Strength of Round Structural Pins

Abstract

The design and performance of pinned connections has been investigated and reported in the literature extensively. Most of this work is concentrated on the connected plates, with relatively little attention given to the pins themselves. This paper summarizes past theoretical and experimental investigations of the performance of structural pins and uses that information to evaluate a practical design method that is consistent with a current lifting device design standard. The design of pins has customarily evaluated shear strength and bending strength independently. This is shown to be an acceptable practice as the maximum shear and the maximum moment normally do not occur at the same location. Comparison of the design loads based on the cited lifting device design standard to the failure loads of 13 pins of various material grades and dimensions shows a very high degree of scatter. The current practice of designing structural pins based on limit states of either first yield or a fully yielded section is reasonable and can be performed reliably, thus providing a pin design that is shown to be compliant with the design standard and capable of performing its necessary function. If design based on the failure load is required by a particular application, the proposed design must be investigated by destructive testing. The primary goal of this paper is to evaluate design methods applicable to round structural pins, with a particular emphasis on such pins used in lifting equipment. The calculations discussed address the stresses that occur when a pin is used in its intended service, the loading that initially will cause some permanent deformation of the pin, and the loading at and beyond which excessive permanent deformation will occur. Test results that show the loads that cause complete failure of the pins are also presented and discussed. Of particular note within this last subject is the difficulty of predicting the failure load of a pin, primarily due to variations of the material strength and stiffness properties beyond the point at which permanent deformations set in. The results of this study are compared to the provisions of a widely used standard applicable to the design of below-the-hook lifting devices. The suitability of the provisions of this standard for the design of pins used in lifting device service is confirmed.