Flexural Behavior And Mechanical Model Of Laminated Channel Beams In Modular Steel Buildings

Modular steel buildings are increasingly popular and widely applied in modern urban engineering with the advantages in shortening construction period and alleviating engineering pollution.For this innovative structural system,the connection strength between modules plays a key role to the whole mechanical property.In traditional modular steel buildings,a group of modules were assembled with only corner connections,which leads to the individual working between adjacent components.In order to improve the integrity of modular steel buildings,floor and ceiling beams were overlapped with different interfacial connections and formed the laminated beams.Full-scale experimental investigation,refined and simplified FE analysis and theoretical study were conducted to systematically study the flexural performance and mechanical models of laminated beams.The main research contents and results are as follows:(1)Investigation on bending performance of steel laminated beams under the vertical load.The four-point loading tests were carried out on 7 groups of full-scale single beam and laminated channel beams with different interfacial connections.The interfacial slip was accurately captured using DIC measuring method.The results show that large deformation failure occurs in mid-span and obvious slippage occurs in the interface under vertical load.The initial flexural rigidity and flexural capacity of laminated steel beams are obviously increased as compared to the independent bending beams.With strengthening of the interfacial connection,the slip stiffness of the floor and ceiling beams are increases gradually.The neutral axes of layers in bolt-connected laminated beams tend to the interface during the loading process.Moreover,with heightening of interfacial slip stiffness,the neutral axes transfer degree increases,and laminated beams perform the higher overall flexural performance.The shear stiffness of the interface has a significant influence on the laminated bending behavior of the floor and ceiling beams.(2)Evaluation on the flexural performance of laminated steel beams under the lateral load.The lateral loading test of full-scale modular steel laminated channel beam and column units was carried out to analyse the effect of layer superposition on mechanical property of modular steel buildings and particularly evaluate the flexural behavior of the laminated steel beams under reversed bending moment.The results show that the slips are observed at the interface of laminated beams.The overall anti-symmetric bending deformation occurs on the laminated steel beams,with the most obvious bending deformation at the beam end area.Compared with the pure friction laminated steel beam,the bolt connected laminated steel beam has higher anti-symmetric bending stiffness and bearing capacity.The anti-symmetric bending behavior of laminated steel beams is closely related to the strain neutral axis transfer of the layers,and the degree of the neutral axis transfer is the landmark feature of the superposed bending effect of the double beam structure.(3)Study on mechanical behavior and shear slip model of the interface.The shear slip mechanics behavior of the interface is the key to analyze the flexural performance of the laminated beam.The refined FE models were conducted to analyze the slip behavior and load distribution of the interface under the vertical load and the reversed bending moment.The basic differential equation of the laminated steel beam is established and the theoretical equation of the relative slip curve of the laminated steel beam is obtained.The results show that the interfacial slip behavior is an important factor that leads to the failure of laminated steel beams.The relative slippage of the interface has anti-symmetric distribution when the laminated beam is under vertical load,while the relative slippage shows a parabolic distribution and peak at mid-span section under the reversed bending moment.The distribution law of tangential friction load and bolt shear load on the interface is consistent with that of the relative slip distribution.With the increase of the bolt numbers,the shear-slip stiffness of the interface increases gradually,and the slip amplitude decreases correspondingly.Based on the differential equation of laminated steel beams,theoretical equations of the relative slip of laminated steel beams with different load models and boundary conditions are established,which lays a foundation for the establishment of initial equivalent bending stiffness and flexural bearing mechanical model of laminated steel beams considering the interfacial slippage.(4)Study on the laminated bending mechanism of the floor and ceiling beams.The parametric study on the flexural performance of laminated channel beams were performed with the simplified finite element models.Based on the results of parameter analysis,the vertical and lateral experiments and the interfacial mechanical behavior,the superposed mechanism of laminated floor and ceiling beams is revealed.The results show that there is a positive linear correlation between the bending bearing capacity of laminated steel beams and the friction coefficient of the interface.The influence of bolt numbers is more significant on the beam bending mechanical properties.The overall bending stiffness and bearing capacity of the laminated beams highly increases by adding the number of bolts.Compared with the independent bending double beams,the bending bearing mechanism of the laminated steel beam is obviously changed.The normal and tangential loads are generated on the interface of two beams,and the two beams are constrained by each other.The connectors between the layered beams effectively improve the shear stiffness,and obviously restrict the relative slippage of the floor and the ceiling beams,which highly improves the overall flexural performance.During the deformation process of laminated steel beams,the upper and lower beams neutral axes tend to transfer to the interface,and the floor and ceiling beams are subjected to superposed bending effect.The two beams show certain overall beam bending mechanical characteristics,so that the laminated steel beam exhibit the superior bending performance.(5)Study on the mechanical model of initial bending stiffness and deflection curves of laminated channel beams.Based on the basic physical equation of cross-section strain and combined with the slip theory equation of the interface,the theoretical equation of layer neutral axis transformation is derived.The equivalent initial bending stiffness model of the laminated steel beam is established,so as to quantitatively study the superposed bending effect of the floor beam and ceiling beam.Based on the theoretical model of equivalent initial bending stiffness,the theoretical formula of the load-deflection curve under vertical load and the theoretical formula of the moment-rotation curve under reversed bending moment are established.The theoretical capacities obtained by the mechanical model agree well with the experimental and numerical results.This thesis contains 94 figures,22 tables and 165 references.