Experimental Study On Repairing Damaged Reinforced Concrete Columns With Prestressed SMA Wires Under Axial Compression

Due to earthquake,vehicle collision,ship collision and other accidents,reinforced concrete columns of bridges and buildings are often damaged,leading to the shortening of their service life.It is necessary to study the repair methods of damaged reinforced concrete columns.Shape memory alloy（SMA）has shape memory effect,which can be used for active reinforcement of components,and can overcome the shortcomings of traditional reinforcement methods,such as complex process and long construction period.In this paper,the material properties of NiTiNb SMA wire are studied.The damaged RC columns and intact RC columns are strengthened with NiTiNb SMA wire.The axial bearing capacity and deformation capacity of the strengthened specimens are discussed through axial compression test and theoretical calculation.The main contents and conclusions are as follows:（1）Design and manufacture of batch tensile anchorage and lap anchorage for NiTiNb SMA wire.The batch stretching anchorage can greatly reduce the time cost of pre-deformation and the number of cuts in the process of pre-deformation,and can effectively complete the pre-deformation of SMA wire;the anchoring force provided by the unilateral extrusion lap anchorage can support the SMA wire to reach the ultimate stress state,and compared with the U-clip lap anchorage commonly used,it has smaller volume and better anchorage performance.（2）Experimental study on the properties of NiTiNb SMA wire.16% is the best pre-deformation ratio of the NiTiNb SMA wire;after 16% pre-deformation at room temperature,the phase transformation hysteresis width of NiTiNb SMA wire will increase greatly,and it covers the common ambient temperature,which indicates that the NiTiNb SMA wire can realize the lasting reinforcement of the actual engineering structure after 16%pre-deformation at room temperature.（3）Experimental study on repairing damaged reinforced concrete columns with prestressed NiTiNb SMA wires under axial compression.Compared with the intact specimens,the prestressed SMA wire reinforcement method is more effective for the damaged specimens,this repair method can inhibit the development of the original cracks of the damaged specimens,and effectively restore and improve the bearing capacity and deformation capacity of the damaged specimens;compared with the intact specimens strengthened with SMA wire,the deformation range of the damaged specimens repaired with SMA wire is wider in the axial compression test.With the increase of reinforcement amount,the deformation integrity will be enhanced synchronously.Compared with the winding spacing of 20 mm and 30 mm,when the winding spacing of SMA wire is 10 mm,the axial bearing capacity and deformation capacity of the strengthened specimen increase the most,the load displacement curve decreases the most gently,and it can still maintain about 60% of the bearing capacity before failure.（4）Theoretical calculation of axial bearing capacity of reinforced concrete columns strengthened with prestressed NiTiNb SMA wires.That the error between the calculated value and the measured value is less than 6%,and the calculated value is in good agreement with the measured value.