Progressive Collapse Dynamic Effect Analysis Of The High-rise Steel Three-dimensional Garages

The high-rise steel parking structure is one of the main methods to solve the parking problem in metropolitan area because of its beautiful elevation,land-saving,large storage capacity,security and stability.This kind of structure is mainly composed of a outer frame,parking racks or parking boards,hoisting equipments and so on,which makes the overall structure is finer,and higher intelligence.To satisfy the using functions in construction,the floors are canceled and the main load-bearing elements are the beams and columns in the outer frame.As a consequence,the lateral stiffness of outer frame is small and its beams and columns are prone to instability under loads.Meanwhile,these parking structures are generally built in commercial centers or prosperous areas,and the failure of a bearing column at the ground floor will cause heavy casualties and economic losses.Therefore,the research of the high-rise steel parking structure is more important.The main loads of the high-rise steel parking structures are the structural dead weight and the living vehicle loads.For the latter,its location and quantity present stronger randomness during the storage process of vehicles.The vehicle arrangement conditions can't be ignored in the progressive collapse dynamic analysis of the structure.In this thesis,more than 200 representative working conditions are selected from thousands of vehicle arrangement conditions to do research by the use of orthogonal experiment table.In the progressive collapse analysis of the structure,the instantaneous removing column method considering the initial deformation of the structure is adopted.The failure time of the bottom columns is taken as 0.1 times of the natural vibration period of the remaining structure according to the related literatures.The mechanism guidelines and the relevant provisions of the American GSA design criterion are taken as the structural failure criterion to distinguish the failures of the structure and the members respectively.In addition,the nonlinear dynamic analysis method is adopted in the progressive collapse dynamic analysis,considering structural dynamic effects,material nonlinearity and strain-rate effect.For studying the collapse mode of the high-rise steel parking structure,two representative vehicle layout conditions are selected,that is,the structure is fully packed with vehicles and only the side where the failure column lay is packed with vehicles,and at the same time,four different failure modes of the underlying column are considered.Through the study of the collapse modes of the remaining structures under different vehicle layout conditions and failure modes of the underlying column,it is found that the remaining structure is easy to yield to form a plastic zone at the cross section of the beam and the web near the node in the span where the failure column is located,and for different failure modes of the bottom column,the residual structure has different collapse resistance and different load dynamic amplification factors.According to the collapse modes of the high-rise steel parking structure,the collapse resistant capacity can be improved by enhancing the bearing capacity of the underlying column.Therefore,the vertical axial force amplification coefficients of the remaining underlying columns of the 10-,14-and 18-storey parking structures are studied and the maximum values of the vertical axial force amplification coefficients of the underlying columns are obtained.When the number of structural layers is between 10 and 14 or between 14 and 18,the maximum value of the vertical axial force magnification coefficients of the underlying columns can be obtained by linear interpolation.In practical application,the value of the bottom column vertical axis force calculated by normal design multiplying the magnification coefficient can be used as the new design value of the vertical axis force to improve collapse resistant capacity of the high-rise steel parking structure.