API REPORT 07714-CAP-1998 Strength of Simple Joints - Effect of Chord Stress and Diameter-to-Thickness Ratio on the Static Strength of DT Tubular Joints Loaded in Brace Compression
"Scope of Study The study is divided into four main parts: development of guidelines for FE modeling; validation of the FE modeling methodology via comparisons with test results; performance of a comprehensive parametric FE study to determine static joint strength as a function of joint geometry and applied chord stress; and development and evaluation of a parametric strength prediction equation for design guidance. In Section 2@ a general description of the FE methodology is given. The section includes brief descriptions of software packages utilized@ types of finite elements used@ nonlinear formulation and solution methods@ and nonlinear material characterization. In Section 3@ all available experimental results on DT??joints subjected to brace compression and chord loading are examined and compared to OTJRC FE simulation of the tests. In addition to the test series already cited (Boone 1982@ Weinstein 1985@ Togo 1967@ BOMEL 1990@1992) a test performed by Veritec (Hayman 1986) on a DT joint without chord stress is used for validation purposes and as vehicle for sensitivity studies. In Section 4@ the results of an extensive parametric study using the validated FE methodology is presented and discussed. DT joint geometry can be characterized by four non-dimensional parameters@ which are illustrated in Figure 1.1. They are: ??(=d/D)@ the ratio of brace diameter (d) to chord diameter (D);??=D/2T)@ the ratio of chord radius (D/2) to chord wall thickness (T); ?? (=2L/D) the ratio of chord length (2L) to chord diameter (D); and ??(=t/T) the ratio of brace wall thickness (t) to chord wall thickness (T). The primary geometric variables in the parametric study are ??and ?? the ranges considered are [0.3 less than or equal to ??less than or equal to 1.0@ 10 less than or equal to ??less than or equal to 40]. The effect of chord length ?? and boundary conditions is eliminated by determining numerically for each joint geometry a ""long chord length"" sufficient to make the joint response insensitive to the boundary conditions at the ends of the chord. A preliminary sensitivity study indicated that reasonable variations in the thickness ratio ??do not significantly affect joint strength; therefore ??1.0 is used in the parametric study. The level of axial chord stress is measured by the chord stress ratio U (=??Fy)@ the ratio of axial chord stress ??to the yield stress of the steel Fy. The range of chord stress covered in the parametric study is [-0.8 less than or equal to U less than or equal to 0.8]. The section also includes the results of additional sensitivity studies. In Section 5@ a new parametric equation is developed for the prediction of the static strength of DT ??joints subjected to axial chord stress@ using the previously available information in conjunction with the new information developed in this study. comparisons are made with existing screened test and FE databases. The current API RP2A (20th Edition) and the proposed ISO (Draft) provisions are also compared against the same databases. Section 6 provides a summary and conclusion."
API REPORT 07714-CAP-1998 history
1998API REPORT 07714-CAP-1998 Strength of Simple Joints - Effect of Chord Stress and Diameter-to-Thickness Ratio on the Static Strength of DT Tubular Joints Loaded in Brace Compression