Elastic-plastic Dynamics And Aseismic Design Theory Of Steel Structures

Importance of ductility, damping and the energy-dissipating capacity through plasticity in earthquake-resistance and vibration absorption is explored in this thesis through analysis of SDOF with different hysteretic models under impact and harmonic loads. Ideal elastic-plastic (EPP), elastic-linearly-hardening (ELH), shear-slipped (SSP) and bilinear-elastic (BIL) are studied. It is found that the maximum impact load is the static load the structure can support; and formula of the maximum displacement under impact load etc. was presented. Under harmonic loads, when the load frequency is less than the fundament frequency of the SDOF (single degree of freedom) systems, the amplitude is reduced with the increase of the post-yield stiffness. While the frequency of loads exceeded the frequency of structures greatly, the structure amplitude is almost independent of the post-yield stiffness. The energy dissipation capability of plasticity can reduce structural displacement response more than damping, especially in case of resonance. From the study on SDOF (with damping and without damping) elastic and plastic dynamical response under impact and harmonic loads, it can be found that the work of dynamic loads done during the dynamical response of a SDOF system is dependent on the energy-dissipating capacity of system; and no work is done by the harmonic loads in the infinite elastic system without damping.The seismic force modification factor R was studied based on time-history earthquake analysis of SDOF system, the hysteretic models are EPP, ELH, SSP and BIL. The ductility and the damping ratio are taken to be different values in the analysis. The characteristic period of earthquake records is used to normalize the R-spectra to reduce the effects of different earthquake records on R spectra shape. By means of statistical regression analysis the relation of the seismic force modification factor R with the natural period of system and ductility was established for each site and soil condition. This will help to improve the seismic design of steel structures. In this thesis, an important aspect different from other researches is that the ductility and the energy-dissipating capacity are treated as independent factors affecting R. spectra. From the study, it is found that the most important factor determining R is the ductility, R increases with ductility more than linearly. The energy- dissipating capacity, damping, hysteresis model and the post-yield stiffness are the less important factors. The energy dissipating capacity is important only for structures with in short and moderate period (0.3 ≤T IT_g < 5.0). For EPP and ELH models, R decreases with increasing ofdamping, R for 0.05 damping is 10% to 15% smaller than for 0.02 damping. For the shear-slipped model and the bilinear-elastic model, the effect of the damping is similar. For EPP and ELH models, greater post-yield stiffness leads to greater R, but the influence of post-yield stiffness is obvious only when the post yield stiffness is less than 10% of the initial stiffness. Post-yield stiffness has a greater influence when the ductility is large.A new earthquake-resistant system (knee-braced frame, KBF) was investigated, in which an energy...