Study On Vibration Response Of Beam Members Under Explosion Load Based On Refined SDOF

The beam member will do periodic simple harmonic vibration under the action of explosion load.At present,most of the anti-knock analysis of building structures adopts the ideal elastic-plastic resistance model under the condition of no damping.Some scholars take the effect of damping force into consideration,but they think that the damping ratio in the elastic-plastic stage is the same,and this method is not accurate.In fact,the damping ratio in the plastic stage is greater than that in the elastic stage.In order to investigate the influence of various parameters on vibration displacement of beam members under air blast load,air blast load is divided into short-holding spatio-temporal explosion load and long-holding spatiotemporal explosion load in this paper.A plastic strengthening resistance model which is more consistent with the actual material model is selected to solve the elastic-plastic potential transfer and rebound potential transfer of equivalent single free system of structural members under the condition of damping.The displacement calculations under typical conditions of damping ratio0～0.1,ductility ratio 1～5 and plastic strengthening coefficient 0～0.2 are completed,and the vibration displacement is compared with that of an ideal elastoplastic material member without damping.In order to verify the correctness of the theory in this paper,experiments completed by relevant researchers were selected for verification,and the finite element software LSDYNA was used for numerical simulation of I-beam.The specific contents and results show that:(1)Compared with the ideal elastoplastic component,the component with plastic strengthening resistance may enter the plastic rebound stage.The main influencing factor of entering the plastic rebound is the plastic strengthening coefficient,and the smaller the damping ratio,the larger the ductility ratio and the plastic strengthening coefficient,the easier the component will enter the plastic rebound.Under the plastic strengthening resistance model,the peak value of vibration displacement and residual deformation of the component decrease to a certain extent.When the ductility ratio is higher,such as β=5,the reduction rate of the maximum elastoplastic displacement can reach 16.2% and the reduction rate of the residual deformation can reach 60.7%.(2)When the plastic strengthening coefficient is constant,the law and degree of influence of damping on the two types of members under short-duration load are basically the same.If the damping effect is ignored in the vibration of the member,the anti-knock ability of the member will be greatly underestimated.The comparison shows that the influence of damping on the displacement parameters of beam members is greater than that of plastic strengthening coefficient.Both damping and plastic strengthening coefficient make the maximum elastoplastic displacement of member smaller,but damping makes the rebound displacement of member smaller and the residual deformation increase,while plastic strengthening resistance makes the rebound displacement of member larger and the residual deformation decrease.(3)When the damping ratio is constant,most members reach the maximum velocity in the elastic stage,and the plastic strengthening coefficient only has a slight influence on the rebound velocity of members.The damping has a great effect on the peak velocity of the member when the strengthening coefficient of the fixed plastic is constant,and the reduction degree can reach14.3%.Similar to the effect on displacement,damping has a greater effect on the velocity of member than the plastic strengthening coefficient.(4)Long-term load will further increase the influence of plastic strengthening coefficient and damping on the displacement parameters and velocities of members under vibration.But the load time is too long,the member is not easy to enter the plastic rebound.Under long-term load,the peak value of rebound velocity is greater than the peak value of forward velocity when the plastic strengthening coefficient is high.(5)Through the comparison of typical field tests and numerical simulation tests,it can be seen that the theoretical calculation error of each shift parameter in this paper is about 4%,and the error of the finite element simulation is less than 10%.