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A welded bracket supporting the leg of an offshore drilling unit was investigated by means of a photoelastic model after proving to be too complicated for analysis. The steel plates were modeled by plastic sheets and welded joints were simulated with epoxyresin. The model was subjected to different loading and restraint conditions. Stresses were computed from readings taken with a reflecting polariscope. The tests demonstrated that welded structural assemblies may be reasonably simulated by the epoxy-to-plastic combination.


A complex welded bracket supporting the leg of a mobile drilling unit proved to be too complicated for theoretical analysis. An experimental model investigation seemed to be the most logical solution since the large size of the bracket made full-scale testing impractical.

A photoelastic model (Fig. 1) was constructed in which steel plates were modeled by birefringent plastic sheets and welded joints were simulated with epoxy resin; the more usual procedure is to bond the plastic sheets to the actual structure or model itself. Static load was applied to the model by means of dead weights on a pin that transmits forces to a leg of the structure in the prototype. The bracket model was tested with two different degrees of restraint corresponding to two different assumptions about the support offered by the hull of the barge. As in the prototype, reinforcing billets and struts were added to the model structure. Photoelastic readings were taken by means of a reflecting polariscope. With the model fringe values of the plastic sheets known, the stresses in the model were determined. Prototype stresses can be easily scaled from the model stresses.


David Brewster's discovery in 1816 that some materials become doubly refractive when subjected to stress marked the beginning of the science of photoelasticity.

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