Experimental Investigation Of Concrete Columns Reinforced With Superelastic Shape Memory Alloys

Concrete columns possess dramatic carrying capacity under axial load. However, with large stiffness and poor deformation capacity, brittle failures are bound to occur under the ultimate limit state, which make structure seriously damaged. Moreover, there is still deficiences in the well-developed enhancement techniques of carrying capacity under axial load,such as insufficient deformation ability. In recent years, the research and development of intelligent materials provide innovative strategies and methods to enhance the carrying capacity as well as ductility of the concrete structure. Furthermore, solid theory foundations for the research of axially bearing capacity of new type of prestressed reinforced concrete column were provided.Shape memory alloy(SMA) is a kind of intelligent metal materials, possessing superior shape memory effect(SME) and super elasticity(SE), good durability and high damping characteristics. SMA has become an ideal material for the strengthening of carrying capacity and deformation capacity of structure members in civil engineering. In this dissertation, the in-depth research of axial carrying capacity and deformation capacity of prestressed concrete column reinforced with superelastic shape memory alloy wire were carried out through experimental study and theoretical analysis. The main contents are included as follows:(1) Cyclic tests on the mechanical properties of superelastic SMA wire were carried out considering the effect of strain amplitude, loading rate, cycle times and pre-strain. And experimental bases for the design of confining concrete columns tests were provided.(2) Eight concrete columns reinforced with superelastic SMA wires were tested under axial compression. Influence of SMA amount and pre-stress as well as mode on axial carrying and deformation capacity of confined concrete columns were considered. Based on detailing experimental phenomenon and systematical analysis of experimental data, it is found that the superelastic SMA wire can significantly increase the axial mechanical capacity and deformation performance of concrete columns.(3) In order to systematically analyze the axial properties of reinforced concrete column reinforced with superelastic SMA wire, a three-dimensional finite element model was built by ABAQUS. The analysis focuses on the axial carrying capacity and deformation performance of concrete column reinforced with superelastic SMA considering the influence ofamount and pre-strain level.(4) Based on the test results and the existing calculation method of confined concrete column, a simplified utility calculation formula of axial bearing capacity for concrete column reinforced by superelastic SMA wire was proposed. In the proposed formula, the influences of SMA amount and pre-strain level on the axial carrying capacity of the concrete column were considered. Results show that theoretical data well agree with the test data. The research results would have certain guidance function for engineering practice.