Structural Behavior And Stability Design Method Of High-Rise Asymmetrically Braced Steel Storage Racks

The domestic storage industry has experienced a rapid growth in recent years.Steel storage racks play a key role in the storage industry.The high-rise steel storage racks with spine brcaing systems are capable of carrying a treamendous amount of pallet goods while only taking a limited foot-prints,and are thus recognized as the most popular rack system in the storage industry.The high-rise braced racks are thin-walled lightweight steel framing structures.Compared with convensional steel building frames,the high-rise steel storage racks with spine bracings are characterized by the slenderness of the compression members,the semi-rigid stiffness of the joints,as well as the possible torsional behavior of the global structures.In general,the load-transder mechanisms and the failure mechanisms associated with such high-rise racks are not yet fully understood by far.It is of desperate need to develop a proper stability design approach for the high-rise asymmetrically braced steel storage racks.This thesis investigates the behavior of the high-rise steel storage racks from both the element level and the system level.The aim of the thesis is to develop an approach for the stability design of such high-rise braced steel storage racks.The rack-to-spine-bracing joint is one of the key structural elements in the highrise braced steel storage racks.The behavior of the rack-to-spine-bracing joints somehow determines the load-transfer mechanisms of the global rack structures in the down-aisle direction and the strength of the racks.The behavior of the rack-to-spinebracing joints subjected to lateral loads was experimentally established in the thesis.A total of 24 joint specimens were involved in the experimental program.Using a noncontact DIC technique based three-dimensional measuring system,the real-time performace of the components in the rack-to-spine-bracing joints were recorded in the tests.The thesis developed an analytical model for each component associated with the rack-to-spine-bracing joins.Using a component based analytical method,the initial stiffness of the rack-to-spine-bracing joints under consideration was established.The analytical model was well validated against the experimental results.The contribution of each component towards the deformation of the entire rack-to-spine-bracing joints in the elastic range was determined using the proposed analytical model.The baseplate upright connection with bracket is the most commonly used base connections in the high-rise braced steel storage rack systems.Based on the experimental observations reported in the past studies,this thesis proposed two analytical models(i.e.,the baseplate with eccentric/concentric anchor bolts)for the rotational stiffness of the baseplate components associated with the bracket-type base connections of the high-rise racks.The influence of the configurations of the anchor bolts in the baseplates,as well as the influence of the flexural bending mechanisms of the baseplates were explicitly considered in the analytical model for the steel storage rack baseplates upright connections with brackets.Using the proposed baseplate models,a simplified method for predicting the full-range moment-rotation relations of the bracket-type baseplate upright connections was developed.The thesis experimentally investigated the stability performance of the asymmetrically braced steel storage racks under vertical loads.A total of 8 single-spansingle-level rack frames with spine bracings were considered in the experimental program.The tests suggested that the rack frames with asymmetrical spine bracings usually failed by the global flexural-torsional failure of the entire frames.The experimental observations suggested that the in-plane sway magnitude of the rear rack frames and the front rack frames associated with the rack systems was quite different at failure stage.For a particular rack frame with spine bracing system,the instant the global structure failed,the magnitude of the in-plane sway of the front rack frame was at least 50% higher than the sway magnitude of the rear rack frame.Besides,the sway magnitude of the rear rack frame was different from the sway of the associated spine bracing system.The shear deformation of the rack-to-spine-bracing joints between the rear rack frame and the spine bracing system could be observed.The tests indicated that the shear stiffness of the upright frames influenced the magnitude of the global torsional effects of the braced rack structures.The increase of the shear stiffeness of the upright frames would lead to a reduction of the global torsional effect.As a general statement,the global torsional effects of the entire rack structures somehow amplified the in-plane sway magnitude of the rear rack frames and the front rack frames,and resulted in a decrease in the stability strength of the asymmetrically braced steel storage racks.The thesis established a stability design method for the high-rise asymmetrically braced steel storage racks.The global torsional mechanism associated with the entire braced rack structures was explained.The amplification factor of the global torsional effect on the magnitude of the in-plane sway of the rear/front rack frames was determined.A story-based analytical model for the stability analysis of the high-rise braced steel storage racks was developed.The interaction between the rear frames and the front frames of the racks,as well as the global torsional effects,were explicitly considered in the proposed model.The buckling equations associated with the high-rise braced steel storage racks were developed using the proposed model.The equations for determining the effective length factor was also developed.Parametric studies were performed using the proposed buckling equations for the high-rise braced steel storage racks.The influence of the global torsional effects on the strength of the entire highrise racking systems was quantified.