Research On Mechanical Mechanism Of Concrete Filled Steel Tubular Members With Ribs

Concrete filled steel tubular member (CFT) has been widely used in practical engineering works because of its superior load-carrying capacity, plasticity, ductility and mechanics performance. However, under the cycle load and earthquake load, steel tube can occur local buckling failure and concrete can occur shearing or brittle failure. As one of improving measures, strengthening ribs are setted on the steel tube, it is called CFT members with rib. Until now, there is much researches about ribbed square and rectangular CFT members, while researches about ribbed circle CFT members is littel, so it is necessary to carry out the research on mechanical mechanism of circle CFT members.In this thesis, numerical analysis on mechanical mechanism of CFT columns and beams with ribs is carried out using ABAQUS software, and the calculation results are in good agreement with the experimental results.Analysis of axial compression members shows that: (1) The ultimate bearing capacity,ductility and seismic performance of CFT members with ribs can be effectively improved by using ribs , the load-carrying capacity of ribbed memebers increased greater than that of non-ribbed members; (2) The effect of the number of strengthening rib on mechanical performance of members is not very obvious, the ultimate bearing capacity of ribbed members is higher than that of non-ribbed members; (3) Concrete strength have a great influence on the ultimate bearing capacity of members; (4) Steel tube's thickness has a great effect on the ultimate bearing capacity of members, the smaller width-thickness ratio is, the greater bearing capacity is; (5) The vertical and horizontal stress field analysis of steel pipe and core concrete show that strengthening ribs on can effectively improve the core concrete stress state, two different materials can give full play owing to ribs, the number of local buckling is reduced, the strengthening ribs can effectively restrict lateral expansion of the concrete.Analysis of bending members shows that: (1) Bending properties of ribbed members are not more excellent than that of non-ribbed members, and the ductility is weak after peak; (2) Bending performance can be effectively improved with the increase of steel tube's thickness, the degree of elevation is obvious; (3) Concrete strength has no obvious effect on the bending performance of members; (4) Analysis of horizontal and vertical stress field about core concrete shows that the weak tensile strength and high brittleness of concrete enhance and the limit bearing capacity of members is reduce owing to ribs because concrete near to ribs crack ahead of time.