The shape and location of reinforcing bars in the structural material are reconstructed from ultrasonic scattered waveforms in the low frequency. Two linearized inverse scattering methods are investigated for the imaging of reinforcing bars. The Born and Kirchhoff inversions reconstruct domains and boundaries of the bars, respectively. Although the dynamic interaction effect exists in the adjacent part of multiple bars, we can reconstruct the whole shape of bars with the Born inversion. On the other hand, the Kirchhoff inversion leads to the classification of the damaged area around a reinforcing bar. These performances of proposed imaging methods are demonstrated by numerical simulations using the boundary element method.