Equivalent impedance of building columnc and girders against lightning surges

Abstract

AbstractIf a telephone center building is subject to a direct hit by lightning, lightning surge currents flow in the columns, girders, and walls and, hence, the equipment may be damaged or may malfunction due to induction into the communication cables and power lines. Studies on the current and voltage distributions in the building by the direct lightning hit have been carried out. One of the fundamental subjects is the method of estimating the equivalent impedance of actual columns and girders. There has been no sufficient understanding because the dimensions of the steel frames are large and the shapes are extremely complex.In this paper, scaled‐down models of the columns and girders are constructed first and the impedance measurement method for these models is discussed. It is found that the current distributions in the model become almost homogeneous if several return wires are placed around the scaled model of the column so that a measurement close to an actual situation can be carried out.Next, by means of this measurement method, a simple cylindrical conductor rod and the scale model of the column are compared. Hence, it is proven experimentally that the resistance and the inductance of the columns and the girders can be estimated from the computational equation for the cylindrical conductor rod with identical surface area to those of the steel frame and the steel rod, even if the shapes are complex.Finally, the actual columns of a reinforced concrete building are measured and agreement is confirmed between the estimate from the scale model and the actually measured values.