| Faced with the challenges of wide rivers,complex marine environments,and limited urban space,cable-supported bridges are continuously evolving towards larger spans,heavier loads,multiple towers and spans,and more lightweight and aesthetically pleasing designs,which place higher demands on the structural performance,durability,and landscape aesthetics of bridge pylons.PBL-stiffened thin-walled steel-concrete composite pylons have advantages in material utilization,design flexibility,and construction efficiency,which make them more suitable for the development needs of cable-supported bridges.However,the application of steel-concrete composite towers is still in its infancy worldwide,and the basic theoretical research is relatively weak.This dissertation focuses on the PBL-stiffened thin-walled steelconcrete composite towers and conducts a comprehensive and in-depth study on their loadbearing mechanism,computational theory,and design methods using theoretical analysis,experimental investigation,and numerical simulation.The main research content and achievements are as follows:(1)By conducting pull-out tests on 12 PBL connectors and performing finite element parameter analysis,the steel-concrete interface pull-out force transmission mechanism and shallow-embedded PBL connector failure mechanism of composite bridge pylons were revealed.The influence of parameters such as perforated steel plate structure and material strength on the pull-out performance of PBLs was studied.A concrete breakout model for shallow-embedded PBLs under pull-out forces was proposed,along with the corresponding calculation formula for the pull-out resistance.An equivalent spring model of the PBL connector was established,and the calculation formula for elastic tensile stiffness was derived.(2)A total of 16 specimens were tested to investigate the local buckling performance of high-strength steel plates with unilateral restraint from concrete.The local and post-local buckling bearing mechanisms of the unilaterally restrained flat plate were revealed,and the normalized slenderness limit and effective width formula for the unilaterally restrained plate were proposed.Based on the small deflection theory of thin plates,the energy method was used to derive the elastic critical buckling coefficient and relative stiffness limit of the PBL-stiffened plate under unilateral restraint,and the effective area method for calculating the post-buckling strength of the unilaterally restrained PBL-stiffened plate was proposed.(3)By conducting axial compression tests on six PBL-stiffened thin-walled steel-concrete composite columns and performing finite element parameter analysis,the failure mechanism of pylons under axial compression was revealed,and the influence of parameters such as transverse and longitudinal spacing of PBLs and material strength on the axial compression performance of PBL-stiffened thin-walled steel-concrete composite pylons was investigated.Based on the superposition principle and effective area method,a calculation method for the axial compression resistance of PBL-stiffened thin-walled steel-concrete composite pylons considering the local buckling effect of the steel panels was proposed.(4)By conducting eccentric compression tests on eight PBL-stiffened thin-walled steelconcrete composite specimens,the collaborative load-carrying mechanism of tension and compression for PBL-stiffened thin-walled steel-concrete composite pylons under combined bending and compression was revealed.Based on the plastic analysis method and considering the effect of local buckling of the steel panel in the compression zone,a simplified calculation model for the bending resistance of PBL-stiffened thin-walled steel-concrete composite pylons was proposed,along with N-M interaction equations and simplified N-M interaction curves.(5)A local stability analysis mechanical model was established for the wall unit of PBLstiffened thin-walled steel-concrete composite pylons,and the elastic stability critical load and normalized slenderness ratio calculation methods were presented.Based on numerical test results,the axial compression stability coefficient of the wall unit of PBL-stiffened thin-walled steel-concrete composite towers was given,and calculation methods for the axial compression stability and bending stability of the composite pylons were proposed.(6)Building on the previous research results,the overall design process of PBL-stiffened thin-walled steel-concrete composite bridge pylons was examined in consideration of their structural characteristics.Subsequently,design recommendations were proposed to fully utilize the synergy of steel and concrete,and to achieve a higher degree of industrialized construction.Based on the limit state design method adopted by the Chinese highway bridge design,a design method for PBL-stiffened thin-walled steel-concrete composite pylons was proposed. |
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