Experimental And Theoretical Study On The Behavious Of Centrifugal Concrete-Filled Steel Tubular Under Torsion And Combination Actions

In view of the rapid development of electric undertaking and a sharp increase of steel products consumption,the State Development Planning Commission,the former State Water Resources and Hydropower Ministry and State Energy Ministry have been urging that the building of steel towers should be strictly controlled in the construction of transformer substations;and warning that the need of the present 500kv power transmission and transformer trusses can hardly be satisfied by ordinary steel and concrete electric poles or prestressed concrete poles,which have endangered the operation and longevity of the high voltage transmitting line due to the common problem of cracks by gravity. On the basis of comprehensive analyses and studies,now the centrifuge concrete filled thin- walled steel tubular is regarded as one of the ideal substitutes of the traditional concrete poles,and there has been a practical call for the researches on itUnfortunately,present evidence is all for the capabilities of the tube under single load but there is hardly any datum relating to those under the combined loads of bending and shearing torsion that many members applied in electric power projects inevitably bear to different extent.This paper intends to improve this situation with the experimental researches and related theoretical analyses done on the subject. As a result of growing need,in 1999,the research on capabilities of the centrifugal concrete filled thin-walled steel tubular under tension and torsion was started by Zhe Jiang Electric Power Design Institute and the Civil Engineering Department of Zhe Jiang University. This research was also supposed to provide a valuable reference for the construction of 500kV Eastern HangZhou transformer substation project. To guarantee the rationality of the torsion and bending load application,a set of experimental equipments was transformed from a traditional one by exerting tangential force on the brim of the fan board and conducting broad-billed roller application. In the actually fulfilled experiments on the capabilities of the members under different ratios of torsion and bending,the equipments proved to be well qualified in load applying to large-tonnage members. And the theoretical analyses done in this paper are listed below:First,the experimental data on the members of varied parameters under torsion demonstrate the general rule of the deformation while the tubular is under torsion. Thepaper establishes three phases of the deformation of the tubular under torsion,namely,the elastic deformation,the elastic-plastic deformation,and ultimate failure. Through regression analysis,a simplified method is proposed for calculating the capabilities of the tubular under elastoplastic torsion,and the formulary for bearing value,is also recommended as a reference in engineering design. Besides,on the basis of the test data under bending and torsion and the theoretical analysis on the tubular,the relative relationship between the bearing values is derived.Second,based on the elastic theory,this paper deduces the rules of stress distribution and main physical and geometric parameters by analyzing the elastic stress distributions when the tubular is under such conditions as torsion,bending,shearing,combined bending and torsion,and combined shearing and torsion;additionally,taking the strength criteria of concrete and steel as reference,the paper proposes a set of theoretic equations for the relative relationship between the bearing values.Third,a theoretic approach based on total theory of plasticity is for the first time applied to analyze elastoplastic torsion rigidity of the tubular,and the results are well proved by the test data.Also for the first time,the plastic stability of the spiral skew stiffening shell is studied. It is shown in the experiments that there is the comparability between the stability of the members at plastic limit and that of the thin-shelled steel tubular with the spiral skew stiffening concrete rib. Therefore the author addressed the stability of the me...