| As the core force member,steel strand is widely used in civil engineering structures,such as prestressed concrete bridge,cable-stayed bridge,arch bridge suspender.In the long-term service process,the stress level and section damage of steel strand will inevitably occur,which will threaten the structural safety of cable system bridge.It is of great significance to carry out the research on the steel strand detection technology of the bridge in service and to put forward the effective health monitoring technology.Based on the steel strand sprocket wave dispersion property for this point,the semi-analytical finite element algorithm based on writing,analysis of material damping,the influence of the stress level of guided wave modes,study the steel strand sprocket wave propagation under different stress level,get high strength steel wire and steel strand sprocket dispersion curve wave theory,put forward the steel strand notch center frequency-stress level corresponding relation,for the nondestructive testing of steel strand stress level to provide theoretical basis.The main research results are as follows:(1)Based on the semi-analytical finite element method,the dispersion curve of guided wave in high strength steel wire is solved.The semi-analytical wave equation of Cartesian coordinate system is derived,the SAFE algorithm is realized by MATLAB programming independently,and the dispersion curve of guided wave is drawn.Based on the orthogonal separation algorithm,the solution of Pochhammer-Chree equation and the SAFE solution are compared and analyzed.The error is less than 1.5%,which proves the validity of the semi-analytical finite element algorithm in analyzing the propagation characteristics of guided waves.(2)The improved semi-analytical algorithm studies the influence of damping and initial stress effects on guided wave modal propagation.The longitudinal wave velocity decreases linearly with the increase of the stress level.The decay factor curve is calculated,and the energy velocity is defined and calculated.The changes of L(0,1)and F(1,1)guided wave modal velocities under different stress levels are analyzed,and the stress-energy velocity change rate curve is obtained.Overall,the initial stress effect is linear,and the longitudinal wave velocity decreases linearly with the increase of stress,and the velocity change rate is up to 1.85%.It can be explained by the acoustic-elastic effect.Finally,based on stress sensitivity,vibration displacement and attenuation factor,an optimal guided wave monitoring mode selection method is proposed.(3)The semi-analytical finite element solution is performed on the spiral steel wire,and the guided wave mode separation and mode conversion appear in the spiral steel wire.The semi-analytical solution of spiral steel wire in curvilinear coordinate system shows that the phenomenon of mode separation and mode conversion occurs in spiral steel wire.Meanwhile,with the increase of spiral Angle,the bending mode separation becomes more and more intense.The maximum value of P-wave cutoff frequency is16.3k Hz when the spiral Angle is 45°.(4)For the low-order longitudinal wave in the dispersion curve of steel strand,the phenomenon of frequency band loss occurs and the missing frequency band moves to the high frequency region with the increase of stress level.After calculating the dispersion of the strand wire by SAFE,it is observed that the frequency band loss appears in the L(0,1)mode of the strand wire at 69 KHz,and the wave velocity of the guided wave decreases and increases sharply.This phenomenon also appears in the dispersion curves of the two and three related wires,which confirms that the frequency band loss is related to the contact effect between the wires.Dispersion curves of steel strand under different stress levels were calculated and corresponding modal analysis was extracted.It was found that the center frequency of missing frequency band increased logarithmically with the increase of stress levels.(5)The experimental study on the guided wave of steel strand is carried out,and the law of the guided wave velocity changing with the tension is obtained.The results show that the guided wave velocity decreases linearly with the increase of tension.The maximum variation rate of the wave velocity at 200 KHz is-1.51% at 0.8UTS and-2.11% at 300 KHz.The semi-analytical finite element solution of steel strand is verified by comparing and analyzing the results of steel strand with the experimental results. |
PDF Full Text Request