Study On Local Stability Performance And Ultimate Bearing Capacity Of T Rib-stiffened Plates Under Compression

In order to prevent the plate from instability,stiffening ribs should be used to strengthen the stiffness of steel box girder bridge’s compressed flange,steel box arch,steel tower and steel tube structure.When the structural compression is large,T-shaped stiffeners with greater stiffness than I-shaped stiffeners are often used for design,which also leads to more serious stability problems.At present,domestic and foreign scholars have little research on the compressive stability of T-ribbed stiffened plates.In order to rationally apply T ribstiffened plates in the design of steel bridges,this paper studies the local stability of T ribstiffened plates and its calculation method under compression by combining experimental research with finite element analysis.Considering the change of width and thickness of subplates of T rib-stiffened plates,the local stability tests of 13 welded T-ribbed stiffened plate and 9 welded T-ribbed stiffened plate with Q420 steel strength under compression were carried out.The results show that the axial stiffness of the T rib-stiffened plates will be significantly reduced when the local instability of the sub-plate occurs,resulting in the decrease of the slope of the average stressstrain curve,which shows obvious non-linear characteristics.When the width-thickness ratio of the unstable plate is the same,the higher the strength of the material,the greater the reduction of the ultimate bearing capacity.When the strength of the material is the same,the larger the width-thickness ratio of the unstable subplate is,the larger the space for strength improvement after local buckling occurs.The finite element models of local stability test specimens considering the influence of local initial geometric imperfection and numerical welding residual stress have been established.The ultimate compressive strength calculated by the finite element method is slightly less than the ultimate bearing capacity obtained by the test,and the average difference is not more than 3.44%.The failure mode and ultimate compressive strength of the finite element model and local stability test are in good agreement,which proves the correctness of the local stability finite element model.Based on the finite element model verified by experiments,the influence parameters of local stability,such as material constitutive model,welding residual stress and local initial geometric defects,are analyzed respectively.The results show that the stability coefficients of the four-fold line constitutive model and the ideal elastic-plastic constitutive model are close to the actual results.The results of the two-fold line constitutive model show that there is a stress-strengthening section in the curve,and the stability coefficient obtained is larger than that obtained by the two-fold line constitutive model.With the increase of widththickness ratio of unstable substrates,the reduction of stability coefficient after simplified residual stress is greater.When the position of the initial geometric imperfection is located on the sub-plate where the local instability first occurs,the reduction of the stability coefficient is more obvious.The stability factor is the smallest when all the plates are taken into account local initial geometric imperfections.Based on the experimental research and finite element analysis,the ultimate compressive strength of Q345 and Q420 steel members with 194 different structural sizes are calculated.By using cubic polynomial and Perry formula to fit the calculation results of stability bearing capacity,simplified formulas for local stability of single subplate are proposed.The simplified formula for calculating the local stability of T-ribbed stiffened plates is compared with the national standard curves.The results show that the curve fitted by cubic polynomial is in good agreement with the data calculated by finite element method,and the polynomial formula curve is above the Eurocode curve.The curve fitted by Perry formula gradually deviates from the finite element calculation data when the width-thickness ratio of the subplate is large.The curve of Perry formula is between the JTG D64-2015 curve and the ASHTO curve,and is so close to the AASHTO curve.