Shaking Table Experiment And Numerical Analysis Of Base-isolated Structures With Superelastic SMA Helical Springs

Seismic isolation is one of the most effective technologies for earthquake disaster mitigation.Seismic isolation of ground structures such as multi-storey buildings, nuclear reactors,bridges,and liquid storage tanks are designed to preserve structural integrity and to prevent injury to the occupants and damage to the contents by reducing the earthquake-induced forces and deformations in the super-structure.A new kind of seismic isolation system is proposed in this paper,which is made of a linear slide beating and superelastic SMA helical springs.The superelastic SMA helical springs are sited on both sides of the base and pre-draw by a special length. Researches also find that the friction force in linear slide beating can exhaust part of energy that transmitted to superstructure.First of all,introduced in this paper is how to train superelastic SMA wire into superelastic SMA helical spring through thermomechanical way.The theoretical analysis and experiments on the two kinds of trained SMA helical springs proved that the hysteretic characteristics of superelastic SMA helical spring are different from SMA wire.Then a new kind of constitutive model is proposed,and the model parameters of the two trained superelastic SMA helical springs are also fitted.Using the MATLAB software programming to simulate the constitutive model and compare with the experimental data.Results show that the proposed model can describe the hysteretic characters of superelastic SMA helical springs very well.A two-story steel model was made and two series of experiments were taken to study the isolation properties of the system that proposed in this paper.The experiments are aim at studying if the optimal pre-draw length of SMA helical spring existing and the isolation properties of the isolation system that under different earthquakes.The experimental study and the MATLAB simulation analysis result indicated that:(1) An optimal pre-draw length of SMA helical spring existing,which can induce relatively minor "maximum displacement","maximum interstorey drift", "maximum acceleration" and "maximum shear force",and its damping exhausting ability obtained the greatest exertion;(2) The isolation system proposed in this paper can achieve great isolation properties.The "maximum interstorey drift","maximum acceleration" and "maximum shear force" are less than 1/8 of the base fixed responses.Compared with steel spring isolation system which its stiffness equals to equivalent stiffness of SMA helical springs,the SMA helical spring isolation system can achieve better isolation effect,even for the earthquakes of different peak values and different spectrums.The most obvious difference is maximum displacement,SMA helical spring isolation system can achieve much smaller value;(3) Another most important properties of SMA helical spring isolation system is full recentering ability,which means the isolated system can return to its original pace by itself immediately after the earthquake.The fatigue resistance under large strains is considerable.Then we can conclude that the proposed isolation system have another two advantages,that is not only simple in construction(only made up of linear slide bearing and pre-draw SMA helical spring) but also effective(can experience many earthquakes,and does not need to change or repair any parts).