STRENGTH OF BALL JOINTS WITH DIAPHRAGM IN SPACE TRUSSES

Abstract

The strength of hollow steel spheres used as nodes in tubular space trusses is investigated. In the previous papers [Refs. 1,2 and 3], the authors have reported experimental and analytical studies of the strength of balls without any stiffener subjected to direct uniaxial force from the circular tubes welded to ,the ball. In the practice, as a ball is usually fabricated from two cold-formed hemispheres, the ball has often an interior diaphragm in its equatorial plane for the purpose of easily fabricating as well as reinforcement. Uniaxial compressive tests of the ball joint with/without an interior diaphragm were carried out to investigate the effect of the reinforcement. Method of limit analysis is used to estimate the effect of the reinforcement by the interior diaphragm. Further, a practical formula which is obtained by superposing the diaphragm strength on the ball strength is proposed for predicting the strength of the balls with the interior diaphragm.