In this paper, the shielding effectiveness of reinforced concrete structures under electromagnetic pulse (EMP) illumination has been modeled and analyzed below 1 GHz regime. The reinforced concrete provides shielding effectiveness at particular frequencies by the concrete as well as the embedded reinforced conductive grid. The reinforced concrete structures are analyzed using commercial 3-dimensional electromagnetic field solver. The shielding effectiveness has been accessed by computing the effect of concrete, rebar and entire reinforced concrete. These results suggest that decreasing spacing of the rebar and increasing the rebar diameter will decrease transmission coefficient. The single layer having the thickness of rebar of 10, 20 and 30 mm reveal transmission coefficient of -1.89, -2.73 and -4.76 dB/10cm, respectively, at 500 MHz. In addition, double layers rebar structure provides -2.46, -6.16 and -9.55 dB/10cm attenuation, respectively, for the same conditions.