Numerical Simulation Study On The Mechanics Of Interface Damage Detection For Concrete Filled Steel Tubular Structures Using Spectral Element Method

Concrete-filled steel tubular(CFST) structures have been widely employed in civil infrastructures such as super high-rise buildings, long-span space structures, bridges, underground space structures and large scale energy facilities because of their excellent structural performance including higher load-carrying capability, good ductility and energy dissipation capacity, and convenience and economy in construction. The confinement effect of steel tubular makes the core concrete in three-dimensional pressure state, which can improve the compressive strength of concrete; and the local buckling of steel tube can be delayed and restrained by the filled concrete. The interface condition between concrete core and steel tube is an important factor affecting the mechanical performance of CFST structures. The debonding can reduce the confinement effect of steel tub ular on the concrete core and decrease the load-carrying capacity of CFST structures. So the interface debonding detection becomes a significant topic to evaluate the mechanical performance of CFST structures.In recent years, active interface debonding detect ion for CFST structures with Piezoelectric Lead Zirconate Titanate(PZT) technolog y has been proposed due to the deficiency of conventional non-destructive methods foe CFST structures. A series of experiments have proved the effectiveness of this method wh ich has been used in practice. In order to demonstrate the mechanics of the proposed interface debonding detection approach for CFST structures based on stress wave measurement with PZT technology, it is important to carry out numerical study on the stress wave propagation for CFST structures and the effect of interface debonding on stress wave propagation. In this paper, a coupling system composed of a CFST structure and PZT patches was established and analyzed with spectral element method(SEM) for the purpose of the active interface debonding detection for CFST structures with PZT technolog y numerically. The research work in this paper mainly includes the following parts:(1) The basic theory of SEM in wave propagation simulation of structures was introduced and its applications in structural damage detection are summarized.(2) The SEM numerical simulation proprames based on Matlab were developed to investigate the stress wave propagation in CFST structures with and without interface debonding under centralized excitation force. A two dimensional SE model for a CFST section was established and the elastic stress wave propagation in the hybrid section with and without interface debonding defects was simulated under centralized single point excitation to explain the effect of interface debonding on elastic stress wave propagation.(3) A three dimensional SE model was established to analyze static and dynamic behavior of the piezoelectric bimorphs and the highed orders of the element shape function was used to improve the simulation precison. The proposed method can be introduced as a high-order solid element to simulate the piezoelectric plates, which also provide some references to simulate the coupling system couposed of CFST structures and piezoelectric patches with SEM.(4) The coupling model ouposed of CFST structures and piezoelectric patches is established with SEM to investagate the mechanics of the interface debonding detection of CFST structures based on stress wave measurements with PZT technology.Results show that the proposed SEM provides an efficient mumerical method for the stress wave propagation simulation within CFST cou pled with PZT patches and the investagation of the mechanics of interface debondoing detection.