Experimental and theoretical analysis of boltless semi-rigid connectors
The aim of this research was to investigate the behaviour of the semi-rigid boltless connectors used in cold formed thin walled rack structures. A typical beam end connector consists of an end plate welded to the end of a beam and an interlocking arrangement that engages with perforated columns at optional heights; hence supporting the beam and restraining the column. There are a variety of types and designs of connectors in use, characteristic of different rack manufacturers. In general beam end connectors of this type are produced as the result of processes such as forming and punching. These methods produce the interlocking features, "tabs" or "studs" which perform the same role as that of bolts in conventional structural joints. In the experimental part of the work an appraisal of commercially available beam end connectors was undertaken classifying them based on their special features. A selected number of connectors were tested and their moment-rotation characteristics were determined. The results were then compared in conjunction with the deformation modes observed. Stress-sensitive lacquer was used to establish an indication of the stress distributions involved. The outcome of this exercise enabled determination of the parameters governing efficient beam end connector design including the effects of dimensional changes of the accompanying members as well as variation in welding arrangements. Corrections were made to the experimental results to allow for flexibility of beam and upright. Finite Element techniques were used to model the behavior of a boltleS3 semirigid beam end connector. The work was carried out in four stages. An elastic global model was set up to investigate the overall deformation of a beam connector using absolute restraints to simulate the resistance to the rotation of the beam end connector. The global model also determined the stress distribution in the critical regions. A number of ela3to-plastic sub-models were produced with the aim of obtaining the resistance to rotation offered by the accompanying upright. The global model was later modified to incorporate spring stiffness values. Two global models were used to investigate the effect of variation in the number and direction of restraints and the incorporated springs. For every case the beam end connector stiffness value was evaluated and was compared against experimental results. The models were also used to examine the test methods recommended in the current and the forthcoming codes of practice for the industry. The models were used to determine the load distribution in the tabs. This later formed the basis of a design approach capable of estimating the bending carrying capacity of a 3emi-rigid beam end connector.
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