Research On Modeling And Solution Method Of The Lightning Impluse In High-rise Building Structures

With the reduction of urban land and the increasing of urban population, high-rise buildings spring up continuously, however these buildings are vulnerable to lightning. Therefore, to fully understand the phenomena of electromagnetic transient on a building after lightning strike, the mathematical models of impulse current considering the reflection coefficient of the top and bottom of a tall object is established; the three-dimensional electromagnetic coupling model based on the finite element method is proposed to solve the current distribution and the inner magnetic field distribution of the building structure; furthermore the three-dimensional electrothermal coupling model is proposed to analyze the temperature distribution of steel structure simplified with a single cylinder; experiments are carried out to study the current distribution, the magnetic field distribution, the temperature distribution and the electrodynamic force effects through a reduced scale model of a five-story building.Firstly, transient behavior of tall object struck by lightning is studied with the lightning return stroke represented by transmission line(TL) model. Mathematical formulations of lightning current in lightning channel and tall object are presented, which are represented by lumped voltage model, distributed current sources model, as well as Newton equivalent circuit model in engineering model. Current waveforms of lightning strike to flat ground and to tall objects are simulated, which are represented by lumped voltage model and distributed current sources model; the influences of the top and bottom reflection coefficients of a tall object on impulse current waveforms are analyzed; also,the influences of tall object on first return stroke and subsequent return stroke current are analyzed.Secondly, the current and magnetic field distribution of high-rise building struck by lightning is studied. The parameteried lightning impulse simulation model of a high-rise building is established, and with an example of a typical building, the results of different calculation methods are compared. With the proposed coaxial loop test model, the current distributions in the steel structure of the reduced scale model of the five-story building are investigated through experiments, and the magnetic induction intensity of six spatial points at the top floor, the fourth floor and the bottom floor of the building are measured respectively. The simulation results of the proposed electromagnetic coupling model are compared with experimental results, showing that the current distributions agree well, whereas the magnetic induction intensity are slightly different, but the distribution trend of them are the same.Finally, thermal effect and electrodynamic force effect of high-rise buildings are invetigated. The temperature distributions of the reduced scale model of the five-story building subjected to the same amplitude, different amount coulomb long stoke current are studied experimentally. Test results agree well with those simulations by the proposed electrothermal coupling model based on the finite element method. The relationship between the magnitudes, the transferred charges of the long stoke current and the temperature rises are analyzed by simulation, which provides a theoretical and experimental basis for solving these problems. The damage of the reduced scale model of the five-story building struck by impulse currents of different magnitude is studied, and the results indicate that although the amplitude of impulse current is high, because of its short duration the steel structures of the building is not damaged.