Research On The Out-of-plane Stability Of CFST Solid Rib Arches

Concrete-filled steel tubular (CFST) arches have been broadly used in modernbridge engineering in China. Among various CFST arches, single steel tubular anddumbbell-shaped CFST arches, which are called solid rib arches, are accounted alarge part of the total. As the main bearing structure, CFST arches usually haveexcellent in-plane load-carrying capacity compared, however because the relativelyweak out-of-plane rigidity, the out-of-plane stability often arise as the dominateproblem. Therefore, this thesis focuses on the out-of-plane stability of CFST solidrib arches, starting from the study on composite mechanical behavior of CFSTstructures. The main work and research results are as follows.Firstly, single tubular and dumbbell-shaped CFST specimen subjected totorsion moments are carried out, and a finite element method to analyze it is verifiedby the test results. Then experimental of dumbbell-shaped arch model under spatialloading is conducted and the whole behaviors of the model to failure are obtained. Aspatial finite elements model is built to analyze the out-of-plane stability of theCFST solid rib arches.Secondly, instability due to elastic buckling and peak value (ultimateload-carrying capacity considering the stability problem) are analyzed bycalculation of Eigen value and FEM method taking into account the dual nonlinearproblem (material nonlinearity and geometric nonlinearity). The influences ofvarious parameters to the out-of-plane stability are discussed. The analysis resultsshow that out-of-plane slenderness ratio is the most important among all theparameters and the out-of-plane critical load takes a nonlinear decrease as theout-of-plane slenderness ratio increases. Rise-span ratio is another important factor.The total critical load increases with the increase of the rise-span ratio, but it willincrease smoothly not significantly when the rise-span reaches to some value.Moreover, different material parameters have different influences on out-of-planestability, in which the steel ratio has the most significant affect. In addition, elasticbuckling analysis may give a false result when the arch subjected to a out-of-plane force or the arch has an initial out-of-plane geometric imperfection. In this case, thecritical load of the arch failure by out-of-plane instability should be calculated bythe FEM analytical method which considering the double nonlinearity.Thirdly, the thesis is also focused on the analysis of the out-of-plane stabilityunder four basic kinds of loading conditions. The sum value of the critical load ofthe out-of-plane stability of the arch is the largest one when the arch subjected towhole-span uniform load, and it is the second one when the arch is subjected to thehalf-span uniform load. The out-of-plane stability is influenced greater to an archwith single tube section than to an arch with dumbbell-shaped section. Furthermore,the out-of-plane stability of dumbbell-shaped arches is generally higher than that ofthe single steel tube arches.Finally, the thesis puts forward a simplified algorithm about the out-of-planecritical load of CFST solid arches. According to the suggested out-of-planeequivalent length coefficient, Euler formula is applied to calculate the out-of-planebuckling load. Besides, Perry-Robertson formula is used to express the relationshipbetween out-of-plane stability coefficient and out-of-plane normalized slendernessratio, and hence the out-of-plane stability ultimate load-carrying capacity can befurther calculated. Meanwhile, the ratio curve between out-of-plane elastic bucklingcoefficient and out-of-plane stability coefficient is given. The out-of-plane stabilityultimate load-carrying capacity also can be calculated by the out-of-plane elasticbuckling critical load.