ABSTRACT

To provide a basis for the development of interaction curves for tubular beam-columns of annular cross section, a general purpose beam column computer program is developed, and used to determine ultimate load capacities. The paper presents the analytical model and the computer method. The analytical results are compared with published test data as well as experimental data obtained as part of this project.

INTRODUCTION

Previous investigators (2,4,5,12) have shown that tubular members of annular shapes exhibit structural characteristics markedly different than wide flange shapes when subjected to loads causing stresses above first yield. Methods for calculating failure loads and developing interaction diagrams for wide-flange members used as beam-columns have been developed (6,8) and are currently used in design practice. Since a systematic technique to accomplish the same for tubular members is so far not available, an investigation was launched to develop an analytic tool in the form of a computer program which could be used to generate load displacement histories and calculate failure loads of circular steel tubes subjected to the combined effects of axial force and flexure. The purpose of this paper is to briefly document the development of the mathematical model and to present experimental data to check the results of the computer program.

The computer program is capable of accounting for the effects of residual stresses during the generation of the moment-thrust curvature (M-P-?) data, the initial phase in the calculation of beam-column failure loads. The inclusion of any configuration of stress strain relationship may be accomplished by providing appropriate input data in tabular form. However, it should be noted that while this investigation includes the determination of M-P-?data, those provided by other investigators may also be used as a direct input to the computer program. The calculation of failure loads is accomplished by a numerical technique which increases the load in increments until no further load can be supported. At this point, the beam-column is considered to have reached failure.

As part of this investigation, a testing program was devised to obtain experimental data. The program consisted of four model tests of circular tubes loaded eccentrically to failure. These tests and those of other investigators were used to check the validity of the mathematical model presented in this paper.

COMPUTER MODEL

The computer model consists of two major components; generation of M-P-?data, and determination of failure loads. Details of each are described below.

The moment-thrust-curvature data characterizes the behavior of column stubs. It is the fundamental information which defines, for a given strain condition, the required stress distribution and magnitude necessary for equilibrium. An open-form solution technique to determine M-P-?relationships for circular tubes by dividing the cross section into horizontal sectors has been previously developed (4).

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