of Reinforced Concrete Columns After Fire Strengthened With Thin-wall Steel Tube

Reinforcing the RC columns after fire with thin-wall steel tubes and self-leveling micro expansion grouting material have the advantages of the steel tube can be used as the template for grouting material and convenient construction, and the steel tube is not easy to appear local buckling, significantly improve the fire after concrete column bearing capacity and stiffness, etc. Therefore, to carry out the studies of the design method of reinforcement and reconstruction to reinforced concrete structure after fire and establishing the appropriate reinforcement design method is necessary. This paper carried out an experimental study on the seismic performance of RC columns after fire which strengthened with thin-wall steel tubes. The pseudo static tests of two RC columns without fire, two RC columns after fire and ten RC columns after fire which strengthened with thin-wall steel tubes were carried out. The influence law was analyzed on the diameter-thick ratio, the axial compression ratio, the shear span ratio and the strengthening way to the seismic reinforced performance of RC columns after fire. The main contents and conclusions of this dissertation are as follows:(1) Thin-walled steel reinforcement can significantly improve the shear capacity, the limit deformation capacity and energy dissipation capacity after fire concrete column, and the reinforcement test secant stiffness and without the fire is the test of a small difference.(2) The diameter-thick ratio of thin-wall steel tube has a great influence on the shear capacity, the limit deformation capacity, the stiffness and energy dissipation capacity, but has a small influence on the ductility. The limit displacement and the cumulative energy dissipation of RC columns after fire which strengthened with thinwall steel tubes are decreased with the increase of the diameter-thick ratio. When the shear span ratio is 1.78, the shear capacity of the strengthened specimen Z3(diameter-thick ratio 100) and Z6(diameter-thick ratio 150) compared with the unreinforced specimen after fire Z2 respectively increased by 41.8% and 46.9%; When the shear span ratio is 3.0, the shear capacity of the strengthened specimen Z10(diameter-thick ratio 100) and Z14(diameter-thick ratio 150) compared with the unreinforced specimen after fire Z8 respectively increased by 62.5% and 55.5%.(3) The axial compression ratio has a great influence on the shear capacity, the stiffness, the energy dissipation capacity and the ductility, but has a small influence on the limit deformation capacity of reinforced specimens. With an increase of axial load ratio, the shear capacity of strengthened specimen after fire firstly is increased and it follows by decreasing. The energy dissipation capacity and the secant stiffness of strengthened columns after fire are increased with the increase of axial compression ratio. But when the axial compression ratio increases to a certain extent, the increasing rate of stiffness decreased significantly.(4) The shear span ratio had an obvious impact on the shear capacity, ultimate deformation capacity, ductility, stiffness of reinforced specimens. With the increase of shear span ratio, the increase amplitude of shear capacity, ultimate deformation capacity and ductility reduce. When the shear span ratio is 1.78, the limit deformation capacity and the shear capacity of the reinforced specimen respectively increase by 149.6% and 41.8%. While the span ratio is 3.0, the limit deformation capacity and the shear capacity of the reinforced specimen respectively increase by 90.1% and 38.6%.(5) The reinforcement method has a greater impact on the shear capacity, energy dissipation capacity, ductility and stiffness of RC columns after fire which strengthened with thin-wall steel tubes. For the improvement of the shear capacity energy dissipation capacity and stiffness of reinforced specimens, the third reinforcement way is better than the second reinforcement way, and the second way is better than the first way. While for the improvement of reinforced specimens’ ductility, the first reinforcement way is better than the third one and the third one is better than the second. Speaking on the improvement of reinforced specimens’ ultimate deformation capacity, the third reinforcement way is better than the others.(6) Combined with the concrete structure design specifications and the research results of our team, a calculation formula for the shear capacity of the RC columns after fire which strengthened with thin-wall steel tubes is suggested, which can be referenced for the reinforcement of RC columns after fire.