Study On The Second-order Effect Of MDOF System With Material Nonlinearity Under Horizontal Seismc Excitation

The second order effect belongs to the reaml of the geometrically nonlinearproblem, and its influence is prevalent in all types of building structures. Research onthe second-order effect of the multi-degrees-of-freedom structure is mainly concentratedin the equivalent linear method, and basically did not reckon in the second-order effectsgenerated by the component’s deflection. Structure members under large earthquakewill produce elastic and plastic deformation, the deflection of slender membersthemselves also cause second-order effects, how much these factors impact the wholesecond-order effect is the main content in this paper. By numerical simulation,preliminary exploration of the impact caused by materials nonlinearity and component’sdeflection on the whole second-order effect of multi-degrees-of-freedom structure underhorizontal seismc excitation has been done. Conclusions as follows:If the structure is in the linear elastic state, the issue of the second-order effects canbe dealed with equivalent linear method. During dynamic analysis, the equivalent linearmethod which directly modifies the lateral stiffness is more accurate. For high-risebuildings, especially these of long period, it is not precise enough to calculate thesecond-order effect by applying the simplified method more suitable for the first mode.The contribution of higher modes on the structural response should be considered.Considering second-order effects, the lateral stiffness of the structure will bereduced, and the structural vibration period will be extended. With the deepening ofnonlinearity of materials, lateral stiffness will be further reduced, resulting in extensionof the natural period. Therefore，for the structure under static load, the influence ofsecond-order effect on the structural response will be more significant. But underdynamic loads, due to the spectral characteristics and the randomness of ground motion,it is difficult summarize the pattern of changes in the structural dynamic response.In the structural dynamic analysis, second-order effects caused by memberdeflection donot influence the dynamic response of structure significantly.