This paper reports the results of research in welded connections between steel tubes. Static and fatigue behavior of such tubular joints are described.

Static tests include eleven T-joints, three Y-joints and three K-joints. The reserve strengths, the modes of failure and the influence of geometrical parameters on the distribution of elastic stresses are discussed for the specimens tested. Typical contours of isostatics and isobars are given. Nomographs are presented for T-joints. A brief description of the theoretical analyses of tubular joints is incorporated.

Fatigue tests of one hundred smallsize T-joints under different cyclic loadings are also described. The influence of important geometrical parameters on the response of small-size T-joints is discussed.


The recurring problem of joint failures in offshore structures with tubular joints has made it imperative for interested bodies, such as oil companies, universities, and research firms, to embark on experimental and analytical research programs. The factors which influence the behavior of tubular joints are too many and some of these factors are not yet clearly understood. The variety of joints and the different methods of stiffening used in offshore structures suggested that studies were necessary to provide improved design methods that result in economical connections.

In an attempt to furnish the needed research data, a four phase program was planned at the Structures Fatigue Research Laboratory of The University of Texas at Austin, and incorporated the following major objectives:

  1. To study the effect of static loads on various types of connections that include T, Y and K - joints.

  2. To study the effect of fatigue loading on various joints, starting with T joints.

  3. To verify the effect of certain parameters on the stresses and their distribution.

  4. To observe modes of failures of the various joint types.

  5. To correlate, if possible, theoretical analyses with experimental data.

The four phase program that has been considered to incorporate the main objectives includes:

  • Static tests on T, Y and K-joints. (Phase I and II).

  • Fatigue tests on T-joints. (Phase III).

  • Fatigue tests of more complicated joints. (Phase IV).

Phase I, II and part of III have been completed and this report presents a concise summary of the various aspects of these studies, and includes data on T, Y and K joints and the results of fatigue tests performed on a large number of small-size T joint specimens.

The specimens tested under static loads were designed in such a way as to cover a broad and practical range of parameters. The geometrical parameters (see Table I) selected for this research were as follows:

  1. The ratio of chord length to mean chord radius,?.

  2. The ratio of mean radii of brace and chord,?.

  3. The ratio of mean chord radius to chord thickness,?.

  4. The ratio of the brace thickness to the chord thickness, ?.

2. 1 General

The initial portion of the research program dealt with the investigation of the static behavior of T, Y and K-joints.

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